Provided by: ns3-doc_3.22+dfsg-2build1_all 
NAME
ns-3-model-library - ns-3 Model Library
This is the ns-3 Model Library documentation. Primary documentation for the ns-3 project
is available in five forms:
· ns-3 Doxygen: Documentation of the public APIs of the simulator
· Tutorial, Manual, and Model Library (this document) for the latest release and
development tree
· ns-3 wiki
This document is written in reStructuredText for Sphinx and is maintained in the
doc/models directory of ns-3's source code.
ORGANIZATION
This manual compiles documentation for ns-3 models and supporting software that enable
users to construct network simulations. It is important to distinguish between modules
and models:
· ns-3 software is organized into separate modules that are each built as a separate
software library. Individual ns-3 programs can link the modules (libraries) they need
to conduct their simulation.
· ns-3 models are abstract representations of real-world objects, protocols, devices, etc.
An ns-3 module may consist of more than one model (for instance, the internet module
contains models for both TCP and UDP). In general, ns-3 models do not span multiple
software modules, however.
This manual provides documentation about the models of ns-3. It complements two other
sources of documentation concerning models:
· the model APIs are documented, from a programming perspective, using Doxygen. Doxygen
for ns-3 models is available on the project web server.
· the ns-3 core is documented in the developer's manual. ns-3 models make use of the
facilities of the core, such as attributes, default values, random numbers, test
frameworks, etc. Consult the main web site to find copies of the manual.
Finally, additional documentation about various aspects of ns-3 may exist on the project
wiki.
A sample outline of how to write model library documentation can be found by executing the
create-module.py program and looking at the template created in the file
new-module/doc/new-module.rst.
$ cd src
$ ./create-module.py new-module
The remainder of this document is organized alphabetically by module name.
If you are new to ns-3, you might first want to read below about the network module, which
contains some fundamental models for the simulator. The packet model, models for
different address formats, and abstract base classes for objects such as nodes, net
devices, channels, sockets, and applications are discussed there.
ANIMATION
Animation is an important tool for network simulation. While ns-3 does not contain a
default graphical animation tool, we currently have two ways to provide animation, namely
using the PyViz method or the NetAnim method. The PyViz method is described in
http://www.nsnam.org/wiki/PyViz.
We will describe the NetAnim method briefly here.
NetAnim
NetAnim is a standalone, Qt4-based software executable that uses a trace file generated
during an ns-3 simulation to display the topology and animate the packet flow between
nodes.
[image] An example of packet animation on wired-links.UNINDENT
In addition, NetAnim also provides useful features such as tables to display meta-data
of packets like the image below
[image] An example of tables for packet meta-data with protocol filters.UNINDENT
A way to visualize the trajectory of a mobile node
[image] An example of the trajectory of a mobile node.UNINDENT
A way to display the routing-tables of multiple nodes at various points in time
[image]
A way to display counters associated with multiple nodes as a chart or a table
[image]
[image]
A way to view the timeline of packet transmit and receive events
[image]
Methodology
The class ns3::AnimationInterface is responsible for the creation the trace XML file.
AnimationInterface uses the tracing infrastructure to track packet flows between nodes.
AnimationInterface registers itself as a trace hook for tx and rx events before the
simulation begins. When a packet is scheduled for transmission or reception, the
corresponding tx and rx trace hooks in AnimationInterface are called. When the rx hooks
are called, AnimationInterface will be aware of the two endpoints between which a packet
has flowed, and adds this information to the trace file, in XML format along with the
corresponding tx and rx timestamps. The XML format will be discussed in a later section.
It is important to note that AnimationInterface records a packet only if the rx trace
hooks are called. Every tx event must be matched by an rx event.
Downloading NetAnim
If NetAnim is not already available in the ns-3 package you downloaded, you can do the
following:
Please ensure that you have installed mercurial. The latest version of NetAnim can be
downloaded using mercurial with the following command:
$ hg clone http://code.nsnam.org/netanim
Building NetAnim
Prerequisites
Qt4 (4.7 and over) is required to build NetAnim. This can be obtained using the following
ways:
For Debian/Ubuntu Linux distributions:
$ apt-get install qt4-dev-tools
For Red Hat/Fedora based distribution:
$ yum install qt4
$ yum install qt4-devel
For Mac/OSX, see http://qt.nokia.com/downloads/
Build steps
To build NetAnim use the following commands:
$ cd netanim
$ make clean
$ qmake NetAnim.pro (For MAC Users: qmake -spec macx-g++ NetAnim.pro)
$ make
Note: qmake could be "qmake-qt4" in some systems
This should create an executable named "NetAnim" in the same directory:
$ ls -l NetAnim
-rwxr-xr-x 1 john john 390395 2012-05-22 08:32 NetAnim
Usage
Using NetAnim is a two-step process
Step 1:Generate the animation XML trace file during simulation using
"ns3::AnimationInterface" in the ns-3 code base.
Step 2:Load the XML trace file generated in Step 1 with the offline Qt4-based animator
named NetAnim.
Step 1: Generate XML animation trace file
The class "AnimationInterface" under "src/netanim" uses underlying ns-3 trace sources to
construct a timestamped ASCII file in XML format.
Examples are found under src/netanim/examples Example:
$ ./waf -d debug configure --enable-examples
$ ./waf --run "dumbbell-animation"
The above will create an XML file dumbbell-animation.xml
Mandatory
1. Ensure that your program's wscript includes the "netanim" module. An example of such a
wscript is at src/netanim/examples/wscript.
2. Include the header [#include "ns3/netanim-module.h"] in your test program
3. Add the statement
AnimationInterface anim ("animation.xml"); // where "animation.xml" is any arbitrary filename
[for versions before ns-3.13 you also have to use the line "anim.SetXMLOutput() to set the
XML mode and also use anim.StartAnimation();]
Optional
The following are optional but useful steps:
// Step 1
anim.SetMobilityPollInterval (Seconds (1));
AnimationInterface records the position of all nodes every 250 ms by default. The
statement above sets the periodic interval at which AnimationInterface records the
position of all nodes. If the nodes are expected to move very little, it is useful to set
a high mobility poll interval to avoid large XML files.
// Step 2
anim.SetConstantPosition (Ptr< Node > n, double x, double y);
AnimationInterface requires that the position of all nodes be set. In ns-3 this is done by
setting an associated MobilityModel. "SetConstantPosition" is a quick way to set the x-y
coordinates of a node which is stationary.
// Step 3
anim.SetStartTime (Seconds(150)); and anim.SetStopTime (Seconds(150));
AnimationInterface can generate large XML files. The above statements restricts the window
between which AnimationInterface does tracing. Restricting the window serves to focus only
on relevant portions of the simulation and creating manageably small XML files
// Step 4
AnimationInterface anim ("animation.xml", 50000);
Using the above constructor ensures that each animation XML trace file has only 50000
packets. For example, if AnimationInterface captures 150000 packets, using the above
constructor splits the capture into 3 files
· animation.xml - containing the packet range 1-50000
· animation.xml-1 - containing the packet range 50001-100000
· animation.xml-2 - containing the packet range 100001-150000
// Step 5
anim.EnablePacketMetadata (true);
With the above statement, AnimationInterface records the meta-data of each packet in the
xml trace file. Metadata can be used by NetAnim to provide better statistics and filter,
along with providing some brief information about the packet such as TCP sequence number
or source & destination IP address during packet animation.
CAUTION: Enabling this feature will result in larger XML trace files. Please do NOT
enable this feature when using Wimax links.
// Step 6
anim.UpdateNodeDescription (5, "Access-point");
With the above statement, AnimationInterface assigns the text "Access-point" to node 5.
// Step 7
anim.UpdateNodeSize (6, 1.5, 1.5);
With the above statement, AnimationInterface sets the node size to scale by 1.5. NetAnim
automatically scales the graphics view to fit the oboundaries of the topology. This means
that NetAnim, can abnormally scale a node's size too high or too low. Using
AnimationInterface::UpdateNodeSize allows you to overwrite the default scaling in NetAnim
and use your own custom scale.
// Step 8
anim.UpdateNodeCounter (89, 7, 3.4);
With the above statement, AnimationInterface sets the counter with Id == 89, associated
with Node 7 with the value 3.4. The counter with Id 89 is obtained using
AnimationInterface::AddNodeCounter. An example usage for this is in
src/netanim/examples/resources_demo.cc.
Step 2: Loading the XML in NetAnim
1. Assuming NetAnim was built, use the command "./NetAnim" to launch NetAnim. Please
review the section "Building NetAnim" if NetAnim is not available.
2. When NetAnim is opened, click on the File open button at the top-left corner, select
the XML file generated during Step 1.
3. Hit the green play button to begin animation.
Here is a video illustrating this http://www.youtube.com/watch?v=tz_hUuNwFDs
Wiki
For detailed instructions on installing "NetAnim", F.A.Qs and loading the XML trace file
(mentioned earlier) using NetAnim please refer: http://www.nsnam.org/wiki/NetAnim
ANTENNA MODULE
Design documentation
Overview
The Antenna module provides:
1. a new base class (AntennaModel) that provides an interface for the modeling of the
radiation pattern of an antenna;
2. a set of classes derived from this base class that each models the radiation pattern
of different types of antennas.
AntennaModel
The AntennaModel uses the coordinate system adopted in [Balanis] and depicted in Figure
Coordinate system of the AntennaModel. This system is obtained by traslating the cartesian
coordinate system used by the ns-3 MobilityModel into the new origin o which is the
location of the antenna, and then transforming the coordinates of every generic point p of
the space from cartesian coordinates (x,y,z) into spherical coordinates (r, heta,hi).
The antenna model neglects the radial component r, and only considers the angle components
(heta, hi).
An antenna radiation pattern is then expressed as a mathematical function g(heta, hi)
grightarrow thcal{R} that returns the gain (in dB) for each possible direction of
transmission/reception. All angles are expressed in radians.
[image] Coordinate system of the AntennaModel.UNINDENT
Provided models
In this section we describe the antenna radiation pattern models that are included within
the antenna module.
IsotropicAntennaModel
This antenna radiation pattern model provides a unitary gain (0 dB) for all direction.
CosineAntennaModel
This is the cosine model described in [Chunjian]: the antenna gain is determined as:
where hi_{0}
is the azimuthal orientation of the antenna (i.e., its direction of maximum gain) and the
exponential
determines the desired 3dB beamwidth hi_{3dB}.
Note that this radiation pattern is independent of the inclination angle heta.
A major difference between the model of [Chunjian] and the one implemented in the class
CosineAntennaModel is that only the element factor (i.e., what described by the above
formulas) is considered. In fact, [Chunjian] also considered an additional antenna array
factor. The reason why the latter is excluded is that we expect that the average user
would desire to specify a given beamwidth exactly, without adding an array factor at a
latter stage which would in practice alter the effective beamwidth of the resulting
radiation pattern.
ParabolicAntennaModel
This model is based on the parabolic approximation of the main lobe radiation pattern. It
is often used in the context of cellular system to model the radiation pattern of a cell
sector, see for instance [R4-092042a] and [Calcev]. The antenna gain in dB is determined
as:
where hi_{0}
is the azimuthal orientation of the antenna (i.e., its direction of maximum gain),
hi_{3dB}
is its 3 dB beamwidth, and A_{max} is the maximum attenuation in dB of the antenna. Note
that this radiation pattern is independent of the inclination angle heta.
[Balanis]
C.A. Balanis, "Antenna Theory - Analysis and Design", Wiley, 2nd Ed.
[Chunjian]
Li Chunjian, "Efficient Antenna Patterns for Three-Sector WCDMA Systems", Master of
Science Thesis, Chalmers University of Technology, Göteborg, Sweden, 2003
[Calcev]
George Calcev and Matt Dillon, "Antenna Tilt Control in CDMA Networks", in Proc. of
the 2nd Annual International Wireless Internet Conference (WICON), 2006
[R4-092042a]
3GPP TSG RAN WG4 (Radio) Meeting #51, R4-092042, Simulation assumptions and
parameters for FDD HeNB RF requirements.
User Documentation
The antenna moduled can be used with all the wireless technologies and physical layer
models that support it. Currently, this includes the physical layer models based on the
SpectrumPhy. Please refer to the documentation of each of these models for details.
Testing Documentation
In this section we describe the test suites included with the antenna module that verify
its correct functionality.
Angles
The unit test suite angles verifies that the Angles class is constructed properly by
correct conversion from 3D cartesian coordinates according to the available methods
(construction from a single vector and from a pair of vectors). For each method, several
test cases are provided that compare the values (hi,
heta) determied by the constructor to known reference values. The test passes if for each
case the values are equal to the reference up to a tolerance of 10^{-10} which accounts
for numerical errors.
DegreesToRadians
The unit test suite degrees-radians verifies that the methods DegreesToRadians and
RadiansToDegrees work properly by comparing with known reference values in a number of
test cases. Each test case passes if the comparison is equal up to a tolerance of 10^{-10}
which accounts for numerical errors.
IsotropicAntennaModel
The unit test suite isotropic-antenna-model checks that the IsotropicAntennaModel class
works properly, i.e., returns always a 0dB gain regardless of the direction.
CosineAntennaModel
The unit test suite cosine-antenna-model checks that the CosineAntennaModel class works
properly. Several test cases are provided that check for the antenna gain value calculated
at different directions and for different values of the orientation, the reference gain
and the beamwidth. The reference gain is calculated by hand. Each test case passes if the
reference gain in dB is equal to the value returned by CosineAntennaModel within a
tolerance of 0.001, which accounts for the approximation done for the calculation of the
reference values.
ParabolicAntennaModel
The unit test suite parabolic-antenna-model checks that the ParabolicAntennaModel class
works properly. Several test cases are provided that check for the antenna gain value
calculated at different directions and for different values of the orientation, the
maximum attenuation and the beamwidth. The reference gain is calculated by hand. Each test
case passes if the reference gain in dB is equal to the value returned by
ParabolicAntennaModel within a tolerance of 0.001, which accounts for the approximation
done for the calculation of the reference values.
AD HOC ON-DEMAND DISTANCE VECTOR (AODV)
This model implements the base specification of the Ad Hoc On-Demand Distance Vector
(AODV) protocol. The implementation is based on RFC 3561.
The model was written by Elena Buchatskaia and Pavel Boyko of ITTP RAS, and is based on
the ns-2 AODV model developed by the CMU/MONARCH group and optimized and tuned by Samir
Das and Mahesh Marina, University of Cincinnati, and also on the AODV-UU implementation by
Erik Nordström of Uppsala University.
Model Description
The source code for the AODV model lives in the directory src/aodv.
Design
Class ns3::aodv::RoutingProtocol implements all functionality of service packet exchange
and inherits from ns3::Ipv4RoutingProtocol. The base class defines two virtual functions
for packet routing and forwarding. The first one, ns3::aodv::RouteOutput, is used for
locally originated packets, and the second one, ns3::aodv::RouteInput, is used for
forwarding and/or delivering received packets.
Protocol operation depends on many adjustable parameters. Parameters for this
functionality are attributes of ns3::aodv::RoutingProtocol. Parameter default values are
drawn from the RFC and allow the enabling/disabling protocol features, such as
broadcasting HELLO messages, broadcasting data packets and so on.
AODV discovers routes on demand. Therefore, the AODV model buffers all packets while a
route request packet (RREQ) is disseminated. A packet queue is implemented in
aodv-rqueue.cc. A smart pointer to the packet, ns3::Ipv4RoutingProtocol::ErrorCallback,
ns3::Ipv4RoutingProtocol::UnicastForwardCallback, and the IP header are stored in this
queue. The packet queue implements garbage collection of old packets and a queue size
limit.
The routing table implementation supports garbage collection of old entries and state
machine, defined in the standard. It is implemented as a STL map container. The key is a
destination IP address.
Some elements of protocol operation aren't described in the RFC. These elements generally
concern cooperation of different OSI model layers. The model uses the following
heuristics:
· This AODV implementation can detect the presence of unidirectional links and avoid them
if necessary. If the node the model receives an RREQ for is a neighbor, the cause may
be a unidirectional link. This heuristic is taken from AODV-UU implementation and can
be disabled.
· Protocol operation strongly depends on broken link detection mechanism. The model
implements two such heuristics. First, this implementation support HELLO messages.
However HELLO messages are not a good way to perform neighbor sensing in a wireless
environment (at least not over 802.11). Therefore, one may experience bad performance
when running over wireless. There are several reasons for this: 1) HELLO messages are
broadcasted. In 802.11, broadcasting is often done at a lower bit rate than unicasting,
thus HELLO messages can travel further than unicast data. 2) HELLO messages are small,
thus less prone to bit errors than data transmissions, and 3) Broadcast transmissions
are not guaranteed to be bidirectional, unlike unicast transmissions. Second, we use
layer 2 feedback when possible. Link are considered to be broken if frame transmission
results in a transmission failure for all retries. This mechanism is meant for active
links and works faster than the first method.
The layer 2 feedback implementation relies on the TxErrHeader trace source, currently
supported in AdhocWifiMac only.
Scope and Limitations
The model is for IPv4 only. The following optional protocol optimizations are not
implemented:
1. Expanding ring search.
2. Local link repair.
3. RREP, RREQ and HELLO message extensions.
These techniques require direct access to IP header, which contradicts the assertion from
the AODV RFC that AODV works over UDP. This model uses UDP for simplicity, hindering the
ability to implement certain protocol optimizations. The model doesn't use low layer raw
sockets because they are not portable.
Future Work
No announced plans.
References
Usage
Examples
Helpers
Attributes
Tracing
Logging
Caveats
Validation
Unit tests
Larger-scale performance tests
APPLICATIONS
Placeholder chapter
BRIDGE NETDEVICE
Placeholder chapter
Some examples of the use of Bridge NetDevice can be found in examples/csma/ directory.
BRITE INTEGRATION
This model implements an interface to BRITE, the Boston university Representative Internet
Topology gEnerator [1]. BRITE is a standard tool for generating realistic internet
topologies. The ns-3 model, described herein, provides a helper class to facilitate
generating ns-3 specific topologies using BRITE configuration files. BRITE builds the
original graph which is stored as nodes and edges in the ns-3 BriteTopolgyHelper class. In
the ns-3 integration of BRITE, the generator generates a topology and then provides access
to leaf nodes for each AS generated. ns-3 users can than attach custom topologies to
these leaf nodes either by creating them manually or using topology generators provided in
ns-3.
There are three major types of topologies available in BRITE: Router, AS, and
Hierarchical which is a combination of AS and Router. For the purposes of ns-3
simulation, the most useful are likely to be Router and Hierarchical. Router level
topologies be generated using either the Waxman model or the Barabasi-Albert model. Each
model has different parameters that effect topology creation. For flat router topologies,
all nodes are considered to be in the same AS.
BRITE Hierarchical topologies contain two levels. The first is the AS level. This level
can be also be created by using either the Waxman model or the Barabasi-Albert model.
Then for each node in the AS topology, a router level topology is constructed. These
router level topologies can again either use the Waxman model or the Barbasi-Albert model.
BRITE interconnects these separate router topologies as specified by the AS level
topology. Once the hierarchical topology is constructed, it is flattened into a large
router level topology.
Further information can be found in the BRITE user manual:
http://www.cs.bu.edu/brite/publications/usermanual.pdf
Model Description
The model relies on building an external BRITE library, and then building some ns-3
helpers that call out to the library. The source code for the ns-3 helpers lives in the
directory src/brite/helper.
Design
To generate the BRITE topology, ns-3 helpers call out to the external BRITE library, and
using a standard BRITE configuration file, the BRITE code builds a graph with nodes and
edges according to this configuration file. Please see the BRITE documenation or the
example configuration files in src/brite/examples/conf_files to get a better grasp of
BRITE configuration options. The graph built by BRITE is returned to ns-3, and a ns-3
implementation of the graph is built. Leaf nodes for each AS are available for the user
to either attach custom topologies or install ns-3 applications directly.
References
[1] Alberto Medina, Anukool Lakhina, Ibrahim Matta, and John Byers. BRITE: An Approach to
Universal Topology Generation. In Proceedings of the International Workshop on
Modeling, Analysis and Simulation of Computer and Telecommunications Systems- MASCOTS
'01, Cincinnati, Ohio, August 2001.
Usage
The brite-generic-example can be referenced to see basic usage of the BRITE interface. In
summary, the BriteTopologyHelper is used as the interface point by passing in a BRITE
configuration file. Along with the configuration file a BRITE formatted random seed file
can also be passed in. If a seed file is not passed in, the helper will create a seed
file using ns-3's UniformRandomVariable. Once the topology has been generated by BRITE,
BuildBriteTopology() is called to create the ns-3 representation. Next IP Address can be
assigned to the topology using either AssignIpv4Addresses() or AssignIpv6Addresses(). It
should be noted that each point-to-point link in the topology will be treated as a new
network therefore for IPV4 a /30 subnet should be used to avoid wasting a large amount of
the available address space.
Example BRITE configuration files can be found in /src/brite/examples/conf_files/.
ASBarbasi and ASWaxman are examples of AS only topologies. The RTBarabasi and RTWaxman
files are examples of router only topologies. Finally the TD_ASBarabasi_RTWaxman
configuration file is an example of a Hierarchical topology that uses the Barabasi-Albert
model for the AS level and the Waxman model for each of the router level topologies.
Information on the BRITE parameters used in these files can be found in the BRITE user
manual.
Building BRITE Integration
The first step is to download and build the ns-3 specific BRITE repository:
$ hg clone http://code.nsnam.org/BRITE
$ cd BRITE
$ make
This will build BRITE and create a library, libbrite.so, within the BRITE directory.
Once BRITE has been built successfully, we proceed to configure ns-3 with BRITE support.
Change to your ns-3 directory:
$ ./waf configure --with-brite=/your/path/to/brite/source --enable-examples
Make sure it says 'enabled' beside 'BRITE Integration'. If it does not, then something has
gone wrong. Either you have forgotten to build BRITE first following the steps above, or
ns-3 could not find your BRITE directory.
Next, build ns-3:
$ ./waf
Examples
For an example demonstrating BRITE integration run:
$ ./waf --run 'brite-generic-example'
By enabling the verbose parameter, the example will print out the node and edge
information in a similar format to standard BRITE output. There are many other
command-line parameters including confFile, tracing, and nix, described below:
confFile
A BRITE configuration file. Many different BRITE configuration file examples
exist in the src/brite/examples/conf_files directory, for example,
RTBarabasi20.conf and RTWaxman.conf. Please refer to the conf_files directory
for more examples.
tracing
Enables ascii tracing.
nix Enables nix-vector routing. Global routing is used by default.
The generic BRITE example also support visualization using pyviz, assuming python bindings
in ns-3 are enabled:
$ ./waf --run brite-generic-example --vis
Simulations involving BRITE can also be used with MPI. The total number of MPI instances
is passed to the BRITE topology helper where a modulo divide is used to assign the nodes
for each AS to a MPI instance. An example can be found in src/brite/examples:
$ mpirun -np 2 ./waf --run brite-MPI-example
Please see the ns-3 MPI documentation for information on setting up MPI with ns-3.
BUILDINGS MODULE
cd .. include:: replace.txt
Design documentation
Overview
The Buildings module provides:
1. a new class (Building) that models the presence of a building in a simulation
scenario;
2. a new class (MobilityBuildingInfo) that allows to specify the location, size and
characteristics of buildings present in the simulated area, and allows the placement
of nodes inside those buildings;
3. a container class with the definition of the most useful pathloss models and the
correspondent variables called BuildingsPropagationLossModel.
4. a new propagation model (HybridBuildingsPropagationLossModel) working with the
mobility model just introduced, that allows to model the phenomenon of
indoor/outdoor propagation in the presence of buildings.
5. a simplified model working only with Okumura Hata (OhBuildingsPropagationLossModel)
considering the phenomenon of indoor/outdoor propagation in the presence of
buildings.
The models have been designed with LTE in mind, though their implementation is in fact
independent from any LTE-specific code, and can be used with other ns-3 wireless
technologies as well (e.g., wifi, wimax).
The HybridBuildingsPropagationLossModel pathloss model included is obtained through a
combination of several well known pathloss models in order to mimic different
environmental scenarios such as urban, suburban and open areas. Moreover, the model
considers both outdoor and indoor indoor and outdoor communication has to be included
since HeNB might be installed either within building and either outside. In case of indoor
communication, the model has to consider also the type of building in outdoor <-> indoor
communication according to some general criteria such as the wall penetration losses of
the common materials; moreover it includes some general configuration for the internal
walls in indoor communications.
The OhBuildingsPropagationLossModel pathloss model has been created for simplifying the
previous one removing the thresholds for switching from one model to other. For doing this
it has been used only one propagation model from the one available (i.e., the Okumura
Hata). The presence of building is still considered in the model; therefore all the
considerations of above regarding the building type are still valid. The same
consideration can be done for what concern the environmental scenario and frequency since
both of them are parameters of the model considered.
The Building class
The model includes a specific class called Building which contains a ns3 Box class for
defining the dimension of the building. In order to implements the characteristics of the
pathloss models included, the Building class supports the following attributes:
· building type:
· Residential (default value)
· Office
· Commercial
· external walls type
· Wood
· ConcreteWithWindows (default value)
· ConcreteWithoutWindows
· StoneBlocks
· number of floors (default value 1, which means only ground-floor)
· number of rooms in x-axis (default value 1)
· number of rooms in y-axis (default value 1)
The Building class is based on the following assumptions:
· a buildings is represented as a rectangular parallelepiped (i.e., a box)
· the walls are parallel to the x, y, and z axis
· a building is divided into a grid of rooms, identified by the following parameters:
· number of floors
· number of rooms along the x-axis
· number of rooms along the y-axis
· the z axis is the vertical axis, i.e., floor numbers increase for increasing z axis
values
· the x and y room indices start from 1 and increase along the x and y axis
respectively
· all rooms in a building have equal size
The MobilityBuildingInfo class
The MobilityBuildingInfo class, which inherits from the ns3 class Object, is in charge of
maintaining information about the position of a node with respect to building. The
information managed by MobilityBuildingInfo is:
· whether the node is indoor or outdoor
· if indoor:
· in which building the node is
· in which room the node is positioned (x, y and floor room indices)
The class MobilityBuildingInfo is used by BuildingsPropagationLossModel class, which
inherits from the ns3 class PropagationLossModel and manages the pathloss computation of
the single components and their composition according to the nodes' positions. Moreover,
it implements also the shadowing, that is the loss due to obstacles in the main path
(i.e., vegetation, buildings, etc.).
It is to be noted that, MobilityBuildingInfo can be used by any other propagation model.
However, based on the information at the time of this writing, only the ones defined in
the building module are designed for considering the constraints introduced by the
buildings.
g
ItuR1238PropagationLossModel
This class nmplements a building-dependent indoor propagation loss model based on the ITU
P.1238 modeg{ which includes losses due to type of building (i.e., residential, office and
commercial)ia The analytical expression is given in the following.
nr
{r
aa
where: ry ight. : power loss
N = t r}sidential \ 30 & office \ 22 & commercial\nd{array}
coefficiant [dB]
yl ight.
L_f = t }sidential \ 15+4(n-1) & office \ 6+3(n-1) & commercial\nd{array}
{l
n : number of floors between base station and mobile (n 1)
l2
f : frequency [MHz]
}&
d : distance (where d > 1) [m]
n
BuildingsPropag&ationLossModel
The BuildingsPropagationLossModel provides an additional set of building-dependent
pathloss model elements that are used to implement different pathloss logics. These
pathloss model elements are described in the following subsections.
External Wall Loss (EWL)
This component models the penetration loss through walls for indoor to outdoor
communications and vice-versa. The values are taken from the [cost231] model.
· Wood ~ 4 dB
· Concrete with windows (not metallized) ~ 7 dB
· Concrete without windows ~ 15 dB (spans between 10 and 20 in COST231)
· Stone blocks ~ 12 dB
Internal Walls Loss (IWL)
This component models the penetration loss occurring in indoor-to-indoor communications
within the same building. The total loss is calculated assuming that each single internal
wall has a constant penetration loss L_{siw}, and approximating the number of walls that
are penetrated with the manhattan distance (in number of rooms) between the transmitter
and the receiver. In detail, let x_1, y_1, x_2, y_2 denote the room number along the x and
y axis respectively for user 1 and 2; the total loss L_{IWL} is calculated as
Height Gain Model (HG)
This component model the gain due to the fact that the transmitting device is on a floor
above the ground. In the literature [turkmani] this gain has been evaluated as about 2 dB
per floor. This gain can be applied to all the indoor to outdoor communications and
vice-versa.
Shadowing Model
The shadowing is modeled according to a log-normal distribution with variable standard
deviation as function of the relative position (indoor or outdoor) of the MobilityModel
instances involved. One random value is drawn for each pair of MobilityModels, and stays
constant for that pair during the whole simulation. Thus, the model is appropriate for
static nodes only.
The model considers that the mean of the shadowing loss in dB is always 0. For the
variance, the model considers three possible values of standard deviation, in detail:
ightarrow X_thrm{O}
· outdoor (m_shadowingSigmaOutdoor, defaul value of 7 dB)
N(_thrm{O}, ma_thrm{O}^2).
ightarrow X_thrm{I}
· indoor (m_shadowingSigmaIndoor, defaul value of 10 dB)
N(_thrm{I}, ma_thrm{I}^2).
ightarrow
· external walls penetration (m_shadowingSigmaExtWalls, default value 5 dB)
X_thrm{W} N(_thrm{W}, ma_thrm{W}^2)
The simulator generates a shadowing value per each active link according to nodes'
position the first time the link is used for transmitting. In case of transmissions from
outdoor nodes to indoor ones, and vice-versa, the standard deviation (ma_thrm{IO}) has to
be calculated as the square root of the sum of the quadratic values of the standard
deviatio in case of outdoor nodes and the one for the external walls penetration. This is
due to the fact that that the components producing the shadowing are independent of each
other; therefore, the variance of a distribution resulting from the sum of two independent
normal ones is the sum of the variances.
Pathloss logics
In the following we describe the different pathloss logic that are implemented by
inheriting from BuildingsPropagationLossModel.
HybridBuildingsPropagationLossModel
The HybridBuildingsPropagationLossModel pathloss model included is obtained through a
combination of several well known pathloss models in order to mimic different outdoor and
indoor scenarios, as well as indoor-to-outdoor and outdoor-to-indoor scenarios. In detail,
the class HybridBuildingsPropagationLossModel integrates the following pathloss models:
· OkumuraHataPropagationLossModel (OH) (at frequencies > 2.3 GHz substituted by
Kun2600MhzPropagationLossModel)
· ItuR1411LosPropagationLossModel and ItuR1411NlosOverRooftopPropagationLossModel
(I1411)
· ItuR1238PropagationLossModel (I1238)
· the pathloss elements of the BuildingsPropagationLossModel (EWL, HG, IWL)
The following pseudo-code illustrates how the different pathloss model elements described
above are integrated in HybridBuildingsPropagationLossModel:
if (txNode is outdoor)
then
if (rxNode is outdoor)
then
if (distance > 1 km)
then
if (rxNode or txNode is below the rooftop)
then
L = I1411
else
L = OH
else
L = I1411
else (rxNode is indoor)
if (distance > 1 km)
then
if (rxNode or txNode is below the rooftop)
L = I1411 + EWL + HG
else
L = OH + EWL + HG
else
L = I1411 + EWL + HG
else (txNode is indoor)
if (rxNode is indoor)
then
if (same building)
then
L = I1238 + IWL
else
L = I1411 + 2*EWL
else (rxNode is outdoor)
if (distance > 1 km)
then
if (rxNode or txNode is below the rooftop)
then
L = I1411 + EWL + HG
else
L = OH + EWL + HG
else
L = I1411 + EWL
We note that, for the case of communication between two nodes below rooftop level with
distance is greater then 1 km, we still consider the I1411 model, since OH is specifically
designed for macro cells and therefore for antennas above the roof-top level.
For the ITU-R P.1411 model we consider both the LOS and NLoS versions. In particular, we
considers the LoS propagation for distances that are shorted than a tunable threshold
(m_itu1411NlosThreshold). In case on NLoS propagation, the over the roof-top model is
taken in consideration for modeling both macro BS and SC. In case on NLoS several
parameters scenario dependent have been included, such as average street width,
orientation, etc. The values of such parameters have to be properly set according to the
scenario implemented, the model does not calculate natively their values. In case any
values is provided, the standard ones are used, apart for the height of the mobile and BS,
which instead their integrity is tested directly in the code (i.e., they have to be
greater then zero). In the following we give the expressions of the components of the
model.
We also note that the use of different propagation models (OH, I1411, I1238 with their
variants) in HybridBuildingsPropagationLossModel can result in discontinuities of the
pathloss with respect to distance. A proper tuning of the attributes (especially the
distance threshold attributes) can avoid these discontinuities. However, since the
behavior of each model depends on several other parameters (frequency, node heigth, etc),
there is no default value of these thresholds that can avoid the discontinuities in all
possible configurations. Hence, an appropriate tuning of these parameters is left to the
user.
OhBuildingsPropagationLossModel
The OhBuildingsPropagationLossModel class has been created as a simple means to solve the
discontinuity problems of HybridBuildingsPropagationLossModel without doing
scenario-specific parameter tuning. The solution is to use only one propagation loss
model (i.e., Okumura Hata), while retaining the structure of the pathloss logic for the
calculation of other path loss components (such as wall penetration losses). The result is
a model that is free of discontinuities (except those due to walls), but that is less
realistic overall for a generic scenario with buildings and outdoor/indoor users, e.g.,
because Okumura Hata is not suitable neither for indoor communications nor for outdoor
communications below rooftop level.
In detail, the class OhBuildingsPropagationLossModel integrates the following pathloss
models:
· OkumuraHataPropagationLossModel (OH)
· the pathloss elements of the BuildingsPropagationLossModel (EWL, HG, IWL)
The following pseudo-code illustrates how the different pathloss model elements described
above are integrated in OhBuildingsPropagationLossModel:
if (txNode is outdoor)
then
if (rxNode is outdoor)
then
L = OH
else (rxNode is indoor)
L = OH + EWL
else (txNode is indoor)
if (rxNode is indoor)
then
if (same building)
then
L = OH + IWL
else
L = OH + 2*EWL
else (rxNode is outdoor)
L = OH + EWL
We note that OhBuildingsPropagationLossModel is a significant simplification with respect
to HybridBuildingsPropagationLossModel, due to the fact that OH is used always. While this
gives a less accurate model in some scenarios (especially below rooftop and indoor), it
effectively avoids the issue of pathloss discontinuities that affects
HybridBuildingsPropagationLossModel.
User Documentation
How to use buildings in a simulation
In this section we explain the basic usage of the buildings model within a simulation
program.
Include the headers
Add this at the beginning of your simulation program:
#include <ns3/buildings-module.h>
Create a building
As an example, let's create a residential 10 x 20 x 10 building:
double x_min = 0.0;
double x_max = 10.0;
double y_min = 0.0;
double y_max = 20.0;
double z_min = 0.0;
double z_max = 10.0;
Ptr<Building> b = CreateObject <Building> ();
b->SetBoundaries (Box (x_min, x_max, y_min, y_max, z_min, z_max));
b->SetBuildingType (Building::Residential);
b->SetExtWallsType (Building::ConcreteWithWindows);
b->SetNFloors (3);
b->SetNRoomsX (3);
b->SetNRoomsY (2);
This building has three floors and an internal 3 x 2 grid of rooms of equal size.
The helper class GridBuildingAllocator is also available to easily create a set of
buildings with identical characteristics placed on a rectangular grid. Here's an example
of how to use it:
Ptr<GridBuildingAllocator> gridBuildingAllocator;
gridBuildingAllocator = CreateObject<GridBuildingAllocator> ();
gridBuildingAllocator->SetAttribute ("GridWidth", UintegerValue (3));
gridBuildingAllocator->SetAttribute ("LengthX", DoubleValue (7));
gridBuildingAllocator->SetAttribute ("LengthY", DoubleValue (13));
gridBuildingAllocator->SetAttribute ("DeltaX", DoubleValue (3));
gridBuildingAllocator->SetAttribute ("DeltaY", DoubleValue (3));
gridBuildingAllocator->SetAttribute ("Height", DoubleValue (6));
gridBuildingAllocator->SetBuildingAttribute ("NRoomsX", UintegerValue (2));
gridBuildingAllocator->SetBuildingAttribute ("NRoomsY", UintegerValue (4));
gridBuildingAllocator->SetBuildingAttribute ("NFloors", UintegerValue (2));
gridBuildingAllocator->SetAttribute ("MinX", DoubleValue (0));
gridBuildingAllocator->SetAttribute ("MinY", DoubleValue (0));
gridBuildingAllocator->Create (6);
This will create a 3x2 grid of 6 buildings, each 7 x 13 x 6 m with 2 x 4 rooms inside and
2 foors; the buildings are spaced by 3 m on both the x and the y axis.
Setup nodes and mobility models
Nodes and mobility models are configured as usual, however in order to use them with the
buildings model you need an additional call to BuildingsHelper::Install(), so as to let
the mobility model include the informtion on their position w.r.t. the buildings. Here is
an example:
MobilityHelper mobility;
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
ueNodes.Create (2);
mobility.Install (ueNodes);
BuildingsHelper::Install (ueNodes);
It is to be noted that any mobility model can be used. However, the user is advised to
make sure that the behavior of the mobility model being used is consistent with the
presence of Buildings. For example, using a simple random mobility over the whole
simulation area in presence of buildings might easily results in node moving in and out of
buildings, regardless of the presence of walls.
Place some nodes
You can place nodes in your simulation using several methods, which are described in the
following.
Legacy positioning methods
Any legacy ns-3 positioning method can be used to place node in the simulation. The
important additional step is to For example, you can place nodes manually like this:
Ptr<ConstantPositionMobilityModel> mm0 = enbNodes.Get (0)->GetObject<ConstantPositionMobilityModel> ();
Ptr<ConstantPositionMobilityModel> mm1 = enbNodes.Get (1)->GetObject<ConstantPositionMobilityModel> ();
mm0->SetPosition (Vector (5.0, 5.0, 1.5));
mm1->SetPosition (Vector (30.0, 40.0, 1.5));
MobilityHelper mobility;
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
ueNodes.Create (2);
mobility.Install (ueNodes);
BuildingsHelper::Install (ueNodes);
mm0->SetPosition (Vector (5.0, 5.0, 1.5));
mm1->SetPosition (Vector (30.0, 40.0, 1.5));
Alternatively, you could use any existing PositionAllocator class. The coordinates of the
node will determine whether it is placed outdoor or indoor and, if indoor, in which
building and room it is placed.
Building-specific positioning methods
The following position allocator classes are available to place node in special positions
with respect to buildings:
· RandomBuildingPositionAllocator: Allocate each position by randomly chosing a
building from the list of all buildings, and then randomly chosing a position inside
the building.
· RandomRoomPositionAllocator: Allocate each position by randomly chosing a room from
the list of rooms in all buildings, and then randomly chosing a position inside the
room.
· SameRoomPositionAllocator: Walks a given NodeContainer sequentially, and for each
node allocate a new position randomly in the same room of that node.
· FixedRoomPositionAllocator: Generate a random position uniformly distributed in the
volume of a chosen room inside a chosen building.
Make the Mobility Model Consistent
Important: whenever you use buildings, you have to issue the following command after we
have placed all nodes and buildings in the simulation:
BuildingsHelper::MakeMobilityModelConsistent ();
This command will go through the lists of all nodes and of all buildings, determine for
each user if it is indoor or outdoor, and if indoor it will also determine the building in
which the user is located and the corresponding floor and number inside the building.
Building-aware pathloss model
After you placed buildings and nodes in a simulation, you can use a building-aware
pathloss model in a simulation exactly in the same way you would use any regular path loss
model. How to do this is specific for the wireless module that you are considering (lte,
wifi, wimax, etc.), so please refer to the documentation of that model for specific
instructions.
Main configurable attributes
The Building class has the following configurable parameters:
· building type: Residential, Office and Commercial.
· external walls type: Wood, ConcreteWithWindows, ConcreteWithoutWindows and StoneBlocks.
· building bounds: a Box class with the building bounds.
· number of floors.
· number of rooms in x-axis and y-axis (rooms can be placed only in a grid way).
The BuildingMobilityLossModel parameter configurable with the ns3 attribute system is
represented by the bound (string Bounds) of the simulation area by providing a Box class
with the area bounds. Moreover, by means of its methos the following parameters can be
configured:
· the number of floor the node is placed (default 0).
· the position in the rooms grid.
The BuildingPropagationLossModel class has the following configurable parameters
configurable with the attribute system:
· Frequency: reference frequency (default 2160 MHz), note that by setting the frequency
the wavelength is set accordingly automatically and viceversa).
· Lambda: the wavelength (0.139 meters, considering the above frequency).
· ShadowSigmaOutdoor: the standard deviation of the shadowing for outdoor nodes (defaul
7.0).
· ShadowSigmaIndoor: the standard deviation of the shadowing for indoor nodes (default
8.0).
· ShadowSigmaExtWalls: the standard deviation of the shadowing due to external walls
penetration for outdoor to indoor communications (default 5.0).
· RooftopLevel: the level of the rooftop of the building in meters (default 20 meters).
· Los2NlosThr: the value of distance of the switching point between line-of-sigth and
non-line-of-sight propagation model in meters (default 200 meters).
· ITU1411DistanceThr: the value of distance of the switching point between short range
(ITU 1211) communications and long range (Okumura Hata) in meters (default 200 meters).
· MinDistance: the minimum distance in meters between two nodes for evaluating the
pathloss (considered neglictible before this threshold) (default 0.5 meters).
· Environment: the environment scenario among Urban, SubUrban and OpenAreas (default
Urban).
· CitySize: the dimension of the city among Small, Medium, Large (default Large).
In order to use the hybrid mode, the class to be used is the
HybridBuildingMobilityLossModel, which allows the selection of the proper pathloss model
according to the pathloss logic presented in the design chapter. However, this solution
has the problem that the pathloss model switching points might present discontinuities due
to the different characteristics of the model. This implies that according to the specific
scenario, the threshold used for switching have to be properly tuned. The simple
OhBuildingMobilityLossModel overcome this problem by using only the Okumura Hata model and
the wall penetration losses.
Testing Documentation
Overview
To test and validate the ns-3 Building Pathloss module, some test suites is provided which
are integrated with the ns-3 test framework. To run them, you need to have configured the
build of the simulator in this way:
$ ./waf configure --enable-tests --enable-modules=buildings
$ ./test.py
The above will run not only the test suites belonging to the buildings module, but also
those belonging to all the other ns-3 modules on which the buildings module depends. See
the ns-3 manual for generic information on the testing framework.
You can get a more detailed report in HTML format in this way:
$ ./test.py -w results.html
After the above command has run, you can view the detailed result for each test by opening
the file results.html with a web browser.
You can run each test suite separately using this command:
$ ./test.py -s test-suite-name
For more details about test.py and the ns-3 testing framework, please refer to the ns-3
manual.
Description of the test suites
BuildingsHelper test
The test suite buildings-helper checks that the method
BuildingsHelper::MakeAllInstancesConsistent () works properly, i.e., that the
BuildingsHelper is successful in locating if nodes are outdoor or indoor, and if indoor
that they are located in the correct building, room and floor. Several test cases are
provided with different buildings (having different size, position, rooms and floors) and
different node positions. The test passes if each every node is located correctly.
BuildingPositionAllocator test
The test suite building-position-allocator feature two test cases that check that
respectively RandomRoomPositionAllocator and SameRoomPositionAllocator work properly. Each
test cases involves a single 2x3x2 room building (total 12 rooms) at known coordinates and
respectively 24 and 48 nodes. Both tests check that the number of nodes allocated in each
room is the expected one and that the position of the nodes is also correct.
Buildings Pathloss tests
The test suite buildings-pathloss-model provides different unit tests that compare the
expected results of the buildings pathloss module in specific scenarios with pre
calculated values obtained offline with an Octave script
(test/reference/buildings-pathloss.m). The tests are considered passed if the two values
are equal up to a tolerance of 0.1, which is deemed appropriate for the typical usage of
pathloss values (which are in dB).
In the following we detailed the scenarios considered, their selection has been done for
covering the wide set of possible pathloss logic combinations. The pathloss logic results
therefore implicitly tested.
Test #1 Okumura Hata
In this test we test the standard Okumura Hata model; therefore both eNB and UE are placed
outside at a distance of 2000 m. The frequency used is the E-UTRA band #5, which
correspond to 869 MHz (see table 5.5-1 of 36.101). The test includes also the validation
of the areas extensions (i.e., urban, suburban and open-areas) and of the city size
(small, medium and large).
Test #2 COST231 Model
This test is aimed at validating the COST231 model. The test is similar to the Okumura
Hata one, except that the frequency used is the EUTRA band #1 (2140 MHz) and that the test
can be performed only for large and small cities in urban scenarios due to model
limitations.
Test #3 2.6 GHz model
This test validates the 2.6 GHz Kun model. The test is similar to Okumura Hata one except
that the frequency is the EUTRA band #7 (2620 MHz) and the test can be performed only in
urban scenario.
Test #4 ITU1411 LoS model
This test is aimed at validating the ITU1411 model in case of line of sight within street
canyons transmissions. In this case the UE is placed at 100 meters far from the eNB, since
the threshold for switching between LoS and NLoS is left to default one (i.e., 200 m.).
Test #5 ITU1411 NLoS model
This test is aimed at validating the ITU1411 model in case of non line of sight over the
rooftop transmissions. In this case the UE is placed at 900 meters far from the eNB, in
order to be above the threshold for switching between LoS and NLoS is left to default one
(i.e., 200 m.).
Test #6 ITUP1238 model
This test is aimed at validating the ITUP1238 model in case of indoor transmissions. In
this case both the UE and the eNB are placed in a residential building with walls made of
concrete with windows. Ue is placed at the second floor and distances 30 meters far from
the eNB, which is placed at the first floor.
Test #7 Outdoor -> Indoor with Okumura Hata model
This test validates the outdoor to indoor transmissions for large distances. In this case
the UE is placed in a residential building with wall made of concrete with windows and
distances 2000 meters from the outdoor eNB.
Test #8 Outdoor -> Indoor with ITU1411 model
This test validates the outdoor to indoor transmissions for short distances. In this case
the UE is placed in a residential building with walls made of concrete with windows and
distances 100 meters from the outdoor eNB.
Test #9 Indoor -> Outdoor with ITU1411 model
This test validates the outdoor to indoor transmissions for very short distances. In this
case the eNB is placed in the second floor of a residential building with walls made of
concrete with windows and distances 100 meters from the outdoor UE (i.e., LoS
communication). Therefore the height gain has to be included in the pathloss evaluation.
Test #10 Indoor -> Outdoor with ITU1411 model
This test validates the outdoor to indoor transmissions for short distances. In this case
the eNB is placed in the second floor of a residential building with walls made of
concrete with windows and distances 500 meters from the outdoor UE (i.e., NLoS
communication). Therefore the height gain has to be included in the pathloss evaluation.
Buildings Shadowing Test
The test suite buildings-shadowing-test is a unit test intended to verify the statistical
distribution of the shadowing model implemented by BuildingsPathlossModel. The shadowing
is modeled according to a normal distribution with mean = 0 and variable standard
deviation ma, according to models commonly used in literature. Three test cases are
provided, which cover the cases of indoor, outdoor and indoor-to-outdoor communications.
Each test case generates 1000 different samples of shadowing for different pairs of
MobilityModel instances in a given scenario. Shadowing values are obtained by subtracting
from the total loss value returned by HybridBuildingsPathlossModel the path loss component
which is constant and pre-determined for each test case. The test verifies that the sample
mean and sample variance of the shadowing values fall within the 99% confidence interval
of the sample mean and sample variance. The test also verifies that the shadowing values
returned at successive times for the same pair of MobilityModel instances is constant.
References
[turkmani]
Turkmani A.M.D., J.D. Parson and D.G. Lewis, "Radio propagation into buildings at
441, 900 and 1400 MHz", in Proc. of 4th Int. Conference on Land Mobile Radio, 1987.
CLICK MODULAR ROUTER INTEGRATION
Click is a software architecture for building configurable routers. By using different
combinations of packet processing units called elements, a Click router can be made to
perform a specific kind of functionality. This flexibility provides a good platform for
testing and experimenting with different protocols.
Model Description
The source code for the Click model lives in the directory src/click.
Design
ns-3's design is well suited for an integration with Click due to the following reasons:
· Packets in ns-3 are serialised/deserialised as they move up/down the stack. This allows
ns-3 packets to be passed to and from Click as they are.
· This also means that any kind of ns-3 traffic generator and transport should work easily
on top of Click.
· By striving to implement click as an Ipv4RoutingProtocol instance, we can avoid
significant changes to the LL and MAC layer of the ns-3 code.
The design goal was to make the ns-3-click public API simple enough such that the user
needs to merely add an Ipv4ClickRouting instance to the node, and inform each Click node
of the Click configuration file (.click file) that it is to use.
This model implements the interface to the Click Modular Router and provides the
Ipv4ClickRouting class to allow a node to use Click for external routing. Unlike normal
Ipv4RoutingProtocol sub types, Ipv4ClickRouting doesn't use a RouteInput() method, but
instead, receives a packet on the appropriate interface and processes it accordingly. Note
that you need to have a routing table type element in your Click graph to use Click for
external routing. This is needed by the RouteOutput() function inherited from
Ipv4RoutingProtocol. Furthermore, a Click based node uses a different kind of L3 in the
form of Ipv4L3ClickProtocol, which is a trimmed down version of Ipv4L3Protocol.
Ipv4L3ClickProtocol passes on packets passing through the stack to Ipv4ClickRouting for
processing.
Developing a Simulator API to allow ns-3 to interact with Click
Much of the API is already well defined, which allows Click to probe for information from
the simulator (like a Node's ID, an Interface ID and so forth). By retaining most of the
methods, it should be possible to write new implementations specific to ns-3 for the same
functionality.
Hence, for the Click integration with ns-3, a class named Ipv4ClickRouting will handle the
interaction with Click. The code for the same can be found in
src/click/model/ipv4-click-routing.{cc,h}.
Packet hand off between ns-3 and Click
There are four kinds of packet hand-offs that can occur between ns-3 and Click.
· L4 to L3
· L3 to L4
· L3 to L2
· L2 to L3
To overcome this, we implement Ipv4L3ClickProtocol, a stripped down version of
Ipv4L3Protocol. Ipv4L3ClickProtocol passes packets to and from Ipv4ClickRouting
appropriately to perform routing.
Scope and Limitations
· In its current state, the NS-3 Click Integration is limited to use only with L3, leaving
NS-3 to handle L2. We are currently working on adding Click MAC support as well. See the
usage section to make sure that you design your Click graphs accordingly.
· Furthermore, ns-3-click will work only with userlevel elements. The complete list of
elements are available at http://read.cs.ucla.edu/click/elements. Elements that have
'all', 'userlevel' or 'ns' mentioned beside them may be used.
· As of now, the ns-3 interface to Click is Ipv4 only. We will be adding Ipv6 support in
the future.
References
· Eddie Kohler, Robert Morris, Benjie Chen, John Jannotti, and M. Frans Kaashoek. The
click modular router. ACM Transactions on Computer Systems 18(3), August 2000, pages
263-297.
· Lalith Suresh P., and Ruben Merz. Ns-3-click: click modular router integration for ns-3.
In Proc. of 3rd International ICST Workshop on NS-3 (WNS3), Barcelona, Spain. March,
2011.
· Michael Neufeld, Ashish Jain, and Dirk Grunwald. Nsclick: bridging network simulation
and deployment. MSWiM '02: Proceedings of the 5th ACM international workshop on Modeling
analysis and simulation of wireless and mobile systems, 2002, Atlanta, Georgia, USA.
http://doi.acm.org/10.1145/570758.570772
Usage
Building Click
The first step is to clone Click from the github repository and build it:
$ git clone https://github.com/kohler/click
$ cd click/
$ ./configure --disable-linuxmodule --enable-nsclick --enable-wifi
$ make
The --enable-wifi flag may be skipped if you don't intend on using Click with Wifi. *
Note: You don't need to do a 'make install'.
Once Click has been built successfully, change into the ns-3 directory and configure ns-3
with Click Integration support:
$ ./waf configure --enable-examples --enable-tests --with-nsclick=/path/to/click/source
Hint: If you have click installed one directory above ns-3 (such as in the ns-3-allinone
directory), and the name of the directory is 'click' (or a symbolic link to the directory
is named 'click'), then the --with-nsclick specifier is not necessary; the ns-3 build
system will successfully find the directory.
If it says 'enabled' beside 'NS-3 Click Integration Support', then you're good to go.
Note: If running modular ns-3, the minimum set of modules required to run all ns-3-click
examples is wifi, csma and config-store.
Next, try running one of the examples:
$ ./waf --run nsclick-simple-lan
You may then view the resulting .pcap traces, which are named nsclick-simple-lan-0-0.pcap
and nsclick-simple-lan-0-1.pcap.
Click Graph Instructions
The following should be kept in mind when making your Click graph:
· Only userlevel elements can be used.
· You will need to replace FromDevice and ToDevice elements with FromSimDevice and
ToSimDevice elements.
· Packets to the kernel are sent up using ToSimDevice(tap0,IP).
· For any node, the device which sends/receives packets to/from the kernel, is named
'tap0'. The remaining interfaces should be named eth0, eth1 and so forth (even if you're
using wifi). Please note that the device numbering should begin from 0. In future, this
will be made flexible so that users can name devices in their Click file as they wish.
· A routing table element is a mandatory. The OUTports of the routing table element should
correspond to the interface number of the device through which the packet will
ultimately be sent out. Violating this rule will lead to really weird packet traces.
This routing table element's name should then be passed to the Ipv4ClickRouting protocol
object as a simulation parameter. See the Click examples for details.
· The current implementation leaves Click with mainly L3 functionality, with ns-3 handling
L2. We will soon begin working to support the use of MAC protocols on Click as well.
This means that as of now, Click's Wifi specific elements cannot be used with ns-3.
Debugging Packet Flows from Click
From any point within a Click graph, you may use the Print (‐
http://read.cs.ucla.edu/click/elements/print) element and its variants for pretty printing
of packet contents. Furthermore, you may generate pcap traces of packets flowing through a
Click graph by using the ToDump (http://read.cs.ucla.edu/click/elements/todump) element as
well. For instance:
myarpquerier
-> Print(fromarpquery,64)
-> ToDump(out_arpquery,PER_NODE 1)
-> ethout;
and ...will print the contents of packets that flow out of the ArpQuerier, then generate a
pcap trace file which will have a suffix 'out_arpquery', for each node using the Click
file, before pushing packets onto 'ethout'.
Helper
To have a node run Click, the easiest way would be to use the ClickInternetStackHelper
class in your simulation script. For instance:
ClickInternetStackHelper click;
click.SetClickFile (myNodeContainer, "nsclick-simple-lan.click");
click.SetRoutingTableElement (myNodeContainer, "u/rt");
click.Install (myNodeContainer);
The example scripts inside src/click/examples/ demonstrate the use of Click based nodes in
different scenarios. The helper source can be found inside
src/click/helper/click-internet-stack-helper.{h,cc}
Examples
The following examples have been written, which can be found in src/click/examples/:
· nsclick-simple-lan.cc and nsclick-raw-wlan.cc: A Click based node communicating with a
normal ns-3 node without Click, using Csma and Wifi respectively. It also demonstrates
the use of TCP on top of Click, something which the original nsclick implementation for
NS-2 couldn't achieve.
· nsclick-udp-client-server-csma.cc and nsclick-udp-client-server-wifi.cc: A 3 node LAN
(Csma and Wifi respectively) wherein 2 Click based nodes run a UDP client, that sends
packets to a third Click based node running a UDP server.
· nsclick-routing.cc: One Click based node communicates to another via a third node that
acts as an IP router (using the IP router Click configuration). This demonstrates
routing using Click.
Scripts are available within <click-dir>/conf/ that allow you to generate Click files for
some common scenarios. The IP Router used in nsclick-routing.cc was generated from the
make-ip-conf.pl file and slightly adapted to work with ns-3-click.
Validation
This model has been tested as follows:
· Unit tests have been written to verify the internals of Ipv4ClickRouting. This can be
found in src/click/ipv4-click-routing-test.cc. These tests verify whether the methods
inside Ipv4ClickRouting which deal with Device name to ID, IP Address from device name
and Mac Address from device name bindings work as expected.
· The examples have been used to test Click with actual simulation scenarios. These can be
found in src/click/examples/. These tests cover the following: the use of different
kinds of transports on top of Click, TCP/UDP, whether Click nodes can communicate with
non-Click based nodes, whether Click nodes can communicate with each other, using Click
to route packets using static routing.
· Click has been tested with Csma, Wifi and Point-to-Point devices. Usage instructions are
available in the preceding section.
CSMA NETDEVICE
This is the introduction to CSMA NetDevice chapter, to complement the Csma model doxygen.
Overview of the CSMA model
The ns-3 CSMA device models a simple bus network in the spirit of Ethernet. Although it
does not model any real physical network you could ever build or buy, it does provide some
very useful functionality.
Typically when one thinks of a bus network Ethernet or IEEE 802.3 comes to mind. Ethernet
uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection with exponentially
increasing backoff to contend for the shared transmission medium. The ns-3 CSMA device
models only a portion of this process, using the nature of the globally available channel
to provide instantaneous (faster than light) carrier sense and priority-based collision
"avoidance." Collisions in the sense of Ethernet never happen and so the ns-3 CSMA device
does not model collision detection, nor will any transmission in progress be "jammed."
CSMA Layer Model
There are a number of conventions in use for describing layered communications
architectures in the literature and in textbooks. The most common layering model is the
ISO seven layer reference model. In this view the CsmaNetDevice and CsmaChannel pair
occupies the lowest two layers -- at the physical (layer one), and data link (layer two)
positions. Another important reference model is that specified by RFC 1122, "Requirements
for Internet Hosts -- Communication Layers." In this view the CsmaNetDevice and
CsmaChannel pair occupies the lowest layer -- the link layer. There is also a seemingly
endless litany of alternative descriptions found in textbooks and in the literature. We
adopt the naming conventions used in the IEEE 802 standards which speak of LLC, MAC, MII
and PHY layering. These acronyms are defined as:
· LLC: Logical Link Control;
· MAC: Media Access Control;
· MII: Media Independent Interface;
· PHY: Physical Layer.
In this case the LLC and MAC are sublayers of the OSI data link layer and the MII and PHY
are sublayers of the OSI physical layer.
The "top" of the CSMA device defines the transition from the network layer to the data
link layer. This transition is performed by higher layers by calling either
CsmaNetDevice::Send or CsmaNetDevice::SendFrom.
In contrast to the IEEE 802.3 standards, there is no precisely specified PHY in the CSMA
model in the sense of wire types, signals or pinouts. The "bottom" interface of the
CsmaNetDevice can be thought of as as a kind of Media Independent Interface (MII) as seen
in the "Fast Ethernet" (IEEE 802.3u) specifications. This MII interface fits into a
corresponding media independent interface on the CsmaChannel. You will not find the
equivalent of a 10BASE-T or a 1000BASE-LX PHY.
The CsmaNetDevice calls the CsmaChannel through a media independent interface. There is a
method defined to tell the channel when to start "wiggling the wires" using the method
CsmaChannel::TransmitStart, and a method to tell the channel when the transmission process
is done and the channel should begin propagating the last bit across the "wire":
CsmaChannel::TransmitEnd.
When the TransmitEnd method is executed, the channel will model a single uniform signal
propagation delay in the medium and deliver copes of the packet to each of the devices
attached to the packet via the CsmaNetDevice::Receive method.
There is a "pin" in the device media independent interface corresponding to "COL"
(collision). The state of the channel may be sensed by calling CsmaChannel::GetState. Each
device will look at this "pin" before starting a send and will perform appropriate backoff
operations if required.
Properly received packets are forwarded up to higher levels from the CsmaNetDevice via a
callback mechanism. The callback function is initialized by the higher layer (when the net
device is attached) using CsmaNetDevice::SetReceiveCallback and is invoked upon "proper"
reception of a packet by the net device in order to forward the packet up the protocol
stack.
CSMA Channel Model
The class CsmaChannel models the actual transmission medium. There is no fixed limit for
the number of devices connected to the channel. The CsmaChannel models a data rate and a
speed-of-light delay which can be accessed via the attributes "DataRate" and "Delay"
respectively. The data rate provided to the channel is used to set the data rates used by
the transmitter sections of the CSMA devices connected to the channel. There is no way to
independently set data rates in the devices. Since the data rate is only used to calculate
a delay time, there is no limitation (other than by the data type holding the value) on
the speed at which CSMA channels and devices can operate; and no restriction based on any
kind of PHY characteristics.
The CsmaChannel has three states, IDLE, TRANSMITTING and PROPAGATING. These three states
are "seen" instantaneously by all devices on the channel. By this we mean that if one
device begins or ends a simulated transmission, all devices on the channel are immediately
aware of the change in state. There is no time during which one device may see an IDLE
channel while another device physically further away in the collision domain may have
begun transmitting with the associated signals not propagated down the channel to other
devices. Thus there is no need for collision detection in the CsmaChannel model and it is
not implemented in any way.
We do, as the name indicates, have a Carrier Sense aspect to the model. Since the
simulator is single threaded, access to the common channel will be serialized by the
simulator. This provides a deterministic mechanism for contending for the channel. The
channel is allocated (transitioned from state IDLE to state TRANSMITTING) on a first-come
first-served basis. The channel always goes through a three state process:
IDLE -> TRANSMITTING -> PROPAGATING -> IDLE
The TRANSMITTING state models the time during which the source net device is actually
wiggling the signals on the wire. The PROPAGATING state models the time after the last bit
was sent, when the signal is propagating down the wire to the "far end."
The transition to the TRANSMITTING state is driven by a call to
CsmaChannel::TransmitStart which is called by the net device that transmits the packet. It
is the responsibility of that device to end the transmission with a call to
CsmaChannel::TransmitEnd at the appropriate simulation time that reflects the time elapsed
to put all of the packet bits on the wire. When TransmitEnd is called, the channel
schedules an event corresponding to a single speed-of-light delay. This delay applies to
all net devices on the channel identically. You can think of a symmetrical hub in which
the packet bits propagate to a central location and then back out equal length cables to
the other devices on the channel. The single "speed of light" delay then corresponds to
the time it takes for: 1) a signal to propagate from one CsmaNetDevice through its cable
to the hub; plus 2) the time it takes for the hub to forward the packet out a port; plus
3) the time it takes for the signal in question to propagate to the destination net
device.
The CsmaChannel models a broadcast medium so the packet is delivered to all of the devices
on the channel (including the source) at the end of the propagation time. It is the
responsibility of the sending device to determine whether or not it receives a packet
broadcast over the channel.
The CsmaChannel provides following Attributes:
· DataRate: The bitrate for packet transmission on connected devices;
· Delay: The speed of light transmission delay for the channel.
CSMA Net Device Model
The CSMA network device appears somewhat like an Ethernet device. The CsmaNetDevice
provides following Attributes:
· Address: The Mac48Address of the device;
· SendEnable: Enable packet transmission if true;
· ReceiveEnable: Enable packet reception if true;
· EncapsulationMode: Type of link layer encapsulation to use;
· RxErrorModel: The receive error model;
· TxQueue: The transmit queue used by the device;
· InterframeGap: The optional time to wait between "frames";
· Rx: A trace source for received packets;
· Drop: A trace source for dropped packets.
The CsmaNetDevice supports the assignment of a "receive error model." This is an
ErrorModel object that is used to simulate data corruption on the link.
Packets sent over the CsmaNetDevice are always routed through the transmit queue to
provide a trace hook for packets sent out over the network. This transmit queue can be set
(via attribute) to model different queuing strategies.
Also configurable by attribute is the encapsulation method used by the device. Every
packet gets an EthernetHeader that includes the destination and source MAC addresses, and
a length/type field. Every packet also gets an EthernetTrailer which includes the FCS.
Data in the packet may be encapsulated in different ways.
By default, or by setting the "EncapsulationMode" attribute to "Dix", the encapsulation is
according to the DEC, Intel, Xerox standard. This is sometimes called EthernetII framing
and is the familiar destination MAC, source MAC, EtherType, Data, CRC format.
If the "EncapsulationMode" attribute is set to "Llc", the encapsulation is by LLC SNAP. In
this case, a SNAP header is added that contains the EtherType (IP or ARP).
The other implemented encapsulation modes are IP_ARP (set "EncapsulationMode" to "IpArp")
in which the length type of the Ethernet header receives the protocol number of the
packet; or ETHERNET_V1 (set "EncapsulationMode" to "EthernetV1") in which the length type
of the Ethernet header receives the length of the packet. A "Raw" encapsulation mode is
defined but not implemented -- use of the RAW mode results in an assertion.
Note that all net devices on a channel must be set to the same encapsulation mode for
correct results. The encapsulation mode is not sensed at the receiver.
The CsmaNetDevice implements a random exponential backoff algorithm that is executed if
the channel is determined to be busy (TRANSMITTING or PPROPAGATING) when the device wants
to start propagating. This results in a random delay of up to pow (2, retries) - 1
microseconds before a retry is attempted. The default maximum number of retries is 1000.
Using the CsmaNetDevice
The CSMA net devices and channels are typically created and configured using the
associated CsmaHelper object. The various ns-3 device helpers generally work in a similar
way, and their use is seen in many of our example programs.
The conceptual model of interest is that of a bare computer "husk" into which you plug net
devices. The bare computers are created using a NodeContainer helper. You just ask this
helper to create as many computers (we call them Nodes) as you need on your network:
NodeContainer csmaNodes;
csmaNodes.Create (nCsmaNodes);
Once you have your nodes, you need to instantiate a CsmaHelper and set any attributes you
may want to change.:
CsmaHelper csma;
csma.SetChannelAttribute ("DataRate", StringValue ("100Mbps"));
csma.SetChannelAttribute ("Delay", TimeValue (NanoSeconds (6560)));
csma.SetDeviceAttribute ("EncapsulationMode", StringValue ("Dix"));
csma.SetDeviceAttribute ("FrameSize", UintegerValue (2000));
Once the attributes are set, all that remains is to create the devices and install them on
the required nodes, and to connect the devices together using a CSMA channel. When we
create the net devices, we add them to a container to allow you to use them in the future.
This all takes just one line of code.:
NetDeviceContainer csmaDevices = csma.Install (csmaNodes);
We recommend thinking carefully about changing these Attributes, since it can result in
behavior that surprises users. We allow this because we believe flexibility is important.
As an example of a possibly surprising effect of changing Attributes, consider the
following:
The Mtu Attribute indicates the Maximum Transmission Unit to the device. This is the size
of the largest Protocol Data Unit (PDU) that the device can send. This Attribute defaults
to 1500 bytes and corresponds to a number found in RFC 894, "A Standard for the
Transmission of IP Datagrams over Ethernet Networks." The number is actually derived from
the maximum packet size for 10Base5 (full-spec Ethernet) networks -- 1518 bytes. If you
subtract DIX encapsulation overhead for Ethernet packets (18 bytes) you will end up with a
maximum possible data size (MTU) of 1500 bytes. One can also find that the MTU for IEEE
802.3 networks is 1492 bytes. This is because LLC/SNAP encapsulation adds an extra eight
bytes of overhead to the packet. In both cases, the underlying network hardware is
limited to 1518 bytes, but the MTU is different because the encapsulation is different.
If one leaves the Mtu Attribute at 1500 bytes and changes the encapsulation mode Attribute
to Llc, the result will be a network that encapsulates 1500 byte PDUs with LLC/SNAP
framing resulting in packets of 1526 bytes. This would be illegal in many networks, but
we allow you do do this. This results in a simulation that quite subtly does not reflect
what you might be expecting since a real device would balk at sending a 1526 byte packet.
There also exist jumbo frames (1500 < MTU <= 9000 bytes) and super-jumbo (MTU > 9000
bytes) frames that are not officially sanctioned by IEEE but are available in some
high-speed (Gigabit) networks and NICs. In the CSMA model, one could leave the
encapsulation mode set to Dix, and set the Mtu to 64000 bytes -- even though an associated
CsmaChannel DataRate was left at 10 megabits per second (certainly not Gigabit Ethernet).
This would essentially model an Ethernet switch made out of vampire-tapped 1980s-style
10Base5 networks that support super-jumbo datagrams, which is certainly not something that
was ever made, nor is likely to ever be made; however it is quite easy for you to
configure.
Be careful about assumptions regarding what CSMA is actually modelling and how
configuration (Attributes) may allow you to swerve considerably away from reality.
CSMA Tracing
Like all ns-3 devices, the CSMA Model provides a number of trace sources. These trace
sources can be hooked using your own custom trace code, or you can use our helper
functions to arrange for tracing to be enabled on devices you specify.
Upper-Level (MAC) Hooks
From the point of view of tracing in the net device, there are several interesting points
to insert trace hooks. A convention inherited from other simulators is that packets
destined for transmission onto attached networks pass through a single "transmit queue" in
the net device. We provide trace hooks at this point in packet flow, which corresponds
(abstractly) only to a transition from the network to data link layer, and call them
collectively the device MAC hooks.
When a packet is sent to the CSMA net device for transmission it always passes through the
transmit queue. The transmit queue in the CsmaNetDevice inherits from Queue, and therefore
inherits three trace sources:
· An Enqueue operation source (see Queue::m_traceEnqueue);
· A Dequeue operation source (see Queue::m_traceDequeue);
· A Drop operation source (see Queue::m_traceDrop).
The upper-level (MAC) trace hooks for the CsmaNetDevice are, in fact, exactly these three
trace sources on the single transmit queue of the device.
The m_traceEnqueue event is triggered when a packet is placed on the transmit queue. This
happens at the time that CsmaNetDevice::Send or CsmaNetDevice::SendFrom is called by a
higher layer to queue a packet for transmission.
The m_traceDequeue event is triggered when a packet is removed from the transmit queue.
Dequeues from the transmit queue can happen in three situations: 1) If the underlying
channel is idle when the CsmaNetDevice::Send or CsmaNetDevice::SendFrom is called, a
packet is dequeued from the transmit queue and immediately transmitted; 2) If the
underlying channel is idle, a packet may be dequeued and immediately transmitted in an
internal TransmitCompleteEvent that functions much like a transmit complete interrupt
service routine; or 3) from the random exponential backoff handler if a timeout is
detected.
Case (3) implies that a packet is dequeued from the transmit queue if it is unable to be
transmitted according to the backoff rules. It is important to understand that this will
appear as a Dequeued packet and it is easy to incorrectly assume that the packet was
transmitted since it passed through the transmit queue. In fact, a packet is actually
dropped by the net device in this case. The reason for this behavior is due to the
definition of the Queue Drop event. The m_traceDrop event is, by definition, fired when a
packet cannot be enqueued on the transmit queue because it is full. This event only fires
if the queue is full and we do not overload this event to indicate that the CsmaChannel is
"full."
Lower-Level (PHY) Hooks
Similar to the upper level trace hooks, there are trace hooks available at the lower
levels of the net device. We call these the PHY hooks. These events fire from the device
methods that talk directly to the CsmaChannel.
The trace source m_dropTrace is called to indicate a packet that is dropped by the device.
This happens in two cases: First, if the receive side of the net device is not enabled
(see CsmaNetDevice::m_receiveEnable and the associated attribute "ReceiveEnable").
The m_dropTrace is also used to indicate that a packet was discarded as corrupt if a
receive error model is used (see CsmaNetDevice::m_receiveErrorModel and the associated
attribute "ReceiveErrorModel").
The other low-level trace source fires on reception of an accepted packet (see
CsmaNetDevice::m_rxTrace). A packet is accepted if it is destined for the broadcast
address, a multicast address, or to the MAC address assigned to the net device.
Summary
The ns3 CSMA model is a simplistic model of an Ethernet-like network. It supports a
Carrier-Sense function and allows for Multiple Access to a shared medium. It is not
physical in the sense that the state of the medium is instantaneously shared among all
devices. This means that there is no collision detection required in this model and none
is implemented. There will never be a "jam" of a packet already on the medium. Access to
the shared channel is on a first-come first-served basis as determined by the simulator
scheduler. If the channel is determined to be busy by looking at the global state, a
random exponential backoff is performed and a retry is attempted.
Ns-3 Attributes provide a mechanism for setting various parameters in the device and
channel such as addresses, encapsulation modes and error model selection. Trace hooks are
provided in the usual manner with a set of upper level hooks corresponding to a transmit
queue and used in ASCII tracing; and also a set of lower level hooks used in pcap tracing.
Although the ns-3 CsmaChannel and CsmaNetDevice does not model any kind of network you
could build or buy, it does provide us with some useful functionality. You should,
however, understand that it is explicitly not Ethernet or any flavor of IEEE 802.3 but an
interesting subset.
DATA COLLECTION
This chapter describes the ns-3 Data Collection Framework (DCF), which provides
capabilities to obtain data generated by models in the simulator, to perform on-line
reduction and data processing, and to marshal raw or transformed data into various output
formats.
The framework presently supports standalone ns-3 runs that don't rely on any external
program execution control. The objects provided by the DCF may be hooked to ns-3 trace
sources to enable data processing.
The source code for the classes lives in the directory src/stats.
This chapter is organized as follows. First, an overview of the architecture is
presented. Next, the helpers for these classes are presented; this initial treatment
should allow basic use of the data collection framework for many use cases. Users who
wish to produce output outside of the scope of the current helpers, or who wish to create
their own data collection objects, should read the remainder of the chapter, which goes
into detail about all of the basic DCF object types and provides low-level coding
examples.
Design
The DCF consists of three basic classes:
· Probe is a mechanism to instrument and control the output of simulation data that is
used to monitor interesting events. It produces output in the form of one or more ns-3
trace sources. Probe objects are hooked up to one or more trace sinks (called
Collectors), which process samples on-line and prepare them for output.
· Collector consumes the data generated by one or more Probe objects. It performs
transformations on the data, such as normalization, reduction, and the computation of
basic statistics. Collector objects do not produce data that is directly output by the
ns-3 run; instead, they output data downstream to another type of object, called
Aggregator, which performs that function. Typically, Collectors output their data in
the form of trace sources as well, allowing collectors to be chained in series.
· Aggregator is the end point of the data collected by a network of Probes and Collectors.
The main responsibility of the Aggregator is to marshal data and their corresponding
metadata, into different output formats such as plain text files, spreadsheet files, or
databases.
All three of these classes provide the capability to dynamically turn themselves on or off
throughout a simulation.
Any standalone ns-3 simulation run that uses the DCF will typically create at least one
instance of each of the three classes above.
[image] Data Collection Framework overview.UNINDENT
The overall flow of data processing is depicted in Data Collection Framework overview.
On the left side, a running ns-3 simulation is depicted. In the course of running the
simulation, data is made available by models through trace sources, or via other means.
The diagram depicts that probes can be connected to these trace sources to receive data
asynchronously, or probes can poll for data. Data is then passed to a collector object
that transforms the data. Finally, an aggregator can be connected to the outputs of the
collector, to generate plots, files, or databases.
[image] Data Collection Framework aggregation.UNINDENT
A variation on the above figure is provided in Data Collection Framework aggregation.
This second figure illustrates that the DCF objects may be chained together in a manner
that downstream objects take inputs from multiple upstream objects. The figure
conceptually shows that multiple probes may generate output that is fed into a single
collector; as an example, a collector that outputs a ratio of two counters would
typically acquire each counter data from separate probes. Multiple collectors can also
feed into a single aggregator, which (as its name implies) may collect a number of data
streams for inclusion into a single plot, file, or database.
Data Collection Helpers
The full flexibility of the data collection framework is provided by the interconnection
of probes, collectors, and aggregators. Performing all of these interconnections leads to
many configuration statements in user programs. For ease of use, some of the most common
operations can be combined and encapsulated in helper functions. In addition, some
statements involving ns-3 trace sources do not have Python bindings, due to limitations in
the bindings.
Data Collection Helpers Overview
In this section, we provide an overview of some helper classes that have been created to
ease the configuration of the data collection framework for some common use cases. The
helpers allow users to form common operations with only a few statements in their C++ or
Python programs. But, this ease of use comes at the cost of significantly less
flexibility than low-level configuration can provide, and the need to explicitly code
support for new Probe types into the helpers (to work around an issue described below).
The emphasis on the current helpers is to marshal data out of ns-3 trace sources into
gnuplot plots or text files, without a high degree of output customization or statistical
processing (initially). Also, the use is constrained to the available probe types in
ns-3. Later sections of this documentation will go into more detail about creating new
Probe types, as well as details about hooking together Probes, Collectors, and Aggregators
in custom arrangements.
To date, two Data Collection helpers have been implemented:
· GnuplotHelper
· FileHelper
GnuplotHelper
The GnuplotHelper is a helper class for producing output files used to make gnuplots. The
overall goal is to provide the ability for users to quickly make plots from data exported
in ns-3 trace sources. By default, a minimal amount of data transformation is performed;
the objective is to generate plots with as few (default) configuration statements as
possible.
GnuplotHelper Overview
The GnuplotHelper will create 3 different files at the end of the simulation:
· A space separated gnuplot data file
· A gnuplot control file
· A shell script to generate the gnuplot
There are two configuration statements that are needed to produce plots. The first
statement configures the plot (filename, title, legends, and output type, where the output
type defaults to PNG if unspecified):
void ConfigurePlot (const std::string &outputFileNameWithoutExtension,
const std::string &title,
const std::string &xLegend,
const std::string &yLegend,
const std::string &terminalType = ".png");
The second statement hooks the trace source of interest:
void PlotProbe (const std::string &typeId,
const std::string &path,
const std::string &probeTraceSource,
const std::string &title);
The arguments are as follows:
· typeId: The ns-3 TypeId of the Probe
· path: The path in the ns-3 configuration namespace to one or more trace sources
· probeTraceSource: Which output of the probe (itself a trace source) should be plotted
· title: The title to associate with the dataset(s) (in the gnuplot legend)
A variant on the PlotProbe above is to specify a fifth optional argument that controls
where in the plot the key (legend) is placed.
A fully worked example (from seventh.cc) is shown below:
// Create the gnuplot helper.
GnuplotHelper plotHelper;
// Configure the plot.
// Configure the plot. The first argument is the file name prefix
// for the output files generated. The second, third, and fourth
// arguments are, respectively, the plot title, x-axis, and y-axis labels
plotHelper.ConfigurePlot ("seventh-packet-byte-count",
"Packet Byte Count vs. Time",
"Time (Seconds)",
"Packet Byte Count",
"png");
// Specify the probe type, trace source path (in configuration namespace), and
// probe output trace source ("OutputBytes") to plot. The fourth argument
// specifies the name of the data series label on the plot. The last
// argument formats the plot by specifying where the key should be placed.
plotHelper.PlotProbe (probeType,
tracePath,
"OutputBytes",
"Packet Byte Count",
GnuplotAggregator::KEY_BELOW);
In this example, the probeType and tracePath are as follows (for IPv4):
probeType = "ns3::Ipv4PacketProbe";
tracePath = "/NodeList/*/$ns3::Ipv4L3Protocol/Tx";
The probeType is a key parameter for this helper to work. This TypeId must be registered
in the system, and the signature on the Probe's trace sink must match that of the trace
source it is being hooked to. Probe types are pre-defined for a number of data types
corresponding to ns-3 traced values, and for a few other trace source signatures such as
the 'Tx' trace source of ns3::Ipv4L3Protocol class.
Note that the trace source path specified may contain wildcards. In this case, multiple
datasets are plotted on one plot; one for each matched path.
The main output produced will be three files:
seventh-packet-byte-count.dat
seventh-packet-byte-count.plt
seventh-packet-byte-count.sh
At this point, users can either hand edit the .plt file for further customizations, or
just run it through gnuplot. Running sh seventh-packet-byte-count.sh simply runs the plot
through gnuplot, as shown below.
[image] 2-D Gnuplot Created by seventh.cc Example..UNINDENT
It can be seen that the key elements (legend, title, legend placement, xlabel, ylabel,
and path for the data) are all placed on the plot. Since there were two matches to the
configuration path provided, the two data series are shown:
· Packet Byte Count-0 corresponds to /NodeList/0/$ns3::Ipv4L3Protocol/Tx
· Packet Byte Count-1 corresponds to /NodeList/1/$ns3::Ipv4L3Protocol/Tx
GnuplotHelper ConfigurePlot
The GnuplotHelper's ConfigurePlot() function can be used to configure plots.
It has the following prototype:
void ConfigurePlot (const std::string &outputFileNameWithoutExtension,
const std::string &title,
const std::string &xLegend,
const std::string &yLegend,
const std::string &terminalType = ".png");
It has the following arguments:
┌───────────────────────────────┬──────────────────────────────────┐
│Argument │ Description │
├───────────────────────────────┼──────────────────────────────────┤
│outputFileNameWithoutExtension │ Name of gnuplot related files to │
│ │ write with no extension. │
├───────────────────────────────┼──────────────────────────────────┤
│title │ Plot title string to use for │
│ │ this plot. │
└───────────────────────────────┴──────────────────────────────────┘
│xLegend │ The legend for the x horizontal │
│ │ axis. │
├───────────────────────────────┼──────────────────────────────────┤
│yLegend │ The legend for the y vertical │
│ │ axis. │
├───────────────────────────────┼──────────────────────────────────┤
│terminalType │ Terminal type setting string for │
│ │ output. The default terminal │
│ │ type is "png". │
└───────────────────────────────┴──────────────────────────────────┘
The GnuplotHelper's ConfigurePlot() function configures plot related parameters for this
gnuplot helper so that it will create a space separated gnuplot data file named
outputFileNameWithoutExtension + ".dat", a gnuplot control file named
outputFileNameWithoutExtension + ".plt", and a shell script to generate the gnuplot named
outputFileNameWithoutExtension + ".sh".
An example of how to use this function can be seen in the seventh.cc code described above
where it was used as follows:
plotHelper.ConfigurePlot ("seventh-packet-byte-count",
"Packet Byte Count vs. Time",
"Time (Seconds)",
"Packet Byte Count",
"png");
GnuplotHelper PlotProbe
The GnuplotHelper's PlotProbe() function can be used to plot values generated by probes.
It has the following prototype:
void PlotProbe (const std::string &typeId,
const std::string &path,
const std::string &probeTraceSource,
const std::string &title,
enum GnuplotAggregator::KeyLocation keyLocation = GnuplotAggregator::KEY_INSIDE);
It has the following arguments:
┌─────────────────┬──────────────────────────────────┐
│Argument │ Description │
├─────────────────┼──────────────────────────────────┤
│typeId │ The type ID for the probe │
│ │ created by this helper. │
├─────────────────┼──────────────────────────────────┤
│path │ Config path to access the trace │
│ │ source. │
├─────────────────┼──────────────────────────────────┤
│probeTraceSource │ The probe trace source to │
│ │ access. │
├─────────────────┼──────────────────────────────────┤
│title │ The title to be associated to │
│ │ this dataset │
├─────────────────┼──────────────────────────────────┤
│keyLocation │ The location of the key in the │
│ │ plot. The default location is │
│ │ inside. │
└─────────────────┴──────────────────────────────────┘
The GnuplotHelper's PlotProbe() function plots a dataset generated by hooking the ns-3
trace source with a probe created by the helper, and then plotting the values from the
probeTraceSource. The dataset will have the provided title, and will consist of the
'newValue' at each timestamp.
If the config path has more than one match in the system because there is a wildcard, then
one dataset for each match will be plotted. The dataset titles will be suffixed with the
matched characters for each of the wildcards in the config path, separated by spaces. For
example, if the proposed dataset title is the string "bytes", and there are two wildcards
in the path, then dataset titles like "bytes-0 0" or "bytes-12 9" will be possible as
labels for the datasets that are plotted.
An example of how to use this function can be seen in the seventh.cc code described above
where it was used (with variable substitution) as follows:
plotHelper.PlotProbe ("ns3::Ipv4PacketProbe",
"/NodeList/*/$ns3::Ipv4L3Protocol/Tx",
"OutputBytes",
"Packet Byte Count",
GnuplotAggregator::KEY_BELOW);
Other Examples
Gnuplot Helper Example
A slightly simpler example than the seventh.cc example can be found in
src/stats/examples/gnuplot-helper-example.cc. The following 2-D gnuplot was created using
the example.
[image] 2-D Gnuplot Created by gnuplot-helper-example.cc Example..UNINDENT
In this example, there is an Emitter object that increments its counter according to a
Poisson process and then emits the counter's value as a trace source.
Ptr<Emitter> emitter = CreateObject<Emitter> ();
Names::Add ("/Names/Emitter", emitter);
Note that because there are no wildcards in the path used below, only 1 datastream was
drawn in the plot. This single datastream in the plot is simply labeled "Emitter Count",
with no extra suffixes like one would see if there were wildcards in the path.
// Create the gnuplot helper.
GnuplotHelper plotHelper;
// Configure the plot.
plotHelper.ConfigurePlot ("gnuplot-helper-example",
"Emitter Counts vs. Time",
"Time (Seconds)",
"Emitter Count",
"png");
// Plot the values generated by the probe. The path that we provide
// helps to disambiguate the source of the trace.
plotHelper.PlotProbe ("ns3::Uinteger32Probe",
"/Names/Emitter/Counter",
"Output",
"Emitter Count",
GnuplotAggregator::KEY_INSIDE);
FileHelper
The FileHelper is a helper class used to put data values into a file. The overall goal is
to provide the ability for users to quickly make formatted text files from data exported
in ns-3 trace sources. By default, a minimal amount of data transformation is performed;
the objective is to generate files with as few (default) configuration statements as
possible.
FileHelper Overview
The FileHelper will create 1 or more text files at the end of the simulation.
The FileHelper can create 4 different types of text files:
· Formatted
· Space separated (the default)
· Comma separated
· Tab separated
Formatted files use C-style format strings and the sprintf() function to print their
values in the file being written.
The following text file with 2 columns of formatted values named
seventh-packet-byte-count-0.txt was created using more new code that was added to the
original ns-3 Tutorial example's code. Only the first 10 lines of this file are shown
here for brevity.
Time (Seconds) = 1.000e+00 Packet Byte Count = 40
Time (Seconds) = 1.004e+00 Packet Byte Count = 40
Time (Seconds) = 1.004e+00 Packet Byte Count = 576
Time (Seconds) = 1.009e+00 Packet Byte Count = 576
Time (Seconds) = 1.009e+00 Packet Byte Count = 576
Time (Seconds) = 1.015e+00 Packet Byte Count = 512
Time (Seconds) = 1.017e+00 Packet Byte Count = 576
Time (Seconds) = 1.017e+00 Packet Byte Count = 544
Time (Seconds) = 1.025e+00 Packet Byte Count = 576
Time (Seconds) = 1.025e+00 Packet Byte Count = 544
...
The following different text file with 2 columns of formatted values named
seventh-packet-byte-count-1.txt was also created using the same new code that was added to
the original ns-3 Tutorial example's code. Only the first 10 lines of this file are shown
here for brevity.
Time (Seconds) = 1.002e+00 Packet Byte Count = 40
Time (Seconds) = 1.007e+00 Packet Byte Count = 40
Time (Seconds) = 1.013e+00 Packet Byte Count = 40
Time (Seconds) = 1.020e+00 Packet Byte Count = 40
Time (Seconds) = 1.028e+00 Packet Byte Count = 40
Time (Seconds) = 1.036e+00 Packet Byte Count = 40
Time (Seconds) = 1.045e+00 Packet Byte Count = 40
Time (Seconds) = 1.053e+00 Packet Byte Count = 40
Time (Seconds) = 1.061e+00 Packet Byte Count = 40
Time (Seconds) = 1.069e+00 Packet Byte Count = 40
...
The new code that was added to produce the two text files is below. More details about
this API will be covered in a later section.
Note that because there were 2 matches for the wildcard in the path, 2 separate text files
were created. The first text file, which is named "seventh-packet-byte-count-0.txt",
corresponds to the wildcard match with the "*" replaced with "0". The second text file,
which is named "seventh-packet-byte-count-1.txt", corresponds to the wildcard match with
the "*" replaced with "1". Also, note that the function call to WriteProbe() will give an
error message if there are no matches for a path that contains wildcards.
// Create the file helper.
FileHelper fileHelper;
// Configure the file to be written.
fileHelper.ConfigureFile ("seventh-packet-byte-count",
FileAggregator::FORMATTED);
// Set the labels for this formatted output file.
fileHelper.Set2dFormat ("Time (Seconds) = %.3e\tPacket Byte Count = %.0f");
// Write the values generated by the probe.
fileHelper.WriteProbe ("ns3::Ipv4PacketProbe",
"/NodeList/*/$ns3::Ipv4L3Protocol/Tx",
"OutputBytes");
FileHelper ConfigureFile
The FileHelper's ConfigureFile() function can be used to configure text files.
It has the following prototype:
void ConfigureFile (const std::string &outputFileNameWithoutExtension,
enum FileAggregator::FileType fileType = FileAggregator::SPACE_SEPARATED);
It has the following arguments:
┌───────────────────────────────┬──────────────────────────────────┐
│Argument │ Description │
├───────────────────────────────┼──────────────────────────────────┤
│outputFileNameWithoutExtension │ Name of output file to write │
│ │ with no extension. │
├───────────────────────────────┼──────────────────────────────────┤
│fileType │ Type of file to write. The │
│ │ default type of file is space │
│ │ separated. │
└───────────────────────────────┴──────────────────────────────────┘
The FileHelper's ConfigureFile() function configures text file related parameters for the
file helper so that it will create a file named outputFileNameWithoutExtension plus
possible extra information from wildcard matches plus ".txt" with values printed as
specified by fileType. The default file type is space-separated.
An example of how to use this function can be seen in the seventh.cc code described above
where it was used as follows:
fileHelper.ConfigureFile ("seventh-packet-byte-count",
FileAggregator::FORMATTED);
FileHelper WriteProbe
The FileHelper's WriteProbe() function can be used to write values generated by probes to
text files.
It has the following prototype:
void WriteProbe (const std::string &typeId,
const std::string &path,
const std::string &probeTraceSource);
It has the following arguments:
┌─────────────────┬──────────────────────────────────┐
│Argument │ Description │
├─────────────────┼──────────────────────────────────┤
│typeId │ The type ID for the probe to be │
│ │ created. │
├─────────────────┼──────────────────────────────────┤
│path │ Config path to access the trace │
│ │ source. │
├─────────────────┼──────────────────────────────────┤
│probeTraceSource │ The probe trace source to │
│ │ access. │
└─────────────────┴──────────────────────────────────┘
The FileHelper's WriteProbe() function creates output text files generated by hooking the
ns-3 trace source with a probe created by the helper, and then writing the values from the
probeTraceSource. The output file names will have the text stored in the member variable
m_outputFileNameWithoutExtension plus ".txt", and will consist of the 'newValue' at each
timestamp.
If the config path has more than one match in the system because there is a wildcard, then
one output file for each match will be created. The output file names will contain the
text in m_outputFileNameWithoutExtension plus the matched characters for each of the
wildcards in the config path, separated by dashes, plus ".txt". For example, if the value
in m_outputFileNameWithoutExtension is the string "packet-byte-count", and there are two
wildcards in the path, then output file names like "packet-byte-count-0-0.txt" or
"packet-byte-count-12-9.txt" will be possible as names for the files that will be created.
An example of how to use this function can be seen in the seventh.cc code described above
where it was used as follows:
fileHelper.WriteProbe ("ns3::Ipv4PacketProbe",
"/NodeList/*/$ns3::Ipv4L3Protocol/Tx",
"OutputBytes");
Other Examples
File Helper Example
A slightly simpler example than the seventh.cc example can be found in
src/stats/examples/file-helper-example.cc. This example only uses the FileHelper.
The following text file with 2 columns of formatted values named file-helper-example.txt
was created using the example. Only the first 10 lines of this file are shown here for
brevity.
Time (Seconds) = 0.203 Count = 1
Time (Seconds) = 0.702 Count = 2
Time (Seconds) = 1.404 Count = 3
Time (Seconds) = 2.368 Count = 4
Time (Seconds) = 3.364 Count = 5
Time (Seconds) = 3.579 Count = 6
Time (Seconds) = 5.873 Count = 7
Time (Seconds) = 6.410 Count = 8
Time (Seconds) = 6.472 Count = 9
...
In this example, there is an Emitter object that increments its counter according to a
Poisson process and then emits the counter's value as a trace source.
Ptr<Emitter> emitter = CreateObject<Emitter> ();
Names::Add ("/Names/Emitter", emitter);
Note that because there are no wildcards in the path used below, only 1 text file was
created. This single text file is simply named "file-helper-example.txt", with no extra
suffixes like you would see if there were wildcards in the path.
// Create the file helper.
FileHelper fileHelper;
// Configure the file to be written.
fileHelper.ConfigureFile ("file-helper-example",
FileAggregator::FORMATTED);
// Set the labels for this formatted output file.
fileHelper.Set2dFormat ("Time (Seconds) = %.3e\tCount = %.0f");
// Write the values generated by the probe. The path that we
// provide helps to disambiguate the source of the trace.
fileHelper.WriteProbe ("ns3::Uinteger32Probe",
"/Names/Emitter/Counter",
"Output");
Scope and Limitations
Currently, only these Probes have been implemented and connected to the GnuplotHelper and
to the FileHelper:
· BooleanProbe
· DoubleProbe
· Uinteger8Probe
· Uinteger16Probe
· Uinteger32Probe
· TimeProbe
· PacketProbe
· ApplicationPacketProbe
· Ipv4PacketProbe
These Probes, therefore, are the only TypeIds available to be used in PlotProbe() and
WriteProbe().
In the next few sections, we cover each of the fundamental object types (Probe, Collector,
and Aggregator) in more detail, and show how they can be connected together using
lower-level API.
Probes
This section details the functionalities provided by the Probe class to an ns-3
simulation, and gives examples on how to code them in a program. This section is meant for
users interested in developing simulations with the ns-3 tools and using the Data
Collection Framework, of which the Probe class is a part, to generate data output with
their simulation's results.
Probe Overview
A Probe object is supposed to be connected to a variable from the simulation whose values
throughout the experiment are relevant to the user. The Probe will record what were
values assumed by the variable throughout the simulation and pass such data to another
member of the Data Collection Framework. While it is out of this section's scope to
discuss what happens after the Probe produces its output, it is sufficient to say that, by
the end of the simulation, the user will have detailed information about what values were
stored inside the variable being probed during the simulation.
Typically, a Probe is connected to an ns-3 trace source. In this manner, whenever the
trace source exports a new value, the Probe consumes the value (and exports it downstream
to another object via its own trace source).
The Probe can be thought of as kind of a filter on trace sources. The main reasons for
possibly hooking to a Probe rather than directly to a trace source are as follows:
· Probes may be dynamically turned on and off during the simulation with calls to Enable()
and Disable(). For example, the outputting of data may be turned off during the
simulation warmup phase.
· Probes may perform operations on the data to extract values from more complicated
structures; for instance, outputting the packet size value from a received ns3::Packet.
· Probes register a name in the ns3::Config namespace (using Names::Add ()) so that other
objects may refer to them.
· Probes provide a static method that allows one to manipulate a Probe by name, such as
what is done in ns2measure [Cic06]
Stat::put ("my_metric", ID, sample);
The ns-3 equivalent of the above ns2measure code is, e.g.
DoubleProbe::SetValueByPath ("/path/to/probe", sample);
Creation
Note that a Probe base class object can not be created because it is an abstract base
class, i.e. it has pure virtual functions that have not been implemented. An object of
type DoubleProbe, which is a subclass of the Probe class, will be created here to show
what needs to be done.
One declares a DoubleProbe in dynamic memory by using the smart pointer class (Ptr<T>). To
create a DoubleProbe in dynamic memory with smart pointers, one just needs to call the
ns-3 method CreateObject():
Ptr<DoubleProbe> myprobe = CreateObject<DoubleProbe> ();
The declaration above creates DoubleProbes using the default values for its attributes.
There are four attributes in the DoubleProbe class; two in the base class object
DataCollectionObject, and two in the Probe base class:
· "Name" (DataCollectionObject), a StringValue
· "Enabled" (DataCollectionObject), a BooleanValue
· "Start" (Probe), a TimeValue
· "Stop" (Probe), a TimeValue
One can set such attributes at object creation by using the following method:
Ptr<DoubleProbe> myprobe = CreateObjectWithAttributes<DoubleProbe> (
"Name", StringValue ("myprobe"),
"Enabled", BooleanValue (false),
"Start", TimeValue (Seconds (100.0)),
"Stop", TimeValue (Seconds (1000.0)));
Start and Stop are Time variables which determine the interval of action of the Probe. The
Probe will only output data if the current time of the Simulation is inside of that
interval. The special time value of 0 seconds for Stop will disable this attribute (i.e.
keep the Probe on for the whole simulation). Enabled is a flag that turns the Probe on or
off, and must be set to true for the Probe to export data. The Name is the object's name
in the DCF framework.
Importing and exporting data
ns-3 trace sources are strongly typed, so the mechanisms for hooking Probes to a trace
source and for exporting data belong to its subclasses. For instance, the default
distribution of ns-3 provides a class DoubleProbe that is designed to hook to a trace
source exporting a double value. We'll next detail the operation of the DoubleProbe, and
then discuss how other Probe classes may be defined by the user.
DoubleProbe Overview
The DoubleProbe connects to a double-valued ns-3 trace source, and itself exports a
different double-valued ns-3 trace source.
The following code, drawn from src/stats/examples/double-probe-example.cc, shows the basic
operations of plumbing the DoubleProbe into a simulation, where it is probing a Counter
exported by an emitter object (class Emitter).
Ptr<Emitter> emitter = CreateObject<Emitter> ();
Names::Add ("/Names/Emitter", emitter);
...
Ptr<DoubleProbe> probe1 = CreateObject<DoubleProbe> ();
// Connect the probe to the emitter's Counter
bool connected = probe1->ConnectByObject ("Counter", emitter);
The following code is probing the same Counter exported by the same emitter object. This
DoubleProbe, however, is using a path in the configuration namespace to make the
connection. Note that the emitter registered itself in the configuration namespace after
it was created; otherwise, the ConnectByPath would not work.
Ptr<DoubleProbe> probe2 = CreateObject<DoubleProbe> ();
// Note, no return value is checked here
probe2->ConnectByPath ("/Names/Emitter/Counter");
The next DoubleProbe shown that is shown below will have its value set using its path in
the configuration namespace. Note that this time the DoubleProbe registered itself in the
configuration namespace after it was created.
Ptr<DoubleProbe> probe3 = CreateObject<DoubleProbe> ();
probe3->SetName ("StaticallyAccessedProbe");
// We must add it to the config database
Names::Add ("/Names/Probes", probe3->GetName (), probe3);
The emitter's Count() function is now able to set the value for this DoubleProbe as
follows:
void
Emitter::Count (void)
{
...
m_counter += 1.0;
DoubleProbe::SetValueByPath ("/Names/StaticallyAccessedProbe", m_counter);
...
}
The above example shows how the code calling the Probe does not have to have an explicit
reference to the Probe, but can direct the value setting through the Config namespace.
This is similar in functionality to the Stat::Put method introduced by ns2measure paper
[Cic06], and allows users to temporarily insert Probe statements like printf statements
within existing ns-3 models. Note that in order to be able to use the DoubleProbe in this
example like this, 2 things were necessary:
1. the stats module header file was included in the example .cc file
2. the example was made dependent on the stats module in its wscript file.
Analogous things need to be done in order to add other Probes in other places in the ns-3
code base.
The values for the DoubleProbe can also be set using the function DoubleProbe::SetValue(),
while the values for the DoubleProbe can be gotten using the function
DoubleProbe::GetValue().
The DoubleProbe exports double values in its "Output" trace source; a downstream object
can hook a trace sink (NotifyViaProbe) to this as follows:
connected = probe1->TraceConnect ("Output", probe1->GetName (), MakeCallback (&NotifyViaProbe));
Other probes
Besides the DoubleProbe, the following Probes are also available:
· Uinteger8Probe connects to an ns-3 trace source exporting an uint8_t.
· Uinteger16Probe connects to an ns-3 trace source exporting an uint16_t.
· Uinteger32Probe connects to an ns-3 trace source exporting an uint32_t.
· PacketProbe connects to an ns-3 trace source exporting a packet.
· ApplicationPacketProbe connects to an ns-3 trace source exporting a packet and a socket
address.
· Ipv4PacketProbe connects to an ns-3 trace source exporting a packet, an IPv4 object, and
an interface.
Creating new Probe types
To create a new Probe type, you need to perform the following steps:
· Be sure that your new Probe class is derived from the Probe base class.
· Be sure that the pure virtual functions that your new Probe class inherits from the
Probe base class are implemented.
· Find an existing Probe class that uses a trace source that is closest in type to the
type of trace source your Probe will be using.
· Copy that existing Probe class's header file (.h) and implementation file (.cc) to two
new files with names matching your new Probe.
· Replace the types, arguments, and variables in the copied files with the appropriate
type for your Probe.
· Make necessary modifications to make the code compile and to make it behave as you would
like.
Examples
Two examples will be discussed in detail here:
· Double Probe Example
· IPv4 Packet Plot Example
Double Probe Example
The double probe example has been discussed previously. The example program can be found
in src/stats/examples/double-probe-example.cc. To summarize what occurs in this program,
there is an emitter that exports a counter that increments according to a Poisson process.
In particular, two ways of emitting data are shown:
1. through a traced variable hooked to one Probe:
TracedValue<double> m_counter; // normally this would be integer type
2. through a counter whose value is posted to a second Probe, referenced by its name in
the Config system:
void
Emitter::Count (void)
{
NS_LOG_FUNCTION (this);
NS_LOG_DEBUG ("Counting at " << Simulator::Now ().GetSeconds ());
m_counter += 1.0;
DoubleProbe::SetValueByPath ("/Names/StaticallyAccessedProbe", m_counter);
Simulator::Schedule (Seconds (m_var->GetValue ()), &Emitter::Count, this);
}
Let's look at the Probe more carefully. Probes can receive their values in a multiple
ways:
1. by the Probe accessing the trace source directly and connecting a trace sink to it
2. by the Probe accessing the trace source through the config namespace and connecting a
trace sink to it
3. by the calling code explicitly calling the Probe's SetValue() method
4. by the calling code explicitly calling SetValueByPath
("/path/through/Config/namespace", ...)
The first two techniques are expected to be the most common. Also in the example, the
hooking of a normal callback function is shown, as is typically done in ns-3. This
callback function is not associated with a Probe object. We'll call this case 0) below.
// This is a function to test hooking a raw function to the trace source
void
NotifyViaTraceSource (std::string context, double oldVal, double newVal)
{
NS_LOG_DEBUG ("context: " << context << " old " << oldVal << " new " << newVal);
}
First, the emitter needs to be setup:
Ptr<Emitter> emitter = CreateObject<Emitter> ();
Names::Add ("/Names/Emitter", emitter);
// The Emitter object is not associated with an ns-3 node, so
// it won't get started automatically, so we need to do this ourselves
Simulator::Schedule (Seconds (0.0), &Emitter::Start, emitter);
The various DoubleProbes interact with the emitter in the example as shown below.
Case 0):
// The below shows typical functionality without a probe
// (connect a sink function to a trace source)
//
connected = emitter->TraceConnect ("Counter", "sample context", MakeCallback (&NotifyViaTraceSource));
NS_ASSERT_MSG (connected, "Trace source not connected");
case 1):
//
// Probe1 will be hooked directly to the Emitter trace source object
//
// probe1 will be hooked to the Emitter trace source
Ptr<DoubleProbe> probe1 = CreateObject<DoubleProbe> ();
// the probe's name can serve as its context in the tracing
probe1->SetName ("ObjectProbe");
// Connect the probe to the emitter's Counter
connected = probe1->ConnectByObject ("Counter", emitter);
NS_ASSERT_MSG (connected, "Trace source not connected to probe1");
case 2):
//
// Probe2 will be hooked to the Emitter trace source object by
// accessing it by path name in the Config database
//
// Create another similar probe; this will hook up via a Config path
Ptr<DoubleProbe> probe2 = CreateObject<DoubleProbe> ();
probe2->SetName ("PathProbe");
// Note, no return value is checked here
probe2->ConnectByPath ("/Names/Emitter/Counter");
case 4) (case 3 is not shown in this example):
//
// Probe3 will be called by the emitter directly through the
// static method SetValueByPath().
//
Ptr<DoubleProbe> probe3 = CreateObject<DoubleProbe> ();
probe3->SetName ("StaticallyAccessedProbe");
// We must add it to the config database
Names::Add ("/Names/Probes", probe3->GetName (), probe3);
And finally, the example shows how the probes can be hooked to generate output:
// The probe itself should generate output. The context that we provide
// to this probe (in this case, the probe name) will help to disambiguate
// the source of the trace
connected = probe3->TraceConnect ("Output",
"/Names/Probes/StaticallyAccessedProbe/Output",
MakeCallback (&NotifyViaProbe));
NS_ASSERT_MSG (connected, "Trace source not .. connected to probe3 Output");
The following callback is hooked to the Probe in this example for illustrative purposes;
normally, the Probe would be hooked to a Collector object.
// This is a function to test hooking it to the probe output
void
NotifyViaProbe (std::string context, double oldVal, double newVal)
{
NS_LOG_DEBUG ("context: " << context << " old " << oldVal << " new " << newVal);
}
IPv4 Packet Plot Example
The IPv4 packet plot example is based on the fifth.cc example from the ns-3 Tutorial. It
can be found in src/stats/examples/ipv4-packet-plot-example.cc.
node 0 node 1
+----------------+ +----------------+
| ns-3 TCP | | ns-3 TCP |
+----------------+ +----------------+
| 10.1.1.1 | | 10.1.1.2 |
+----------------+ +----------------+
| point-to-point | | point-to-point |
+----------------+ +----------------+
| |
+---------------------+
We'll just look at the Probe, as it illustrates that Probes may also unpack values from
structures (in this case, packets) and report those values as trace source outputs, rather
than just passing through the same type of data.
There are other aspects of this example that will be explained later in the documentation.
The two types of data that are exported are the packet itself (Output) and a count of the
number of bytes in the packet (OutputBytes).
TypeId
Ipv4PacketProbe::GetTypeId ()
{
static TypeId tid = TypeId ("ns3::Ipv4PacketProbe")
.SetParent<Probe> ()
.AddConstructor<Ipv4PacketProbe> ()
.AddTraceSource ( "Output",
"The packet plus its IPv4 object and interface that serve as the output for this probe",
MakeTraceSourceAccessor (&Ipv4PacketProbe::m_output))
.AddTraceSource ( "OutputBytes",
"The number of bytes in the packet",
MakeTraceSourceAccessor (&Ipv4PacketProbe::m_outputBytes))
;
return tid;
}
When the Probe's trace sink gets a packet, if the Probe is enabled, then it will output
the packet on its Output trace source, but it will also output the number of bytes on the
OutputBytes trace source.
void
Ipv4PacketProbe::TraceSink (Ptr<const Packet> packet, Ptr<Ipv4> ipv4, uint32_t interface)
{
NS_LOG_FUNCTION (this << packet << ipv4 << interface);
if (IsEnabled ())
{
m_packet = packet;
m_ipv4 = ipv4;
m_interface = interface;
m_output (packet, ipv4, interface);
uint32_t packetSizeNew = packet->GetSize ();
m_outputBytes (m_packetSizeOld, packetSizeNew);
m_packetSizeOld = packetSizeNew;
}
}
References
[Cic06]
Claudio Cicconetti, Enzo Mingozzi, Giovanni Stea, "An Integrated Framework for
Enabling Effective Data Collection and Statistical Analysis with ns2, Workshop on
ns-2 (WNS2), Pisa, Italy, October 2006.
Collectors
This section is a placeholder to detail the functionalities provided by the Collector
class to an ns-3 simulation, and gives examples on how to code them in a program.
Note: As of ns-3.18, Collectors are still under development and not yet provided as part
of the framework.
Aggregators
This section details the functionalities provided by the Aggregator class to an ns-3
simulation. This section is meant for users interested in developing simulations with the
ns-3 tools and using the Data Collection Framework, of which the Aggregator class is a
part, to generate data output with their simulation's results.
Aggregator Overview
An Aggregator object is supposed to be hooked to one or more trace sources in order to
receive input. Aggregators are the end point of the data collected by the network of
Probes and Collectors during the simulation. It is the Aggregator's job to take these
values and transform them into their final output format such as plain text files,
spreadsheet files, plots, or databases.
Typically, an aggregator is connected to one or more Collectors. In this manner, whenever
the Collectors' trace sources export new values, the Aggregator can process the value so
that it can be used in the final output format where the data values will reside after the
simulation.
Note the following about Aggregators:
· Aggregators may be dynamically turned on and off during the simulation with calls to
Enable() and Disable(). For example, the aggregating of data may be turned off during
the simulation warmup phase, which means those values won't be included in the final
output medium.
· Aggregators receive data from Collectors via callbacks. When a Collector is associated
to an aggregator, a call to TraceConnect is made to establish the Aggregator's trace
sink method as a callback.
To date, two Aggregators have been implemented:
· GnuplotAggregator
· FileAggregator
GnuplotAggregator
The GnuplotAggregator produces output files used to make gnuplots.
The GnuplotAggregator will create 3 different files at the end of the simulation:
· A space separated gnuplot data file
· A gnuplot control file
· A shell script to generate the gnuplot
Creation
An object of type GnuplotAggregator will be created here to show what needs to be done.
One declares a GnuplotAggregator in dynamic memory by using the smart pointer class
(Ptr<T>). To create a GnuplotAggregator in dynamic memory with smart pointers, one just
needs to call the ns-3 method CreateObject(). The following code from
src/stats/examples/gnuplot-aggregator-example.cc shows how to do this:
string fileNameWithoutExtension = "gnuplot-aggregator";
// Create an aggregator.
Ptr<GnuplotAggregator> aggregator =
CreateObject<GnuplotAggregator> (fileNameWithoutExtension);
The first argument for the constructor, fileNameWithoutExtension, is the name of the
gnuplot related files to write with no extension. This GnuplotAggregator will create a
space separated gnuplot data file named "gnuplot-aggregator.dat", a gnuplot control file
named "gnuplot-aggregator.plt", and a shell script to generate the gnuplot named +
"gnuplot-aggregator.sh".
The gnuplot that is created can have its key in 4 different locations:
· No key
· Key inside the plot (the default)
· Key above the plot
· Key below the plot
The following gnuplot key location enum values are allowed to specify the key's position:
enum KeyLocation {
NO_KEY,
KEY_INSIDE,
KEY_ABOVE,
KEY_BELOW
};
If it was desired to have the key below rather than the default position of inside, then
you could do the following.
aggregator->SetKeyLocation(GnuplotAggregator::KEY_BELOW);
Examples
One example will be discussed in detail here:
· Gnuplot Aggregator Example
Gnuplot Aggregator Example
An example that exercises the GnuplotAggregator can be found in
src/stats/examples/gnuplot-aggregator-example.cc.
The following 2-D gnuplot was created using the example.
[image] 2-D Gnuplot Created by gnuplot-aggregator-example.cc Example..UNINDENT
This code from the example shows how to construct the GnuplotAggregator as was discussed
above.
void Create2dPlot ()
{
using namespace std;
string fileNameWithoutExtension = "gnuplot-aggregator";
string plotTitle = "Gnuplot Aggregator Plot";
string plotXAxisHeading = "Time (seconds)";
string plotYAxisHeading = "Double Values";
string plotDatasetLabel = "Data Values";
string datasetContext = "Dataset/Context/String";
// Create an aggregator.
Ptr<GnuplotAggregator> aggregator =
CreateObject<GnuplotAggregator> (fileNameWithoutExtension);
Various GnuplotAggregator attributes are set including the 2-D dataset that will be
plotted.
// Set the aggregator's properties.
aggregator->SetTerminal ("png");
aggregator->SetTitle (plotTitle);
aggregator->SetLegend (plotXAxisHeading, plotYAxisHeading);
// Add a data set to the aggregator.
aggregator->Add2dDataset (datasetContext, plotDatasetLabel);
// aggregator must be turned on
aggregator->Enable ();
Next, the 2-D values are calculated, and each one is individually written to the
GnuplotAggregator using the Write2d() function.
double time;
double value;
// Create the 2-D dataset.
for (time = -5.0; time <= +5.0; time += 1.0)
{
// Calculate the 2-D curve
//
// 2
// value = time .
//
value = time * time;
// Add this point to the plot.
aggregator->Write2d (datasetContext, time, value);
}
// Disable logging of data for the aggregator.
aggregator->Disable ();
}
FileAggregator
The FileAggregator sends the values it receives to a file.
The FileAggregator can create 4 different types of files:
· Formatted
· Space separated (the default)
· Comma separated
· Tab separated
Formatted files use C-style format strings and the sprintf() function to print their
values in the file being written.
Creation
An object of type FileAggregator will be created here to show what needs to be done.
One declares a FileAggregator in dynamic memory by using the smart pointer class (Ptr<T>).
To create a FileAggregator in dynamic memory with smart pointers, one just needs to call
the ns-3 method CreateObject. The following code from
src/stats/examples/file-aggregator-example.cc shows how to do this:
string fileName = "file-aggregator-formatted-values.txt";
// Create an aggregator that will have formatted values.
Ptr<FileAggregator> aggregator =
CreateObject<FileAggregator> (fileName, FileAggregator::FORMATTED);
The first argument for the constructor, filename, is the name of the file to write; the
second argument, fileType, is type of file to write. This FileAggregator will create a
file named "file-aggregator-formatted-values.txt" with its values printed as specified by
fileType, i.e., formatted in this case.
The following file type enum values are allowed:
enum FileType {
FORMATTED,
SPACE_SEPARATED,
COMMA_SEPARATED,
TAB_SEPARATED
};
Examples
One example will be discussed in detail here:
· File Aggregator Example
File Aggregator Example
An example that exercises the FileAggregator can be found in
src/stats/examples/file-aggregator-example.cc.
The following text file with 2 columns of values separated by commas was created using the
example.
-5,25
-4,16
-3,9
-2,4
-1,1
0,0
1,1
2,4
3,9
4,16
5,25
This code from the example shows how to construct the FileAggregator as was discussed
above.
void CreateCommaSeparatedFile ()
{
using namespace std;
string fileName = "file-aggregator-comma-separated.txt";
string datasetContext = "Dataset/Context/String";
// Create an aggregator.
Ptr<FileAggregator> aggregator =
CreateObject<FileAggregator> (fileName, FileAggregator::COMMA_SEPARATED);
FileAggregator attributes are set.
// aggregator must be turned on
aggregator->Enable ();
Next, the 2-D values are calculated, and each one is individually written to the
FileAggregator using the Write2d() function.
double time;
double value;
// Create the 2-D dataset.
for (time = -5.0; time <= +5.0; time += 1.0)
{
// Calculate the 2-D curve
//
// 2
// value = time .
//
value = time * time;
// Add this point to the plot.
aggregator->Write2d (datasetContext, time, value);
}
// Disable logging of data for the aggregator.
aggregator->Disable ();
}
The following text file with 2 columns of formatted values was also created using the
example.
Time = -5.000e+00 Value = 25
Time = -4.000e+00 Value = 16
Time = -3.000e+00 Value = 9
Time = -2.000e+00 Value = 4
Time = -1.000e+00 Value = 1
Time = 0.000e+00 Value = 0
Time = 1.000e+00 Value = 1
Time = 2.000e+00 Value = 4
Time = 3.000e+00 Value = 9
Time = 4.000e+00 Value = 16
Time = 5.000e+00 Value = 25
This code from the example shows how to construct the FileAggregator as was discussed
above.
void CreateFormattedFile ()
{
using namespace std;
string fileName = "file-aggregator-formatted-values.txt";
string datasetContext = "Dataset/Context/String";
// Create an aggregator that will have formatted values.
Ptr<FileAggregator> aggregator =
CreateObject<FileAggregator> (fileName, FileAggregator::FORMATTED);
FileAggregator attributes are set, including the C-style format string to use.
// Set the format for the values.
aggregator->Set2dFormat ("Time = %.3e\tValue = %.0f");
// aggregator must be turned on
aggregator->Enable ();
Next, the 2-D values are calculated, and each one is individually written to the
FileAggregator using the Write2d() function.
double time;
double value;
// Create the 2-D dataset.
for (time = -5.0; time <= +5.0; time += 1.0)
{
// Calculate the 2-D curve
//
// 2
// value = time .
//
value = time * time;
// Add this point to the plot.
aggregator->Write2d (datasetContext, time, value);
}
// Disable logging of data for the aggregator.
aggregator->Disable ();
}
Adaptors
This section details the functionalities provided by the Adaptor class to an ns-3
simulation. This section is meant for users interested in developing simulations with the
ns-3 tools and using the Data Collection Framework, of which the Adaptor class is a part,
to generate data output with their simulation's results.
Note: the term 'adaptor' may also be spelled 'adapter'; we chose the spelling aligned
with the C++ standard.
Adaptor Overview
An Adaptor is used to make connections between different types of DCF objects.
To date, one Adaptor has been implemented:
· TimeSeriesAdaptor
Time Series Adaptor
The TimeSeriesAdaptor lets Probes connect directly to Aggregators without needing any
Collector in between.
Both of the implemented DCF helpers utilize TimeSeriesAdaptors in order to take probed
values of different types and output the current time plus the value with both converted
to doubles.
The role of the TimeSeriesAdaptor class is that of an adaptor, which takes raw-valued
probe data of different types and outputs a tuple of two double values. The first is a
timestamp, which may be set to different resolutions (e.g. Seconds, Milliseconds, etc.) in
the future but which is presently hardcoded to Seconds. The second is the conversion of a
non-double value to a double value (possibly with loss of precision).
Scope/Limitations
This section discusses the scope and limitations of the Data Collection Framework.
Currently, only these Probes have been implemented in DCF:
· BooleanProbe
· DoubleProbe
· Uinteger8Probe
· Uinteger16Probe
· Uinteger32Probe
· TimeProbe
· PacketProbe
· ApplicationPacketProbe
· Ipv4PacketProbe
Currently, no Collectors are available in the DCF, although a BasicStatsCollector is under
development.
Currently, only these Aggregators have been implemented in DCF:
· GnuplotAggregator
· FileAggregator
Currently, only this Adaptor has been implemented in DCF:
Time-Series Adaptor.
Future Work
This section discusses the future work to be done on the Data Collection Framework.
Here are some things that still need to be done:
· Hook up more trace sources in ns-3 code to get more values out of the simulator.
· Implement more types of Probes than there currently are.
· Implement more than just the single current 2-D Collector, BasicStatsCollector.
· Implement more Aggregators.
· Implement more than just Adaptors.
DSDV ROUTING
Destination-Sequenced Distance Vector (DSDV) routing protocol is a pro-active,
table-driven routing protocol for MANETs developed by Charles E. Perkins and Pravin
Bhagwat in 1994. It uses the hop count as metric in route selection.
This model was developed by the ResiliNets research group at the University of Kansas. A
paper on this model exists at this URL.
DSDV Routing Overview
DSDV Routing Table: Every node will maintain a table listing all the other nodes it has
known either directly or through some neighbors. Every node has a single entry in the
routing table. The entry will have information about the node's IP address, last known
sequence number and the hop count to reach that node. Along with these details the table
also keeps track of the nexthop neighbor to reach the destination node, the timestamp of
the last update received for that node.
The DSDV update message consists of three fields, Destination Address, Sequence Number and
Hop Count.
Each node uses 2 mechanisms to send out the DSDV updates. They are,
1.
Periodic Updates
Periodic updates are sent out after every m_periodicUpdateInterval(default:15s).
In this update the node broadcasts out its entire routing table.
2.
Trigger Updates
Trigger Updates are small updates in-between the periodic updates. These updates
are sent out whenever a node receives a DSDV packet that caused a change in its
routing table. The original paper did not clearly mention when for what change
in the table should a DSDV update be sent out. The current implemntation sends
out an update irrespective of the change in the routing table.
The updates are accepted based on the metric for a particular node. The first factor
determinig the acceptance of an update is the sequence number. It has to accept the update
if the sequence number of the update message is higher irrespective of the metric. If the
update with same sequence number is received, then the update with least metric (hopCount)
is given precedence.
In highly mobile scenarios, there is a high chance of route fluctuations, thus we have the
concept of weighted settling time where an update with change in metric will not be
advertised to neighbors. The node waits for the settling time to make sure that it did not
receive the update from its old neighbor before sending out that update.
The current implementation covers all the above features of DSDV. The current
implementation also has a request queue to buffer packets that have no routes to
destination. The default is set to buffer up to 5 packets per destination.
References
Link to the Paper: http://portal.acm.org/citation.cfm?doid=190314.190336
DSR ROUTING
Dynamic Source Routing (DSR) protocol is a reactive routing protocol designed specifically
for use in multi-hop wireless ad hoc networks of mobile nodes.
This model was developed by the ResiliNets research group at the University of Kansas.
DSR Routing Overview
This model implements the base specification of the Dynamic Source Routing (DSR) protocol.
Implementation is based on RFC 4728, with some extensions and modifications to the RFC
specifications.
DSR operates on a on-demand behavior. Therefore, our DSR model buffers all packets while a
route request packet (RREQ) is disseminated. We implement a packet buffer in
dsr-rsendbuff.cc. The packet queue implements garbage collection of old packets and a
queue size limit. When the packet is sent out from the send buffer, it will be queued in
maintenance buffer for next hop acknowledgment.
The maintenance buffer then buffers the already sent out packets and waits for the
notification of packet delivery. Protocol operation strongly depends on broken link
detection mechanism. We implement the three heuristics recommended based the RFC as
follows:
First, we use link layer feedback when possible, which is also the fastest mechanism of
these three to detect link errors. A link is considered to be broken if frame transmission
results in a transmission failure for all retries. This mechanism is meant for active
links and works much faster than in its absence. DSR is able to detect the link layer
transmission failure and notify that as broken. Recalculation of routes will be triggered
when needed. If user does not want to use link layer acknowledgment, it can be tuned by
setting "LinkAcknowledgment" attribute to false in "dsr-routing.cc".
Second, passive acknowledgment should be used whenever possible. The node turns on
"promiscuous" receive mode, in which it can receive packets not destined for itself, and
when the node assures the delivery of that data packet to its destination, it cancels the
passive acknowledgment timer.
Last, we use a network layer acknowledge scheme to notify the receipt of a packet. Route
request packet will not be acknowledged or retransmitted.
The Route Cache implementation support garbage collection of old entries and state
machine, as defined in the standard. It implements as a STL map container. The key is the
destination IP address.
DSR operates with direct access to IP header, and operates between network and transport
layer. When packet is sent out from transport layer, it passes itself to DSR and DSR
header is appended.
We have two caching mechanisms: path cache and link cache. The path cache saves the whole
path in the cache. The paths are sorted based on the hop count, and whenever one path is
not able to be used, we change to the next path. The link cache is a slightly better
design in the sense that it uses different subpaths and uses Implemented Link Cache using
Dijsktra algorithm, and this part is implemented by Song Luan <lsuper@mail.ustc.edu.cn>.
The following optional protocol optimizations aren't implemented:
· Flow state
· First Hop External (F), Last Hop External (L) flags
· Handling unknown DSR options
·
Two types of error headers:
1. flow state not supported option
2. unsupported option (not going to happen in simulation)
DSR update in ns-3.17
We originally used "TxErrHeader" in Ptr<WifiMac> to indicate the transmission error of a
specific packet in link layer, however, it was not working quite correctly since even when
the packet was dropped, this header was not recorded in the trace file. We used to a
different path on implementing the link layer notification mechanism. We look into the
trace file by finding packet receive event. If we find one receive event for the data
packet, we count that as the indicator for successful data delivery.
Useful parameters
+------------------------- +------------------------------------+-------------+
| Parameter | Description | Default |
+==========================+====================================+=============+
| MaxSendBuffLen | Maximum number of packets that can | 64 |
| | be stored in send buffer | |
+------------------------- +------------------------------------+-------------+
| MaxSendBuffTime | Maximum time packets can be queued | Seconds(30) |
| | in the send buffer | |
+------------------------- +------------------------------------+-------------+
| MaxMaintLen | Maximum number of packets that can | 50 |
| | be stored in maintenance buffer | |
+------------------------- +------------------------------------+-------------+
| MaxMaintTime | Maximum time packets can be queued | Seconds(30) |
| | in maintenance buffer | |
+------------------------- +------------------------------------+-------------+
| MaxCacheLen | Maximum number of route entries | 64 |
| | that can be stored in route cache | |
+------------------------- +------------------------------------+-------------+
| RouteCacheTimeout | Maximum time the route cache can | Seconds(300)|
| | be queued in route cache | |
+------------------------- +------------------------------------+-------------+
| RreqRetries | Maximum number of retransmissions | 16 |
| | for request discovery of a route | |
+------------------------- +------------------------------------+-------------+
| CacheType | Use Link Cache or use Path Cache | "LinkCache" |
| | | |
+------------------------- +------------------------------------+-------------+
| LinkAcknowledgment | Enable Link layer acknowledgment | True |
| | mechanism | |
+------------------------- +------------------------------------+-------------+
Implementation modification
·
The DsrFsHeader has added 3 fields: message type, source id, destination id, and these
changes only for post-processing
1. Message type is used to identify the data packet from control packet
2. source id is used to identify the real source of the data packet since we have
to deliver the packet hop-by-hop and the ipv4header is not carrying the real
source and destination ip address as needed
3. destination id is for same reason of above
· Route Reply header is not word-aligned in DSR RFC, change it to word-aligned in
implementation
· DSR works as a shim header between transport and network protocol, it needs its own
forwarding mechanism, we are changing the packet transmission to hop-by-hop delivery, so
we added two fields in dsr fixed header to notify packet delivery
Current Route Cache implementation
This implementation used "path cache", which is simple to implement and ensures loop-free
paths:
· the path cache has automatic expire policy
· the cache saves multiple route entries for a certain destination and sort the entries
based on hop counts
· the MaxEntriesEachDst can be tuned to change the maximum entries saved for a single
destination
· when adding mulitiple routes for one destination, the route is compared based on
hop-count and expire time, the one with less hop count or relatively new route is
favored
· Future implementation may include "link cache" as another possibility
DSR Instructions
The following should be kept in mind when running DSR as routing protocol:
· NodeTraversalTime is the time it takes to traverse two neighboring nodes and should be
chosen to fit the transmission range
· PassiveAckTimeout is the time a packet in maintenance buffer wait for passive
acknowledgment, normally set as two times of NodeTraversalTime
· RouteCacheTimeout should be set smaller value when the nodes' velocity become higher.
The default value is 300s.
Helper
To have a node run DSR, the easiest way would be to use the DsrHelper and DsrMainHelpers
in your simulation script. For instance:
DsrHelper dsr;
DsrMainHelper dsrMain;
dsrMain.Install (dsr, adhocNodes);
The example scripts inside src/dsr/examples/ demonstrate the use of DSR based nodesin
different scenarios. The helper source can be found inside
src/dsr/helper/dsr-main-helper.{h,cc} and src/dsr/helper/dsr-helper.{h,cc}
Examples
The example can be found in src/dsr/examples/:
· dsr.cc use DSR as routing protocol within a traditional MANETs environment[3].
DSR is also built in the routing comparison case in examples/routing/:
· manet-routing-compare.cc is a comparison case with built in MANET routing protocols and
can generate its own results.
Validation
This model has been tested as follows:
· Unit tests have been written to verify the internals of DSR. This can be found in
src/dsr/test/dsr-test-suite.cc. These tests verify whether the methods inside DSR module
which deal with packet buffer, headers work correctly.
· Simulation cases similar to [3] have been tested and have comparable results.
· manet-routing-compare.cc has been used to compare DSR with three of other routing
protocols.
A paper was presented on these results at the Workshop on ns-3 in 2011.
Limitations
The model is not fully compliant with RFC 4728. As an example, Dsr fixed size header has
been extended and it is four octects longer then the RFC specification. As a consequence,
the DSR headers can not be correctly decoded by Wireshark.
The model full compliance with the RFC is planned for the future.
References
[1] Original paper: http://www.monarch.cs.rice.edu/monarch-papers/dsr-chapter00.pdf
[2] RFC 4728 http://www6.ietf.org/rfc/rfc4728.txt
[3] Broch's comparison paper: http://www.monarch.cs.rice.edu/monarch-papers/mobicom98.ps
EMULATION OVERVIEW
ns-3 has been designed for integration into testbed and virtual machine environments. We
have addressed this need by providing two kinds of net devices. The first kind of device
is a file descriptor net device (FdNetDevice), which is a generic device type that can
read and write from a file descriptor. By associating this file descriptor with different
things on the host system, different capabilities can be provided. For instance, the
FdNetDevice can be associated with an underlying packet socket to provide emulation
capabilities. This allows ns-3 simulations to send data on a "real" network. The second
kind, called a Tap NetDevice allows a "real" host to participate in an ns-3 simulation as
if it were one of the simulated nodes. An ns-3 simulation may be constructed with any
combination of simulated or emulated devices.
Note: Prior to ns-3.17, the emulation capability was provided by a special device called
an Emu NetDevice; the Emu NetDevice has been replaced by the FdNetDevice.
One of the use-cases we want to support is that of a testbed. A concrete example of an
environment of this kind is the ORBIT testbed. ORBIT is a laboratory emulator/field trial
network arranged as a two dimensional grid of 400 802.11 radio nodes. We integrate with
ORBIT by using their "imaging" process to load and run ns-3 simulations on the ORBIT
array. We can use our EmuFdNetDevice to drive the hardware in the testbed and we can
accumulate results either using the ns-3 tracing and logging functions, or the native
ORBIT data gathering techniques. See http://www.orbit-lab.org/ for details on the ORBIT
testbed.
A simulation of this kind is shown in the following figure:
[image] Example Implementation of Testbed Emulation..UNINDENT
You can see that there are separate hosts, each running a subset of a "global"
simulation. Instead of an ns-3 channel connecting the hosts, we use real hardware
provided by the testbed. This allows ns-3 applications and protocol stacks attached to a
simulation node to communicate over real hardware.
We expect the primary use for this configuration will be to generate repeatable
experimental results in a real-world network environment that includes all of the ns-3
tracing, logging, visualization and statistics gathering tools.
In what can be viewed as essentially an inverse configuration, we allow "real" machines
running native applications and protocol stacks to integrate with an ns-3 simulation.
This allows for the simulation of large networks connected to a real machine, and also
enables virtualization. A simulation of this kind is shown in the following figure:
[image] Implementation overview of emulated channel..UNINDENT
Here, you will see that there is a single host with a number of virtual machines running
on it. An ns-3 simulation is shown running in the virtual machine shown in the center of
the figure. This simulation has a number of nodes with associated ns-3 applications and
protocol stacks that are talking to an ns-3 channel through native simulated ns-3 net
devices.
There are also two virtual machines shown at the far left and far right of the figure.
These VMs are running native (Linux) applications and protocol stacks. The VM is
connected into the simulation by a Linux Tap net device. The user-mode handler for the
Tap device is instantiated in the simulation and attached to a proxy node that
represents the native VM in the simulation. These handlers allow the Tap devices on the
native VMs to behave as if they were ns-3 net devices in the simulation VM. This, in
turn, allows the native software and protocol suites in the native VMs to believe that
they are connected to the simulated ns-3 channel.
We expect the typical use case for this environment will be to analyze the behavior of
native applications and protocol suites in the presence of large simulated ns-3
networks.
File Descriptor NetDevice
The src/fd-net-device module provides the FdNetDevice class, which is able to read and
write traffic using a file descriptor provided by the user. This file descriptor can be
associated to a TAP device, to a raw socket, to a user space process generating/consuming
traffic, etc. The user has full freedom to define how external traffic is generated and
ns-3 traffic is consumed.
Different mechanisms to associate a simulation to external traffic can be provided through
helper classes. Three specific helpers are provided:
· EmuFdNetDeviceHelper (to associate the ns-3 device with a physical device in the host
machine)
· TapFdNetDeviceHelper (to associate the ns-3 device with the file descriptor from a tap
device in the host machine)
· PlanteLabFdNetDeviceHelper (to automate the creation of tap devices in PlanetLab nodes,
enabling ns-3 simulations that can send and receive traffic though the Internet using
PlanetLab resource.
Model Description
The source code for this module lives in the directory src/fd-net-device.
The FdNetDevice is a special type of ns-3 NetDevice that reads traffic to and from a file
descriptor. That is, unlike pure simulation NetDevice objects that write frames to and
from a simulated channel, this FdNetDevice directs frames out of the simulation to a file
descriptor. The file descriptor may be associated to a Linux TUN/TAP device, to a socket,
or to a user-space process.
It is up to the user of this device to provide a file descriptor. The type of file
descriptor being provided determines what is being modelled. For instance, if the file
descriptor provides a raw socket to a WiFi card on the host machine, the device being
modelled is a WiFi device.
From the conceptual "top" of the device looking down, it looks to the simulated node like
a device supporting a 48-bit IEEE MAC address that can be bridged, supports broadcast, and
uses IPv4 ARP or IPv6 Neighbor Discovery, although these attributes can be tuned on a
per-use-case basis.
Design
The FdNetDevice implementation makes use of a reader object, extended from the FdReader
class in the ns-3 src/core module, which manages a separate thread from the main ns-3
execution thread, in order to read traffic from the file descriptor.
Upon invocation of the StartDevice method, the reader object is initialized and starts the
reading thread. Before device start, a file descriptor must be previously associated to
the FdNetDevice with the SetFileDescriptor invocation.
The creation and configuration of the file descriptor can be left to a number of helpers,
described in more detail below. When this is done, the invocation of SetFileDescriptor is
responsibility of the helper and must not be directly invoked by the user.
Upon reading an incoming frame from the file descriptor, the reader will pass the frame to
the ReceiveCallback method, whose task it is to schedule the reception of the frame by the
device as a ns-3 simulation event. Since the new frame is passed from the reader thread to
the main ns-3 simulation thread, thread-safety issues are avoided by using the
ScheduleWithContext call instead of the regular Schedule call.
In order to avoid overwhelming the scheduler when the incoming data rate is too high, a
counter is kept with the number of frames that are currently scheduled to be received by
the device. If this counter reaches the value given by the RxQueueSize attribute in the
device, then the new frame will be dropped silently.
The actual reception of the new frame by the device occurs when the scheduled FordwarUp
method is invoked by the simulator. This method acts as if a new frame had arrived from a
channel attached to the device. The device then decapsulates the frame, removing any layer
2 headers, and forwards it to upper network stack layers of the node. The ForwardUp
method will remove the frame headers, according to the frame encapsulation type defined by
the EncapsulationMode attribute, and invoke the receive callback passing an IP packet.
An extra header, the PI header, can be present when the file descriptor is associated to a
TAP device that was created without setting the IFF_NO_PI flag. This extra header is
removed if EncapsulationMode is set to DIXPI value.
In the opposite direction, packets generated inside the simulation that are sent out
through the device, will be passed to the Send method, which will in turn invoke the
SendFrom method. The latter method will add the necessary layer 2 headers, and simply
write the newly created frame to the file descriptor.
Scope and Limitations
Users of this device are cautioned that there is no flow control across the file
descriptor boundary, when using in emulation mode. That is, in a Linux system, if the
speed of writing network packets exceeds the ability of the underlying physical device to
buffer the packets, backpressure up to the writing application will be applied to avoid
local packet loss. No such flow control is provided across the file descriptor interface,
so users must be aware of this limitation.
As explained before, the RxQueueSize attribute limits the number of packets that can be
pending to be received by the device. Frames read from the file descriptor while the
number of pending packets is in its maximum will be silently dropped.
The mtu of the device defaults to the Ethernet II MTU value. However, helpers are supposed
to set the mtu to the right value to reflect the characteristics of the network interface
associated to the file descriptor. If no helper is used, then the responsibility of
setting the correct mtu value for the device falls back to the user. The size of the read
buffer on the file descriptor reader is set to the mtu value in the StartDevice method.
The FdNetDevice class currently supports three encapsulation modes, DIX for Ethernet II
frames, LLC for 802.2 LLC/SNAP frames, and DIXPI for Ethernet II frames with an additional
TAP PI header. This means that traffic traversing the file descriptor is expected to be
Ethernet II compatible. Attaching an FdNetDevice to a wireless interface is possible as
long as the driver provides Ethernet II frames to the socket API. Note that to associate
a FdNetDevice to a wireless card in ad-hoc mode, the MAC address of the device must be set
to the real card MAC address, else any incoming traffic a fake MAC address will be
discarded by the driver.
As mentioned before, three helpers are provided with the fd-net-device module. Each
individual helper (file descriptor type) may have platform limitations. For instance,
threading, real-time simulation mode, and the ability to create TUN/TAP devices are
prerequisites to using the provided helpers. Support for these modes can be found in the
output of the waf configure step, e.g.:
Threading Primitives : enabled
Real Time Simulator : enabled
Emulated Net Device : enabled
Tap Bridge : enabled
It is important to mention that while testing the FdNetDevice we have found an upper bound
limit for TCP throughput when using 1Gb Ethernet links of 60Mbps. This limit is most
likely due to the processing power of the computers involved in the tests.
Usage
The usage pattern for this type of device is similar to other net devices with helpers
that install to node pointers or node containers. When using the base FdNetDeviceHelper
the user is responsible for creating and setting the file descriptor by himself.
FdNetDeviceHelper fd;
NetDeviceContainer devices = fd.Install (nodes);
// file descriptor generation
...
device->SetFileDescriptor (fd);
Most commonly a FdNetDevice will be used to interact with the host system. In these cases
it is almost certain that the user will want to run in real-time emulation mode, and to
enable checksum computations. The typical program statements are as follows:
GlobalValue::Bind ("SimulatorImplementationType", StringValue ("ns3::RealtimeSimulatorImpl"));
GlobalValue::Bind ("ChecksumEnabled", BooleanValue (true));
The easiest way to set up an experiment that interacts with a Linux host system is to user
the Emu and Tap helpers. Perhaps the most unusual part of these helper implementations
relates to the requirement for executing some of the code with super-user permissions.
Rather than force the user to execute the entire simulation as root, we provide a small
"creator" program that runs as root and does any required high-permission sockets work.
The easiest way to set the right privileges for the "creator" programs, is by enabling the
--enable-sudo flag when performing waf configure.
We do a similar thing for both the Emu and the Tap devices. The high-level view is that
the CreateFileDescriptor method creates a local interprocess (Unix) socket, forks, and
executes the small creation program. The small program, which runs as suid root, creates a
raw socket and sends back the raw socket file descriptor over the Unix socket that is
passed to it as a parameter. The raw socket is passed as a control message (sometimes
called ancillary data) of type SCM_RIGHTS.
Helpers
EmuFdNetDeviceHelper
The EmuFdNetDeviceHelper creates a raw socket to an underlying physical device, and
provides the socket descriptor to the FdNetDevice. This allows the ns-3 simulation to
read frames from and write frames to a network device on the host.
The emulation helper permits to transparently integrate a simulated ns-3 node into a
network composed of real nodes.
+----------------------+ +-----------------------+
| host 1 | | host 2 |
+----------------------+ +-----------------------+
| ns-3 simulation | | |
+----------------------+ | Linux |
| ns-3 Node | | Network Stack |
| +----------------+ | | +----------------+ |
| | ns-3 TCP | | | | TCP | |
| +----------------+ | | +----------------+ |
| | ns-3 IP | | | | IP | |
| +----------------+ | | +----------------+ |
| | FdNetDevice | | | | | |
| | 10.1.1.1 | | | | | |
| +----------------+ | | + ETHERNET + |
| | raw socket | | | | | |
|--+----------------+--| | +----------------+ |
| | eth0 | | | | eth0 | |
+-------+------+-------+ +--------+------+-------+
10.1.1.11 10.1.1.12
| |
+----------------------------+
This helper replaces the functionality of the EmuNetDevice found in ns-3 prior to ns-3.17,
by bringing this type of device into the common framework of the FdNetDevice. The
EmuNetDevice was deprecated in favor of this new helper.
The device is configured to perform MAC spoofing to separate simulation network traffic
from other network traffic that may be flowing to and from the host.
One can use this helper in a testbed situation where the host on which the simulation is
running has a specific interface of interest which drives the testbed hardware. You would
also need to set this specific interface into promiscuous mode and provide an appropriate
device name to the ns-3 simulation. Additionally, hardware offloading of segmentation and
checksums should be disabled.
The helper only works if the underlying interface is up and in promiscuous mode. Packets
will be sent out over the device, but we use MAC spoofing. The MAC addresses will be
generated (by default) using the Organizationally Unique Identifier (OUI) 00:00:00 as a
base. This vendor code is not assigned to any organization and so should not conflict with
any real hardware.
It is always up to the user to determine that using these MAC addresses is okay on your
network and won't conflict with anything else (including another simulation using such
devices) on your network. If you are using the emulated FdNetDevice configuration in
separate simulations, you must consider global MAC address assignment issues and ensure
that MAC addresses are unique across all simulations. The emulated net device respects the
MAC address provided in the Address attribute so you can do this manually. For larger
simulations, you may want to set the OUI in the MAC address allocation function.
Before invoking the Install method, the correct device name must be configured on the
helper using the SetDeviceName method. The device name is required to identify which
physical device should be used to open the raw socket.
EmuFdNetDeviceHelper emu;
emu.SetDeviceName (deviceName);
NetDeviceContainer devices = emu.Install (node);
Ptr<NetDevice> device = devices.Get (0);
device->SetAttribute ("Address", Mac48AddressValue (Mac48Address::Allocate ()));
TapFdNetDeviceHelper
A Tap device is a special type of Linux device for which one end of the device appears to
the kernel as a virtual net_device, and the other end is provided as a file descriptor to
user-space. This file descriptor can be passed to the FdNetDevice. Packets forwarded to
the TAP device by the kernel will show up in the FdNetDevice in ns-3.
Users should note that this usage of TAP devices is different than that provided by the
TapBridge NetDevice found in src/tap-bridge. The model in this helper is as follows:
+-------------------------------------+
| host |
+-------------------------------------+
| ns-3 simulation | |
+----------------------+ |
| ns-3 Node | |
| +----------------+ | |
| | ns-3 TCP | | |
| +----------------+ | |
| | ns-3 IP | | |
| +----------------+ | |
| | FdNetDevice | | |
|--+----------------+--+ +------+ |
| | TAP | | eth0 | |
| +------+ +------+ |
| 192.168.0.1 | |
+-------------------------------|-----+
|
|
------------ (Internet) -----
In the above, the configuration requires that the host be able to forward traffic
generated by the simulation to the Internet.
The model in TapBridge (in another module) is as follows:
+--------+
| Linux |
| host | +----------+
| ------ | | ghost |
| apps | | node |
| ------ | | -------- |
| stack | | IP | +----------+
| ------ | | stack | | node |
| TAP | |==========| | -------- |
| device | <----- IPC ------> | tap | | IP |
+--------+ | bridge | | stack |
| -------- | | -------- |
| ns-3 | | ns-3 |
| net | | net |
| device | | device |
+----------+ +----------+
|| ||
+---------------------------+
| ns-3 channel |
+---------------------------+
In the above, packets instead traverse ns-3 NetDevices and Channels.
The usage pattern for this example is that the user sets the MAC address and either (or
both) the IPv4 and IPv6 addresses and masks on the device, and the PI header if needed.
For example:
TapFdNetDeviceHelper helper;
helper.SetDeviceName (deviceName);
helper.SetModePi (modePi);
helper.SetTapIpv4Address (tapIp);
helper.SetTapIpv4Mask (tapMask);
...
helper.Install (node);
PlanetLabFdNetDeviceHelper
PlanetLab is a world wide distributed network testbed composed of nodes connected to the
Internet. Running ns-3 simulations in PlanetLab nodes using the
PlanetLabFdNetDeviceHelper allows to send simulated traffic generated by ns-3 directly to
the Internet. This setup can be useful to validate ns-3 Internet protocols or other future
protocols implemented in ns-3.
To run experiments using PlanetLab nodes it is required to have a PlanetLab account. Only
members of PlanetLab partner institutions can obtain such accounts ( for more information
visit http://www.planet-lab.org/ or http://www.planet-lab.eu ). Once the account is
obtained, a PlanetLab slice must be requested in order to conduct experiments. A slice
represents an experiment unit related to a group of PlanetLab users, and can be associated
to virtual machines in different PlanetLab nodes. Slices can also be customized by adding
configuration tags to it (this is done by PlanetLab administrators).
The PlanetLabFdNetDeviceHelper creates TAP devices on PlanetLab nodes using specific
PlanetLab mechanisms (i.e. the vsys system), and associates the TAP device to a
FdNetDevice in ns-3. The functionality provided by this helper is similar to that
provided by the FdTapNetDeviceHelper, except that the underlying mechanisms to create the
TAP device are different.
+-------------------------------------+
| PlanetLab host |
+-------------------------------------+
| ns-3 simulation | |
+----------------------+ |
| ns-3 Node | |
| +----------------+ | |
| | ns-3 TCP | | |
| +----------------+ | |
| | ns-3 IP | | |
| +----------------+ | |
| | FdNetDevice | | |
|--+----------------+--+ +------+ |
| | TAP | | eth0 | |
| +------+ +------+ |
| 192.168.0.1 | |
+-------------------------------|-----+
|
|
------------ (Internet) -----
In order to be able to assign private IPv4 addresses to the TAP devices, account holders
must request the vsys_vnet tag to be added to their slice by PlanetLab administrators.
The vsys_vnet tag is associated to private network segment and only addresses from this
segment can be used in experiments.
The syntax used to create a TAP device with this helper is similar to that used for the
previously described helpers:
PlanetLabFdNetDeviceHelper helper;
helper.SetTapIpAddress (tapIp);
helper.SetTapMask (tapMask);
...
helper.Install (node);
PlanetLab nodes have a Fedora based distribution, so ns-3 can be installed following the
instructions for ns-3 Linux installation.
Attributes
The FdNetDevice provides a number of attributes:
· Address: The MAC address of the device
· Start: The simulation start time to spin up the device thread
· Stop: The simulation start time to stop the device thread
· EncapsulationMode: Link-layer encapsulation format
·
RxQueueSize: The buffer size of the read queue on the file descriptor
thread (default of 1000 packets)
Start and Stop do not normally need to be specified unless the user wants to limit the
time during which this device is active. Address needs to be set to some kind of unique
MAC address if the simulation will be interacting with other real devices somehow using
real MAC addresses. Typical code:
device->SetAttribute ("Address", Mac48AddressValue (Mac48Address::Allocate ()));
Output
Ascii and PCAP tracing is provided similar to the other ns-3 NetDevice types, through the
helpers, such as (e.g.):
:: EmuFdNetDeviceHelper emu; NetDeviceContainer devices = emu.Install (node);
emu.EnablePcap ("emu-ping", device, true);
The standard set of Mac-level NetDevice trace sources is provided.
· MaxTx: Trace source triggered when ns-3 provides the device with a new frame to send
· MaxTxDrop: Trace source if write to file descriptor fails
· MaxPromiscRx: Whenever any valid Mac frame is received
· MaxRx: Whenever a valid Mac frame is received for this device
· Sniffer: Non-promiscuous packet sniffer
· PromiscSniffer: Promiscuous packet sniffer (for tcpdump-like traces)
Examples
Several examples are provided:
· dummy-network.cc: This simple example creates two nodes and interconnects them with a
Unix pipe by passing the file descriptors from the socketpair into the FdNetDevice
objects of the respective nodes.
· realtime-dummy-network.cc: Same as dummy-network.cc but uses the real time simulator
implementnation instead of the default one.
· fd2fd-onoff.cc: This example is aimed at measuring the throughput of the FdNetDevice in
a pure simulation. For this purpose two FdNetDevices, attached to different nodes but in
a same simulation, are connected using a socket pair. TCP traffic is sent at a
saturating data rate.
· fd-emu-onoff.cc: This example is aimed at measuring the throughput of the FdNetDevice
when using the EmuFdNetDeviceHelper to attach the simulated device to a real device in
the host machine. This is achieved by saturating the channel with TCP traffic.
· fd-emu-ping.cc: This example uses the EmuFdNetDeviceHelper to send ICMP traffic over a
real channel.
· fd-emu-udp-echo.cc: This example uses the EmuFdNetDeviceHelper to send UDP traffic over
a real channel.
· fd-planetlab-ping.cc: This example shows how to set up an experiment to send ICMP
traffic from a PlanetLab node to the Internet.
· fd-tap-ping.cc: This example uses the TapFdNetDeviceHelper to send ICMP traffic over a
real channel.
Tap NetDevice
The Tap NetDevice can be used to allow a host system or virtual machines to interact with
a simulation.
TapBridge Model Overview
The Tap Bridge is designed to integrate "real" internet hosts (or more precisely, hosts
that support Tun/Tap devices) into ns-3 simulations. The goal is to make it appear to a
"real" host node in that it has an ns-3 net device as a local device. The concept of a
"real host" is a bit slippery since the "real host" may actually be virtualized using
readily available technologies such as VMware, VirtualBox or OpenVZ.
Since we are, in essence, connecting the inputs and outputs of an ns-3 net device to the
inputs and outputs of a Linux Tap net device, we call this arrangement a Tap Bridge.
There are three basic operating modes of this device available to users. Basic
functionality is essentially identical, but the modes are different in details regarding
how the arrangement is created and configured; and what devices can live on which side of
the bridge.
We call these three modes the ConfigureLocal, UseLocal and UseBridge modes. The first
"word" in the camel case mode identifier indicates who has the responsibility for creating
and configuring the taps. For example, the "Configure" in ConfigureLocal mode indicates
that it is the TapBridge that has responsibility for configuring the tap. In UseLocal
mode and UseBridge modes, the "Use" prefix indicates that the TapBridge is asked to "Use"
an existing configuration.
In other words, in ConfigureLocal mode, the TapBridge has the responsibility for creating
and configuring the TAP devices. In UseBridge or UseLocal modes, the user provides a
configuration and the TapBridge adapts to that configuration.
TapBridge ConfigureLocal Mode
In the ConfigureLocal mode, the configuration of the tap device is ns-3
configuration-centric. Configuration information is taken from a device in the ns-3
simulation and a tap device matching the ns-3 attributes is automatically created. In
this case, a Linux computer is made to appear as if it was directly connected to a
simulated ns-3 network.
This is illustrated below:
+--------+
| Linux |
| host | +----------+
| ------ | | ghost |
| apps | | node |
| ------ | | -------- |
| stack | | IP | +----------+
| ------ | | stack | | node |
| TAP | |==========| | -------- |
| device | <----- IPC ------> | tap | | IP |
+--------+ | bridge | | stack |
| -------- | | -------- |
| ns-3 | | ns-3 |
| net | | net |
| device | | device |
+----------+ +----------+
|| ||
+---------------------------+
| ns-3 channel |
+---------------------------+
In this case, the "ns-3 net device" in the "ghost node" appears as if it were actually
replacing the TAP device in the Linux host. The ns-3 simulation creates the TAP device on
the underlying Linux OS and configures the IP and MAC addresses of the TAP device to match
the values assigned to the simulated ns-3 net device. The "IPC" link shown above is the
network tap mechanism in the underlying OS. The whole arrangement acts as a conventional
bridge; but a bridge between devices that happen to have the same shared MAC and IP
addresses.
Here, the user is not required to provide any configuration information specific to the
tap. A tap device will be created and configured by ns-3 according to its defaults, and
the tap device will have its name assigned by the underlying operating system according to
its defaults.
If the user has a requirement to access the created tap device, he or she may optionally
provide a "DeviceName" attribute. In this case, the created OS tap device will be named
accordingly.
The ConfigureLocal mode is the default operating mode of the Tap Bridge.
TapBridge UseLocal Mode
The UseLocal mode is quite similar to the ConfigureLocal mode. The significant difference
is, as the mode name implies, the TapBridge is going to "Use" an existing tap device
previously created and configured by the user. This mode is particularly useful when a
virtualization scheme automatically creates tap devices and ns-3 is used to provide
simulated networks for those devices.
+--------+
| Linux |
| host | +----------+
| ------ | | ghost |
| apps | | node |
| ------ | | -------- |
| stack | | IP | +----------+
| ------ | | stack | | node |
| TAP | |==========| | -------- |
| device | <----- IPC ------> | tap | | IP |
| MAC X | | bridge | | stack |
+--------+ | -------- | | -------- |
| ns-3 | | ns-3 |
| net | | net |
| device | | device |
| MAC Y | | MAC Z |
+----------+ +----------+
|| ||
+---------------------------+
| ns-3 channel |
+---------------------------+
In this case, the pre-configured MAC address of the "Tap device" (MAC X) will not be the
same as that of the bridged "ns-3 net device" (MAC Y) shown in the illustration above. In
order to bridge to ns-3 net devices which do not support SendFrom() (especially wireless
STA nodes) we impose a requirement that only one Linux device (with one unique MAC address
-- here X) generates traffic that flows across the IPC link. This is because the MAC
addresses of traffic across the IPC link will be "spoofed" or changed to make it appear to
Linux and ns-3 that they have the same address. That is, traffic moving from the Linux
host to the ns-3 ghost node will have its MAC address changed from X to Y and traffic from
the ghost node to the Linux host will have its MAC address changed from Y to X. Since
there is a one-to-one correspondence between devices, there may only be one MAC source
flowing from the Linux side. This means that Linux bridges with more than one net device
added are incompatible with UseLocal mode.
In UseLocal mode, the user is expected to create and configure a tap device completely
outside the scope of the ns-3 simulation using something like:
$ sudo tunctl -t tap0
$ sudo ifconfig tap0 hw ether 08:00:2e:00:00:01
$ sudo ifconfig tap0 10.1.1.1 netmask 255.255.255.0 up
To tell the TapBridge what is going on, the user will set either directly into the
TapBridge or via the TapBridgeHelper, the "DeviceName" attribute. In the case of the
configuration above, the "DeviceName" attribute would be set to "tap0" and the "Mode"
attribute would be set to "UseLocal".
One particular use case for this mode is in the OpenVZ environment. There it is possible
to create a Tap device on the "Hardware Node" and move it into a Virtual Private Server.
If the TapBridge is able to use an existing tap device it is then possible to avoid the
overhead of an OS bridge in that environment.
TapBridge UseBridge Mode
The simplest mode for those familiar with Linux networking is the UseBridge mode. Again,
the "Use" prefix indicates that the TapBridge is going to Use an existing configuration.
In this case, the TapBridge is going to logically extend a Linux bridge into ns-3.
This is illustrated below:
+---------+
| Linux | +----------+
| ------- | | ghost |
| apps | | node |
| ------- | | -------- |
| stack | | IP | +----------+
| ------- | +--------+ | stack | | node |
| Virtual | | TAP | |==========| | -------- |
| Device | | Device | <---- IPC -----> | tap | | IP |
+---------+ +--------+ | bridge | | stack |
|| || | -------- | | -------- |
+--------------------+ | ns-3 | | ns-3 |
| OS (brctl) Bridge | | net | | net |
+--------------------+ | device | | device |
+----------+ +----------+
|| ||
+---------------------------+
| ns-3 channel |
+---------------------------+
In this case, a computer running Linux applications, protocols, etc., is connected to a
ns-3 simulated network in such a way as to make it appear to the Linux host that the TAP
device is a real network device participating in the Linux bridge.
In the ns-3 simulation, a TapBridge is created to match each TAP Device. The name of the
TAP Device is assigned to the Tap Bridge using the "DeviceName" attribute. The TapBridge
then logically extends the OS bridge to encompass the ns-3 net device.
Since this mode logically extends an OS bridge, there may be many Linux net devices on the
non-ns-3 side of the bridge. Therefore, like a net device on any bridge, the ns-3 net
device must deal with the possibly of many source addresses. Thus, ns-3 devices must
support SendFrom() (NetDevice::SupportsSendFrom() must return true) in order to be
configured for use in UseBridge mode.
It is expected that the user will do something like the following to configure the bridge
and tap completely outside ns-3:
$ sudo brctl addbr mybridge
$ sudo tunctl -t mytap
$ sudo ifconfig mytap hw ether 00:00:00:00:00:01
$ sudo ifconfig mytap 0.0.0.0 up
$ sudo brctl addif mybridge mytap
$ sudo brctl addif mybridge ...
$ sudo ifconfig mybridge 10.1.1.1 netmask 255.255.255.0 up
To tell the TapBridge what is going on, the user will set either directly into the
TapBridge or via the TapBridgeHelper, the "DeviceName" attribute. In the case of the
configuration above, the "DeviceName" attribute would be set to "mytap" and the "Mode"
attribute would be set to "UseBridge".
This mode is especially useful in the case of virtualization where the configuration of
the virtual hosts may be dictated by another system and not be changable to suit ns-3.
For example, a particular VM scheme may create virtual "vethx" or "vmnetx" devices that
appear local to virtual hosts. In order to connect to such systems, one would need to
manually create TAP devices on the host system and brigde these TAP devices to the
existing (VM) virtual devices. The job of the Tap Bridge in this case is to extend the
bridge to join a ns-3 net device.
TapBridge ConfigureLocal Operation
In ConfigureLocal mode, the TapBridge and therefore its associated ns-3 net device appears
to the Linux host computer as a network device just like any arbitrary "eth0" or "ath0"
might appear. The creation and configuration of the TAP device is done by the ns-3
simulation and no manual configuration is required by the user. The IP addresses, MAC
addresses, gateways, etc., for created TAP devices are extracted from the simulation
itself by querying the configuration of the ns-3 device and the TapBridge Attributes.
Since the MAC addresses are identical on the Linux side and the ns-3 side, we can use
Send() on the ns-3 device which is available on all ns-3 net devices. Since the MAC
addresses are identical there is no requirement to hook the promiscuous callback on the
receive side. Therefore there are no restrictions on the kinds of net device that are
usable in ConfigureLocal mode.
The TapBridge appears to an ns-3 simulation as a channel-less net device. This device
must not have an IP address associated with it, but the bridged (ns-3) net device must
have an IP address. Be aware that this is the inverse of an ns-3 BridgeNetDevice (or a
conventional bridge in general) which demands that its bridge ports not have IP addresses,
but allows the bridge device itself to have an IP address.
The host computer will appear in a simulation as a "ghost" node that contains one
TapBridge for each NetDevice that is being bridged. From the perspective of a simulation,
the only difference between a ghost node and any other node will be the presence of the
TapBridge devices. Note however, that the presence of the TapBridge does affect the
connectivity of the net device to the IP stack of the ghost node.
Configuration of address information and the ns-3 devices is not changed in any way if a
TapBridge is present. A TapBridge will pick up the addressing information from the ns-3
net device to which it is connected (its "bridged" net device) and use that information to
create and configure the TAP device on the real host.
The end result of this is a situation where one can, for example, use the standard ping
utility on a real host to ping a simulated ns-3 node. If correct routes are added to the
internet host (this is expected to be done automatically in future ns-3 releases), the
routing systems in ns-3 will enable correct routing of the packets across simulated ns-3
networks. For an example of this, see the example program, tap-wifi-dumbbell.cc in the
ns-3 distribution.
The Tap Bridge lives in a kind of a gray world somewhere between a Linux host and an ns-3
bridge device. From the Linux perspective, this code appears as the user mode handler for
a TAP net device. In ConfigureLocal mode, this Tap device is automatically created by the
ns-3 simulation. When the Linux host writes to one of these automatically created
/dev/tap devices, the write is redirected into the TapBridge that lives in the ns-3 world;
and from this perspective, the packet write on Linux becomes a packet read in the Tap
Bridge. In other words, a Linux process writes a packet to a tap device and this packet
is redirected by the network tap mechanism toan ns-3 process where it is received by the
TapBridge as a result of a read operation there. The TapBridge then writes the packet to
the ns-3 net device to which it is bridged; and therefore it appears as if the Linux host
sent a packet directly through an ns-3 net device onto an ns-3 network.
In the other direction, a packet received by the ns-3 net device connected to the Tap
Bridge is sent via a receive callback to the TapBridge. The TapBridge then takes that
packet and writes it back to the host using the network tap mechanism. This write to the
device will appear to the Linux host as if a packet has arrived on a net device; and
therefore as if a packet received by the ns-3 net device during a simulation has appeared
on a real Linux net device.
The upshot is that the Tap Bridge appears to bridge a tap device on a Linux host in the
"real world" to an ns-3 net device in the simulation. Because the TAP device and the
bridged ns-3 net device have the same MAC address and the network tap IPC link is not
externalized, this particular kind of bridge makes it appear that a ns-3 net device is
actually installed in the Linux host.
In order to implement this on the ns-3 side, we need a "ghost node" in the simulation to
hold the bridged ns-3 net device and the TapBridge. This node should not actually do
anything else in the simulation since its job is simply to make the net device appear in
Linux. This is not just arbitrary policy, it is because:
· Bits sent to the TapBridge from higher layers in the ghost node (using the TapBridge
Send method) are completely ignored. The TapBridge is not, itself, connected to any
network, neither in Linux nor in ns-3. You can never send nor receive data over a
TapBridge from the ghost node.
· The bridged ns-3 net device has its receive callback disconnected from the ns-3 node and
reconnected to the Tap Bridge. All data received by a bridged device will then be sent
to the Linux host and will not be received by the node. From the perspective of the
ghost node, you can send over this device but you cannot ever receive.
Of course, if you understand all of the issues you can take control of your own destiny
and do whatever you want -- we do not actively prevent you from using the ghost node for
anything you decide. You will be able to perform typical ns-3 operations on the ghost
node if you so desire. The internet stack, for example, must be there and functional on
that node in order to participate in IP address assignment and global routing. However,
as mentioned above, interfaces talking to any TapBridge or associated bridged net devices
will not work completely. If you understand exactly what you are doing, you can set up
other interfaces and devices on the ghost node and use them; or take advantage of the
operational send side of the bridged devices to create traffic generators. We generally
recommend that you treat this node as a ghost of the Linux host and leave it to itself,
though.
TapBridge UseLocal Mode Operation
As described in above, the TapBridge acts like a bridge from the "real" world into the
simulated ns-3 world. In the case of the ConfigureLocal mode, life is easy since the IP
address of the Tap device matches the IP address of the ns-3 device and the MAC address of
the Tap device matches the MAC address of the ns-3 device; and there is a one-to-one
relationship between the devices.
Things are slightly complicated when a Tap device is externally configured with a
different MAC address than the ns-3 net device. The conventional way to deal with this
kind of difference is to use promiscuous mode in the bridged device to receive packets
destined for the different MAC address and forward them off to Linux. In order to move
packets the other way, the conventional solution is SendFrom() which allows a caller to
"spoof" or change the source MAC address to match the different Linux MAC address.
We do have a specific requirement to be able to bridge Linux Virtual Machines onto
wireless STA nodes. Unfortunately, the 802.11 spec doesn't provide a good way to
implement SendFrom(), so we have to work around that problem.
To this end, we provided the UseLocal mode of the Tap Bridge. This mode allows you
approach the problem as if you were creating a bridge with a single net device. A single
allowed address on the Linux side is remembered in the TapBridge, and all packets coming
from the Linux side are repeated out the ns-3 side using the ns-3 device MAC source
address. All packets coming in from the ns-3 side are repeated out the Linux side using
the remembered MAC address. This allows us to use Send() on the ns-3 device side which is
available on all ns-3 net devices.
UseLocal mode is identical to the ConfigureLocal mode except for the creation and
configuration of the tap device and the MAC address spoofing.
TapBridge UseBridge Operation
As described in the ConfigureLocal mode section, when the Linux host writes to one of the
/dev/tap devices, the write is redirected into the TapBridge that lives in the ns-3 world.
In the case of the UseBridge mode, these packets will need to be sent out on the ns-3
network as if they were sent on a device participating in the Linux bridge. This means
calling the SendFrom() method on the bridged device and providing the source MAC address
found in the packet.
In the other direction, a packet received by an ns-3 net device is hooked via callback to
the TapBridge. This must be done in promiscuous mode since the goal is to bridge the ns-3
net device onto the OS (brctl) bridge of which the TAP device is a part.
For these reasons, only ns-3 net devices that support SendFrom() and have a hookable
promiscuous receive callback are allowed to participate in UseBridge mode TapBridge
configurations.
Tap Bridge Channel Model
There is no channel model associated with the Tap Bridge. In fact, the intention is make
it appear that the real internet host is connected to the channel of the bridged net
device.
Tap Bridge Tracing Model
Unlike most ns-3 devices, the TapBridge does not provide any standard trace sources. This
is because the bridge is an intermediary that is essentially one function call away from
the bridged device. We expect that the trace hooks in the bridged device will be
sufficient for most users,
Using the TapBridge
We expect that most users will interact with the TapBridge device through the
TapBridgeHelper. Users of other helper classes, such as CSMA or Wifi, should be
comfortable with the idioms used there.
ENERGY FRAMEWORK
Energy consumption is a key issue for wireless devices, and wireless network researchers
often need to investigate the energy consumption at a node or in the overall network while
running network simulations in ns-3. This requires ns-3 to support energy consumption
modeling. Further, as concepts such as fuel cells and energy scavenging are becoming
viable for low power wireless devices, incorporating the effect of these emerging
technologies into simulations requires support for modeling diverse energy sources in
ns-3. The ns-3 Energy Framework provides the basis for energy consumption, energy source
and energy harvesting modeling.
Model Description
The source code for the Energy Framework is currently at: src/energy.
Design
The ns-3 Energy Framework is composed of 3 parts: Energy Source, Device Energy Model and
Energy Harvester. The framework is implemented into the src/energy/models folder.
Energy Source
The Energy Source represents the power supply on each node. A node can have one or more
energy sources, and each energy source can be connected to multiple device energy models.
Connecting an energy source to a device energy model implies that the corresponding device
draws power from the source. The basic functionality of the Energy Source is to provide
energy for devices on the node. When energy is completely drained from the Energy Source,
it notifies the devices on node such that each device can react to this event. Further,
each node can access the Energy Source Objects for information such as remaining energy or
energy fraction (battery level). This enables the implementation of energy aware protocols
in ns-3.
In order to model a wide range of power supplies such as batteries, the Energy Source must
be able to capture characteristics of these supplies. There are 2 important
characteristics or effects related to practical batteries:
Rate Capacity Effect
Decrease of battery lifetime when the current draw is higher than the rated value
of the battery.
Recovery Effect
Increase of battery lifetime when the battery is alternating between discharge and
idle states.
In order to incorporate the Rate Capacity Effect, the Energy Source uses current draw from
all the devices on the same node to calculate energy consumption. Moreover, multiple
Energy Harvesters can be connected to the Energy Source in order to replenish its energy.
The Energy Source periodically polls all the devices and energy harvesters on the same
node to calculate the total current drain and hence the energy consumption. When a device
changes state, its corresponding Device Energy Model will notify the Energy Source of this
change and new total current draw will be calculated. Similarly, every Energy Harvester
update triggers an update to the connected Energy Source.
The Energy Source base class keeps a list of devices (Device Energy Model objects) and
energy harvesters (Energy Harvester objects) that are using the particular Energy Source
as power supply. When energy is completely drained, the Energy Source will notify all
devices on this list. Each device can then handle this event independently, based on the
desired behavior that should be followed in case of power outage.
Device Energy Model
The Device Energy Model is the energy consumption model of a device installed on the node.
It is designed to be a state based model where each device is assumed to have a number of
states, and each state is associated with a power consumption value. Whenever the state of
the device changes, the corresponding Device Energy Model will notify the Energy Source of
the new current draw of the device. The Energy Source will then calculate the new total
current draw and update the remaining energy.
The Device Energy Model can also be used for devices that do not have finite number of
states. For example, in an electric vehicle, the current draw of the motor is determined
by its speed. Since the vehicle's speed can take continuous values within a certain range,
it is infeasible to define a set of discrete states of operation. However, by converting
the speed value into current directly, the same set of Device Energy Model APIs can still
be used.
Energy Harvester
The energy harvester represents the elements that harvest energy from the environment and
recharge the Energy Source to which it is connected. The energy harvester includes the
complete implementation of the actual energy harvesting device (e.g., a solar panel) and
the environment (e.g., the solar radiation). This means that in implementing an energy
harvester, the energy contribution of the environment and the additional energy
requirements of the energy harvesting device such as the conversion efficiency and the
internal power consumption of the device needs to be jointly modeled.
WiFi Radio Energy Model
The WiFi Radio Energy Model is the energy consumption model of a Wifi net device. It
provides a state for each of the available states of the PHY layer: Idle, CcaBusy, Tx, Rx,
ChannelSwitch, Sleep. Each of such states is associated with a value (in Ampere) of the
current draw (see below for the corresponding attribute names). A Wifi Radio Energy Model
PHY Listener is registered to the Wifi PHY in order to be notified of every Wifi PHY state
transition. At every transition, the energy consumed in the previous state is computed and
the energy source is notified in order to update its remaining energy.
The Wifi Tx Current Model gives the possibility to compute the current draw in the
transmit state as a function of the nominal tx power (in dBm), as observed in several
experimental measurements. To this purpose, the Wifi Radio Energy Model PHY Listener is
notified of the nominal tx power used to transmit the current frame and passes such a
value to the Wifi Tx Current Model which takes care of updating the current draw in the Tx
state. Hence, the energy consumption is correctly computed even if the Wifi Remote Station
Manager performs per-frame power control. Currently, a Linear Wifi Tx Current Model is
implemented which computes the tx current as a linear function (according to parameters
that can be specified by the user) of the nominal tx power in dBm.
The Wifi Radio Energy Model offers the possibility to specify a callback that is invoked
when the energy source is depleted. If such a callback is not specified when the Wifi
Radio Energy Model Helper is used to install the model on a device, a callback is
implicitly made so that the Wifi PHY is put in the SLEEP mode (hence no frame is
transmitted nor received afterwards) when the energy source is depleted. Likewise, it is
possible to specify a callback that is invoked when the energy source is recharged (which
might occur in case an energy harvester is connected to the energy source). If such a
callback is not specified when the Wifi Radio Energy Model Helper is used to install the
model on a device, a callback is implicitly made so that the Wifi PHY is resumed from the
SLEEP mode when the energy source is recharged.
Future Work
For Device Energy Models, we are planning to include support for other PHY layer models
provided in ns-3 such as WiMAX, and to model the energy consumptions of other non
communicating devices, like a generic sensor and a CPU. For Energy Sources, we are
planning to included new types of Energy Sources such as Supercapacitor and Nickel-Metal
Hydride (Ni-MH) battery. For the Energy Harvesters, we are planning to implement an energy
harvester that recharges the energy sources according to the power levels defined in a
user customizable dataset of real measurements.
References
[1] ns-2 Energy model:
http://www.cubinlab.ee.unimelb.edu.au/~jrid/Docs/Manuel-NS2/node204.html
[2] H. Wu, S. Nabar and R. Poovendran. An Energy Framework for the Network Simulator 3
(ns-3).
[3] M. Handy and D. Timmermann. Simulation of mobile wireless networks with accurate
modelling of non-linear battery effects. In Proc. of Applied simulation and Modeling
(ASM), 2003.
[4] D. N. Rakhmatov and S. B. Vrudhula. An analytical high-level battery model for use in
energy management of portable electronic systems. In Proc. of IEEE/ACM International
Conference on Computer Aided Design (ICCAD'01), pages 488-493, November 2001.
[5] D. N. Rakhmatov, S. B. Vrudhula, and D. A. Wallach. Battery lifetime prediction for
energy-aware computing. In Proc. of the 2002 International Symposium on Low Power
Electronics and Design (ISLPED'02), pages 154-159, 2002.
[6] C. Tapparello, H. Ayatollahi and W. Heinzelman. Extending the Energy Framework for
Network Simulator 3 (ns-3). Workshop on ns-3 (WNS3), Poster Session, Atlanta, GA,
USA. May, 2014.
Usage
The main way that ns-3 users will typically interact with the Energy Framework is through
the helper API and through the publicly visible attributes of the framework. The helper
API is defined in src/energy/helper/*.h.
In order to use the energy framework, the user must install an Energy Source for the node
of interest, the corresponding Device Energy Model for the network devices and, if
necessary, the one or more Energy Harvester. Energy Source (objects) are aggregated onto
each node by the Energy Source Helper. In order to allow multiple energy sources per node,
we aggregate an Energy Source Container rather than directly aggregating a source object.
The Energy Source object keeps a list of Device Energy Model and Energy Harvester objects
using the source as power supply. Device Energy Model objects are installed onto the
Energy Source by the Device Energy Model Helper, while Energy Harvester object are
installed by the Energy Harvester Helper. User can access the Device Energy Model objects
through the Energy Source object to obtain energy consumption information of individual
devices. Moreover, the user can access to the Energy Harvester objects in order to gather
information regarding the current harvestable power and the total energy harvested by the
harvester.
Examples
The example directories, src/examples/energy and examples/energy, contain some basic code
that shows how to set up the framework.
Helpers
Energy Source Helper
Base helper class for Energy Source objects, this helper Aggregates Energy Source object
onto a node. Child implementation of this class creates the actual Energy Source object.
Device Energy Model Helper
Base helper class for Device Energy Model objects, this helper attaches Device Energy
Model objects onto Energy Source objects. Child implementation of this class creates the
actual Device Energy Model object.
Energy Harvesting Helper
Base helper class for Energy Harvester objects, this helper attaches Energy Harvester
objects onto Energy Source objects. Child implementation of this class creates the actual
Energy Harvester object.
Attributes
Attributes differ between Energy Sources, Devices Energy Models and Energy Harvesters
implementations, please look at the specific child class for details.
Basic Energy Source
· BasicEnergySourceInitialEnergyJ: Initial energy stored in basic energy source.
· BasicEnergySupplyVoltageV: Initial supply voltage for basic energy source.
· PeriodicEnergyUpdateInterval: Time between two consecutive periodic energy updates.
RV Battery Model
· RvBatteryModelPeriodicEnergyUpdateInterval: RV battery model sampling interval.
· RvBatteryModelOpenCircuitVoltage: RV battery model open circuit voltage.
· RvBatteryModelCutoffVoltage: RV battery model cutoff voltage.
· RvBatteryModelAlphaValue: RV battery model alpha value.
· RvBatteryModelBetaValue: RV battery model beta value.
· RvBatteryModelNumOfTerms: The number of terms of the infinite sum for estimating battery
level.
WiFi Radio Energy Model
· IdleCurrentA: The default radio Idle current in Ampere.
· CcaBusyCurrentA: The default radio CCA Busy State current in Ampere.
· TxCurrentA: The radio Tx current in Ampere.
· RxCurrentA: The radio Rx current in Ampere.
· SwitchingCurrentA: The default radio Channel Switch current in Ampere.
· SleepCurrentA: The radio Sleep current in Ampere.
· TxCurrentModel: A pointer to the attached tx current model.
Basic Energy Harvester
· PeriodicHarvestedPowerUpdateInterval: Time between two consecutive periodic updates of
the harvested power.
· HarvestablePower: Random variables that represents the amount of power that is provided
by the energy harvester.
Tracing
Traced values differ between Energy Sources, Devices Energy Models and Energy Harvesters
implementations, please look at the specific child class for details.
Basic Energy Source
· RemainingEnergy: Remaining energy at BasicEnergySource.
RV Battery Model
· RvBatteryModelBatteryLevel: RV battery model battery level.
· RvBatteryModelBatteryLifetime: RV battery model battery lifetime.
WiFi Radio Energy Model
· TotalEnergyConsumption: Total energy consumption of the radio device.
Basic Energy Harvester
· HarvestedPower: Current power provided by the BasicEnergyHarvester.
· TotalEnergyHarvested: Total energy harvested by the BasicEnergyHarvester.
Validation
Comparison of the Energy Framework against actual devices have not been performed. Current
implementation of the Energy Framework is checked numerically for computation errors. The
RV battery model is validated by comparing results with what was presented in the original
RV battery model paper.
FLOW MONITOR
Model Description
The source code for the new module lives in the directory src/flow-monitor.
The Flow Monitor module goal is to provide a flexible system to measure the performance of
network protocols. The module uses probes, installed in network nodes, to track the
packets exchanged by the nodes, and it will measure a number of parameters. Packets are
divided according to the flow they belong to, where each flow is defined according to the
probe's characteristics (e.g., for IP, a flow is defined as the packets with the same
{protocol, source (IP, port), destination (IP, port)} tuple.
The statistics are collected for each flow can be exported in XML format. Moreover, the
user can access the probes directly to request specific stats about each flow.
Design
Flow Monitor module is designed in a modular way. It can be extended by subclassing
ns3::FlowProbe and ns3::FlowClassifier.
The full module design is described in [FlowMonitor]
Scope and Limitations
At the moment, probes and classifiers are available for IPv4 and IPv6.
Each probe will classify packets in four points:
· When a packet is sent (SendOutgoing IPv[4,6] traces)
· When a packet is forwarded (UnicastForward IPv[4,6] traces)
· When a packet is received (LocalDeliver IPv[4,6] traces)
· When a packet is dropped (Drop IPv[4,6] traces)
Since the packets are tracked at IP level, any retransmission caused by L4 protocols
(e.g., TCP) will be seen by the probe as a new packet.
A Tag will be added to the packet (ns3::Ipv[4,6]FlowProbeTag). The tag will carry basic
packet's data, useful for the packet's classification.
It must be underlined that only L4 (TCP, UDP) packets are, so far, classified. Moreover,
only unicast packets will be classified. These limitations may be removed in the future.
The data collected for each flow are:
· timeFirstTxPacket: when the first packet in the flow was transmitted;
· timeLastTxPacket: when the last packet in the flow was transmitted;
· timeFirstRxPacket: when the first packet in the flow was received by an end node;
· timeLastRxPacket: when the last packet in the flow was received;
· delaySum: the sum of all end-to-end delays for all received packets of the flow;
· jitterSum: the sum of all end-to-end delay jitter (delay variation) values for all
received packets of the flow, as defined in RFC 3393;
· txBytes, txPackets: total number of transmitted bytes / packets for the flow;
· rxBytes, rxPackets: total number of received bytes / packets for the flow;
· lostPackets: total number of packets that are assumed to be lost (not reported over 10
seconds);
· timesForwarded: the number of times a packet has been reportedly forwarded;
· delayHistogram, jitterHistogram, packetSizeHistogram: histogram versions for the delay,
jitter, and packet sizes, respectively;
· packetsDropped, bytesDropped: the number of lost packets and bytes, divided according to
the loss reason code (defined in the probe).
It is worth pointing out that the probes measure the packet bytes including IP headers.
The L2 headers are not included in the measure.
These stats will be written in XML form upon request (see the Usage section).
References
[FlowMonitor]
G. Carneiro, P. Fortuna, and M. Ricardo. 2009. FlowMonitor: a network monitoring framework
for the network simulator 3 (NS-3). In Proceedings of the Fourth International ICST
Conference on Performance Evaluation Methodologies and Tools (VALUETOOLS '09).
http://dx.doi.org/10.4108/ICST.VALUETOOLS2009.7493
Usage
The module usage is extremely simple. The helper will take care of about everything.
The typical use is:
// Flow monitor
Ptr<FlowMonitor> flowMonitor;
FlowMonitorHelper flowHelper;
flowMonitor = flowHelper.InstallAll();
Simulator::Stop (Seconds(stop_time));
Simulator::Run ();
flowMonitor->SerializeToXmlFile("NameOfFile.xml", true, true);
the SerializeToXmlFile () function 2nd and 3rd parameters are used respectively to
activate/deactivate the histograms and the per-probe detailed stats.
Other possible alternatives can be found in the Doxygen documentation.
Helpers
The helper API follows the pattern usage of normal helpers. Through the helper you can
install the monitor in the nodes, set the monitor attributes, and print the statistics.
One important thing is: the ns3::FlowMonitorHelper must be instantiated only once in the
main.
Attributes
The module provides the following attributes in ns3::FlowMonitor:
· MaxPerHopDelay (Time, default 10s): The maximum per-hop delay that should be considered;
· StartTime (Time, default 0s): The time when the monitoring starts;
· DelayBinWidth (double, default 0.001): The width used in the delay histogram;
· JitterBinWidth (double, default 0.001): The width used in the jitter histogram;
· PacketSizeBinWidth (double, default 20.0): The width used in the packetSize histogram;
· FlowInterruptionsBinWidth (double, default 0.25): The width used in the
flowInterruptions histogram;
· FlowInterruptionsMinTime (double, default 0.5): The minimum inter-arrival time that is
considered a flow interruption.
Output
The main model output is an XML formatted report about flow statistics. An example is:
<?xml version="1.0" ?>
<FlowMonitor>
<FlowStats>
<Flow flowId="1" timeFirstTxPacket="+0.0ns" timeFirstRxPacket="+20067198.0ns" timeLastTxPacket="+2235764408.0ns" timeLastRxPacket="+2255831606.0ns" delaySum="+138731526300.0ns" jitterSum="+1849692150.0ns" lastDelay="+20067198.0ns" txBytes="2149400" rxBytes="2149400" txPackets="3735" rxPackets="3735" lostPackets="0" timesForwarded="7466">
</Flow>
</FlowStats>
<Ipv4FlowClassifier>
<Flow flowId="1" sourceAddress="10.1.3.1" destinationAddress="10.1.2.2" protocol="6" sourcePort="49153" destinationPort="50000" />
</Ipv4FlowClassifier>
<Ipv6FlowClassifier>
</Ipv6FlowClassifier>
<FlowProbes>
<FlowProbe index="0">
<FlowStats flowId="1" packets="3735" bytes="2149400" delayFromFirstProbeSum="+0.0ns" >
</FlowStats>
</FlowProbe>
<FlowProbe index="2">
<FlowStats flowId="1" packets="7466" bytes="2224020" delayFromFirstProbeSum="+199415389258.0ns" >
</FlowStats>
</FlowProbe>
<FlowProbe index="4">
<FlowStats flowId="1" packets="3735" bytes="2149400" delayFromFirstProbeSum="+138731526300.0ns" >
</FlowStats>
</FlowProbe>
</FlowProbes>
</FlowMonitor>
The output was generated by a TCP flow from 10.1.3.1 to 10.1.2.2.
It is worth noticing that the index 2 probe is reporting more packets and more bytes than
the other probles. That's a perfectly normal behaviour, as packets are fragmented at IP
level in that node.
It should also be observed that the receiving node's probe (index 4) doesn't count the
fragments, as the reassembly is done before the probing point.
Examples
The examples are located in src/flow-monitor/examples.
Moreover, the following examples use the flow-monitor module:
· examples/matrix-topology/matrix-topology.cc
· examples/routing/manet-routing-compare.cc
· examples/routing/simple-global-routing.cc
· examples/tcp/tcp-variants-comparison.cc
· examples/wireless/multirate.cc
· examples/wireless/wifi-hidden-terminal.cc
Troubleshooting
Do not define more than one ns3::FlowMonitorHelper in the simulation.
Validation
The paper in the references contains a full description of the module validation against a
test network.
Tests are provided to ensure the Histogram correct functionality.
INTERNET MODELS
Internet Stack
Internet stack aggregation
A bare class Node is not very useful as-is; other objects must be aggregated to it to
provide useful node functionality.
The ns-3 source code directory src/internet provides implementation of TCP/IPv4- and
IPv6-related components. These include IPv4, ARP, UDP, TCP, IPv6, Neighbor Discovery, and
other related protocols.
Internet Nodes are not subclasses of class Node; they are simply Nodes that have had a
bunch of IP-related objects aggregated to them. They can be put together by hand, or via a
helper function InternetStackHelper::Install () which does the following to all nodes
passed in as arguments:
void
InternetStackHelper::Install (Ptr<Node> node) const
{
if (m_ipv4Enabled)
{
/* IPv4 stack */
if (node->GetObject<Ipv4> () != 0)
{
NS_FATAL_ERROR ("InternetStackHelper::Install (): Aggregating "
"an InternetStack to a node with an existing Ipv4 object");
return;
}
CreateAndAggregateObjectFromTypeId (node, "ns3::ArpL3Protocol");
CreateAndAggregateObjectFromTypeId (node, "ns3::Ipv4L3Protocol");
CreateAndAggregateObjectFromTypeId (node, "ns3::Icmpv4L4Protocol");
// Set routing
Ptr<Ipv4> ipv4 = node->GetObject<Ipv4> ();
Ptr<Ipv4RoutingProtocol> ipv4Routing = m_routing->Create (node);
ipv4->SetRoutingProtocol (ipv4Routing);
}
if (m_ipv6Enabled)
{
/* IPv6 stack */
if (node->GetObject<Ipv6> () != 0)
{
NS_FATAL_ERROR ("InternetStackHelper::Install (): Aggregating "
"an InternetStack to a node with an existing Ipv6 object");
return;
}
CreateAndAggregateObjectFromTypeId (node, "ns3::Ipv6L3Protocol");
CreateAndAggregateObjectFromTypeId (node, "ns3::Icmpv6L4Protocol");
// Set routing
Ptr<Ipv6> ipv6 = node->GetObject<Ipv6> ();
Ptr<Ipv6RoutingProtocol> ipv6Routing = m_routingv6->Create (node);
ipv6->SetRoutingProtocol (ipv6Routing);
/* register IPv6 extensions and options */
ipv6->RegisterExtensions ();
ipv6->RegisterOptions ();
}
if (m_ipv4Enabled || m_ipv6Enabled)
{
/* UDP and TCP stacks */
CreateAndAggregateObjectFromTypeId (node, "ns3::UdpL4Protocol");
node->AggregateObject (m_tcpFactory.Create<Object> ());
Ptr<PacketSocketFactory> factory = CreateObject<PacketSocketFactory> ();
node->AggregateObject (factory);
}
}
Where multiple implementations exist in ns-3 (TCP, IP routing), these objects are added by
a factory object (TCP) or by a routing helper (m_routing).
Note that the routing protocol is configured and set outside this function. By default,
the following protocols are added:
void InternetStackHelper::Initialize ()
{
SetTcp ("ns3::TcpL4Protocol");
Ipv4StaticRoutingHelper staticRouting;
Ipv4GlobalRoutingHelper globalRouting;
Ipv4ListRoutingHelper listRouting;
Ipv6ListRoutingHelper listRoutingv6;
Ipv6StaticRoutingHelper staticRoutingv6;
listRouting.Add (staticRouting, 0);
listRouting.Add (globalRouting, -10);
listRoutingv6.Add (staticRoutingv6, 0);
SetRoutingHelper (listRouting);
SetRoutingHelper (listRoutingv6);
}
By default, IPv4 and IPv6 are enabled.
Internet Node structure
An IP-capable Node (an ns-3 Node augmented by aggregation to have one or more IP stacks)
has the following internal structure.
Layer-3 protocols
At the lowest layer, sitting above the NetDevices, are the "layer 3" protocols, including
IPv4, IPv6, ARP and so on. The class Ipv4L3Protocol is an implementation class whose
public interface is typically class Ipv4, but the Ipv4L3Protocol public API is also used
internally at present.
In class Ipv4L3Protocol, one method described below is Receive ():
/**
* Lower layer calls this method after calling L3Demux::Lookup
* The ARP subclass needs to know from which NetDevice this
* packet is coming to:
* - implement a per-NetDevice ARP cache
* - send back arp replies on the right device
*/
void Receive( Ptr<NetDevice> device, Ptr<const Packet> p, uint16_t protocol,
const Address &from, const Address &to, NetDevice::PacketType packetType);
First, note that the Receive () function has a matching signature to the ReceiveCallback
in the class Node. This function pointer is inserted into the Node's protocol handler when
AddInterface () is called. The actual registration is done with a statement such as
follows:
RegisterProtocolHandler ( MakeCallback (&Ipv4Protocol::Receive, ipv4),
Ipv4L3Protocol::PROT_NUMBER, 0);
The Ipv4L3Protocol object is aggregated to the Node; there is only one such Ipv4L3Protocol
object. Higher-layer protocols that have a packet to send down to the Ipv4L3Protocol
object can call GetObject<Ipv4L3Protocol> () to obtain a pointer, as follows:
Ptr<Ipv4L3Protocol> ipv4 = m_node->GetObject<Ipv4L3Protocol> ();
if (ipv4 != 0)
{
ipv4->Send (packet, saddr, daddr, PROT_NUMBER);
}
This class nicely demonstrates two techniques we exploit in ns-3 to bind objects together:
callbacks, and object aggregation.
Once IPv4 routing has determined that a packet is for the local node, it forwards it up
the stack. This is done with the following function:
void
Ipv4L3Protocol::LocalDeliver (Ptr<const Packet> packet, Ipv4Header const&ip, uint32_t iif)
The first step is to find the right Ipv4L4Protocol object, based on IP protocol number.
For instance, TCP is registered in the demux as protocol number 6. Finally, the Receive()
function on the Ipv4L4Protocol (such as TcpL4Protocol::Receive is called.
We have not yet introduced the class Ipv4Interface. Basically, each NetDevice is paired
with an IPv4 representation of such device. In Linux, this class Ipv4Interface roughly
corresponds to the struct in_device; the main purpose is to provide address-family
specific information (addresses) about an interface.
All the classes have appropriate traces in order to track sent, received and lost packets.
The users is encouraged to use them so to find out if (and where) a packet is dropped. A
common mistake is to forget the effects of local queues when sending packets, e.g., the
ARP queue. This can be particularly puzzling when sending jumbo packets or packet bursts
using UDP. The ARP cache pending queue is limited (3 datagrams) and IP packets might be
fragmented, easily overfilling the ARP cache queue size. In those cases it is useful to
increase the ARP cache pending size to a proper value, e.g.:
Config::SetDefault ("ns3::ArpCache::PendingQueueSize", UintegerValue (MAX_BURST_SIZE/L2MTU*3));
The IPv6 implementation follows a similar architecture. Dual-stacked nodes (one with
support for both IPv4 and IPv6) will allow an IPv6 socket to receive IPv4 connections as a
standard dual-stacked system does. A socket bound and listening to an IPv6 endpoint can
receive an IPv4 connection and will return the remote address as an IPv4-mapped address.
Support for the IPV6_V6ONLY socket option does not currently exist.
Layer-4 protocols and sockets
We next describe how the transport protocols, sockets, and applications tie together. In
summary, each transport protocol implementation is a socket factory. An application that
needs a new socket
For instance, to create a UDP socket, an application would use a code snippet such as the
following:
Ptr<Udp> udpSocketFactory = GetNode ()->GetObject<Udp> ();
Ptr<Socket> m_socket = socketFactory->CreateSocket ();
m_socket->Bind (m_local_address);
...
The above will query the node to get a pointer to its UDP socket factory, will create one
such socket, and will use the socket with an API similar to the C-based sockets API, such
as Connect () and Send (). The address passed to the Bind (), Connect (), or Send ()
functions may be a Ipv4Address, Ipv6Address, or Address. If a Address is passed in and
contains anything other than a Ipv4Address or Ipv6Address, these functions will return an
error. The Bind (void) and Bind6 (void) functions bind to "0.0.0.0" and "::"
respectively.
The socket can also be bound to a specific NetDevice though the BindToNetDevice
(Ptr<NetDevice> netdevice) function. BindToNetDevice (Ptr<NetDevice> netdevice) will bind
the socket to "0.0.0.0" and "::" (equivalent to calling Bind () and Bind6 (), unless the
socket has been already bound to a specific address. Summarizing, the correct sequence
is:
Ptr<Udp> udpSocketFactory = GetNode ()->GetObject<Udp> ();
Ptr<Socket> m_socket = socketFactory->CreateSocket ();
m_socket->BindToNetDevice (n_netDevice);
...
or:
Ptr<Udp> udpSocketFactory = GetNode ()->GetObject<Udp> ();
Ptr<Socket> m_socket = socketFactory->CreateSocket ();
m_socket->Bind (m_local_address);
m_socket->BindToNetDevice (n_netDevice);
...
The following raises an error:
Ptr<Udp> udpSocketFactory = GetNode ()->GetObject<Udp> ();
Ptr<Socket> m_socket = socketFactory->CreateSocket ();
m_socket->BindToNetDevice (n_netDevice);
m_socket->Bind (m_local_address);
...
See the chapter on ns-3 sockets for more information.
We have described so far a socket factory (e.g. class Udp) and a socket, which may be
specialized (e.g., class UdpSocket). There are a few more key objects that relate to the
specialized task of demultiplexing a packet to one or more receiving sockets. The key
object in this task is class Ipv4EndPointDemux. This demultiplexer stores objects of
class Ipv4EndPoint. This class holds the addressing/port tuple (local port, local
address, destination port, destination address) associated with the socket, and a receive
callback. This receive callback has a receive function registered by the socket. The
Lookup () function to Ipv4EndPointDemux returns a list of Ipv4EndPoint objects (there may
be a list since more than one socket may match the packet). The layer-4 protocol copies
the packet to each Ipv4EndPoint and calls its ForwardUp () method, which then calls the
Receive () function registered by the socket.
An issue that arises when working with the sockets API on real systems is the need to
manage the reading from a socket, using some type of I/O (e.g., blocking, non-blocking,
asynchronous, ...). ns-3 implements an asynchronous model for socket I/O; the application
sets a callback to be notified of received data ready to be read, and the callback is
invoked by the transport protocol when data is available. This callback is specified as
follows:
void Socket::SetRecvCallback (Callback<void, Ptr<Socket>,
Ptr<Packet>,
const Address&> receivedData);
The data being received is conveyed in the Packet data buffer. An example usage is in
class PacketSink:
m_socket->SetRecvCallback (MakeCallback(&PacketSink::HandleRead, this));
To summarize, internally, the UDP implementation is organized as follows:
· a UdpImpl class that implements the UDP socket factory functionality
· a UdpL4Protocol class that implements the protocol logic that is socket-independent
· a UdpSocketImpl class that implements socket-specific aspects of UDP
· a class called Ipv4EndPoint that stores the addressing tuple (local port, local address,
destination port, destination address) associated with the socket, and a receive
callback for the socket.
IP-capable node interfaces
Many of the implementation details, or internal objects themselves, of IP-capable Node
objects are not exposed at the simulator public API. This allows for different
implementations; for instance, replacing the native ns-3 models with ported TCP/IP stack
code.
The C++ public APIs of all of these objects is found in the src/network directory,
including principally:
· address.h
· socket.h
· node.h
· packet.h
These are typically base class objects that implement the default values used in the
implementation, implement access methods to get/set state variables, host attributes, and
implement publicly-available methods exposed to clients such as CreateSocket.
Example path of a packet
These two figures show an example stack trace of how packets flow through the Internet
Node objects.
[image] Send path of a packet..UNINDENT
[image] Receive path of a packet..UNINDENT
IPv4
Placeholder chapter
IPv6
This chapter describes the ns-3 IPv6 model capabilities and limitations along with its
usage and examples.
IPv6 model description
The IPv6 model is loosely patterned after the Linux implementation; the implementation is
not complete as some features of IPv6 are not of much interest to simulation studies, and
some features of IPv6 are simply not modeled yet in ns-3.
The base class Ipv6 defines a generic API, while the class Ipv6L3Protocol is the actual
class implementing the protocol. The actual classes used by the IPv6 stack are located
mainly in the directory src/internet.
The implementation of IPv6 is contained in the following files:
src/internet/model/icmpv6-header.{cc,h}
src/internet/model/icmpv6-l4-protocol.{cc,h}
src/internet/model/ipv6.{cc,h}
src/internet/model/ipv6-address-generator.{cc,h}
src/internet/model/ipv6-autoconfigured-prefix.{cc,h}
src/internet/model/ipv6-end-point.{cc,h}
src/internet/model/ipv6-end-point-demux.{cc,h}
src/internet/model/ipv6-extension.{cc,h}
src/internet/model/ipv6-extension-demux.{cc,h}
src/internet/model/ipv6-extension-header.{cc,h}
src/internet/model/ipv6-header.{cc,h}
src/internet/model/ipv6-interface.{cc,h}
src/internet/model/ipv6-interface-address.{cc,h}
src/internet/model/ipv6-l3-protocol.{cc,h}
src/internet/model/ipv6-list-routing.{cc,h}
src/internet/model/ipv6-option.{cc,h}
src/internet/model/ipv6-option-demux.{cc,h}
src/internet/model/ipv6-option-header.{cc,h}
src/internet/model/ipv6-packet-info-tag.{cc,h}
src/internet/model/ipv6-pmtu-cache.{cc,h}
src/internet/model/ipv6-raw-socket-factory.{cc,h}
src/internet/model/ipv6-raw-socket-factory-impl.{cc,h}
src/internet/model/ipv6-raw-socket-impl.{cc,h}
src/internet/model/ipv6-route.{cc,h}
src/internet/model/ipv6-routing-protocol.{cc,h}
src/internet/model/ipv6-routing-table-entry.{cc,h}
src/internet/model/ipv6-static-routing.{cc,h}
src/internet/model/ndisc-cache.{cc,h}
src/network/utils/inet6-socket-address.{cc,h}
src/network/utils/ipv6-address.{cc,h}
Also some helpers are involved with IPv6:
src/internet/helper/internet-stack-helper.{cc,h}
src/internet/helper/ipv6-address-helper.{cc,h}
src/internet/helper/ipv6-interface-container.{cc,h}
src/internet/helper/ipv6-list-routing-helper.{cc,h}
src/internet/helper/ipv6-routing-helper.{cc,h}
src/internet/helper/ipv6-static-routing-helper.{cc,h}
The model files can be roughly divided into:
· protocol models (e.g., ipv6, ipv6-l3-protocol, icmpv6-l4-protocol, etc.)
· routing models (i.e., anything with 'routing' in its name)
· sockets and interfaces (e.g., ipv6-raw-socket, ipv6-interface, ipv6-end-point, etc.)
· address-related things
· headers, option headers, extension headers, etc.
· accessory classes (e.g., ndisc-cache)
Usage
The following description is based on using the typical helpers found in the example code.
IPv6 does not need to be activated in a node. it is automatically added to the available
protocols once the Internet Stack is installed.
In order to not install IPv6 along with IPv4, it is possible to use
ns3::InternetStackHelper method SetIpv6StackInstall (bool enable) before installing the
InternetStack in the nodes.
Note that to have an IPv6-only network (i.e., to not install the IPv4 stack in a node) one
should use ns3::InternetStackHelper method SetIpv4StackInstall (bool enable) before the
stack installation.
As an example, in the following code node 0 will have both IPv4 and IPv6, node 1 only only
IPv6 and node 2 only IPv4:
NodeContainer n;
n.Create (3);
InternetStackHelper internet;
InternetStackHelper internetV4only;
InternetStackHelper internetV6only;
internetV4only.SetIpv6StackInstall (false);
internetV6only.SetIpv4StackInstall (false);
internet.Install (n.Get (0));
internetV6only.Install (n.Get (1));
internetV4only.Install (n.Get (2));
IPv6 addresses assignment
In order to use IPv6 on a network, the first thing to do is assigning IPv6 addresses.
Any IPv6-enabled ns-3 node will have at least one NetDevice: the ns3::LoopbackNetDevice.
The loopback device address is ::1. All the other NetDevices will have one or more IPv6
addresses:
· One link-local address: fe80::interface ID, where interface ID is derived from the
NetDevice MAC address.
· Zero or more global addresses, e.g., 2001:db8::1.
Typically the first address on an interface will be the link-local one, with the global
address(es) being the following ones.
IPv6 global addresses might be:
· manually assigned
· auto-generated
ns-3 can use both methods, and it's quite important to understand the implications of
both.
Manually assigned IPv6 adddresses
This is probably the easiest and most used method. As an example:
Ptr<Node> n0 = CreateObject<Node> ();
Ptr<Node> n1 = CreateObject<Node> ();
NodeContainer net (n0, n1);
CsmaHelper csma;
NetDeviceContainer ndc = csma.Install (net);
NS_LOG_INFO ("Assign IPv6 Addresses.");
Ipv6AddressHelper ipv6;
ipv6.SetBase (Ipv6Address ("2001:db8::"), Ipv6Prefix (64));
Ipv6InterfaceContainer ic = ipv6.Assign (ndc);
This method will add two global IPv6 addresses to the nodes. Note that, as usual for IPv6,
all the nodes will also have a link-local address. Typically the first address on an
interface will be the link-local one, with the global address(es) being the following
ones.
Note that the global addesses will be derived from the MAC address. As a consequence,
expect to have addresses similar to 2001:db8::200:ff:fe00:1.
It is possible to repeat the above to assign more than one global address to a node.
However, due to the Ipv6AddressHelper singleton nature, one should first assign all the
adddresses of a network, then change the network base (SetBase), then do a new assignment.
Alternatively, it is possible to assign a specific address to a node:
Ptr<Node> n0 = CreateObject<Node> ();
NodeContainer net (n0);
CsmaHelper csma;
NetDeviceContainer ndc = csma.Install (net);
NS_LOG_INFO ("Specifically Assign an IPv6 Address.");
Ipv6AddressHelper ipv6;
Ptr<NetDevice> device = ndc.Get (0);
Ptr<Node> node = device->GetNode ();
Ptr<Ipv6> ipv6proto = node->GetObject<Ipv6> ();
int32_t ifIndex = 0;
ifIndex = ipv6proto->GetInterfaceForDevice (device);
Ipv6InterfaceAddress ipv6Addr = Ipv6InterfaceAddress (Ipv6Address ("2001:db8:f00d:cafe::42"), Ipv6Prefix (64));
ipv6proto->AddAddress (ifIndex, ipv6Addr);
Auto-generated IPv6 adddresses
This is accomplished by relying on the RADVD protocol, implemented by the class Radvd. At
the time there is no helper for this application, and the use is rather difficult (see
examples/ipv6/radvd.cc).
Upon using this method, the nodes will acquire dynamically (i.e., during the simulation)
one (or more) global address(es) according to the RADVD configuration. These addresses
will be bases on the RADVD announced prefix and the node's EUI-64.
Random-generated IPv6 adddresses
While IPv6 real nodes will use randomly generated addresses to protect privacy, ns-3 does
NOT have this capability. This feature haven't been so far considered as interesting for
simulation.
Duplicate Address Detection (DAD)
Nodes will perform DAD (it can be disabled using an Icmpv6L4Protocol attribute). Upon
receiving a DAD, however, nodes will not react to it. As is: DAD reaction is incomplete so
far. The main reason relies on the missing random-generated address capability. Moreover,
since ns-3 nodes will usually be well-behaving, therea should't be any Duplicate Address.
This might be changed in the future, so as to avoid issues with real-world integrated
simulations.
Host and Router behaviour in IPv6 and ns-3
In IPv6 there is a clear distinction between routers and hosts. As one might expect,
routers can forward packets from an interface to another interface, while hosts drop
packets not directed to them.
Unfortunately, forwarding is not the only thing affected by this distinction, and
forwarding itself might be fine-tuned, e.g., to forward packets incoming from an interface
and drop packets from another interface.
In ns-3 a node is configured to be an host by default. There are two main ways to change
this behaviour:
· Using ns3::Ipv6InterfaceContainer SetForwarding(uint32_t i, bool router) where i is the
interface index in the container.
· Changing the ns3::Ipv6 attribute IpForward.
Either one can be used during the simulation.
A fine-grained setup can be accomplished by using ns3::Ipv6Interface SetForwarding (bool
forward); which allows to change the behaviour on a per-interface-basis.
Note that the node-wide configuration only serves as a convenient method to enable/disable
the ns3::Ipv6Interface specific setting. An Ipv6Interface added to a node with forwarding
enabled will be set to be forwarding as well. This is really important when a node has
interfaces added during the simulation.
According to the ns3::Ipv6Interface forwarding state, the following happens:
· Forwarding OFF
· The node will NOT reply to Router Solicitation
· The node will react to Router Advertisement
· The node will periodically send Router Solicitation
· Routing protocols MUST DROP packets not directed to the node
· Forwarding ON
· The node will reply to Router Solicitation
· The node will NOT react to Router Advertisement
· The node will NOT send Router Solicitation
· Routing protocols MUST forward packets
The behaviour is matching ip-sysctl.txt (‐
http://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt) with the difference that
it's not possible to override the behaviour using esoteric settings (e.g., forwarding but
accept router advertisements, accept_ra=2, or forwarding but send router solicitations
forwarding=2).
Consider carefully the implications of packet forwarding. As an example, a node will NOT
send ICMPv6 PACKET_TOO_BIG messages from an interface with frowarding off. This is
completely normal, as the Routing protocol will drop the packet before attempting to
forward it.
Helpers
Typically the helpers used in IPv6 setup are:
· ns3::InternetStackHelper
· ns3::Ipv6AddressHelper
· ns3::Ipv6InterfaceContainer
The use is almost identical to the corresponding IPv4 case, e.g.:
NodeContainer n;
n.Create (4);
NS_LOG_INFO ("Create IPv6 Internet Stack");
InternetStackHelper internetv6;
internetv6.Install (n);
NS_LOG_INFO ("Create channels.");
CsmaHelper csma;
NetDeviceContainer d = csma.Install (n);
NS_LOG_INFO ("Create networks and assign IPv6 Addresses.");
Ipv6AddressHelper ipv6;
ipv6.SetBase (Ipv6Address ("2001:db8::"), Ipv6Prefix (64));
Ipv6InterfaceContainer iic = ipv6.Assign (d);
Additionally, a common task is to enable forwarding on one of the nodes and to setup a
default route toward it in the other nodes, e.g.:
iic.SetForwarding (0, true);
iic.SetDefaultRouteInAllNodes (0);
This will enable forwarding on the node 0 and will setup a default route in
ns3::Ipv6StaticRouting on all the other nodes. Note that this requires that
Ipv6StaticRouting is present in the nodes.
The IPv6 routing helpers enable the user to perform specific tasks on the particular
routing algorith and to print the routing tables.
Attributes
Many classes in the ns-3 IPv6 implementation contain attributes. The most useful ones are:
· ns3::Ipv6
· IpForward, boolean, default false. Globally enable or disable IP forwarding for all
current and future IPv6 devices.
· MtuDiscover, boolean, default true. If disabled, every interface will have its MTU
set to 1280 bytes.
· ns3::Ipv6L3Protocol
· DefaultTtl, uint8_t, default 64. The TTL value set by default on all outgoing packets
generated on this node.
· SendIcmpv6Redirect, boolean, default true. Send the ICMPv6 Redirect when appropriate.
· ns3::Icmpv6L4Protocol
· DAD, boolean, default true. Always do DAD (Duplicate Address Detection) check.
· ns3::NdiscCache
· UnresolvedQueueSize, uint32_t, default 3. Size of the queue for packets pending an NA
reply.
Output
The IPv6 stack provides some useful trace sources:
· ns3::Ipv6L3Protocol
· Tx, Send IPv6 packet to outgoing interface.
· Rx, Receive IPv6 packet from incoming interface.
· Drop, Drop IPv6 packet.
· ns3::Ipv6Extension
· Drop, Drop IPv6 packet.
The latest trace source is generated when a packet contains an unknown option blocking its
processing.
Mind that ns3::NdiscCache could drop packets as well, and they are not logged in a trace
source (yet). This might generate some confusion in the sent/received packets counters.
Advanced Usage
IPv6 maximum transmission unit (MTU) and fragmentation
ns-3 NetDevices define the MTU according to the L2 simulated Device. IPv6 requires that
the minimum MTU is 1280 bytes, so all NetDevices are required to support at least this
MTU. This is the link-MTU.
In order to support different MTUs in a source-destination path, ns-3 IPv6 model can
perform fragmentation. This can be either triggered by receiving a packet bigger than the
link-MTU from the L4 protocols (UDP, TCP, etc.), or by receving an ICMPv6 PACKET_TOO_BIG
message. The model mimics RFC 1981, with the following notable exceptions:
· L4 protocols are not informed of the Path MTU change
· TCP can not change its Segment Size according to the Path-MTU.
Both limitations are going to be removed in due time.
The Path-MTU cache is currently based on the source-destination IPv6 addresses. Further
classifications (e.g., flow label) are possible but not yet implemented.
The Path-MTU default validity time is 10 minutes. After the cache entry expiration, the
Path-MTU information is removed and the next packet will (eventually) trigger a new ICMPv6
PACKET_TOO_BIG message. Note that 1) this is consistent with the RFC specification and 2)
L4 protocols are responsible for retransmitting the packets.
Examples
The examples for IPv6 are in the directory examples/ipv6. These examples focus on the most
interesting IPv6 peculiarities, such as fragmentation, redirect and so on.
Moreover, most TCP and UDP examples located in examples/udp, examples/tcp, etc. have a
command-line option to use IPv6 instead of IPv4.
Troubleshooting
There are just a few pitfalls to avoid while using ns-3 IPv6.
Routing loops
Since the only (so far) routing scheme available for IPv6 is ns3::Ipv6StaticRouting,
default router have to be setup manually. When there are two or more routers in a network
(e.g., node A and node B), avoid using the helper function SetDefaultRouteInAllNodes for
more than one router.
The consequence would be to install a default route to B in A and a default route pointing
to A in B, generating a loop.
Global address leakage
Remember that addresses in IPv6 are global by definition. When using IPv6 with an
emulation ns-3 capability, avoid at all costs address leakage toward the global Internet.
It is advisable to setup an external firewall to prevent leakage.
2001:DB8::/32 addresses
IPv6 standard (RFC 3849) defines the 2001:DB8::/32 address class for the documentation.
This manual uses this convention. The addresses in this class are, however, only usable in
a document, and routers should discard them.
Validation
The IPv6 protocols has not yet been extensively validated against real implementations.
The actual tests involve mainly performing checks of the .pcap trace files with Wireshark,
and the results are positive.
Routing overview
ns-3 is intended to support traditional routing approaches and protocols, support ports of
open source routing implementations, and facilitate research into unorthodox routing
techniques. The overall routing architecture is described below in Routing architecture.
Users who wish to just read about how to configure global routing for wired topologies can
read Global centralized routing. Unicast routing protocols are described in Unicast
routing. Multicast routing is documented in Multicast routing.
Routing architecture
[image] Overview of routing.UNINDENT
Overview of routing shows the overall routing architecture for Ipv4. The key objects are
Ipv4L3Protocol, Ipv4RoutingProtocol(s) (a class to which all routing/forwarding has been
delegated from Ipv4L3Protocol), and Ipv4Route(s).
Ipv4L3Protocol must have at least one Ipv4RoutingProtocol added to it at simulation
setup time. This is done explicitly by calling Ipv4::SetRoutingProtocol ().
The abstract base class Ipv4RoutingProtocol () declares a minimal interface, consisting
of two methods: RouteOutput () and RouteInput (). For packets traveling outbound from
a host, the transport protocol will query Ipv4 for the Ipv4RoutingProtocol object
interface, and will request a route via Ipv4RoutingProtocol::RouteOutput (). A Ptr to
Ipv4Route object is returned. This is analagous to a dst_cache entry in Linux. The
Ipv4Route is carried down to the Ipv4L3Protocol to avoid a second lookup there. However,
some cases (e.g. Ipv4 raw sockets) will require a call to RouteOutput() directly from
Ipv4L3Protocol.
For packets received inbound for forwarding or delivery, the following steps occur.
Ipv4L3Protocol::Receive() calls Ipv4RoutingProtocol::RouteInput(). This passes the
packet ownership to the Ipv4RoutingProtocol object. There are four callbacks associated
with this call:
· LocalDeliver
· UnicastForward
· MulticastForward
· Error
The Ipv4RoutingProtocol must eventually call one of these callbacks for each packet that
it takes responsibility for. This is basically how the input routing process works in
Linux.
[image] Ipv4Routing specialization..UNINDENT
This overall architecture is designed to support different routing approaches, including
(in the future) a Linux-like policy-based routing implementation, proactive and
on-demand routing protocols, and simple routing protocols for when the simulation user
does not really care about routing.
Ipv4Routing specialization. illustrates how multiple routing protocols derive from this
base class. A class Ipv4ListRouting (implementation class Ipv4ListRoutingImpl) provides
the existing list routing approach in ns-3. Its API is the same as base class
Ipv4Routing except for the ability to add multiple prioritized routing protocols
(Ipv4ListRouting::AddRoutingProtocol(), Ipv4ListRouting::GetRoutingProtocol()).
The details of these routing protocols are described below in Unicast routing. For now,
we will first start with a basic unicast routing capability that is intended to globally
build routing tables at simulation time t=0 for simulation users who do not care about
dynamic routing.
Global centralized routing
Global centralized routing is sometimes called "God" routing; it is a special
implementation that walks the simulation topology and runs a shortest path algorithm, and
populates each node's routing tables. No actual protocol overhead (on the simulated links)
is incurred with this approach. It does have a few constraints:
· Wired only: It is not intended for use in wireless networks.
· Unicast only: It does not do multicast.
· Scalability: Some users of this on large topologies (e.g. 1000 nodes) have noticed that
the current implementation is not very scalable. The global centralized routing will be
modified in the future to reduce computations and runtime performance.
Presently, global centralized IPv4 unicast routing over both point-to-point and shared
(CSMA) links is supported.
By default, when using the ns-3 helper API and the default InternetStackHelper, global
routing capability will be added to the node, and global routing will be inserted as a
routing protocol with lower priority than the static routes (i.e., users can insert routes
via Ipv4StaticRouting API and they will take precedence over routes found by global
routing).
Global Unicast Routing API
The public API is very minimal. User scripts include the following:
#include "ns3/internet-module.h"
If the default InternetStackHelper is used, then an instance of global routing will be
aggregated to each node. After IP addresses are configured, the following function call
will cause all of the nodes that have an Ipv4 interface to receive forwarding tables
entered automatically by the GlobalRouteManager:
Ipv4GlobalRoutingHelper::PopulateRoutingTables ();
Note: A reminder that the wifi NetDevice will work but does not take any wireless effects
into account. For wireless, we recommend OLSR dynamic routing described below.
It is possible to call this function again in the midst of a simulation using the
following additional public function:
Ipv4GlobalRoutingHelper::RecomputeRoutingTables ();
which flushes the old tables, queries the nodes for new interface information, and
rebuilds the routes.
For instance, this scheduling call will cause the tables to be rebuilt at time 5 seconds:
Simulator::Schedule (Seconds (5),
&Ipv4GlobalRoutingHelper::RecomputeRoutingTables);
There are two attributes that govern the behavior. The first is
Ipv4GlobalRouting::RandomEcmpRouting. If set to true, packets are randomly routed across
equal-cost multipath routes. If set to false (default), only one route is consistently
used. The second is Ipv4GlobalRouting::RespondToInterfaceEvents. If set to true,
dynamically recompute the global routes upon Interface notification events (up/down, or
add/remove address). If set to false (default), routing may break unless the user manually
calls RecomputeRoutingTables() after such events. The default is set to false to preserve
legacy ns-3 program behavior.
Global Routing Implementation
This section is for those readers who care about how this is implemented. A singleton
object (GlobalRouteManager) is responsible for populating the static routes on each node,
using the public Ipv4 API of that node. It queries each node in the topology for a
"globalRouter" interface. If found, it uses the API of that interface to obtain a "link
state advertisement (LSA)" for the router. Link State Advertisements are used in OSPF
routing, and we follow their formatting.
It is important to note that all of these computations are done before packets are flowing
in the network. In particular, there are no overhead or control packets being exchanged
when using this implementation. Instead, this global route manager just walks the list of
nodes to build the necessary information and configure each node's routing table.
The GlobalRouteManager populates a link state database with LSAs gathered from the entire
topology. Then, for each router in the topology, the GlobalRouteManager executes the OSPF
shortest path first (SPF) computation on the database, and populates the routing tables on
each node.
The quagga (http://www.quagga.net) OSPF implementation was used as the basis for the
routing computation logic. One benefit of following an existing OSPF SPF implementation is
that OSPF already has defined link state advertisements for all common types of network
links:
· point-to-point (serial links)
· point-to-multipoint (Frame Relay, ad hoc wireless)
· non-broadcast multiple access (ATM)
· broadcast (Ethernet)
Therefore, we think that enabling these other link types will be more straightforward now
that the underlying OSPF SPF framework is in place.
Presently, we can handle IPv4 point-to-point, numbered links, as well as shared broadcast
(CSMA) links. Equal-cost multipath is also supported. Although wireless link types are
supported by the implementation, note that due to the nature of this implementation, any
channel effects will not be considered and the routing tables will assume that every node
on the same shared channel is reachable from every other node (i.e. it will be treated
like a broadcast CSMA link).
The GlobalRouteManager first walks the list of nodes and aggregates a GlobalRouter
interface to each one as follows:
typedef std::vector < Ptr<Node> >::iterator Iterator;
for (Iterator i = NodeList::Begin (); i != NodeList::End (); i++)
{
Ptr<Node> node = *i;
Ptr<GlobalRouter> globalRouter = CreateObject<GlobalRouter> (node);
node->AggregateObject (globalRouter);
}
This interface is later queried and used to generate a Link State Advertisement for each
router, and this link state database is fed into the OSPF shortest path computation logic.
The Ipv4 API is finally used to populate the routes themselves.
Unicast routing
There are presently seven unicast routing protocols defined for IPv4 and three for IPv6:
· class Ipv4StaticRouting (covering both unicast and multicast)
· IPv4 Optimized Link State Routing (OLSR) (a MANET protocol defined in RFC 3626)
· IPv4 Ad Hoc On Demand Distance Vector (AODV) (a MANET protocol defined in RFC 3561)
· IPv4 Destination Sequenced Distance Vector (DSDV) (a MANET protocol)
· IPv4 Dynamic Source Routing (DSR) (a MANET protocol)
· class Ipv4ListRouting (used to store a prioritized list of routing protocols)
· class Ipv4GlobalRouting (used to store routes computed by the global route manager, if
that is used)
· class Ipv4NixVectorRouting (a more efficient version of global routing that stores
source routes in a packet header field)
· class Ipv6ListRouting (used to store a prioritized list of routing protocols)
· class Ipv6StaticRouting
· class RipNg - the IPv6 RIPng protocol (RFC 2080)
In the future, this architecture should also allow someone to implement a Linux-like
implementation with routing cache, or a Click modular router, but those are out of scope
for now.
Ipv[4,6]ListRouting
This section describes the current default ns-3 Ipv[4,6]RoutingProtocol. Typically,
multiple routing protocols are supported in user space and coordinate to write a single
forwarding table in the kernel. Presently in ns-3, the implementation instead allows for
multiple routing protocols to build/keep their own routing state, and the IP
implementation will query each one of these routing protocols (in some order determined by
the simulation author) until a route is found.
We chose this approach because it may better facilitate the integration of disparate
routing approaches that may be difficult to coordinate the writing to a single table,
approaches where more information than destination IP address (e.g., source routing) is
used to determine the next hop, and on-demand routing approaches where packets must be
cached.
Ipv[4,6]4ListRouting::AddRoutingProtocol
Classes Ipv4ListRouting and Ipv6ListRouting provides a pure virtual function declaration
for the method that allows one to add a routing protocol:
void AddRoutingProtocol (Ptr<Ipv4RoutingProtocol> routingProtocol,
int16_t priority);
void AddRoutingProtocol (Ptr<Ipv6RoutingProtocol> routingProtocol,
int16_t priority);
These methods are implemented respectively by class Ipv4ListRoutingImpl and by class
Ipv6ListRoutingImpl in the internet module.
The priority variable above governs the priority in which the routing protocols are
inserted. Notice that it is a signed int. By default in ns-3, the helper classes will
instantiate a Ipv[4,6]ListRoutingImpl object, and add to it an Ipv[4,6]StaticRoutingImpl
object at priority zero. Internally, a list of Ipv[4,6]RoutingProtocols is stored, and
and the routing protocols are each consulted in decreasing order of priority to see
whether a match is found. Therefore, if you want your Ipv4RoutingProtocol to have priority
lower than the static routing, insert it with priority less than 0; e.g.:
Ptr<MyRoutingProtocol> myRoutingProto = CreateObject<MyRoutingProtocol> ();
listRoutingPtr->AddRoutingProtocol (myRoutingProto, -10);
Upon calls to RouteOutput() or RouteInput(), the list routing object will search the list
of routing protocols, in priority order, until a route is found. Such routing protocol
will invoke the appropriate callback and no further routing protocols will be searched.
Optimized Link State Routing (OLSR)
This IPv4 routing protocol was originally ported from the OLSR-UM implementation for ns-2.
The implementation is found in the src/olsr directory, and an example script is in
examples/simple-point-to-point-olsr.cc.
Typically, OLSR is enabled in a main program by use of an OlsrHelper class that installs
OLSR into an Ipv4ListRoutingProtocol object. The following sample commands will enable
OLSR in a simulation using this helper class along with some other routing helper objects.
The setting of priority value 10, ahead of the staticRouting priority of 0, means that
OLSR will be consulted for a route before the node's static routing table.:
NodeContainer c:
...
// Enable OLSR
NS_LOG_INFO ("Enabling OLSR Routing.");
OlsrHelper olsr;
Ipv4StaticRoutingHelper staticRouting;
Ipv4ListRoutingHelper list;
list.Add (staticRouting, 0);
list.Add (olsr, 10);
InternetStackHelper internet;
internet.SetRoutingHelper (list);
internet.Install (c);
Once installed,the OLSR "main interface" can be set with the SetMainInterface() command.
If the user does not specify a main address, the protocol will select the first primary IP
address that it finds, starting first the loopback interface and then the next
non-loopback interface found, in order of Ipv4 interface index. The loopback address of
127.0.0.1 is not selected. In addition, a number of protocol constants are defined in
olsr-routing-protocol.cc.
Olsr is started at time zero of the simulation, based on a call to Object::Start() that
eventually calls OlsrRoutingProtocol::DoStart(). Note: a patch to allow the user to start
and stop the protocol at other times would be welcome.
Presently, OLSR is limited to use with an Ipv4ListRouting object, and does not respond to
dynamic changes to a device's IP address or link up/down notifications; i.e. the topology
changes are due to loss/gain of connectivity over a wireless channel.
RIPng
This IPv6 routing protocol (RFC 2080) is the evolution of the well-known RIPv1 anf RIPv2
(see RFC 1058 and RFC 1723) routing protocols for IPv4.
The protocol is very simple, and it is normally suitable for flat, simple network
topologies.
RIPng is strongly based on RIPv1 and RIPv2, and it have the very same goals and
limitations. In particular, RIP considers any route with a metric equal or greater than 16
as unreachable. As a consequence, the maximum number of hops is the network must be less
than 15 (the number of routers is not set). Users are encouraged to read RFC 2080 and RFC
1058 to fully understand RIPng behaviour and limitations.
Routing convergence
RIPng uses a Distance-Vector algorithm, and routes are updated according to the
Bellman-Ford algorithm (sometimes known as Ford-Fulkerson algorithm). The algorithm has a
convergence time of O(|V|*|E|) where |V| and |E| are the number of vertices (routers) and
edges (links) respectively. It should be stressed that the convergence time is the number
of steps in the algorithm, and each step is triggered by a message. Since Triggered
Updates (i.e., when a route is changed) have a 1-5 seconds cooldown, the toplogy can
require some time to be stabilized.
Users should be aware that, during routing tables construction, the routers might drop
packets. Data traffic should be sent only after a time long enough to allow RIPng to build
the network topology. Usually 80 seconds should be enough to have a suboptimal (but
working) routing setup. This includes the time needed to propagate the routes to the most
distant router (16 hops) with Triggered Updates.
If the network topology is changed (e.g., a link is broken), the recovery time might be
quite high, and it might be even higher than the initial setup time. Moreover, the network
topology recovery is affected by the Split Horizoning strategy.
The example examples/routing/ripng-simple-network.cc shows both the network setup and
network recovery phases.
Split Horizoning
Split Horizon is a strategy to prevent routing instability. Three options are possible:
· No Split Horizon
· Split Horizon
· Poison Reverse
In the first case, routes are advertised on all the router's interfaces. In the second
case, routers will not advertise a route on the interface from which it was learned.
Poison Reverse will advertise the route on the interface from which it was learned, but
with a metric of 16 (infinity). For a full analysis of the three techniques, see RFC
1058, section 2.2.
The example ripng-simple-network.cc is based on the network toplogy described in the RFC,
but it does not show the effect described there.
The reason are the Triggered Updates, together with the fact that when a router
invalidates a route, it will immediately propagate the route unreachability, thus
preventing most of the issues described in the RFC.
However, with complex toplogies, it is still possible to have route instability phenomena
similar to the one described in the RFC after a link failure. As a consequence, all the
considerations about Split Horizon remanins valid.
Default routes
RIPng protocol should be installed only on routers. As a consequence, nodes will not know
what is the default router.
To overcome this limitation, users should either install the default route manually (e.g.,
by resorting to Ipv6StaticRouting), or by using RADVd. RADVd is available in ns-3 in the
Applications module, and it is strongly suggested.
Protocol parameters and options
The RIPng ns-3 implementation allows to change all the timers associated with route
updates and routes lifetime.
Moreover, users can change the interface metrics on a per-node basis.
The type of Split Horizoning (to avoid routes back-propagation) can be selected on a
per-node basis, with the choices being "no split horizon", "split horizon" and "poison
reverse". See RFC 2080 for further details, and RFC 1058 for a complete discussion on the
split horizoning strategies.
Limitations
There is no support for the Next Hop option (RFC 2080, Section 2.1.1). The Next Hop
option is useful when RIPng is not being run on all of the routers on a network. Support
for this option may be considered in the future.
There is no support for CIDR prefix aggregation. As a result, both routing tables and
route advertisements may be larger than necessary. Prefix aggregation may be added in the
future.
Multicast routing
The following function is used to add a static multicast route to a node:
void
Ipv4StaticRouting::AddMulticastRoute (Ipv4Address origin,
Ipv4Address group,
uint32_t inputInterface,
std::vector<uint32_t> outputInterfaces);
A multicast route must specify an origin IP address, a multicast group and an input
network interface index as conditions and provide a vector of output network interface
indices over which packets matching the conditions are sent.
Typically there are two main types of multicast routes: routes of the first kind are used
during forwarding. All of the conditions must be explicitly provided. The second kind of
routes are used to get packets off of a local node. The difference is in the input
interface. Routes for forwarding will always have an explicit input interface specified.
Routes off of a node will always set the input interface to a wildcard specified by the
index Ipv4RoutingProtocol::IF_INDEX_ANY.
For routes off of a local node wildcards may be used in the origin and multicast group
addresses. The wildcard used for Ipv4Adresses is that address returned by
Ipv4Address::GetAny () -- typically "0.0.0.0". Usage of a wildcard allows one to specify
default behavior to varying degrees.
For example, making the origin address a wildcard, but leaving the multicast group
specific allows one (in the case of a node with multiple interfaces) to create different
routes using different output interfaces for each multicast group.
If the origin and multicast addresses are made wildcards, you have created essentially a
default multicast address that can forward to multiple interfaces. Compare this to the
actual default multicast address that is limited to specifying a single output interface
for compatibility with existing functionality in other systems.
Another command sets the default multicast route:
void
Ipv4StaticRouting::SetDefaultMulticastRoute (uint32_t outputInterface);
This is the multicast equivalent of the unicast version SetDefaultRoute. We tell the
routing system what to do in the case where a specific route to a destination multicast
group is not found. The system forwards packets out the specified interface in the hope
that "something out there" knows better how to route the packet. This method is only used
in initially sending packets off of a host. The default multicast route is not consulted
during forwarding -- exact routes must be specified using AddMulticastRoute for that case.
Since we're basically sending packets to some entity we think may know better what to do,
we don't pay attention to "subtleties" like origin address, nor do we worry about
forwarding out multiple interfaces. If the default multicast route is set, it is returned
as the selected route from LookupStatic irrespective of origin or multicast group if
another specific route is not found.
Finally, a number of additional functions are provided to fetch and remove multicast
routes:
uint32_t GetNMulticastRoutes (void) const;
Ipv4MulticastRoute *GetMulticastRoute (uint32_t i) const;
Ipv4MulticastRoute *GetDefaultMulticastRoute (void) const;
bool RemoveMulticastRoute (Ipv4Address origin,
Ipv4Address group,
uint32_t inputInterface);
void RemoveMulticastRoute (uint32_t index);
TCP models in ns-3
This chapter describes the TCP models available in ns-3.
Generic support for TCP
ns-3 was written to support multiple TCP implementations. The implementations inherit from
a few common header classes in the src/network directory, so that user code can swap out
implementations with minimal changes to the scripts.
There are two important abstract base classes:
· class TcpSocket: This is defined in src/internet/model/tcp-socket.{cc,h}. This class
exists for hosting TcpSocket attributes that can be reused across different
implementations. For instance, the attribute InitialCwnd can be used for any of the
implementations that derive from class TcpSocket.
· class TcpSocketFactory: This is used by the layer-4 protocol instance to create TCP
sockets of the right type.
There are presently three implementations of TCP available for ns-3.
· a natively implemented TCP for ns-3
· support for the Network Simulation Cradle (NSC)
· support for Direct Code Exectution (DCE)
It should also be mentioned that various ways of combining virtual machines with ns-3
makes available also some additional TCP implementations, but those are out of scope for
this chapter.
ns-3 TCP
Until ns-3.10 release, ns-3 contained a port of the TCP model from GTNetS. This
implementation was substantially rewritten by Adriam Tam for ns-3.10. The model is a full
TCP, in that it is bidirectional and attempts to model the connection setup and close
logic.
The implementation of TCP is contained in the following files:
src/internet/model/tcp-header.{cc,h}
src/internet/model/tcp-l4-protocol.{cc,h}
src/internet/model/tcp-socket-factory-impl.{cc,h}
src/internet/model/tcp-socket-base.{cc,h}
src/internet/model/tcp-tx-buffer.{cc,h}
src/internet/model/tcp-rx-buffer.{cc,h}
src/internet/model/tcp-rfc793.{cc,h}
src/internet/model/tcp-tahoe.{cc,h}
src/internet/model/tcp-reno.{cc,h}
src/internet/model/tcp-westwood.{cc,h}
src/internet/model/tcp-newreno.{cc,h}
src/internet/model/rtt-estimator.{cc,h}
src/network/model/sequence-number.{cc,h}
Different variants of TCP congestion control are supported by subclassing the common base
class TcpSocketBase. Several variants are supported, including RFC 793 (no congestion
control), Tahoe, Reno, Westwood, Westwood+, and NewReno. NewReno is used by default. See
the Usage section of this document for on how to change the default TCP variant used in
simulation.
Usage
In many cases, usage of TCP is set at the application layer by telling the ns-3
application which kind of socket factory to use.
Using the helper functions defined in src/applications/helper and src/network/helper, here
is how one would create a TCP receiver:
// Create a packet sink on the star "hub" to receive these packets
uint16_t port = 50000;
Address sinkLocalAddress(InetSocketAddress (Ipv4Address::GetAny (), port));
PacketSinkHelper sinkHelper ("ns3::TcpSocketFactory", sinkLocalAddress);
ApplicationContainer sinkApp = sinkHelper.Install (serverNode);
sinkApp.Start (Seconds (1.0));
sinkApp.Stop (Seconds (10.0));
Similarly, the below snippet configures OnOffApplication traffic source to use TCP:
// Create the OnOff applications to send TCP to the server
OnOffHelper clientHelper ("ns3::TcpSocketFactory", Address ());
The careful reader will note above that we have specified the TypeId of an abstract base
class TcpSocketFactory. How does the script tell ns-3 that it wants the native ns-3 TCP
vs. some other one? Well, when internet stacks are added to the node, the default TCP
implementation that is aggregated to the node is the ns-3 TCP. This can be overridden as
we show below when using Network Simulation Cradle. So, by default, when using the ns-3
helper API, the TCP that is aggregated to nodes with an Internet stack is the native ns-3
TCP.
To configure behavior of TCP, a number of parameters are exported through the ns-3
attribute system. These are documented in the Doxygen
<http://www.nsnam.org/doxygen/classns3_1_1_tcp_socket.html> for class TcpSocket. For
example, the maximum segment size is a settable attribute.
To set the default socket type before any internet stack-related objects are created, one
may put the following statement at the top of the simulation program:
Config::SetDefault ("ns3::TcpL4Protocol::SocketType", StringValue ("ns3::TcpTahoe"));
For users who wish to have a pointer to the actual socket (so that socket operations like
Bind(), setting socket options, etc. can be done on a per-socket basis), Tcp sockets can
be created by using the Socket::CreateSocket() method. The TypeId passed to
CreateSocket() must be of type ns3::SocketFactory, so configuring the underlying socket
type must be done by twiddling the attribute associated with the underlying TcpL4Protocol
object. The easiest way to get at this would be through the attribute configuration
system. In the below example, the Node container "n0n1" is accessed to get the zeroth
element, and a socket is created on this node:
// Create and bind the socket...
TypeId tid = TypeId::LookupByName ("ns3::TcpTahoe");
Config::Set ("/NodeList/*/$ns3::TcpL4Protocol/SocketType", TypeIdValue (tid));
Ptr<Socket> localSocket =
Socket::CreateSocket (n0n1.Get (0), TcpSocketFactory::GetTypeId ());
Above, the "*" wild card for node number is passed to the attribute configuration system,
so that all future sockets on all nodes are set to Tahoe, not just on node 'n0n1.Get (0)'.
If one wants to limit it to just the specified node, one would have to do something like:
// Create and bind the socket...
TypeId tid = TypeId::LookupByName ("ns3::TcpTahoe");
std::stringstream nodeId;
nodeId << n0n1.Get (0)->GetId ();
std::string specificNode = "/NodeList/" + nodeId.str () + "/$ns3::TcpL4Protocol/SocketType";
Config::Set (specificNode, TypeIdValue (tid));
Ptr<Socket> localSocket =
Socket::CreateSocket (n0n1.Get (0), TcpSocketFactory::GetTypeId ());
Once a TCP socket is created, one will want to follow conventional socket logic and either
connect() and send() (for a TCP client) or bind(), listen(), and accept() (for a TCP
server). See Sockets-APIs for a review of how sockets are used in ns-3.
Validation
Several TCP validation test results can be found in the wiki page describing this
implementation.
Current limitations
· SACK is not supported
Network Simulation Cradle
The Network Simulation Cradle (NSC) is a framework for wrapping real-world network code
into simulators, allowing simulation of real-world behavior at little extra cost. This
work has been validated by comparing situations using a test network with the same
situations in the simulator. To date, it has been shown that the NSC is able to produce
extremely accurate results. NSC supports four real world stacks: FreeBSD, OpenBSD, lwIP
and Linux. Emphasis has been placed on not changing any of the network stacks by hand. Not
a single line of code has been changed in the network protocol implementations of any of
the above four stacks. However, a custom C parser was built to programmatically change
source code.
NSC has previously been ported to ns-2 and OMNeT++, and was was added to ns-3 in September
2008 (ns-3.2 release). This section describes the ns-3 port of NSC and how to use it.
To some extent, NSC has been superseded by the Linux kernel support within Direct Code
Execution (DCE). However, NSC is still available through the bake build system. NSC
supports Linux kernels 2.6.18 and 2.6.26, but newer versions of the kernel have not been
ported.
Prerequisites
Presently, NSC has been tested and shown to work on these platforms: Linux i386 and Linux
x86-64. NSC does not support powerpc. Use on FreeBSD or OS X is unsupported (although it
may be able to work).
Building NSC requires the packages flex and bison.
Configuring and Downloading
As of ns-3.17 or later, NSC must either be downloaded separately from its own repository,
or downloading when using the bake build system of ns-3.
For ns-3.17 or later releases, when using bake, one must configure NSC as part of an
"allinone" configuration, such as:
$ cd bake
$ python bake.py configure -e ns-allinone-3.19
$ python bake.py download
$ python bake.py build
Instead of a released version, one may use the ns-3 development version by specifying
"ns-3-allinone" to the configure step above.
NSC may also be downloaded from its download site using Mercurial:
$ hg clone https://secure.wand.net.nz/mercurial/nsc
Prior to the ns-3.17 release, NSC was included in the allinone tarball and the released
version did not need to be separately downloaded.
Building and validating
NSC may be built as part of the bake build process; alternatively, one may build NSC by
itself using its build system; e.g.:
$ cd nsc-dev
$ python scons.py
Once NSC has been built either manually or through the bake system, change into the ns-3
source directory and try running the following configuration:
$ ./waf configure
If NSC has been previously built and found by waf, then you will see:
Network Simulation Cradle : enabled
If NSC has not been found, you will see:
Network Simulation Cradle : not enabled (NSC not found (see option --with-nsc))
In this case, you must pass the relative or absolute path to the NSC libraries with the
"--with-nsc" configure option; e.g.
$ ./waf configure --with-nsc=/path/to/my/nsc/directory
For ns-3 releases prior to the ns-3.17 release, using the build.py script in ns-3-allinone
directory, NSC will be built by default unless the platform does not support it. To
explicitly disable it when building ns-3, type:
$ ./waf configure --enable-examples --enable-tests --disable-nsc
If waf detects NSC, then building ns-3 with NSC is performed the same way with waf as
without it. Once ns-3 is built, try running the following test suite:
$ ./test.py -s ns3-tcp-interoperability
If NSC has been successfully built, the following test should show up in the results:
PASS TestSuite ns3-tcp-interoperability
This confirms that NSC is ready to use.
Usage
There are a few example files. Try:
$ ./waf --run tcp-nsc-zoo
$ ./waf --run tcp-nsc-lfn
These examples will deposit some .pcap files in your directory, which can be examined by
tcpdump or wireshark.
Let's look at the examples/tcp/tcp-nsc-zoo.cc file for some typical usage. How does it
differ from using native ns-3 TCP? There is one main configuration line, when using NSC
and the ns-3 helper API, that needs to be set:
InternetStackHelper internetStack;
internetStack.SetNscStack ("liblinux2.6.26.so");
// this switches nodes 0 and 1 to NSCs Linux 2.6.26 stack.
internetStack.Install (n.Get(0));
internetStack.Install (n.Get(1));
The key line is the SetNscStack. This tells the InternetStack helper to aggregate
instances of NSC TCP instead of native ns-3 TCP to the remaining nodes. It is important
that this function be called before calling the Install() function, as shown above.
Which stacks are available to use? Presently, the focus has been on Linux 2.6.18 and Linux
2.6.26 stacks for ns-3. To see which stacks were built, one can execute the following find
command at the ns-3 top level directory:
$ find nsc -name "*.so" -type f
nsc/linux-2.6.18/liblinux2.6.18.so
nsc/linux-2.6.26/liblinux2.6.26.so
This tells us that we may either pass the library name liblinux2.6.18.so or
liblinux2.6.26.so to the above configuration step.
Stack configuration
NSC TCP shares the same configuration attributes that are common across TCP sockets, as
described above and documented in Doxygen
Additionally, NSC TCP exports a lot of configuration variables into the ns-3 attributes
system, via a sysctl-like interface. In the examples/tcp/tcp-nsc-zoo example, you can see
the following configuration:
// this disables TCP SACK, wscale and timestamps on node 1 (the attributes
represent sysctl-values).
Config::Set ("/NodeList/1/$ns3::Ns3NscStack<linux2.6.26>/net.ipv4.tcp_sack",
StringValue ("0"));
Config::Set ("/NodeList/1/$ns3::Ns3NscStack<linux2.6.26>/net.ipv4.tcp_timestamps",
StringValue ("0"));
Config::Set ("/NodeList/1/$ns3::Ns3NscStack<linux2.6.26>/net.ipv4.tcp_window_scaling",
StringValue ("0"));
These additional configuration variables are not available to native ns-3 TCP.
Also note that default values for TCP attributes in ns-3 TCP may differ from the nsc TCP
implementation. Specifically in ns-3:
1. TCP default MSS is 536
2. TCP Delayed Ack count is 2
Therefore when making comparisons between results obtained using nsc and ns-3 TCP, care
must be taken to ensure these values are set appropriately. See
/examples/tcp/tcp-nsc-comparision.cc for an example.
NSC API
This subsection describes the API that NSC presents to ns-3 or any other simulator. NSC
provides its API in the form of a number of classes that are defined in
sim/sim_interface.h in the nsc directory.
· INetStack INetStack contains the 'low level' operations for the operating system network
stack, e.g. in and output functions from and to the network stack (think of this as the
'network driver interface'. There are also functions to create new TCP or UDP sockets.
· ISendCallback This is called by NSC when a packet should be sent out to the network.
This simulator should use this callback to re-inject the packet into the simulator so
the actual data can be delivered/routed to its destination, where it will eventually be
handed into Receive() (and eventually back to the receivers NSC instance via
INetStack->if_receive() ).
· INetStreamSocket This is the structure defining a particular connection endpoint (file
descriptor). It contains methods to operate on this endpoint, e.g. connect, disconnect,
accept, listen, send_data/read_data, ...
· IInterruptCallback This contains the wakeup callback, which is called by NSC whenever
something of interest happens. Think of wakeup() as a replacement of the operating
systems wakeup function: Whenever the operating system would wake up a process that has
been waiting for an operation to complete (for example the TCP handshake during
connect()), NSC invokes the wakeup() callback to allow the simulator to check for state
changes in its connection endpoints.
ns-3 implementation
The ns-3 implementation makes use of the above NSC API, and is implemented as follows.
The three main parts are:
· ns3::NscTcpL4Protocol: a subclass of Ipv4L4Protocol (and two nsc classes: ISendCallback
and IInterruptCallback)
· ns3::NscTcpSocketImpl: a subclass of TcpSocket
· ns3::NscTcpSocketFactoryImpl: a factory to create new NSC sockets
src/internet/model/nsc-tcp-l4-protocol is the main class. Upon Initialization, it loads an
nsc network stack to use (via dlopen()). Each instance of this class may use a different
stack. The stack (=shared library) to use is set using the SetNscLibrary() method (at this
time its called indirectly via the internet stack helper). The nsc stack is then set up
accordingly (timers etc). The NscTcpL4Protocol::Receive() function hands the packet it
receives (must be a complete tcp/ip packet) to the nsc stack for further processing. To
be able to send packets, this class implements the nsc send_callback method. This method
is called by nsc whenever the nsc stack wishes to send a packet out to the network. Its
arguments are a raw buffer, containing a complete TCP/IP packet, and a length value. This
method therefore has to convert the raw data to a Ptr<Packet> usable by ns-3. In order to
avoid various ipv4 header issues, the nsc ip header is not included. Instead, the tcp
header and the actual payload are put into the Ptr<Packet>, after this the Packet is
passed down to layer 3 for sending the packet out (no further special treatment is needed
in the send code path).
This class calls ns3::NscTcpSocketImpl both from the nsc wakeup() callback and from the
Receive path (to ensure that possibly queued data is scheduled for sending).
src/internet/model/nsc-tcp-socket-impl implements the nsc socket interface. Each instance
has its own nscTcpSocket. Data that is Send() will be handed to the nsc stack via
m_nscTcpSocket->send_data(). (and not to nsc-tcp-l4, this is the major difference compared
to ns-3 TCP). The class also queues up data that is Send() before the underlying
descriptor has entered an ESTABLISHED state. This class is called from the nsc-tcp-l4
class, when the nsc-tcp-l4 wakeup() callback is invoked by nsc. nsc-tcp-socket-impl then
checks the current connection state (SYN_SENT, ESTABLISHED, LISTEN...) and schedules
appropriate callbacks as needed, e.g. a LISTEN socket will schedule Accept to see if a new
connection must be accepted, an ESTABLISHED socket schedules any pending data for writing,
schedule a read callback, etc.
Note that ns3::NscTcpSocketImpl does not interact with nsc-tcp directly: instead, data is
redirected to nsc. nsc-tcp calls the nsc-tcp-sockets of a node when its wakeup callback is
invoked by nsc.
Limitations
· NSC only works on single-interface nodes; attempting to run it on a multi-interface node
will cause a program error.
· Cygwin and OS X PPC are not supported; OS X Intel is not supported but may work
· The non-Linux stacks of NSC are not supported in ns-3
· Not all socket API callbacks are supported
For more information, see this wiki page.
CoDel queue implementation in ns-3
This chapter describes the CoDel ([Nic12], [Nic14]) queue implementation in ns-3.
Developed by Kathleen Nichols and Van Jacobson as a solution to the bufferbloat [Buf14]
problem, CoDel (Controlled Delay Management) is a queuing discipline that uses a packet's
sojourn time (time in queue) to make decisions on packet drops.
Model Description
The source code for the CoDel model is located in the directory src/internet/model and
consists of 2 files codel-queue.h and codel-queue.cc defining a CoDelQueue class and a
helper CoDelTimestampTag class. The code was ported to ns-3 by Andrew McGregor based on
Linux kernel code implemented by Dave Täht and Eric Dumazet.
· class CoDelQueue: This class implements the main CoDel algorithm:
· CoDelQueue::DoEnqueue (): This routine tags a packet with the current time before
pushing it into the queue. The timestamp tag is used by CoDelQueue::DoDequeue() to
compute the packet's sojourn time. If the queue is full upon the packet arrival, this
routine will drop the packet and record the number of drops due to queue overflow,
which is stored in m_dropOverLimit.
· CoDelQueue::ShouldDrop (): This routine is CoDelQueue::DoDequeue()'s helper routine
that determines whether a packet should be dropped or not based on its sojourn time.
If the sojourn time goes above m_target and remains above continuously for at least
m_interval, the routine returns true indicating that it is OK to drop the packet.
Otherwise, it returns false.
· CoDelQueue::DoDequeue (): This routine performs the actual packet drop based on
CoDelQueue::ShouldDrop ()'s return value and schedules the next drop.
· class CoDelTimestampTag: This class implements the timestamp tagging for a packet. This
tag is used to compute the packet's sojourn time (the difference between the time the
packet is dequeued and the time it is pushed into the queue).
There are 2 branches to CoDelQueue::DoDequeue ():
1. If the queue is currently in the dropping state, which means the sojourn time has
remained above m_target for more than m_interval, the routine determines if it's OK to
leave the dropping state or it's time for the next drop. When CoDelQueue::ShouldDrop ()
returns false, the queue can move out of the dropping state (set m_dropping to false).
Otherwise, the queue continuously drops packets and updates the time for next drop
(m_dropNext) until one of the following conditions is met:
1. The queue is empty, upon which the queue leaves the dropping state and exits
CoDelQueue::ShouldDrop () routine;
2. CoDelQueue::ShouldDrop () returns false (meaning the sojourn time goes below
m_target) upon which the queue leaves the dropping state;
3. It is not yet time for next drop (m_dropNext is less than current time) upon
which the queue waits for the next packet dequeue to check the condition again.
2. If the queue is not in the dropping state, the routine enters the dropping state and
drop the first packet if CoDelQueue::ShouldDrop () returns true (meaning the sojourn
time has gone above m_target for at least m_interval for the first time or it has gone
above again after the queue leaves the dropping state).
References
[Nic12]
K. Nichols and V. Jacobson, Controlling Queue Delay, ACM Queue, Vol. 10 No. 5, May 2012.
Available online at http://queue.acm.org/detail.cfm?id=2209336.
[Nic14]
K. Nichols and V. Jacobson, Internet-Draft: Controlled Delay Active Queue Management,
March 2014. Available online at
http://tools.ietf.org/html/draft-nichols-tsvwg-codel-02.
[Buf14]
Bufferbloat.net. Available online at http://www.bufferbloat.net/.
Attributes
The key attributes that the CoDelQueue class holds include the following:
· Mode: CoDel operating mode (BYTES, PACKETS, or ILLEGAL). The default mode is BYTES.
· MaxPackets: The maximum number of packets the queue can hold. The default value is
DEFAULT_CODEL_LIMIT, which is 1000 packets.
· MaxBytes: The maximum number of bytes the queue can hold. The default value is 1500 *
DEFAULT_CODEL_LIMIT, which is 1500 * 1000 bytes.
· MinBytes: The CoDel algorithm minbytes parameter. The default value is 1500 bytes.
· Interval: The sliding-minimum window. The default value is 100 ms.
· Target: The CoDel algorithm target queue delay. The default value is 5 ms.
Examples
The first example is codel-vs-droptail-basic-test.cc located in src/internet/examples. To
run the file (the first invocation below shows the available command-line options):
$ ./waf --run "codel-vs-droptail-basic-test --PrintHelp"
$ ./waf --run "codel-vs-droptail-basic-test --queueType=CoDel --pcapFileName=codel.pcap --cwndTrFileName=cwndCodel.tr"
The expected output from the previous commands are two files: codel.pcap file and
cwndCoDel.tr (ASCII trace) file The .pcap file can be analyzed using wireshark or
tcptrace:
$ tcptrace -l -r -n -W codel.pcap
The second example is codel-vs-droptail-asymmetric.cc located in src/internet/examples.
This example is intended to model a typical cable modem deployment scenario. To run the
file:
$ ./waf --run "codel-vs-droptail-asymmetric --PrintHelp"
$ ./waf --run codel-vs-droptail-asymmetric
The expected output from the previous commands is six pcap files:
· codel-vs-droptail-asymmetric-CoDel-server-lan.pcap
· codel-vs-droptail-asymmetric-CoDel-router-wan.pcap
· codel-vs-droptail-asymmetric-CoDel-router-lan.pcap
· codel-vs-droptail-asymmetric-CoDel-cmts-wan.pcap
· codel-vs-droptail-asymmetric-CoDel-cmts-lan.pcap
· codel-vs-droptail-asymmetric-CoDel-host-lan.pcap
One attribute file:
· codel-vs-droptail-asymmetric-CoDel.attr
Five ASCII trace files:
· codel-vs-droptail-asymmetric-CoDel-drop.tr
· codel-vs-droptail-asymmetric-CoDel-drop-state.tr
· codel-vs-droptail-asymmetric-CoDel-sojourn.tr
· codel-vs-droptail-asymmetric-CoDel-length.tr
· codel-vs-droptail-asymmetric-CoDel-cwnd.tr
Validation
The CoDel model is tested using CoDelQueueTestSuite class defined in
src/internet/test/codel-queue-test-suite.cc. The suite includes 5 test cases:
· Test 1: The first test checks the enqueue/dequeue with no drops and makes sure that
CoDel attributes can be set correctly.
· Test 2: The second test checks the enqueue with drops due to queue overflow.
· Test 3: The third test checks the NewtonStep() arithmetic against explicit port of Linux
implementation
· Test 4: The fourth test checks the ControlLaw() against explicit port of Linux
implementation
· Test 5: The fifth test checks the enqueue/dequeue with drops according to CoDel
algorithm
The test suite can be run using the following commands:
$ ./waf configure --enable-examples --enable-tests
$ ./waf build
$ ./test.py -s codel-queue
or
$ NS_LOG="CoDelQueue" ./waf --run "test-runner --suite=codel-queue"
PageBreak
LOW-RATE WIRELESS PERSONAL AREA NETWORK (LR-WPAN)
This chapter describes the implementation of ns-3 models for the low-rate, wireless
personal area network (LR-WPAN) as specified by IEEE standard 802.15.4 (2006).
Model Description
The source code for the lr-wpan module lives in the directory src/lr-wpan.
Design
The model design closely follows the standard from an architectural standpoint.
[image] Architecture and scope of lr-wpan models.UNINDENT
The grey areas in the figure (adapted from Fig 3. of IEEE Std. 802.15.4-2006) show the
scope of the model.
The Spectrum NetDevice from Nicola Baldo is the basis for the implementation.
The implementation also plans to borrow from the ns-2 models developed by Zheng and Lee
in the future.
APIs
The APIs closely follow the standard, adapted for ns-3 naming conventions and idioms. The
APIs are organized around the concept of service primitives as shown in the following
figure adapted from Figure 14 of IEEE Std. 802.15.4-2006.
[image] Service primitives.UNINDENT
The APIs are organized around four conceptual services and service access points (SAP):
· MAC data service (MCPS)
· MAC management service (MLME)
· PHY data service (PD)
· PHY management service (PLME)
In general, primitives are standardized as follows (e.g. Sec 7.1.1.1.1 of IEEE
802.15.4-2006)::
MCPS-DATA.request (
SrcAddrMode,
DstAddrMode,
DstPANId,
DstAddr,
msduLength,
msdu,
msduHandle,
TxOptions,
SecurityLevel,
KeyIdMode,
KeySource,
KeyIndex
)
This maps to ns-3 classes and methods such as::
struct McpsDataRequestParameters
{
uint8_t m_srcAddrMode;
uint8_t m_dstAddrMode;
...
};
void
LrWpanMac::McpsDataRequest (McpsDataRequestParameters params)
{
...
}
MAC
The MAC at present implements the unslotted CSMA/CA variant, without beaconing. Currently
there is no support for coordinators and the relavant APIs.
The implemented MAC is similar to Contiki's NullMAC, i.e., a MAC without sleep features.
The radio is assumed to be always active (receiving or transmitting), of completely shut
down. Frame reception is not disabled while performing the CCA.
The main API supported is the data transfer API (McpsDataRequest/Indication/Confirm).
CSMA/CA according to Stc 802.15.4-2006, section 7.5.1.4 is supported. Frame reception and
rejection according to Std 802.15.4-2006, section 7.5.6.2 is supported, including
acknowledgements. Only short addressing completely implemented. Various trace sources are
supported, and trace sources can be hooked to sinks.
PHY
The physical layer components consist of a Phy model, an error rate model, and a loss
model. The error rate model presently models the error rate for IEEE 802.15.4 2.4 GHz
AWGN channel for OQPSK; the model description can be found in IEEE Std 802.15.4-2006,
section E.4.1.7. The Phy model is based on SpectrumPhy and it follows specification
described in section 6 of IEEE Std 802.15.4-2006. It models PHY service specifications,
PPDU formats, PHY constants and PIB attributes. It currently only supports the transmit
power spectral density mask specified in 2.4 GHz per section 6.5.3.1. The noise power
density assumes uniformly distributed thermal noise across the frequency bands. The loss
model can fully utilize all existing simple (non-spectrum phy) loss models. The Phy model
uses the existing single spectrum channel model. The physical layer is modeled on packet
level, that is, no preamble/SFD detection is done. Packet reception will be started with
the first bit of the preamble (which is not modeled), if the SNR is more than -5 dB, see
IEEE Std 802.15.4-2006, appendix E, Figure E.2. Reception of the packet will finish after
the packet was completely transmitted. Other packets arriving during reception will add up
to the interference/noise.
Currently the receiver sensitivity is set to a fixed value of -106.58 dBm. This
corresponds to a packet error rate of 1% for 20 byte reference packets for this signal
power, according to IEEE Std 802.15.4-2006, section 6.1.7. In the future we will provide
support for changing the sensitivity to different values.
[image] Packet error rate vs. signal power.UNINDENT
NetDevice
Although it is expected that other technology profiles (such as 6LoWPAN and ZigBee) will
write their own NetDevice classes, a basic LrWpanNetDevice is provided, which encapsulates
the common operations of creating a generic LrWpan device and hooking things together.
Scope and Limitations
Future versions of this document will contain a PICS proforma similar to Appendix D of
IEEE 802.15.4-2006. The current emphasis is on the unslotted mode of 802.15.4 operation
for use in Zigbee, and the scope is limited to enabling a single mode (CSMA/CA) with basic
data transfer capabilities. Association with PAN coordinators is not yet supported, nor
the use of extended addressing. Interference is modeled as AWGN but this is currently not
thoroughly tested.
The NetDevice Tx queue is not limited, i.e., packets are never dropped due to queue
becoming full. They may be dropped due to excessive transmission retries or channel access
failure.
References
· Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for
Low-Rate Wireless Personal Area Networks (WPANs), IEEE Computer Society, IEEE Std
802.15.4-2006, 8 September 2006.
·
J. Zheng and Myung J. Lee, "A comprehensive performance study of IEEE 802.15.4," Sensor
Network Operations, IEEE Press, Wiley Interscience, Chapter 4, pp. 218-237, 2006.
Usage
Enabling lr-wpan
Add lr-wpan to the list of modules built with ns-3.
Helper
The helper is patterned after other device helpers. In particular, tracing (ascii and
pcap) is enabled similarly, and enabling of all lr-wpan log components is performed
similarly. Use of the helper is exemplified in examples/lr-wpan-data.cc. For ascii
tracing, the transmit and receive traces are hooked at the Mac layer.
The default propagation loss model added to the channel, when this helper is used, is the
LogDistancePropagationLossModel with default parameters.
Examples
The following examples have been written, which can be found in src/lr-wpan/examples/:
· lr-wpan-data.cc: A simple example showing end-to-end data transfer.
· lr-wpan-error-distance-plot.cc: An example to plot variations of the packet success
ratio as a function of distance.
· lr-wpan-error-model-plot.cc: An example to test the phy.
· lr-wpan-packet-print.cc: An example to print out the MAC header fields.
· lr-wpan-phy-test.cc: An example to test the phy.
In particular, the module enables a very simplified end-to-end data transfer scenario,
implemented in lr-wpan-data.cc. The figure shows a sequence of events that are triggered
when the MAC receives a DataRequest from the higher layer. It invokes a Clear Channel
Assessment (CCA) from the PHY, and if successful, sends the frame down to the PHY where it
is transmitted over the channel and results in a DataIndication on the peer node.
[image] Data example for simple LR-WPAN data transfer end-to-end.UNINDENT
The example lr-wpan-error-distance-plot.cc plots the packet success ratio (PSR) as a
function of distance, using the default LogDistance propagation loss model and the
802.15.4 error model. The channel (default 11), packet size (default 20 bytes) and
transmit power (default 0 dBm) can be varied by command line arguments. The program
outputs a file named 802.15.4-psr-distance.plt. Loading this file into gnuplot yields a
file 802.15.4-psr-distance.eps, which can be converted to pdf or other formats. The
default output is shown below.
[image] Default output of the program lr-wpan-error-distance-plot.cc.UNINDENT
Tests
The following tests have been written, which can be found in src/lr-wpan/tests/:
· lr-wpan-ack-test.cc: Check that acknowledgments are being used and issued in the
correct order.
· lr-wpan-collision-test.cc: Test correct reception of packets with interference and
collisions.
· lr-wpan-error-model-test.cc: Check that the error model gives predictable values.
· lr-wpan-packet-test.cc: Test the 802.15.4 MAC header/trailer classes
· lr-wpan-pd-plme-sap-test.cc: Test the PLME and PD SAP per IEEE 802.15.4
· lr-wpan-spectrum-value-helper-test.cc: Test that the conversion between power
(expressed as a scalar quantity) and spectral power, and back again, falls within a 25%
tolerance across the range of possible channels and input powers.
Validation
The model has not been validated against real hardware. The error model has been
validated against the data in IEEE Std 802.15.4-2006, section E.4.1.7 (Figure E.2). The
MAC behavior (CSMA backoff) has been validated by hand against expected behavior. The
below plot is an example of the error model validation and can be reproduced by running
lr-wpan-error-model-plot.cc:
[image] Default output of the program lr-wpan-error-model-plot.cc.UNINDENT
LTE MODULE
Design Documentation
Overview
An overview of the LTE-EPC simulation model is depicted in the figure Overview of the
LTE-EPC simulation model. There are two main components:
· the LTE Model. This model includes the LTE Radio Protocol stack (RRC, PDCP, RLC, MAC,
PHY). These entities reside entirely within the UE and the eNB nodes.
· the EPC Model. This models includes core network interfaces, protocols and entities.
These entities and protocols reside within the SGW, PGW and MME nodes, and partially
within the eNB nodes.
[image] Overview of the LTE-EPC simulation model.UNINDENT
Design Criteria
LTE Model
The LTE model has been designed to support the evaluation of the following aspects of LTE
systems:
· Radio Resource Management
· QoS-aware Packet Scheduling
· Inter-cell Interference Coordination
· Dynamic Spectrum Access
In order to model LTE systems to a level of detail that is sufficient to allow a correct
evaluation of the above mentioned aspects, the following requirements have been
considered:
1. At the radio level, the granularity of the model should be at least that of the
Resource Block (RB). In fact, this is the fundamental unit being used for resource
allocation. Without this minimum level of granularity, it is not possible to model
accurately packet scheduling and inter-cell-interference. The reason is that, since
packet scheduling is done on a per-RB basis, an eNB might transmit on a subset only
of all the available RBs, hence interfering with other eNBs only on those RBs where
it is transmitting. Note that this requirement rules out the adoption of a system
level simulation approach, which evaluates resource allocation only at the
granularity of call/bearer establishment.
2. The simulator should scale up to tens of eNBs and hundreds of User Equipments (UEs).
This rules out the use of a link level simulator, i.e., a simulator whose radio
interface is modeled with a granularity up to the symbol level. This is because to
have a symbol level model it is necessary to implement all the PHY layer signal
processing, whose huge computational complexity severely limits simulation. In fact,
link-level simulators are normally limited to a single eNB and one or a few UEs.
3. It should be possible within the simulation to configure different cells so that
they use different carrier frequencies and system bandwidths. The bandwidth used by
different cells should be allowed to overlap, in order to support dynamic spectrum
licensing solutions such as those described in [Ofcom2600MHz] and [RealWireless].
The calculation of interference should handle appropriately this case.
4. To be more representative of the LTE standard, as well as to be as close as possible
to real-world implementations, the simulator should support the MAC Scheduler API
published by the FemtoForum [FFAPI]. This interface is expected to be used by
femtocell manufacturers for the implementation of scheduling and Radio Resource
Management (RRM) algorithms. By introducing support for this interface in the
simulator, we make it possible for LTE equipment vendors and operators to test in a
simulative environment exactly the same algorithms that would be deployed in a real
system.
5. The LTE simulation model should contain its own implementation of the API defined in
[FFAPI]. Neither binary nor data structure compatibility with vendor-specific
implementations of the same interface are expected; hence, a compatibility layer
should be interposed whenever a vendor-specific MAC scheduler is to be used with the
simulator. This requirement is necessary to allow the simulator to be independent
from vendor-specific implementations of this interface specification. We note that
[FFAPI] is a logical specification only, and its implementation (e.g., translation
to some specific programming language) is left to the vendors.
6. The model is to be used to simulate the transmission of IP packets by the upper
layers. With this respect, it shall be considered that in LTE the Scheduling and
Radio Resource Management do not work with IP packets directly, but rather with RLC
PDUs, which are obtained by segmentation and concatenation of IP packets done by the
RLC entities. Hence, these functionalities of the RLC layer should be modeled
accurately.
EPC Model
The main objective of the EPC model is to provides means for the simulation of end-to-end
IP connectivity over the LTE model. To this aim, it supports for the interconnection of
multiple UEs to the Internet, via a radio access network of multiple eNBs connected to a
single SGW/PGW node, as shown in Figure Overview of the LTE-EPC simulation model.
The following design choices have been made for the EPC model:
1. The only Packet Data Network (PDN) type supported is IPv4.
2. The SGW and PGW functional entities are implemented within a single node, which is
hence referred to as the SGW/PGW node.
3. The scenarios with inter-SGW mobility are not of interests. Hence, a single SGW/PGW
node will be present in all simulations scenarios
4. A requirement for the EPC model is that it can be used to simulate the end-to-end
performance of realistic applications. Hence, it should be possible to use with the
EPC model any regular ns-3 application working on top of TCP or UDP.
5. Another requirement is the possibility of simulating network topologies with the
presence of multiple eNBs, some of which might be equipped with a backhaul
connection with limited capabilities. In order to simulate such scenarios, the user
data plane protocols being used between the eNBs and the SGW/PGW should be modeled
accurately.
6. It should be possible for a single UE to use different applications with different
QoS profiles. Hence, multiple EPS bearers should be supported for each UE. This
includes the necessary classification of TCP/UDP traffic over IP done at the UE in
the uplink and at the PGW in the downlink.
7. The focus of the EPC model is mainly on the EPC data plane. The accurate modeling of
the EPC control plane is, for the time being, not a requirement; hence, the
necessary control plane interactions can be modeled in a simplified way by
leveraging on direct interaction among the different simulation objects via the
provided helper objects.
8. The focus of the EPC model is on simulations of active users in ECM connected mode.
Hence, all the functionality that is only relevant for ECM idle mode (in particular,
tracking area update and paging) are not modeled at all.
9. The model should allow the possibility to perform an X2-based handover between two
eNBs.
Architecture
LTE Model
UE architecture
The architecture of the LTE radio protocol stack model of the UE is represented in the
figures LTE radio protocol stack architecture for the UE on the data plane and LTE radio
protocol stack architecture for the UE on the control plane which highlight respectively
the data plane and the control plane.
[image] LTE radio protocol stack architecture for the UE on the data plane.UNINDENT
[image] LTE radio protocol stack architecture for the UE on the control plane.UNINDENT
The architecture of the PHY/channel model of the UE is represented in figure PHY and
channel model architecture for the UE.
[image] PHY and channel model architecture for the UE.UNINDENT
eNB architecture
The architecture of the LTE radio protocol stack model of the eNB is represented in the
figures LTE radio protocol stack architecture for the eNB on the data plane and LTE radio
protocol stack architecture for the eNB on the control plane which highlight respectively
the data plane and the control plane.
[image] LTE radio protocol stack architecture for the eNB on the data plane.UNINDENT
[image] LTE radio protocol stack architecture for the eNB on the control plane.UNINDENT
The architecture of the PHY/channel model of the eNB is represented in figure PHY and
channel model architecture for the eNB.
[image] PHY and channel model architecture for the eNB.UNINDENT
EPC Model
EPC data plane
In Figure LTE-EPC data plane protocol stack, we represent the end-to-end LTE-EPC data
plane protocol stack as it is modeled in the simulator. From the figure, it is evident
that the biggest simplification introduced in the data plane model is the inclusion of the
SGW and PGW functionality within a single SGW/PGW node, which removes the need for the S5
or S8 interfaces specified by 3GPP. On the other hand, for both the S1-U protocol stack
and the LTE radio protocol stack all the protocol layers specified by 3GPP are present.
[image] LTE-EPC data plane protocol stack.UNINDENT
EPC control plane
The architecture of the implementation of the control plane model is shown in figure EPC
control model. The control interfaces that are modeled explicitly are the S1-AP, the X2-AP
and the S11 interfaces.
We note that the S1-AP and the S11 interfaces are modeled in a simplified fashion, by
using just one pair of interface classes to model the interaction between entities that
reside on different nodes (the eNB and the MME for the S1-AP interface, and the MME and
the SGW for the S11 interface). In practice, this means that the primitives of these
interfaces are mapped to a direct function call between the two objects. On the other
hand, the X2-AP interface is being modeled using protocol data units sent over an X2 link
(modeled as a point-to-point link); for this reason, the X2-AP interface model is more
realistic.
[image] EPC control model.UNINDENT
Channel and Propagation
For channel modeling purposes, the LTE module uses the SpectrumChannel interface provided
by the spectrum module. At the time of this writing, two implementations of such interface
are available: SingleModelSpectrumChannel and MultiModelSpectrumChannel, and the LTE
module requires the use of the MultiModelSpectrumChannel in order to work properly. This
is because of the need to support different frequency and bandwidth configurations. All
the the propagation models supported by MultiModelSpectrumChannel can be used within the
LTE module.
Use of the Buildings model with LTE
The recommended propagation model to be used with the LTE module is the one provided by
the Buildings module, which was in fact designed specifically with LTE (though it can be
used with other wireless technologies as well). Please refer to the documentation of the
Buildings module for generic information on the propagation model it provides.
In this section we will highlight some considerations that specifically apply when the
Buildings module is used together with the LTE module.
The naming convention used in the following will be:
· User equipment: UE
· Macro Base Station: MBS
· Small cell Base Station (e.g., pico/femtocell): SC
The LTE module considers FDD only, and implements downlink and uplink propagation
separately. As a consequence, the following pathloss computations are performed
· MBS <-> UE (indoor and outdoor)
· SC (indoor and outdoor) <-> UE (indoor and outdoor)
The LTE model does not provide the following pathloss computations:
· UE <-> UE
· MBS <-> MBS
· MBS <-> SC
· SC <-> SC
The Buildings model does not know the actual type of the node; i.e., it is not aware of
whether a transmitter node is a UE, a MBS, or a SC. Rather, the Buildings model only cares
about the position of the node: whether it is indoor and outdoor, and what is its z-axis
respect to the rooftop level. As a consequence, for an eNB node that is placed outdoor and
at a z-coordinate above the rooftop level, the propagation models typical of MBS will be
used by the Buildings module. Conversely, for an eNB that is placed outdoor but below the
rooftop, or indoor, the propagation models typical of pico and femtocells will be used.
For communications involving at least one indoor node, the corresponding wall penetration
losses will be calculated by the Buildings model. This covers the following use cases:
· MBS <-> indoor UE
· outdoor SC <-> indoor UE
· indoor SC <-> indoor UE
· indoor SC <-> outdoor UE
Please refer to the documentation of the Buildings module for details on the actual models
used in each case.
Fading Model
The LTE module includes a trace-based fading model derived from the one developed during
the GSoC 2010 [Piro2011]. The main characteristic of this model is the fact that the
fading evaluation during simulation run-time is based on per-calculated traces. This is
done to limit the computational complexity of the simulator. On the other hand, it needs
huge structures for storing the traces; therefore, a trade-off between the number of
possible parameters and the memory occupancy has to be found. The most important ones are:
· users' speed: relative speed between users (affects the Doppler frequency, which in
turns affects the time-variance property of the fading)
· number of taps (and relative power): number of multiple paths considered, which
affects the frequency property of the fading.
· time granularity of the trace: sampling time of the trace.
· frequency granularity of the trace: number of values in frequency to be evaluated.
· length of trace: ideally large as the simulation time, might be reduced by windowing
mechanism.
· number of users: number of independent traces to be used (ideally one trace per
user).
With respect to the mathematical channel propagation model, we suggest the one provided by
the rayleighchan function of Matlab, since it provides a well accepted channel
modelization both in time and frequency domain. For more information, the reader is
referred to [mathworks].
The simulator provides a matlab script
(src/lte/model/fading-traces/fading-trace-generator.m) for generating traces based on the
format used by the simulator. In detail, the channel object created with the rayleighchan
function is used for filtering a discrete-time impulse signal in order to obtain the
channel impulse response. The filtering is repeated for different TTI, thus yielding
subsequent time-correlated channel responses (one per TTI). The channel response is then
processed with the pwelch function for obtaining its power spectral density values, which
are then saved in a file with the proper format compatible with the simulator model.
Since the number of variable it is pretty high, generate traces considering all of them
might produce a high number of traces of huge size. On this matter, we considered the
following assumptions of the parameters based on the 3GPP fading propagation conditions
(see Annex B.2 of [TS36104]):
· users' speed: typically only a few discrete values are considered, i.e.:
· 0 and 3 kmph for pedestrian scenarios
· 30 and 60 kmph for vehicular scenarios
· 0, 3, 30 and 60 for urban scenarios
· channel taps: only a limited number of sets of channel taps are normally considered,
for example three models are mentioned in Annex B.2 of [TS36104].
· time granularity: we need one fading value per TTI, i.e., every 1 ms (as this is the
granularity in time of the ns-3 LTE PHY model).
· frequency granularity: we need one fading value per RB (which is the frequency
granularity of the spectrum model used by the ns-3 LTE model).
· length of the trace: the simulator includes the windowing mechanism implemented
during the GSoC 2011, which consists of picking up a window of the trace each window
length in a random fashion.
· per-user fading process: users share the same fading trace, but for each user a
different starting point in the trace is randomly picked up. This choice was made to
avoid the need to provide one fading trace per user.
According to the parameters we considered, the following formula express in detail the
total size S_{traces} of the fading traces:
where S_{sample} is the size in bytes of the sample (e.g., 8 in case of double precision,
4 in case of float precision), N_{RB} is the number of RB or set of RBs to be considered,
T_{trace} is the total length of the trace, T_{sample} is the time resolution of the trace
(1 ms), and N_{scenarios} is the number of fading scenarios that are desired (i.e.,
combinations of different sets of channel taps and user speed values). We provide traces
for 3 different scenarios one for each taps configuration defined in Annex B.2 of
[TS36104]:
· Pedestrian: with nodes' speed of 3 kmph.
· Vehicular: with nodes' speed of 60 kmph.
· Urban: with nodes' speed of 3 kmph.
hence N_{scenarios} = 3. All traces have T_{trace} = 10 s and RB_{NUM} = 100. This results
in a total 24 MB bytes of traces.
Antennas
Being based on the SpectrumPhy, the LTE PHY model supports antenna modeling via the ns-3
AntennaModel class. Hence, any model based on this class can be associated with any eNB or
UE instance. For instance, the use of the CosineAntennaModel associated with an eNB device
allows to model one sector of a macro base station. By default, the IsotropicAntennaModel
is used for both eNBs and UEs.
PHY
Overview
The physical layer model provided in this LTE simulator is based on the one described in
[Piro2011], with the following modifications. The model now includes the inter cell
intereference calculation and the simulation of uplink traffic, including both packet
transmission and CQI generation.
Subframe Structure
The subframe is divided into control and data part as described in Figure LTE subframe
division..
[image] LTE subframe division..UNINDENT
Considering the granularity of the simulator based on RB, the control and the reference
signaling have to be consequently modeled considering this constraint. According to the
standard [TS36211], the downlink control frame starts at the beginning of each subframe
and lasts up to three symbols across the whole system bandwidth, where the actual
duration is provided by the Physical Control Format Indicator Channel (PCFICH). The
information on the allocation are then mapped in the remaining resource up to the
duration defined by the PCFICH, in the so called Physical Downlink Control Channel
(PDCCH). A PDCCH transports a single message called Downlink Control Information (DCI)
coming from the MAC layer, where the scheduler indicates the resource allocation for a
specific user. The PCFICH and PDCCH are modeled with the transmission of the control
frame of a fixed duration of 3/14 of milliseconds spanning in the whole available
bandwidth, since the scheduler does not estimate the size of the control region. This
implies that a single transmission block models the entire control frame with a fixed
power (i.e., the one used for the PDSCH) across all the available RBs. According to this
feature, this transmission represents also a valuable support for the Reference Signal
(RS). This allows of having every TTI an evaluation of the interference scenario since
all the eNB are transmitting (simultaneously) the control frame over the respective
available bandwidths. We note that, the model does not include the power boosting since
it does not reflect any improvement in the implemented model of the channel estimation.
The Sounding Reference Signal (SRS) is modeled similar to the downlink control frame.
The SRS is periodically placed in the last symbol of the subframe in the whole system
bandwidth. The RRC module already includes an algorithm for dynamically assigning the
periodicity as function of the actual number of UEs attached to a eNB according to the
UE-specific procedure (see Section 8.2 of [TS36213]).
MAC to Channel delay
To model the latency of real MAC and PHY implementations, the PHY model simulates a
MAC-to-channel delay in multiples of TTIs (1ms). The transmission of both data and control
packets are delayed by this amount.
CQI feedback
The generation of CQI feedback is done accordingly to what specified in [FFAPI]. In
detail, we considered the generation of periodic wideband CQI (i.e., a single value of
channel state that is deemed representative of all RBs in use) and inband CQIs (i.e., a
set of value representing the channel state for each RB).
The CQI index to be reported is obtained by first obtaining a SINR measurement and then
passing this SINR measurement the Adaptive Modulation and Coding which will map it to the
CQI index.
In downlink, the SINR used to generate CQI feedback can be calculated in two different
ways:
1. Ctrl method: SINR is calculated combining the signal power from the reference
signals (which in the simulation is equivalent to the PDCCH) and the interference
power from the PDCCH. This approach results in considering any neighboring eNB as an
interferer, regardless of whether this eNB is actually performing any PDSCH
transmission, and regardless of the power and RBs used for eventual interfering
PDSCH transmissions.
2. Mixed method: SINR is calculated combining the signal power from the reference
signals (which in the simulation is equivalent to the PDCCH) and the interference
power from the PDSCH. This approach results in considering as interferers only those
neighboring eNBs that are actively transmitting data on the PDSCH, and allows to
generate inband CQIs that account for different amounts of interference on different
RBs according to the actual interference level. In the case that no PDSCH
transmission is performed by any eNB, this method consider that interference is
zero, i.e., the SINR will be calculated as the ratio of signal to noise only.
To switch between this two CQI generation approaches, LteHelper::UsePdschForCqiGeneration
needs to be configured: false for first approach and true for second approach (true is
default value):
Config::SetDefault ("ns3::LteHelper::UsePdschForCqiGeneration", BooleanValue (true));
In uplink, two types of CQIs are implemented:
· SRS based, periodically sent by the UEs.
· PUSCH based, calculated from the actual transmitted data.
The scheduler interface include an attribute system calld UlCqiFilter for managing the
filtering of the CQIs according to their nature, in detail:
· SRS_UL_CQI for storing only SRS based CQIs.
· PUSCH_UL_CQI for storing only PUSCH based CQIs.
· ALL_UL_CQI for storing all the CQIs received.
It has to be noted that, the FfMacScheduler provides only the interface and it is matter
of the actual scheduler implementation to include the code for managing these attibutes
(see scheduler related section for more information on this matter).
Interference Model
The PHY model is based on the well-known Gaussian interference models, according to which
the powers of interfering signals (in linear units) are summed up together to determine
the overall interference power.
The sequence diagram of Figure Sequence diagram of the PHY interference calculation
procedure shows how interfering signals are processed to calculate the SINR, and how SINR
is then used for the generation of CQI feedback.
[image] Sequence diagram of the PHY interference calculation procedure.UNINDENT
LTE Spectrum Model
The usage of the radio spectrum by eNBs and UEs in LTE is described in [TS36101]. In the
simulator, radio spectrum usage is modeled as follows. Let f_c denote the LTE Absolute
Radio Frequency Channel Number, which identifies the carrier frequency on a 100 kHz
raster; furthermore, let B be the Transmission Bandwidth Configuration in number of
Resource Blocks. For every pair (f_c,B) used in the simulation we define a corresponding
SpectrumModel using the functionality provided by the sec-spectrum-module . model using
the Spectrum framework described in [Baldo2009]. f_c and B can be configured for every
eNB instantiated in the simulation; hence, each eNB can use a different spectrum model.
Every UE will automatically use the spectrum model of the eNB it is attached to. Using the
MultiModelSpectrumChannel described in [Baldo2009], the interference among eNBs that use
different spectrum models is properly accounted for. This allows to simulate dynamic
spectrum access policies, such as for example the spectrum licensing policies that are
discussed in [Ofcom2600MHz].
Data PHY Error Model
The simulator includes an error model of the data plane (i.e., PDSCH and PUSCH) according
to the standard link-to-system mapping (LSM) techniques. The choice is aligned with the
standard system simulation methodology of OFDMA radio transmission technology. Thanks to
LSM we are able to maintain a good level of accuracy and at the same time limiting the
computational complexity increase. It is based on the mapping of single link layer
performance obtained by means of link level simulators to system (in our case network)
simulators. In particular link the layer simulator is used for generating the performance
of a single link from a PHY layer perspective, usually in terms of code block error rate
(BLER), under specific static conditions. LSM allows the usage of these parameters in more
complex scenarios, typical of system/network simulators, where we have more links,
interference and "colored" channel propagation phenomena (e.g., frequency selective
fading).
To do this the Vienna LTE Simulator [ViennaLteSim] has been used for what concerns the
extraction of link layer performance and the Mutual Information Based Effective SINR
(MIESM) as LSM mapping function using part of the work recently published by the Signet
Group of University of Padua [PaduaPEM].
MIESM
The specific LSM method adopted is the one based on the usage of a mutual information
metric, commonly referred to as the mutual information per per coded bit (MIB or MMIB when
a mean of multiples MIBs is involved). Another option would be represented by the
Exponential ESM (EESM); however, recent studies demonstrate that MIESM outperforms EESM in
terms of accuracy [LozanoCost].
[image] MIESM computational procedure diagram.UNINDENT
The mutual information (MI) is dependent on the constellation mapping and can be
calculated per transport block (TB) basis, by evaluating the MI over the symbols and the
subcarrier. However, this would be too complex for a network simulator. Hence, in our
implementation a flat channel response within the RB has been considered; therefore the
overall MI of a TB is calculated averaging the MI evaluated per each RB used in the TB.
In detail, the implemented scheme is depicted in Figure MIESM computational procedure
diagram, where we see that the model starts by evaluating the MI value for each RB,
represented in the figure by the SINR samples. Then the equivalent MI is evaluated per
TB basis by averaging the MI values. Finally, a further step has to be done since the
link level simulator returns the performance of the link in terms of block error rate
(BLER) in a addive white guassian noise (AWGN) channel, where the blocks are the code
blocks (CBs) independently encoded/decoded by the turbo encoder. On this matter the
standard 3GPP segmentation scheme has been used for estimating the actual CB size
(described in section 5.1.2 of [TS36212]). This scheme divides the the TB in N_{K_-}
blocks of size K_- and N_{K+} blocks of size K_+. Therefore the overall TB BLER (TBLER)
can be expressed as
where the CBLER_i is the BLER of the CB i obtained according to the link level simulator
CB BLER curves. For estimating the CBLER_i, the MI evaluation has been implemented
according to its numerical approximation defined in [wimaxEmd]. Moreover, for reducing
the complexity of the computation, the approximation has been converted into lookup
tables. In detail, Gaussian cumulative model has been used for approximating the AWGN
BLER curves with three parameters which provides a close fit to the standard AWGN
performances, in formula:
where x is the MI of the TB, b_{ECR} represents the "transition center" and c_{ECR} is
related to the "transition width" of the Gaussian cumulative distribution for each
Effective Code Rate (ECR) which is the actual transmission rate according to the channel
coding and MCS. For limiting the computational complexity of the model we considered
only a subset of the possible ECRs in fact we would have potentially 5076 possible ECRs
(i.e., 27 MCSs and 188 CB sizes). On this respect, we will limit the CB sizes to some
representative values (i.e., 40, 140, 160, 256, 512, 1024, 2048, 4032, 6144), while for
the others the worst one approximating the real one will be used (i.e., the smaller CB
size value available respect to the real one). This choice is aligned to the typical
performance of turbo codes, where the CB size is not strongly impacting on the BLER.
However, it is to be notes that for CB sizes lower than 1000 bits the effect might be
relevant (i.e., till 2 dB); therefore, we adopt this unbalanced sampling interval for
having more precision where it is necessary. This behaviour is confirmed by the figures
presented in the Annes Section.
BLER Curves
On this respect, we reused part of the curves obtained within [PaduaPEM]. In detail, we
introduced the CB size dependency to the CB BLER curves with the support of the developers
of [PaduaPEM] and of the LTE Vienna Simulator. In fact, the module released provides the
link layer performance only for what concerns the MCSs (i.e, with a given fixed ECR). In
detail the new error rate curves for each has been evaluated with a simulation campaign
with the link layer simulator for a single link with AWGN noise and for CB size of 104,
140, 256, 512, 1024, 2048, 4032 and 6144. These curves has been mapped with the Gaussian
cumulative model formula presented above for obtaining the correspondents b_{ECR} and
c_{ECR} parameters.
The BLER perfomance of all MCS obtained with the link level simulator are plotted in the
following figures (blue lines) together with their correspondent mapping to the Gaussian
cumulative distribution (red dashed lines).
[image] BLER for MCS 1, 2, 3 and 4..UNINDENT
[image] BLER for MCS 5, 6, 7 and 8..UNINDENT
[image] BLER for MCS 9, 10, 11 and 12..UNINDENT
[image] BLER for MCS 13, 14, 15 and 16..UNINDENT
[image] BLER for MCS 17, 17, 19 and 20..UNINDENT
[image] BLER for MCS 21, 22, 23 and 24..UNINDENT
[image] BLER for MCS 25, 26, 27 and 28..UNINDENT
[image] BLER for MCS 29..UNINDENT
Integration of the BLER curves in the ns-3 LTE module
The model implemented uses the curves for the LSM of the recently LTE PHY Error Model
released in the ns3 community by the Signet Group [PaduaPEM] and the new ones generated
for different CB sizes. The LteSpectrumPhy class is in charge of evaluating the TB BLER
thanks to the methods provided by the LteMiErrorModel class, which is in charge of
evaluating the TB BLER according to the vector of the perceived SINR per RB, the MCS and
the size in order to proper model the segmentation of the TB in CBs. In order to obtain
the vector of the perceived SINR two instances of LtePemSinrChunkProcessor (child of
LteChunkProcessor dedicated to evaluate the SINR for obtaining physical error performance)
have been attached to UE downlink and eNB uplink LteSpectrumPhy modules for evaluating the
error model distribution respectively of PDSCH (UE side) and ULSCH (eNB side).
The model can be disabled for working with a zero-losses channel by setting the PemEnabled
attribute of the LteSpectrumPhy class (by default is active). This can be done according
to the standard ns3 attribute system procedure, that is:
Config::SetDefault ("ns3::LteSpectrumPhy::DataErrorModelEnabled", BooleanValue (false));
Control Channels PHY Error Model
The simulator includes the error model for downlink control channels (PCFICH and PDCCH),
while in uplink it is assumed and ideal error-free channel. The model is based on the
MIESM approach presented before for considering the effects of the frequency selective
channel since most of the control channels span the whole available bandwidth.
PCFICH + PDCCH Error Model
The model adopted for the error distribution of these channels is based on an evaluation
study carried out in the RAN4 of 3GPP, where different vendors investigated the
demodulation performance of the PCFICH jointly with PDCCH. This is due to the fact that
the PCFICH is the channel in charge of communicating to the UEs the actual dimension of
the PDCCH (which spans between 1 and 3 symbols); therefore the correct decodification of
the DCIs depends on the correct interpretation of both ones. In 3GPP this problem have
been evaluated for improving the cell-edge performance [FujitsuWhitePaper], where the
interference among neighboring cells can be relatively high due to signal degradation. A
similar problem has been notices in femto-cell scenario and, more in general, in HetNet
scenarios the bottleneck has been detected mainly as the PCFICH channel [Bharucha2011],
where in case of many eNBs are deployed in the same service area, this channel may collide
in frequency, making impossible the correct detection of the PDCCH channel, too.
In the simulator, the SINR perceived during the reception has been estimated according to
the MIESM model presented above in order to evaluate the error distribution of PCFICH and
PDCCH. In detail, the SINR samples of all the RBs are included in the evaluation of the MI
associated to the control frame and, according to this values, the effective SINR (eSINR)
is obtained by inverting the MI evaluation process. It has to be noted that, in case of
MIMO transmission, both PCFICH and the PDCCH use always the transmit diversity mode as
defined by the standard. According to the eSINR perceived the decodification error
probability can be estimated as function of the results presented in [R4-081920]. In case
an error occur, the DCIs discarded and therefore the UE will be not able to receive the
correspondent Tbs, therefore resulting lost.
MIMO Model
The use of multiple antennas both at transmitter and receiver side, known as
multiple-input and multiple-output (MIMO), is a problem well studied in literature during
the past years. Most of the work concentrate on evaluating analytically the gain that the
different MIMO schemes might have in term of capacity; however someones provide also
information of the gain in terms of received power [CatreuxMIMO].
According to the considerations above, a model more flexible can be obtained considering
the gain that MIMO schemes bring in the system from a statistical point of view. As
highlighted before, [CatreuxMIMO] presents the statistical gain of several MIMO solutions
respect to the SISO one in case of no correlation between the antennas. In the work the
gain is presented as the cumulative distribution function (CDF) of the output SINR for
what concern SISO, MIMO-Alamouti, MIMO-MMSE, MIMO-OSIC-MMSE and MIMO-ZF schemes.
Elaborating the results, the output SINR distribution can be approximated with a
log-normal one with different mean and variance as function of the scheme considered.
However, the variances are not so different and they are approximatively equal to the one
of the SISO mode already included in the shadowing component of the
BuildingsPropagationLossModel, in detail:
· SISO: = 13.5 and ma = 20 [dB].
· MIMO-Alamouti: = 17.7 and ma = 11.1 [dB].
· MIMO-MMSE: = 10.7 and ma = 16.6 [dB].
· MIMO-OSIC-MMSE: = 12.6 and ma = 15.5 [dB].
· MIMO-ZF: = 10.3 and ma = 12.6 [dB].
Therefore the PHY layer implements the MIMO model as the gain perceived by the receiver
when using a MIMO scheme respect to the one obtained using SISO one. We note that, these
gains referred to a case where there is no correlation between the antennas in MIMO
scheme; therefore do not model degradation due to paths correlation.
UE PHY Measurements Model
According to [TS36214], the UE has to report a set of measurements of the eNBs that the
device is able to perceive: the the reference signal received power (RSRP) and the
reference signal received quality (RSRQ). The former is a measure of the received power of
a specific eNB, while the latter includes also channel interference and thermal noise.
The UE has to report the measurements jointly with the physical cell identity (PCI) of the
cell. Both the RSRP and RSRQ measurements are performed during the reception of the RS,
while the PCI is obtained with the Primary Synchronization Signal (PSS). The PSS is sent
by the eNB each 5 subframes and in detail in the subframes 1 and 6. In real systems, only
504 distinct PCIs are available, and hence it could occur that two nearby eNBs use the
same PCI; however, in the simulator we model PCIs using simulation metadata, and we allow
up to 65535 distinct PCIs, thereby avoiding PCI collisions provided that less that 65535
eNBs are simulated in the same scenario.
According to [TS36133] sections 9.1.4 and 9.1.7, RSRP is reported by PHY layer in dBm
while RSRQ in dB. The values of RSRP and RSRQ are provided to higher layers through the
C-PHY SAP (by means of UeMeasurementsParameters struct) every 200 ms as defined in
[TS36331]. Layer 1 filtering is performed by averaging the all the measurements collected
during the last window slot. The periodicity of reporting can be adjusted for research
purposes by means of the LteUePhy::UeMeasurementsFilterPeriod attribute.
The formulas of the RSRP and RSRQ can be simplified considering the assumption of the PHY
layer that the channel is flat within the RB, the finest level of accuracy. In fact, this
implies that all the REs within a RB have the same power, therefore:
where P(k,m) represents the signal power of the RE m within the RB k, which, as observed
before, is constant within the same RB and equal to P(k), M is the number of REs carrying
the RS in a RB and K is the number of RBs. It is to be noted that P(k), and in general all
the powers defined in this section, is obtained in the simulator from the PSD of the RB
(which is provided by the LteInterferencePowerChunkProcessor), in detail:
where PSD_{RB}(k) is the power spectral density of the RB k, 180000 is the bandwidth in Hz
of the RB and 12 is the number of REs per RB in an OFDM symbol. Similarly, for RSSI we
have
where S is the number of OFDM symbols carrying RS in a RB and R is the number of REs
carrying a RS in a OFDM symbol (which is fixed to 2) while P(k,s,r), I(k,s,r) and N(k,s,r)
represent respectively the perceived power of the serving cell, the interference power and
the noise power of the RE r in symbol s. As for RSRP, the measurements within a RB are
always equals among each others according to the PHY model; therefore P(k,s,r) = P(k),
I(k,s,r) = I(k) and N(k,s,r) = N(k), which implies that the RSSI can be calculated as:
Considering the constraints of the PHY reception chain implementation, and in order to
maintain the level of computational complexity low, only RSRP can be directly obtained for
all the cells. This is due to the fact that LteSpectrumPhy is designed for evaluating the
interference only respect to the signal of the serving eNB. This implies that the PHY
layer is optimized for managing the power signals information with the serving eNB as a
reference. However, RSRP and RSRQ of neighbor cell i can be extracted by the current
information available of the serving cell j as detailed in the following:
where RSRP_i is the RSRP of the neighbor cell i, P_i(k) is the power perceived at any RE
within the RB k, K is the total number of RBs, RSSI_i is the RSSI of the neighbor cell i
when the UE is attached to cell j (which, since it is the sum of all the received powers,
coincides with RSSI_j), I_j(k) is the total interference perceived by UE in any RE of RB k
when attached to cell i (obtained by the LteInterferencePowerChunkProcessor), P_j(k) is
the power perceived of cell j in any RE of the RB k and N is the power noise spectral
density in any RE. The sample is considered as valid in case of the RSRQ evaluated is
above the LteUePhy::RsrqUeMeasThreshold attribute.
HARQ
The HARQ scheme implemented is based on a incremental redundancy (IR) solutions combined
with multiple stop-and-wait processes for enabling a continuous data flow. In detail, the
solution adopted is the soft combining hybrid IR Full incremental redundancy (also called
IR Type II), which implies that the retransmissions contain only new information respect
to the previous ones. The resource allocation algorithm of the HARQ has been implemented
within the respective scheduler classes (i.e., RrFfMacScheduler and PfFfMacScheduler,
refer to their correspondent sections for more info), while the decodification part of the
HARQ has been implemented in the LteSpectrumPhy and LteHarqPhy classes which will be
detailed in this section.
According to the standard, the UL retransmissions are synchronous and therefore are
allocated 7 ms after the original transmission. On the other hand, for the DL, they are
asynchronous and therefore can be allocated in a more flexible way starting from 7 ms and
it is a matter of the specific scheduler implementation. The HARQ processes behavior is
depicted in Figure:ref:fig-harq-processes-scheme.
At the MAC layer, the HARQ entity residing in the scheduler is in charge of controlling
the 8 HARQ processes for generating new packets and managing the retransmissions both for
the DL and the UL. The scheduler collects the HARQ feedback from eNB and UE PHY layers
(respectively for UL and DL connection) by means of the FF API primitives
SchedUlTriggerReq and SchedUlTriggerReq. According to the HARQ feedback and the RLC
buffers status, the scheduler generates a set of DCIs including both retransmissions of
HARQ blocks received erroneous and new transmissions, in general, giving priority to the
former. On this matter, the scheduler has to take into consideration one constraint when
allocating the resource for HARQ retransmissions, it must use the same modulation order of
the first transmission attempt (i.e., QPSK for MCS in [0..9], 16QAM for MCS in [10..16]
and 64QAM for MCS in [17..28]). This restriction comes from the specification of the rate
matcher in the 3GPP standard [TS36212], where the algorithm fixes the modulation order for
generating the different blocks of the redundancy versions.
The PHY Error Model model (i.e., the LteMiErrorModel class already presented before) has
been extended for considering IR HARQ according to [wimaxEmd], where the parameters for
the AWGN curves mapping for MIESM mapping in case of retransmissions are given by:
where X is the number of original information bits, C_i are number of coded bits, M_i are
the mutual informations per HARQ block received on the total number of q retransmissions.
Therefore, in order to be able to return the error probability with the error model
implemented in the simulator evaluates the R_{eff} and the MI_{I eff} and return the value
of error probability of the ECR of the same modulation with closest lower rate respect to
the R_{eff}. In order to consider the effect of HARQ retransmissions a new sets of curves
have been integrated respect to the standard one used for the original MCS. The new curves
are intended for covering the cases when the most conservative MCS of a modulation is used
which implies the generation of R_{eff} lower respect to the one of standard MCSs. On this
matter the curves for 1, 2 and 3 retransmissions have been evaluated for 10 and 17. For
MCS 0 we considered only the first retransmission since the produced code rate is already
very conservative (i.e., 0.04) and returns an error rate enough robust for the reception
(i.e., the downturn of the BLER is centered around -18 dB). It is to be noted that, the
size of first TB transmission has been assumed as containing all the information bits to
be coded; therefore X is equal to the size of the first TB sent of a an HARQ process. The
model assumes that the eventual presence of parity bits in the codewords is already
considered in the link level curves. This implies that as soon as the minimum R_{eff} is
reached the model is not including the gain due to the transmission of further parity
bits.
[image] HARQ processes behavior in LTE.UNINDENT
The part of HARQ devoted to manage the decodification of the HARQ blocks has been
implemented in the LteHarqPhy and LteSpectrumPhy classes. The former is in charge of
maintaining the HARQ information for each active process . The latter interacts with
LteMiErrorModel class for evaluating the correctness of the blocks received and includes
the messaging algorithm in charge of communicating to the HARQ entity in the scheduler
the result of the decodifications. These messages are encapsulated in the
dlInfoListElement for DL and ulInfoListElement for UL and sent through the PUCCH and the
PHICH respectively with an ideal error free model according to the assumptions in their
implementation. A sketch of the iteration between HARQ and LTE protocol stack in
represented in Figure:ref:fig-harq-architecture.
Finally, the HARQ engine is always active both at MAC and PHY layer; however, in case of
the scheduler does not support HARQ the system will continue to work with the HARQ
functions inhibited (i.e., buffers are filled but not used). This implementation
characteristic gives backward compatibility with schedulers implemented before HARQ
integration.
[image] Interaction between HARQ and LTE protocol stack.UNINDENT
MAC
Resource Allocation Model
We now briefly describe how resource allocation is handled in LTE, clarifying how it is
modeled in the simulator. The scheduler is in charge of generating specific structures
called Data Control Indication (DCI) which are then transmitted by the PHY of the eNB to
the connected UEs, in order to inform them of the resource allocation on a per subframe
basis. In doing this in the downlink direction, the scheduler has to fill some specific
fields of the DCI structure with all the information, such as: the Modulation and Coding
Scheme (MCS) to be used, the MAC Transport Block (TB) size, and the allocation bitmap
which identifies which RBs will contain the data transmitted by the eNB to each user.
For the mapping of resources to physical RBs, we adopt a localized mapping approach (see
[Sesia2009], Section 9.2.2.1); hence in a given subframe each RB is always allocated to
the same user in both slots. The allocation bitmap can be coded in different formats; in
this implementation, we considered the Allocation Type 0 defined in [TS36213], according
to which the RBs are grouped in Resource Block Groups (RBG) of different size determined
as a function of the Transmission Bandwidth Configuration in use.
For certain bandwidth values not all the RBs are usable, since the group size is not a
common divisor of the group. This is for instance the case when the bandwidth is equal to
25 RBs, which results in a RBG size of 2 RBs, and therefore 1 RB will result not
addressable. In uplink the format of the DCIs is different, since only adjacent RBs can
be used because of the SC-FDMA modulation. As a consequence, all RBs can be allocated by
the eNB regardless of the bandwidth configuration.
Adaptive Modulation and Coding
The simulator provides two Adaptive Modulation and Coding (AMC) models: one based on the
GSoC model [Piro2011] and one based on the physical error model (described in the
following sections).
The former model is a modified version of the model described in [Piro2011], which in turn
is inspired from [Seo2004]. Our version is described in the following. Let i denote the
generic user, and let mma_i be its SINR. We get the spectral efficiency \ta_i of user i
using the following equations:
The procedure described in [R1-081483] is used to get the corresponding MCS scheme. The
spectral efficiency is quantized based on the channel quality indicator (CQI), rounding to
the lowest value, and is mapped to the corresponding MCS scheme.
Finally, we note that there are some discrepancies between the MCS index in [R1-081483]
and that indicated by the standard: [TS36213] Table 7.1.7.1-1 says that the MCS index
goes from 0 to 31, and 0 appears to be a valid MCS scheme (TB size is not 0) but in
[R1-081483] the first useful MCS index is 1. Hence to get the value as intended by the
standard we need to subtract 1 from the index reported in [R1-081483].
The alternative model is based on the physical error model developed for this simulator
and explained in the following subsections. This scheme is able to adapt the MCS selection
to the actual PHY layer performance according to the specific CQI report. According to
their definition, a CQI index is assigned when a single PDSCH TB with the modulation
coding scheme and code rate correspondent to that CQI index in table 7.2.3-1 of [TS36213]
can be received with an error probability less than 0.1. In case of wideband CQIs, the
reference TB includes all the RBGs available in order to have a reference based on the
whole available resources; while, for subband CQIs, the reference TB is sized as the RBGs.
Transport Block model
The model of the MAC Transport Blocks (TBs) provided by the simulator is simplified with
respect to the 3GPP specifications. In particular, a simulator-specific class
(PacketBurst) is used to aggregate MAC SDUs in order to achieve the simulator's equivalent
of a TB, without the corresponding implementation complexity. The multiplexing of
different logical channels to and from the RLC layer is performed using a dedicated packet
tag (LteRadioBearerTag), which performs a functionality which is partially equivalent to
that of the MAC headers specified by 3GPP.
The FemtoForum MAC Scheduler Interface
This section describes the ns-3 specific version of the LTE MAC Scheduler Interface
Specification published by the FemtoForum [FFAPI].
We implemented the ns-3 specific version of the FemtoForum MAC Scheduler Interface [FFAPI]
as a set of C++ abstract classes; in particular, each primitive is translated to a C++
method of a given class. The term implemented here is used with the same meaning adopted
in [FFAPI], and hence refers to the process of translating the logical interface
specification to a particular programming language. The primitives in [FFAPI] are grouped
in two groups: the CSCHED primitives, which deal with scheduler configuration, and the
SCHED primitives, which deal with the execution of the scheduler. Furthermore, [FFAPI]
defines primitives of two different kinds: those of type REQ go from the MAC to the
Scheduler, and those of type IND/CNF go from the scheduler to the MAC. To translate these
characteristics into C++, we define the following abstract classes that implement Service
Access Points (SAPs) to be used to issue the primitives:
· the FfMacSchedSapProvider class defines all the C++ methods that correspond to SCHED
primitives of type REQ;
· the FfMacSchedSapUser class defines all the C++ methods that correspond to SCHED
primitives of type CNF/IND;
· the FfMacCschedSapProvider class defines all the C++ methods that correspond to
CSCHED primitives of type REQ;
· the FfMacCschedSapUser class defines all the C++ methods that correspond to CSCHED
primitives of type CNF/IND;
There are 3 blocks involved in the MAC Scheduler interface: Control block, Subframe block
and Scheduler block. Each of these blocks provide one part of the MAC Scheduler interface.
The figure below shows the relationship between the blocks and the SAPs defined in our
implementation of the MAC Scheduler Interface.
[image]
In addition to the above principles, the following design choices have been taken:
· The definition of the MAC Scheduler interface classes follows the naming conventions
of the ns-3 Coding Style. In particular, we follow the CamelCase convention for the
primitive names. For example, the primitive CSCHED_CELL_CONFIG_REQ is translated to
CschedCellConfigReq in the ns-3 code.
· The same naming conventions are followed for the primitive parameters. As the
primitive parameters are member variables of classes, they are also prefixed with a
m_.
· regarding the use of vectors and lists in data structures, we note that [FFAPI] is a
pretty much C-oriented API. However, considered that C++ is used in ns-3, and that
the use of C arrays is discouraged, we used STL vectors (std::vector) for the
implementation of the MAC Scheduler Interface, instead of using C arrays as
implicitly suggested by the way [FFAPI] is written.
· In C++, members with constructors and destructors are not allow in unions. Hence all
those data structures that are said to be unions in [FFAPI] have been defined as
structs in our code.
The figure below shows how the MAC Scheduler Interface is used within the eNB.
[image]
The User side of both the CSCHED SAP and the SCHED SAP are implemented within the eNB MAC,
i.e., in the file lte-enb-mac.cc. The eNB MAC can be used with different scheduler
implementations without modifications. The same figure also shows, as an example, how the
Round Robin Scheduler is implemented: to interact with the MAC of the eNB, the Round Robin
scheduler implements the Provider side of the SCHED SAP and CSCHED SAP interfaces. A
similar approach can be used to implement other schedulers as well. A description of each
of the scheduler implementations that we provide as part of our LTE simulation module is
provided in the following subsections.
Round Robin (RR) Scheduler
The Round Robin (RR) scheduler is probably the simplest scheduler found in the literature.
It works by dividing the available resources among the active flows, i.e., those logical
channels which have a non-empty RLC queue. If the number of RBGs is greater than the
number of active flows, all the flows can be allocated in the same subframe. Otherwise, if
the number of active flows is greater than the number of RBGs, not all the flows can be
scheduled in a given subframe; then, in the next subframe the allocation will start from
the last flow that was not allocated. The MCS to be adopted for each user is done
according to the received wideband CQIs.
For what concern the HARQ, RR implements the non adaptive version, which implies that in
allocating the retransmission attempts RR uses the same allocation configuration of the
original block, which means maintaining the same RBGs and MCS. UEs that are allocated for
HARQ retransmissions are not considered for the transmission of new data in case they have
a transmission opportunity available in the same TTI. Finally, HARQ can be disabled with
ns3 attribute system for maintaining backward compatibility with old test cases and code,
in detail:
Config::SetDefault ("ns3::RrFfMacScheduler::HarqEnabled", BooleanValue (false));
The scheduler implements the filtering of the uplink CQIs according to their nature with
UlCqiFilter attibute, in detail:
· SRS_UL_CQI: only SRS based CQI are stored in the internal attributes.
· PUSCH_UL_CQI: only PUSCH based CQI are stored in the internal attributes.
· ALL_UL_CQI: all CQIs are stored in the same internal attibute (i.e., the last CQI
received is stored independently from its nature).
Proportional Fair (PF) Scheduler
The Proportional Fair (PF) scheduler [Sesia2009] works by scheduling a user when its
instantaneous channel quality is high relative to its own average channel condition over
time. Let i,j denote generic users; let t be the subframe index, and k be the resource
block index; let M_{i,k}(t) be MCS usable by user i on resource block k according to what
reported by the AMC model (see Adaptive Modulation and Coding); finally, let S(M, B) be
the TB size in bits as defined in [TS36213] for the case where a number B of resource
blocks is used. The achievable rate R_{i}(k,t) in bit/s for user i on resource block group
k at subframe t is defined as
where au is the TTI duration. At the start of each subframe t, each RBG is assigned to a
certain user. In detail, the index 144}_{k}(t) to which RBG k is assigned at time t is
determined as
where T_{j}(t) is the past througput performance perceived by the user j. According to
the above scheduling algorithm, a user can be allocated to different RBGs, which can be
either adjacent or not, depending on the current condition of the channel and the past
throughput performance T_{j}(t). The latter is determined at the end of the subframe t
using the following exponential moving average approach:
where lpha is the time constant (in number of subframes) of the exponential moving
average, and 384s the actual throughput achieved by the user i in the subframe t. 360 is
measured according to the following procedure. First we determine the MCS 840 j:
then we determine the total number 936 j:
where |
For what concern the HARQ, PF implements the non adaptive version, which implies that in
allocating the retransmission attempts the scheduler uses the same allocation
configuration of the original block, which means maintaining the same RBGs and MCS. UEs
that are allocated for HARQ retransmissions are not considered for the transmission of new
data in case they have a transmission opportunity available in the same TTI. Finally, HARQ
can be disabled with ns3 attribute system for maintaining backward compatibility with old
test cases and code, in detail:
Config::SetDefault ("ns3::PfFfMacScheduler::HarqEnabled", BooleanValue (false));
Maximum Throughput (MT) Scheduler
The Maximum Throughput (MT) scheduler [FCapo2012] aims to maximize the overall throughput
of eNB. It allocates each RB to the user that can achieve the maximum achievable rate in
the current TTI. Currently, MT scheduler in NS-3 has two versions: frequency domain
(FDMT) and time domain (TDMT). In FDMT, every TTI, MAC scheduler allocates RBGs to the UE
who has highest achievable rate calculated by subband CQI. In TDMT, every TTI, MAC
scheduler selects one UE which has highest achievable rate calculated by wideband CQI.
Then MAC scheduler allocates all RBGs to this UE in current TTI. The calculation of
achievable rate in FDMT and TDMT is as same as the one in PF. Let i,j denote generic
users; let t be the subframe index, and k be the resource block index; let M_{i,k}(t) be
MCS usable by user i on resource block k according to what reported by the AMC model (see
Adaptive Modulation and Coding); finally, let S(M, B) be the TB size in bits as defined in
[TS36213] for the case where a number B of resource blocks is used. The achievable rate
R_{i}(k,t) in bit/s for user i on resource block k at subframe t is defined as
where au is the TTI duration. At the start of each subframe t, each RB is assigned to a
certain user. In detail, the index 144}_{k}(t) to which RB k is assigned at time t is
determined as
When there are several UEs having the same achievable rate, current implementation always
selects the first UE created in script. Although MT can maximize cell throughput, it
cannot provide fairness to UEs in poor channel condition.
Throughput to Average (TTA) Scheduler
The Throughput to Average (TTA) scheduler [FCapo2012] can be considered as an intermediate
between MT and PF. The metric used in TTA is calculated as follows:
Here, R_{i}(k,t) in bit/s represents the achievable rate for user i on resource block k at
subframe t. The calculation method already is shown in MT and PF. Meanwhile, R_{i}(t) in
bit/s stands for the achievable rate for i at subframe t. The difference between those two
achievable rates is how to get MCS. For R_{i}(k,t), MCS is calculated by subband CQI while
R_{i}(t) is calculated by wideband CQI. TTA scheduler can only be implemented in frequency
domain (FD) because the achievable rate of particular RBG is only related to FD
scheduling.
Blind Average Throughput Scheduler
The Blind Average Throughput scheduler [FCapo2012] aims to provide equal throughput to all
UEs under eNB. The metric used in TTA is calculated as follows:
where T_{j}(t) is the past throughput performance perceived by the user j and can be
calculated by the same method in PF scheduler. In the time domain blind average throughput
(TD-BET), the scheduler selects the UE with largest priority metric and allocates all RBGs
to this UE. On the other hand, in the frequency domain blind average throughput (FD-BET),
every TTI, the scheduler first selects one UE with lowest pastAverageThroughput (largest
priority metric). Then scheduler assigns one RBG to this UE, it calculates expected
throughput of this UE and uses it to compare with past average throughput T_{j}(t) of
other UEs. The scheduler continues to allocate RBG to this UE until its expected
throughput is not the smallest one among past average throughput T_{j}(t) of all UE. Then
the scheduler will use the same way to allocate RBG for a new UE which has the lowest past
average throughput T_{j}(t) until all RBGs are allocated to UEs. The principle behind this
is that, in every TTI, the scheduler tries the best to achieve the equal throughput among
all UEs.
Token Bank Fair Queue Scheduler
Token Bank Fair Queue (TBFQ) is a QoS aware scheduler which derives from the leaky-bucket
mechanism. In TBFQ, a traffic flow of user i is characterized by following parameters:
· t_{i}: packet arrival rate (byte/sec )
· r_{i}: token generation rate (byte/sec)
· p_{i}: token pool size (byte)
· E_{i}: counter that records the number of token borrowed from or given to the token
bank by flow i ; E_{i} can be smaller than zero
Each K bytes data consumes k tokens. Also, TBFQ maintains a shared token bank (B) so as to
balance the traffic between different flows. If token generation rate r_{i} is bigger than
packet arrival rate t_{i}, then tokens overflowing from token pool are added to the token
bank, and E_{i} is increased by the same amount. Otherwise, flow i needs to withdraw
tokens from token bank based on a priority metric frac{E_{i}}{r_{i}}, and E_{i} is
decreased. Obviously, the user contributes more on token bank has higher priority to
borrow tokens; on the other hand, the user borrows more tokens from bank has lower
priority to continue to withdraw tokens. Therefore, in case of several users having the
same token generation rate, traffic rate and token pool size, user suffers from higher
interference has more opportunity to borrow tokens from bank. In addition, TBFQ can police
the traffic by setting the token generation rate to limit the throughput. Additionally,
TBFQ also maintains following three parameters for each flow:
· Debt limit d_{i}: if E_{i} belows this threshold, user i cannot further borrow tokens
from bank. This is for preventing malicious UE to borrow too much tokens.
· Credit limit c_{i}: the maximum number of tokens UE i can borrow from the bank in one
time.
· Credit threshold C: once E_{i} reaches debt limit, UE i must store C tokens to bank
in order to further borrow token from bank.
LTE in NS-3 has two versions of TBFQ scheduler: frequency domain TBFQ (FD-TBFQ) and time
domain TBFQ (TD-TBFQ). In FD-TBFQ, the scheduler always select UE with highest metric and
allocates RBG with highest subband CQI until there are no packets within UE's RLC buffer
or all RBGs are allocated [FABokhari2009]. In TD-TBFQ, after selecting UE with maximum
metric, it allocates all RBGs to this UE by using wideband CQI [WKWong2004].
Priority Set Scheduler
Priority set scheduler (PSS) is a QoS aware scheduler which combines time domain (TD) and
frequency domain (FD) packet scheduling operations into one scheduler [GMonghal2008]. It
controls the fairness among UEs by a specified Target Bit Rate (TBR).
In TD scheduler part, PSS first selects UEs with non-empty RLC buffer and then divide them
into two sets based on the TBR:
· set 1: UE whose past average throughput is smaller than TBR; TD scheduler calculates
their priority metric in Blind Equal Throughput (BET) style:
· set 2: UE whose past average throughput is larger (or equal) than TBR; TD scheduler
calculates their priority metric in Proportional Fair (PF) style:
UEs belonged to set 1 have higher priority than ones in set 2. Then PSS will select
N_{mux} UEs with highest metric in two sets and forward those UE to FD scheduler. In PSS,
FD scheduler allocates RBG k to UE n that maximums the chosen metric. Two PF schedulers
are used in PF scheduler:
· Proportional Fair scheduled (PFsch)
· Carrier over Interference to Average (CoIta)
where Tsch_{j}(t) is similar past throughput performance perceived by the user j, with the
difference that it is updated only when the i-th user is actually served. CoI[j,k] is an
estimation of the SINR on the RBG k of UE j. Both PFsch and CoIta is for decoupling FD
metric from TD scheduler. In addition, PSS FD scheduler also provide a weight metric W[n]
for helping controlling fairness in case of low number of UEs.
where T_{j}(t) is the past throughput performance perceived by the user j . Therefore, on
RBG k, the FD scheduler selects the UE j that maximizes the product of the frequency
domain metric (Msch, MCoI) by weight W[n]. This strategy will guarantee the throughput of
lower quality UE tend towards the TBR.
Config::SetDefault ("ns3::PfFfMacScheduler::HarqEnabled", BooleanValue (false));
The scheduler implements the filtering of the uplink CQIs according to their nature with
UlCqiFilter attibute, in detail:
· SRS_UL_CQI: only SRS based CQI are stored in the internal attributes.
· PUSCH_UL_CQI: only PUSCH based CQI are stored in the internal attributes.
· ALL_UL_CQI: all CQIs are stored in the same internal attibute (i.e., the last CQI
received is stored independently from its nature).
Channel and QoS Aware Scheduler
The Channel and QoS Aware (CQA) Scheduler [Bbojovic2014] is an LTE MAC downlink scheduling
algorithm that considers the head of line (HOL) delay, the GBR parameters and channel
quality over different subbands. The CQA scheduler is based on joint TD and FD scheduling.
In the TD (at each TTI) the CQA scheduler groups users by priority. The purpose of
grouping is to enforce the FD scheduling to consider first the flows with highest HOL
delay. The grouping metric m_{td} for user j=1,...,N is defined in the following way:
where d_{hol}^{j}(t) is the current value of HOL delay of flow j, and g is a grouping
parameter that determines granularity of the groups, i.e. the number of the flows that
will be considered in the FD scheduling iteration.
The groups of flows selected in the TD iteration are forwarded to the FD scheduling
starting from the flows with the highest value of the m_{td} metric until all RBGs are
assigned in the corresponding TTI. In the FD, for each RBG k=1,...,K, the CQA scheduler
assigns the current RBG to the user j that has the maximum value of the FD metric which we
define in the following way:
where m_{GBR}^j(t) is calculated as follows:
where GBR^j is the bit rate specified in EPS bearer of the flow j, rieRj()shpsaeraged throughput that
is calculated with a moving average, r^{j}(t) is the throughput achieved at the time t,
and lpha is a coefficient such that 0 lpha ..sp For m_{ca}^{(k,j)}(t) we consider two
different metrics: m_{pf}^{(k,j)}(t) and m_{ff}^{(k,j)}(t). m_{pf} is the Proportional
Fair metric which is defined as follows:
where R_e^{(k,j)}(t) is the estimated achievable throughput of user j over RBG k
calculated by the Adaptive Modulation and Coding (AMC) scheme that maps the channel
quality indicator (CQI) value to the transport block size in bits.
The other channel awareness metric that we consider is m_{ff} which is proposed in
[GMonghal2008] and it represents the frequency selective fading gains over RBG k for user
j and is calculated in the following way:
where CQI^{(k,j)}(t) is the last reported CQI value from user j for the k-th RBG.
The user can select whether m_{pf} or m_{ff} is used by setting the attribute
ns3::CqaFfMacScheduler::CqaMetric respectively to "CqaPf" or "CqaFf".
Random Access
The LTE model includes a model of the Random Access procedure based on some simplifying
assumptions, which are detailed in the following for each of the messages and signals
described in the specs [TS36321].
· Random Access (RA) preamble: in real LTE systems this corresponds to a Zadoff-Chu
(ZC) sequence using one of several formats available and sent in the PRACH slots
which could in principle overlap with PUSCH. PRACH Configuration Index 14 is
assumed, i.e., preambles can be sent on any system frame number and subframe number.
The RA preamble is modeled using the LteControlMessage class, i.e., as an ideal
message that does not consume any radio resources. The collision of preamble
transmission by multiple UEs in the same cell are modeled using a protocol
interference model, i.e., whenever two or more identical preambles are transmitted in
same cell at the same TTI, no one of these identical preambles will be received by
the eNB. Other than this collision model, no error model is associated with the
reception of a RA preamble.
· Random Access Response (RAR): in real LTE systems, this is a special MAC PDU sent on
the DL-SCH. Since MAC control elements are not accurately modeled in the simulator
(only RLC and above PDUs are), the RAR is modeled as an LteControlMessage that does
not consume any radio resources. Still, during the RA procedure, the LteEnbMac will
request to the scheduler the allocation of resources for the RAR using the FF MAC
Scheduler primitive SCHED_DL_RACH_INFO_REQ. Hence, an enhanced scheduler
implementation (not available at the moment) could allocate radio resources for the
RAR, thus modeling the consumption of Radio Resources for the transmission of the
RAR.
· Message 3: in real LTE systems, this is an RLC TM SDU sent over resources specified
in the UL Grant in the RAR. In the simulator, this is modeled as a real RLC TM RLC
PDU whose UL resources are allocated by the scheduler upon call to
SCHED_DL_RACH_INFO_REQ.
· Contention Resolution (CR): in real LTE system, the CR phase is needed to address the
case where two or more UE sent the same RA preamble in the same TTI, and the eNB was
able to detect this preamble in spite of the collision. Since this event does not
occur due to the protocol interference model used for the reception of RA preambles,
the CR phase is not modeled in the simulator, i.e., the CR MAC CE is never sent by
the eNB and the UEs consider the RA to be successful upon reception of the RAR. As a
consequence, the radio resources consumed for the transmission of the CR MAC CE are
not modeled.
Figure Sequence diagram of the Contention-based MAC Random Access procedure and Sequence
diagram of the Non-contention-based MAC Random Access procedure shows the sequence
diagrams of respectively the contention-based and non-contention-based MAC random access
procedure, highlighting the interactions between the MAC and the other entities.
[image] Sequence diagram of the Contention-based MAC Random Access procedure.UNINDENT
[image] Sequence diagram of the Non-contention-based MAC Random Access
procedure.UNINDENT
RLC
Overview
The RLC entity is specified in the 3GPP technical specification [TS36322], and comprises
three different types of RLC: Transparent Mode (TM), Unacknowledge Mode (UM) and
Acknowledged Mode (AM). The simulator includes one model for each of these entitities
The RLC entities provide the RLC service interface to the upper PDCP layer and the MAC
service interface to the lower MAC layer. The RLC entities use the PDCP service interface
from the upper PDCP layer and the MAC service interface from the lower MAC layer.
Figure Implementation Model of PDCP, RLC and MAC entities and SAPs shows the
implementation model of the RLC entities and its relationship with all the other entities
and services in the protocol stack.
[image] Implementation Model of PDCP, RLC and MAC entities and SAPs.UNINDENT
Service Interfaces
RLC Service Interface
The RLC service interface is divided into two parts:
· the RlcSapProvider part is provided by the RLC layer and used by the upper PDCP layer
and
· the RlcSapUser part is provided by the upper PDCP layer and used by the RLC layer.
Both the UM and the AM RLC entities provide the same RLC service interface to the upper
PDCP layer.
RLC Service Primitives
The following list specifies which service primitives are provided by the RLC service
interfaces:
· RlcSapProvider::TransmitPdcpPdu
· The PDCP entity uses this primitive to send a PDCP PDU to the lower RLC entity
in the transmitter peer
· RlcSapUser::ReceivePdcpPdu
· The RLC entity uses this primitive to send a PDCP PDU to the upper PDCP entity
in the receiver peer
MAC Service Interface
The MAC service interface is divided into two parts:
· the MacSapProvider part is provided by the MAC layer and used by the upper RLC layer
and
· the MacSapUser part is provided by the upper RLC layer and used by the MAC layer.
MAC Service Primitives
The following list specifies which service primitives are provided by the MAC service
interfaces:
· MacSapProvider::TransmitPdu
· The RLC entity uses this primitive to send a RLC PDU to the lower MAC entity in
the transmitter peer
· MacSapProvider::ReportBufferStatus
· The RLC entity uses this primitive to report the MAC entity the size of pending
buffers in the transmitter peer
· MacSapUser::NotifyTxOpportunity
· The MAC entity uses this primitive to nofify the RLC entity a transmission
opportunity
· MacSapUser::ReceivePdu
· The MAC entity uses this primitive to send an RLC PDU to the upper RLC entity
in the receiver peer
AM RLC
The processing of the data transfer in the Acknowledge Mode (AM) RLC entity is explained
in section 5.1.3 of [TS36322]. In this section we describe some details of the
implementation of the RLC entity.
Buffers for the transmit operations
Our implementation of the AM RLC entity maintains 3 buffers for the transmit operations:
· Transmission Buffer: it is the RLC SDU queue. When the AM RLC entity receives a SDU
in the TransmitPdcpPdu service primitive from the upper PDCP entity, it enqueues it
in the Transmission Buffer. We put a limit on the RLC buffer size and just silently
drop SDUs when the buffer is full.
· Transmitted PDUs Buffer: it is the queue of transmitted RLC PDUs for which an
ACK/NACK has not been received yet. When the AM RLC entity sends a PDU to the MAC
entity, it also puts a copy of the transmitted PDU in the Transmitted PDUs Buffer.
· Retransmission Buffer: it is the queue of RLC PDUs which are considered for
retransmission (i.e., they have been NACKed). The AM RLC entity moves this PDU to the
Retransmission Buffer, when it retransmits a PDU from the Transmitted Buffer.
Transmit operations in downlink
The following sequence diagram shows the interactions between the different entities (RRC,
PDCP, AM RLC, MAC and MAC scheduler) of the eNB in the downlink to perform data
communications.
Figure Sequence diagram of data PDU transmission in downlink shows how the upper layers
send data PDUs and how the data flow is processed by the different entities/services of
the LTE protocol stack.
[image] Sequence diagram of data PDU transmission in downlink.UNINDENT
The PDCP entity calls the Transmit_PDCP_PDU service primitive in order to send a data
PDU. The AM RLC entity processes this service primitive according to the AM data
transfer procedures defined in section 5.1.3 of [TS36322].
When the Transmit_PDCP_PDU service primitive is called, the AM RLC entity performs the
following operations:
· Put the data SDU in the Transmission Buffer.
· Compute the size of the buffers (how the size of buffers is computed will be
explained afterwards).
· Call the Report_Buffer_Status service primitive of the eNB MAC entity in order to
notify to the eNB MAC entity the sizes of the buffers of the AM RLC entity. Then, the
eNB MAC entity updates the buffer status in the MAC scheduler using the
SchedDlRlcBufferReq service primitive of the FF MAC Scheduler API.
Afterwards, when the MAC scheduler decides that some data can be sent, the MAC entity
notifies it to the RLC entity, i.e. it calls the Notify_Tx_Opportunity service primitive,
then the AM RLC entity does the following:
· Create a single data PDU by segmenting and/or concatenating the SDUs in the
Transmission Buffer.
· Move the data PDU from the Transmission Buffer to the Transmitted PDUs Buffer.
· Update state variables according section 5.1.3.1.1 of [TS36322].
· Call the Transmit_PDU primitive in order to send the data PDU to the MAC entity.
Retransmission in downlink
The sequence diagram of Figure Sequence diagram of data PDU retransmission in downlink
shows the interactions between the different entities (AM RLC, MAC and MAC scheduler) of
the eNB in downlink when data PDUs must be retransmitted by the AM RLC entity.
[image] Sequence diagram of data PDU retransmission in downlink.UNINDENT
The transmitting AM RLC entity can receive STATUS PDUs from the peer AM RLC entity.
STATUS PDUs are sent according section 5.3.2 of [TS36322] and the processing of
reception is made according section 5.2.1 of [TS36322].
When a data PDUs is retransmitted from the Transmitted PDUs Buffer, it is also moved to
the Retransmission Buffer.
Transmit operations in uplink
The sequence diagram of Figure Sequence diagram of data PDU transmission in uplink shows
the interactions between the different entities of the UE (RRC, PDCP, RLC and MAC) and the
eNB (MAC and Scheduler) in uplink when data PDUs are sent by the upper layers.
[image] Sequence diagram of data PDU transmission in uplink.UNINDENT
It is similar to the sequence diagram in downlink; the main difference is that in this
case the Report_Buffer_Status is sent from the UE MAC to the MAC Scheduler in the eNB
over the air using the control channel.
Retransmission in uplink
The sequence diagram of Figure Sequence diagram of data PDU retransmission in uplink shows
the interactions between the different entities of the UE (AM RLC and MAC) and the eNB
(MAC) in uplink when data PDUs must be retransmitted by the AM RLC entity.
[image] Sequence diagram of data PDU retransmission in uplink.UNINDENT
Calculation of the buffer size
The Transmission Buffer contains RLC SDUs. A RLC PDU is one or more SDU segments plus an
RLC header. The size of the RLC header of one RLC PDU depends on the number of SDU
segments the PDU contains.
The 3GPP standard (section 6.1.3.1 of [TS36321]) says clearly that, for the uplink, the
RLC and MAC headers are not considered in the buffer size that is to be report as part of
the Buffer Status Report. For the downlink, the behavior is not specified. Neither
[FFAPI] specifies how to do it. Our RLC model works by assuming that the calculation of
the buffer size in the downlink is done exactly as in the uplink, i.e., not considering
the RLC and MAC header size.
We note that this choice affects the interoperation with the MAC scheduler, since, in
response to the Notify_Tx_Opportunity service primitive, the RLC is expected to create a
PDU of no more than the size requested by the MAC, including RLC overhead. Hence, unneeded
fragmentation can occur if (for example) the MAC notifies a transmission exactly equal to
the buffer size previously reported by the RLC. We assume that it is left to the Scheduler
to implement smart strategies for the selection of the size of the transmission
opportunity, in order to eventually avoid the inefficiency of unneeded fragmentation.
Concatenation and Segmentation
The AM RLC entity generates and sends exactly one RLC PDU for each transmission
opportunity even if it is smaller than the size reported by the transmission opportunity.
So for instance, if a STATUS PDU is to be sent, then only this PDU will be sent in that
transmission opportunity.
The segmentation and concatenation for the SDU queue of the AM RLC entity follows the same
philosophy as the same procedures of the UM RLC entity but there are new state variables
(see [TS36322] section 7.1) only present in the AM RLC entity.
It is noted that, according to the 3GPP specs, there is no concatenation for the
Retransmission Buffer.
Re-segmentation
The current model of the AM RLC entity does not support the re-segmentation of the
retransmission buffer. Rather, the AM RLC entity just waits to receive a big enough
transmission opportunity.
Unsupported features
We do not support the following procedures of [TS36322] :
· “Send an indication of successful delivery of RLC SDU” (See section 5.1.3.1.1)
· “Indicate to upper layers that max retransmission has been reached” (See section
5.2.1)
· “SDU discard procedures” (See section 5.3)
· “Re-establishment procedure” (See section 5.4)
We do not support any of the additional primitives of RLC SAP for AM RLC entity. In
particular:
· no SDU discard notified by PDCP
· no notification of successful / failed delivery by AM RLC entity to PDCP entity
UM RLC
In this section we describe the implemnetation of the Unacknowledge Mode (UM) RLC entity.
Transmit operations in downlink
The transmit operations of the UM RLC are similar to those of the AM RLC previously
described in Section Transmit operations in downlink, with the difference that, following
the specifications of [TS36322], retransmission are not performed, and there are no STATUS
PDUs.
Transmit operations in uplink
The transmit operations in the uplink are similar to those of the downlink, with the main
difference that the Report_Buffer_Status is sent from the UE MAC to the MAC Scheduler in
the eNB over the air using the control channel.
Calculation of the buffer size
The calculation of the buffer size for the UM RLC is done using the same approach of the
AM RLC, please refer to section Calculation of the buffer size for the corresponding
description.
TM RLC
In this section we describe the implementation of the Transparent Mode (TM) RLC entity.
Transmit operations in downlink
In the simulator, the TM RLC still provides to the upper layers the same service interface
provided by the AM and UM RLC entities to the PDCP layer; in practice, this interface is
used by an RRC entity (not a PDCP entity) for the transmission of RLC SDUs. This choice is
motivated by the fact that the services provided by the TM RLC to the upper layers,
according to [TS36322], is a subset of those provided by the UM and AM RLC entities to the
PDCP layer; hence, we reused the same interface for simplicity.
The transmit operations in the downlink are performed as follows. When the
Transmit_PDCP_PDU service primitive is called by the upper layers, the TM RLC does the
following:
· put the SDU in the Transmission Buffer
· compute the size of the Transmission Buffer
· call the Report_Buffer_Status service primitive of the eNB MAC entity
Afterwards, when the MAC scheduler decides that some data can be sent by the logical
channel to which the TM RLC entity belongs, the MAC entity notifies it to the TM RLC
entity by calling the Notify_Tx_Opportunity service primitive. Upon reception of this
primitive, the TM RLC entity does the following:
· if the TX opportunity has a size that is greater than or equal to the size of the
head-of-line SDU in the Transmission Buffer
· dequeue the head-of-line SDU from the Transmission Buffer
· create one RLC PDU that contains entirely that SDU, without any RLC header
· Call the Transmit_PDU primitive in order to send the RLC PDU to the MAC entity.
Transmit operations in uplink
The transmit operations in the uplink are similar to those of the downlink, with the main
difference that a transmission opportunity can also arise from the assignment of the UL
GRANT as part of the Random Access procedure, without an explicit Buffer Status Report
issued by the TM RLC entity.
Calculation of the buffer size
As per the specifications [TS36322], the TM RLC does not add any RLC header to the PDUs
being transmitted. Because of this, the buffer size reported to the MAC layer is
calculated simply by summing the size of all packets in the transmission buffer, thus
notifying to the MAC the exact buffer size.
SM RLC
In addition to the AM, UM and TM implementations that are modeled after the 3GPP
specifications, a simplified RLC model is provided, which is called Saturation Mode (SM)
RLC. This RLC model does not accept PDUs from any above layer (such as PDCP); rather, the
SM RLC takes care of the generation of RLC PDUs in response to the notification of
transmission opportunities notified by the MAC. In other words, the SM RLC simulates
saturation conditions, i.e., it assumes that the RLC buffer is always full and can
generate a new PDU whenever notified by the scheduler.
The SM RLC is used for simplified simulation scenarios in which only the LTE Radio model
is used, without the EPC and hence without any IP networking support. We note that,
although the SM RLC is an unrealistic traffic model, it still allows for the correct
simulation of scenarios with multiple flows belonging to different (non real-time) QoS
classes, in order to test the QoS performance obtained by different schedulers. This can
be done since it is the task of the Scheduler to assign transmission resources based on
the characteristics (e.g., Guaranteed Bit Rate) of each Radio Bearer, which are specified
upon the definition of each Bearer within the simulation program.
As for schedulers designed to work with real-time QoS traffic that has delay constraints,
the SM RLC is probably not an appropriate choice. This is because the absence of actual
RLC SDUs (replaced by the artificial generation of Buffer Status Reports) makes it not
possible to provide the Scheduler with meaningful head-of-line-delay information, which is
often the metric of choice for the implementation of scheduling policies for real-time
traffic flows. For the simulation and testing of such schedulers, it is advisable to use
either the UM or the AM RLC models instead.
PDCP
PDCP Model Overview
The reference document for the specification of the PDCP entity is [TS36323]. With respect
to this specification, the PDCP model implemented in the simulator supports only the
following features:
· transfer of data (user plane or control plane);
· maintenance of PDCP SNs;
· transfer of SN status (for use upon handover);
The following features are currently not supported:
· header compression and decompression of IP data flows using the ROHC protocol;
· in-sequence delivery of upper layer PDUs at re-establishment of lower layers;
· duplicate elimination of lower layer SDUs at re-establishment of lower layers for
radio bearers mapped on RLC AM;
· ciphering and deciphering of user plane data and control plane data;
· integrity protection and integrity verification of control plane data;
· timer based discard;
· duplicate discarding.
PDCP Service Interface
The PDCP service interface is divided into two parts:
· the PdcpSapProvider part is provided by the PDCP layer and used by the upper layer
and
· the PdcpSapUser part is provided by the upper layer and used by the PDCP layer.
PDCP Service Primitives
The following list specifies which service primitives are provided by the PDCP service
interfaces:
· PdcpSapProvider::TransmitPdcpSdu
· The RRC entity uses this primitive to send an RRC PDU to the lower PDCP entity
in the transmitter peer
· PdcpSapUser::ReceivePdcpSdu
· The PDCP entity uses this primitive to send an RRC PDU to the upper RRC entity
in the receiver peer
RRC
Features
The RRC model implemented in the simulator provides the following functionality:
· generation (at the eNB) and interpretation (at the UE) of System Information (in
particular the Master Information Block and, at the time of this writing, only System
Information Block Type 1 and 2)
· initial cell selection
· RRC connection establishment procedure
· RRC reconfiguration procedure, supporting the following use cases: + reconfiguration
of the SRS configuration index + reconfiguration of the PHY TX mode (MIMO) +
reconfiguration of UE measurements + data radio bearer setup + handover
· RRC connection re-establishment, supporting the following use cases: + handover
Architecture
The RRC model is divided into the following components:
· the RRC entities LteUeRrc and LteEnbRrc, which implement the state machines of the
RRC entities respectively at the UE and the eNB;
· the RRC SAPs LteUeRrcSapProvider, LteUeRrcSapUser, LteEnbRrcSapProvider,
LteEnbRrcSapUser, which allow the RRC entities to send and receive RRC messages and
information elmenents;
· the RRC protocol classes LteUeRrcProtocolIdeal, LteEnbRrcProtocolIdeal,
LteUeRrcProtocolReal, LteEnbRrcProtocolReal, which implement two different models for
the transmission of RRC messages.
Additionally, the RRC components use various other SAPs in order to interact with the rest
of the protocol stack. A representation of all the SAPs that are used is provided in the
figures LTE radio protocol stack architecture for the UE on the data plane, LTE radio
protocol stack architecture for the UE on the control plane, LTE radio protocol stack
architecture for the eNB on the data plane and LTE radio protocol stack architecture for
the eNB on the control plane.
UE RRC State Machine
In Figure UE RRC State Machine we represent the state machine as implemented in the RRC UE
entity.
[image] UE RRC State Machine.UNINDENT
It is to be noted that most of the states are transient, i.e., once the UE goes into one
of the CONNECTED states it will never switch back to any of the IDLE states. This choice
is done for the following reasons:
· as discussed in the section Design Criteria, the focus of the LTE-EPC simulation
model is on CONNECTED mode
· radio link failure is not currently modeled, as discussed in the section Radio Link
Failure, so an UE cannot go IDLE because of radio link failure
· RRC connection release is currently never triggered neither by the EPC nor by the NAS
Still, we chose to model explicitly the IDLE states, because:
· a realistic UE RRC configuration is needed for handover, which is a required feature,
and in order to have a cleaner implementation it makes sense to use the same UE RRC
configuration also for the initial connection establishment
· it makes easier to implement idle mode cell selection in the future, which is a
highly desirable feature
ENB RRC State Machine
The eNB RRC maintains the state for each UE that is attached to the cell. From an
implementation point of view, the state of each UE is contained in an instance of the
UeManager class. The state machine is represented in Figure ENB RRC State Machine for each
UE.
[image] ENB RRC State Machine for each UE.UNINDENT
Initial Cell Selection
Initial cell selection is an IDLE mode procedure, performed by UE when it has not yet
camped or attached to an eNodeB. The objective of the procedure is to find a suitable cell
and attach to it to gain access to the cellular network.
It is typically done at the beginning of simulation, as depicted in Figure Sample runs of
initial cell selection in UE and timing of related events below. The time diagram on the
left side is illustrating the case where initial cell selection succeed on first try,
while the diagram on the right side is for the case where it fails on the first try and
succeed on the second try. The timing assumes the use of real RRC protocol model (see RRC
protocol models) and no transmission error.
[image] Sample runs of initial cell selection in UE and timing of related
events.UNINDENT
The functionality is based on 3GPP IDLE mode specifications, such as in [TS36300],
[TS36304], and [TS36331]. However, a proper implementation of IDLE mode is still missing
in the simulator, so we reserve several simplifying assumptions:
· multiple carrier frequency is not supported;
· multiple Public Land Mobile Network (PLMN) identities (i.e. multiple network
operators) is not supported;
· RSRQ measurements are not utilized;
· stored information cell selection is not supported;
· "Any Cell Selection" state and camping to an acceptable cell is not supported;
· marking a cell as barred or reserved is not supported;
· cell reselection is not supported, hence it is not possible for UE to camp to a
different cell after the initial camp has been placed; and
· UE's Closed Subscriber Group (CSG) white list contains only one CSG identity.
Also note that initial cell selection is only available for EPC-enabled simulations.
LTE-only simulations must use the manual attachment method. See section
sec-network-attachment of the User Documentation for more information on their differences
in usage.
The next subsections cover different parts of initial cell selection, namely cell search,
broadcast of system information, and cell selection evaluation.
Cell Search
Cell search aims to detect surrounding cells and measure the strength of received signal
from each of these cells. One of these cells will become the UE's entry point to join the
cellular network.
The measurements are based on the RSRP of the received PSS, averaged by Layer 1 filtering,
and performed by the PHY layer, as previously described in more detail in section UE PHY
Measurements Model. PSS is transmitted by eNodeB over the central 72 sub-carriers of the
DL channel (Section 5.1.7.3 [TS36300]), hence we model cell search to operate using a DL
bandwidth of 6 RBs. Note that measurements of RSRQ are not available at this point of time
in simulation. As a consequence, the LteUePhy::RsrqUeMeasThreshold attribute does not
apply during cell search.
By using the measured RSRP, the PHY entity is able to generate a list of detected cells,
each with its corresponding cell ID and averaged RSRP. This list is periodically pushed
via CPHY SAP to the RRC entity as a measurement report.
The RRC entity inspects the report and simply choose the cell with the strongest RSRP, as
also indicated in Section 5.2.3.1 of [TS36304]. Then it instructs back the PHY entity to
synchronize to this particular cell. The actual operating bandwidth of the cell is still
unknown at this time, so the PHY entity listens only to the minimum bandwidth of 6 RBs.
Nevertheless, the PHY entity will be able to receive system broadcast message from this
particular eNodeB, which is the topic of the next subsection.
Broadcast of System Information
System information blocks are broadcasted by eNodeB to UEs at predefined time intervals,
adapted from Section 5.2.1.2 of [TS36331]. The supported system information blocks are:
·
Master Information Block (MIB)
Contains parameters related to the PHY layer, generated during cell
configuration and broadcasted every 10 ms at the beginning of radio frame as a
control message.
·
System Information Block Type 1 (SIB1)
Contains information regarding network access, broadcasted every 20 ms at the
middle of radio frame as a control message. Not used in manual attachment
method. UE must have decoded MIB before it can receive SIB1.
·
System Information Block Type 2 (SIB2)
Contains UL- and RACH-related settings, scheduled to transmit via RRC protocol
at 16 ms after cell configuration, and then repeats every 80 ms (configurable
through LteEnbRrc::SystemInformationPeriodicity attribute. UE must be camped
to a cell in order to be able to receive its SIB2.
Reception of system information is fundamental for UE to advance in its lifecycle. MIB
enables the UE to increase the initial DL bandwidth of 6 RBs to the actual operating
bandwidth of the network. SIB1 provides information necessary for cell selection
evaluation (explained in the next section). And finally SIB2 is required before the UE is
allowed to switch to CONNECTED state.
Cell Selection Evaluation
UE RRC reviews the measurement report produced in Cell Search and the cell access
information provided by SIB1. Once both information is available for a specific cell, the
UE triggers the evaluation process. The purpose of this process is to determine whether
the cell is a suitable cell to camp to.
The evaluation process is a slightly simplified version of Section 5.2.3.2 of [TS36304].
It consists of the following criteria:
· Rx level criterion; and
· closed subscriber group (CSG) criterion.
The first criterion, Rx level, is based on the cell's measured RSRP Q_{rxlevmeas}, which
has to be higher than a required minimum Q_{rxlevmin} in order to pass the criterion:
where Q_{rxlevmin} is determined by each eNodeB and is obtainable by UE from SIB1.
The last criterion, CSG, is a combination of a true-or-false parameter called CSG
indication and a simple number CSG identity. The basic rule is that UE shall not camp to
eNodeB with a different CSG identity. But this rule is only enforced when CSG indication
is valued as true. More details are provided in Section sec-network-attachment of the User
Documentation.
When the cell passes all the above criteria, the cell is deemed as suitable. Then UE
camps to it (IDLE_CAMPED_NORMALLY state).
After this, upper layer may request UE to enter CONNECTED mode. Please refer to section
RRC connection establishment for details on this.
On the other hand, when the cell does not pass the CSG criterion, then the cell is labeled
as acceptable (Section 10.1.1.1 [TS36300]). In this case, the RRC entity will tell the PHY
entity to synchronize to the second strongest cell and repeat the initial cell selection
procedure using that cell. As long as no suitable cell is found, the UE will repeat these
steps while avoiding cells that have been identified as acceptable.
Radio Admission Control
Radio Admission Control is supported by having the eNB RRC reply to an RRC CONNECTION
REQUEST message sent by the UE with either an RRC CONNECTION SETUP message or an RRC
CONNECTION REJECT message, depending on whether the new UE is to be admitted or not. In
the current implementation, the behavior is determined by the boolean attribute
ns3::LteEnbRrc::AdmitRrcConnectionRequest. There is currently no Radio Admission Control
algorithm that dynamically decides whether a new connection shall be admitted or not.
Radio Bearer Configuration
Some implementation choices have been made in the RRC regarding the setup of radio
bearers:
· three Logical Channel Groups (out of four available) are configured for uplink buffer
status report purposes, according to the following policy:
· LCG 0 is for signaling radio bearers
· LCG 1 is for GBR data radio bearers
· LCG 2 is for Non-GBR data radio bearers
Radio Link Failure
Since at this stage the RRC supports the CONNECTED mode only, Radio Link Failure (RLF) is
not handled. The reason is that one of the possible outcomes of RLF (when RRC
re-establishment is unsuccessful) is to leave RRC CONNECTED notifying the NAS of the RRC
connection failure. In order to model RLF properly, RRC IDLE mode should be supported,
including in particular idle mode cell (re-)selection.
With the current model, an UE that experiences bad link quality and that does not perform
handover (because of, e.g., no neighbour cells, handover disabled, handover thresholds
misconfigured) will just stay associated with the same eNB, and the scheduler will stop
allocating resources to it for communications.
UE RRC Measurements Model
UE RRC measurements support
The UE RRC entity provides support for UE measurements; in particular, it implements the
procedures described in Section 5.5 of [TS36331], with the following simplifying
assumptions:
· only E-UTRA intra-frequency measurements are supported, which implies:
· only one measurement object is used during the simulation;
· measurement gaps are not needed to perform the measurements;
· Event B1 and B2 are not implemented;
· only reportStrongestCells purpose is supported, while reportCGI and
reportStrongestCellsForSON purposes are not supported;
· s-Measure is not supported;
· since carrier aggregation is not supported in by the LTE module, the following
assumptions in UE measurements hold true:
· no notion of secondary cell (SCell);
· primary cell (PCell) simply means serving cell;
· Event A6 is not implemented;
· speed dependant scaling of time-to-trigger (Section 5.5.6.2 of [TS36331]) is not
supported.
Overall design
The model is based on the concept of UE measurements consumer, which is an entity that may
request an eNodeB RRC entity to provide UE measurement reports. Consumers are, for
example, Handover algorithm, which compute handover decision based on UE measurement
reports. Test cases and user's programs may also become consumers. Figure Relationship
between UE measurements and its consumers depicts the relationship between these entities.
[image] Relationship between UE measurements and its consumers.UNINDENT
The whole UE measurements function at the RRC level is divided into 4 major parts:
1. Measurement configuration (handled by LteUeRrc::ApplyMeasConfig)
2. Performing measurements (handled by LteUeRrc::DoReportUeMeasurements)
3. Measurement report triggering (handled by LteUeRrc::MeasurementReportTriggering)
4. Measurement reporting (handled by LteUeRrc::SendMeasurementReport)
The following sections will describe each of the parts above.
Measurement configuration
An eNodeB RRC entity configures UE measurements by sending the configuration parameters to
the UE RRC entity. This set of parameters are defined within the MeasConfig Information
Element (IE) of the RRC Connection Reconfiguration message (RRC connection
reconfiguration).
The eNodeB RRC entity implements the configuration parameters and procedures described in
Section 5.5.2 of [TS36331], with the following simplifying assumption:
· configuration (i.e. addition, modification, and removal) can only be done before the
simulation begins;
· all UEs attached to the eNodeB will be configured the same way, i.e. there is no
support for configuring specific measurement for specific UE; and
· it is assumed that there is a one-to-one mapping between the PCI and the E-UTRAN
Global Cell Identifier (EGCI). This is consistent with the PCI modeling assumptions
described in UE PHY Measurements Model.
The eNodeB RRC instance here acts as an intermediary between the consumers and the
attached UEs. At the beginning of simulation, each consumer provides the eNodeB RRC
instance with the UE measurements configuration that it requires. After that, the eNodeB
RRC distributes the configuration to attached UEs.
Users may customize the measurement configuration using several methods. Please refer to
Section sec-configure-ue-measurements of the User Documentation for the description of
these methods.
Performing measurements
UE RRC receives both RSRP and RSRQ measurements on periodical basis from UE PHY, as
described in UE PHY Measurements Model. Layer 3 filtering will be applied to these
received measurements. The implementation of the filtering follows Section 5.5.3.2 of
[TS36331]:
where:
· M_n is the latest received measurement result from the physical layer;
· F_n is the updated filtered measurement result;
· F_{n-1} is the old filtered measurement result, where F_0 = M_1 (i.e. the first
measurement is not filtered); and
· a = (ac{1}{2})^{ac{k}{4}}, where k is the configurable filterCoefficent provided by
the QuantityConfig;
k = 4 is the default value, but can be configured by setting the RsrpFilterCoefficient and
RsrqFilterCoefficient attributes in LteEnbRrc.
Therefore k = 0 will disable Layer 3 filtering. On the other hand, past measurements can
be granted more influence on the filtering results by using larger value of k.
Measurement reporting triggering
In this part, UE RRC will go through the list of active measurement configuration and
check whether the triggering condition is fulfilled in accordance with Section 5.5.4 of
[TS36331]. When at least one triggering condition from all the active measurement
configuration is fulfilled, the measurement reporting procedure (described in the next
subsection) will be initiated.
3GPP defines two kinds of triggerType: periodical and event-based. At the moment, only
event-based criterion is supported. There are various events that can be selected, which
are briefly described in the table below:
List of supported event-based triggering criteria
┌─────────┬──────────────────────────────────┐
│Name │ Description │
├─────────┼──────────────────────────────────┤
│Event A1 │ Serving cell becomes better than │
│ │ threshold │
├─────────┼──────────────────────────────────┤
│Event A2 │ Serving cell becomes worse than │
│ │ threshold │
├─────────┼──────────────────────────────────┤
│Event A3 │ Neighbour becomes offset dB │
│ │ better than serving cell │
├─────────┼──────────────────────────────────┤
│Event A4 │ Neighbour becomes better than │
│ │ threshold │
└─────────┴──────────────────────────────────┘
│Event A5 │ Serving becomes worse than │
│ │ threshold1 AND neighbour becomes │
│ │ better than threshold2 │
└─────────┴──────────────────────────────────┘
Two main conditions to be checked in an event-based trigger are the entering condition and
the leaving condition. More details on these two can be found in Section 5.5.4 of
[TS36331].
An event-based trigger can be further configured by introducing hysteresis and
time-to-trigger. Hysteresis (Hys) defines the distance between the entering and leaving
conditions in dB. Similarly, time-to-trigger introduces delay to both entering and leaving
conditions, but as a unit of time.
The periodical type of reporting trigger is not supported, but its behaviour can be easily
obtained by using an event-based trigger. This can be done by configuring the measurement
in such a way that the entering condition is always fulfilled, for example, by setting the
threshold of Event A1 to zero (the minimum level). As a result, the measurement reports
will always be triggered at every certain interval, as determined by the reportInterval
field within LteRrcSap::ReportConfigEutra, therefore producing the same behaviour as
periodical reporting.
As a limitation with respect to 3GPP specifications, the current model does not support
any cell-specific configuration. These configuration parameters are defined in measurement
object. As a consequence, incorporating a list of black cells into the triggering process
is not supported. Moreover, cell-specific offset (i.e., O_{cn} and O_{cp} in Event A3, A4,
and A5) are not supported as well. The value equal to zero is always assumed in place of
them.
Measurement reporting
This part handles the submission of measurement report from the UE RRC entity to the
serving eNodeB entity via RRC protocol. Several simplifying assumptions have been adopted:
· reportAmount is not applicable (i.e. always assumed to be infinite);
· in measurement reports, the reportQuantity is always assumed to be BOTH, i.e., both
RSRP and RSRQ are always reported, regardless of the triggerQuantity.
Handover
The RRC model supports UE mobility in CONNECTED mode by invoking the X2-based handover
procedure. The model is intra-EUTRAN and intra-frequency, as based on Section 10.1.2.1 of
[TS36300].
This section focuses on the process of triggering a handover. The handover execution
procedure itself is covered in Section X2.
There are two ways to trigger the handover procedure:
· explicitly (or manually) triggered by the simulation program by scheduling an
execution of the method LteEnbRrc::SendHandoverRequest; or
· automatically triggered by the eNodeB RRC entity based on UE measurements and
according to the selected handover algorithm.
Section sec-x2-based-handover of the User Documentation provides some examples on using
both explicit and automatic handover triggers in simulation. The next subsection will
take a closer look on the automatic method, by describing the design aspects of the
handover algorithm interface and the available handover algorithms.
Handover algorithm
Handover in 3GPP LTE has the following properties:
·
UE-assisted
The UE provides input to the network in the form of measurement reports. This
is handled by the UE RRC Measurements Model.
·
Network-controlled
The network (i.e. the source eNodeB and the target eNodeB) decides when to
trigger the handover and oversees its execution.
The handover algorithm operates at the source eNodeB and is responsible in making handover
decisions in an "automatic" manner. It interacts with an eNodeB RRC instance via the
Handover Management SAP interface. These relationships are illustrated in Figure
Relationship between UE measurements and its consumers from the previous section.
The handover algorithm interface consists of the following methods:
·
AddUeMeasReportConfigForHandover
(Handover Algorithm -> eNodeB RRC) Used by the handover algorithm to request
measurement reports from the eNodeB RRC entity, by passing the desired
reporting configuration. The configuration will be applied to all future
attached UEs.
·
ReportUeMeas
(eNodeB RRC -> Handover Algorithm) Based on the UE measurements configured
earlier in AddUeMeasReportConfigForHandover, UE may submit measurement reports
to the eNodeB. The eNodeB RRC entity uses the ReportUeMeas interface to
forward these measurement reports to the handover algorithm.
·
TriggerHandover
(Handover Algorithm -> eNodeB RRC) After examining the measurement reports
(but not necessarily), the handover algorithm may declare a handover. This
method is used to notify the eNodeB RRC entity about this decision, which will
then proceed to commence the handover procedure.
One note for the AddUeMeasReportConfigForHandover. The method will return the measId
(measurement identity) of the newly created measurement configuration. Typically a
handover algorithm would store this unique number. It may be useful in the ReportUeMeas
method, for example when more than one configuration has been requested and the handover
algorithm needs to differentiate incoming reports based on the configuration that
triggered them.
A handover algorithm is implemented by writing a subclass of the LteHandoverAlgorithm
abstract superclass and implementing each of the above mentioned SAP interface methods.
Users may develop their own handover algorithm this way, and then use it in any simulation
by following the steps outlined in Section sec-x2-based-handover of the User
Documentation.
Alternatively, users may choose to use one of the 3 built-in handover algorithms provided
by the LTE module: no-op, A2-A4-RSRQ, and strongest cell handover algorithm. They are
ready to be used in simulations or can be taken as an example of implementing a handover
algorithm. Each of these built-in algorithms is covered in each of the following
subsections.
No-op handover algorithm
The no-op handover algorithm (NoOpHandoverAlgorithm class) is the simplest possible
implementation of handover algorithm. It basically does nothing, i.e., does not call any
of the Handover Management SAP interface methods. Users may choose this handover algorithm
if they wish to disable automatic handover trigger in their simulation.
A2-A4-RSRQ handover algorithm
The A2-A4-RSRQ handover algorithm provides the functionality of the default handover
algorithm originally included in LENA M6 (ns-3.18), ported to the Handover Management SAP
interface as the A2A4RsrqHandoverAlgorithm class.
As the name implies, the algorithm utilizes the Reference Signal Received Quality (RSRQ)
measurements acquired from Event A2 and Event A4. Thus, the algorithm will add 2
measurement configuration to the corresponding eNodeB RRC instance. Their intended use are
described as follows:
· Event A2 (serving cell's RSRQ becomes worse than threshold) is leveraged to indicate
that the UE is experiencing poor signal quality and may benefit from a handover.
· Event A4 (neighbour cell's RSRQ becomes better than threshold) is used to detect
neighbouring cells and acquire their corresponding RSRQ from every attached UE, which
are then stored internally by the algorithm. By default, the algorithm configures
Event A4 with a very low threshold, so that the trigger criteria are always true.
Figure A2-A4-RSRQ handover algorithm below summarizes this procedure.
[image] A2-A4-RSRQ handover algorithm.UNINDENT
Two attributes can be set to tune the algorithm behaviour:
·
ServingCellThreshold
The threshold for Event A2, i.e. a UE must have an RSRQ lower than this
threshold to be considered for a handover.
·
NeighbourCellOffset
The offset that aims to ensure that the UE would receive better signal quality
after the handover. A neighbouring cell is considered as a target cell for the
handover only if its RSRQ is higher than the serving cell's RSRQ by the amount
of this offset.
The value of both attributes are expressed as RSRQ range (Section 9.1.7 of [TS36133]),
which is an integer between 0 and 34, with 0 as the lowest RSRQ.
Strongest cell handover algorithm
The strongest cell handover algorithm, or also sometimes known as the traditional power
budget (PBGT) algorithm, is developed using [Dimou2009] as reference. The idea is to
provide each UE with the best possible Reference Signal Received Power (RSRP). This is
done by performing a handover as soon as a better cell (i.e. with stronger RSRP) is
detected.
Event A3 (neighbour cell's RSRP becomes better than serving cell's RSRP) is chosen to
realize this concept. The A3RsrpHandoverAlgorithm class is the result of the
implementation. Handover is triggered for the UE to the best cell in the measurement
report.
A simulation which uses this algorithm is usually more vulnerable to ping-pong handover
(consecutive handover to the previous source eNodeB within short period of time),
especially when the Fading Model is enabled. This problem is typically tackled by
introducing a certain delay to the handover. The algorithm does this by including
hysteresis and time-to-trigger parameters (Section 6.3.5 of [TS36331]) to the UE
measurements configuration.
Hysteresis (a.k.a. handover margin) delays the handover in regard of RSRP. The value is
expressed in dB, ranges between 0 to 15 dB, and have a 0.5 dB accuracy, e.g., an input
value of 2.7 dB is rounded to 2.5 dB.
On the other hand, time-to-trigger delays the handover in regard of time. 3GPP defines 16
valid values for time-to-trigger (all in milliseconds): 0, 40, 64, 80, 100, 128, 160, 256,
320, 480, 512, 640, 1024, 1280, 2560, and 5120.
The difference between hysteresis and time-to-trigger is illustrated in Figure Effect of
hysteresis and time-to-trigger in strongest cell handover algorithm below, which is taken
from the lena-x2-handover-measures example. It depicts the perceived RSRP of serving cell
and a neighbouring cell by a UE which moves pass the border of the cells.
[image] Effect of hysteresis and time-to-trigger in strongest cell handover
algorithm.UNINDENT
By default, the algorithm uses a hysteresis of 3.0 dB and time-to-trigger of 256 ms.
These values can be tuned through the Hysteresis and TimeToTrigger attributes of the
A3RsrpHandoverAlgorithm class.
Neighbour Relation
LTE module supports a simplified Automatic Neighbour Relation (ANR) function. This is
handled by the LteAnr class, which interacts with an eNodeB RRC instance through the ANR
SAP interface.
Neighbour Relation Table
The ANR holds a Neighbour Relation Table (NRT), similar to the description in Section
22.3.2a of [TS36300]. Each entry in the table is called a Neighbour Relation (NR) and
represents a detected neighbouring cell, which contains the following boolean fields:
·
No Remove
Indicates that the NR shall not be removed from the NRT. This is true by
default for user-provided NR and false otherwise.
·
No X2 Indicates that the NR shall not use an X2 interface in order to initiate
procedures towards the eNodeB parenting the target cell. This is false by
default for user-provided NR, and true otherwise.
·
No HO Indicates that the NR shall not be used by the eNodeB for handover reasons.
This is true in most cases, except when the NR is both user-provided and
network-detected.
Each NR entry may have at least one of the following properties:
·
User-provided
This type of NR is created as instructed by the simulation user. For example,
a NR is created automatically upon a user-initiated establishment of X2
connection between 2 eNodeBs, e.g. as described in Section
sec-x2-based-handover. Another way to create a user-provided NR is to call the
AddNeighbourRelation function explicitly.
·
Network-detected
This type of NR is automatically created during the simulation as a result of
the discovery of a nearby cell.
In order to automatically create network-detected NR, ANR utilizes UE measurements. In
other words, ANR is a consumer of UE measurements, as depicted in Figure Relationship
between UE measurements and its consumers. RSRQ and Event A4 (neighbour becomes better
than threshold) are used for the reporting configuration. The default Event A4 threshold
is set to the lowest possible, i.e., maximum detection capability, but can be changed by
setting the Threshold attribute of LteAnr class. Note that the A2-A4-RSRQ handover
algorithm also utilizes a similar reporting configuration. Despite the similarity, when
both ANR and this handover algorithm are active in the eNodeB, they use separate reporting
configuration.
Also note that automatic setup of X2 interface is not supported. This is the reason why
the No X2 and No HO fields are true in a network-detected but not user-detected NR.
Role of ANR in Simulation
The ANR SAP interface provides the means of communication between ANR and eNodeB RRC. Some
interface functions are used by eNodeB RRC to interact with the NRT, as shown below:
·
AddNeighbourRelation
(eNodeB RRC -> ANR) Add a new user-provided NR entry into the NRT.
·
GetNoRemove
(eNodeB RRC -> ANR) Get the value of No Remove field of an NR entry of the
given cell ID.
·
GetNoHo
(eNodeB RRC -> ANR) Get the value of No HO field of an NR entry of the given
cell ID.
·
GetNoX2
(eNodeB RRC -> ANR) Get the value of No X2 field of an NR entry of the given
cell ID.
Other interface functions exist to support the role of ANR as a UE measurements consumer,
as listed below:
·
AddUeMeasReportConfigForAnr
(ANR -> eNodeB RRC) Used by the ANR to request measurement reports from the
eNodeB RRC entity, by passing the desired reporting configuration. The
configuration will be applied to all future attached UEs.
·
ReportUeMeas
(eNodeB RRC -> ANR) Based on the UE measurements configured earlier in
AddUeMeasReportConfigForAnr, UE may submit measurement reports to the eNodeB.
The eNodeB RRC entity uses the ReportUeMeas interface to forward these
measurement reports to the ANR.
Please refer to the corresponding API documentation for LteAnrSap class for more details
on the usage and the required parameters.
The ANR is utilized by the eNodeB RRC instance as a data structure to keep track of the
situation of nearby neighbouring cells. The ANR also helps the eNodeB RRC instance to
determine whether it is possible to execute a handover procedure to a neighbouring cell.
This is realized by the fact that eNodeB RRC will only allow a handover procedure to
happen if the NR entry of the target cell has both No HO and No X2 fields set to false.
ANR is enabled by default in every eNodeB instance in the simulation. It can be disabled
by setting the AnrEnabled attribute in LteHelper class to false.
RRC sequence diagrams
In this section we provide some sequence diagrams that explain the most important RRC
procedures being modeled.
RRC connection establishment
Figure Sequence diagram of the RRC Connection Establishment procedure shows how the RRC
Connection Establishment procedure is modeled, highlighting the role of the RRC layer at
both the UE and the eNB, as well as the interaction with the other layers.
[image] Sequence diagram of the RRC Connection Establishment procedure.UNINDENT
There are several timeouts related to this procedure, which are listed in the following
Table Timers in RRC connection establishment procedure. If any of these timers expired,
the RRC connection establishment procedure is terminated in failure. In this case, the
upper layer (UE NAS) will immediately attempt to retry the procedure until it completes
successfully.
Timers in RRC connection establishment procedure
┌───────────────┬────────────┬────────────────┬────────────────┬──────────┬────────────────┐
│Name │ Location │ Timer starts │ Timer stops │ Default │ When timer │
│ │ │ │ │ duration │ expired │
├───────────────┼────────────┼────────────────┼────────────────┼──────────┼────────────────┤
│Connection │ eNodeB RRC │ New UE context │ Receive RRC │ 15 ms │ Remove UE │
│request │ │ added │ CONNECTION │ │ context │
│timeout │ │ │ REQUEST │ │ │
├───────────────┼────────────┼────────────────┼────────────────┼──────────┼────────────────┤
│Connection │ UE RRC │ Send RRC │ Receive RRC │ 100 ms │ Reset UE MAC │
│timeout (T300 │ │ CONNECTION │ CONNECTION │ │ │
│timer) │ │ REQUEST │ SETUP or │ │ │
│ │ │ │ REJECT │ │ │
├───────────────┼────────────┼────────────────┼────────────────┼──────────┼────────────────┤
│Connection │ eNodeB RRC │ Send RRC │ Receive RRC │ 100 ms │ Remove UE │
│setup timeout │ │ CONNECTION │ CONNECTION │ │ context │
│ │ │ SETUP │ SETUP COMPLETE │ │ │
├───────────────┼────────────┼────────────────┼────────────────┼──────────┼────────────────┤
│Connection │ eNodeB RRC │ Send RRC │ Never │ 30 ms │ Remove UE │
│rejected │ │ CONNECTION │ │ │ context │
│timeout │ │ REJECT │ │ │ │
└───────────────┴────────────┴────────────────┴────────────────┴──────────┴────────────────┘
RRC connection reconfiguration
Figure Sequence diagram of the RRC Connection Reconfiguration procedure shows how the RRC
Connection Reconfiguration procedure is modeled for the case where MobilityControlInfo is
not provided, i.e., handover is not performed.
[image] Sequence diagram of the RRC Connection Reconfiguration procedure.UNINDENT
Figure Sequence diagram of the RRC Connection Reconfiguration procedure for the handover
case shows how the RRC Connection Reconfiguration procedure is modeled for the case
where MobilityControlInfo is provided, i.e., handover is to be performed. As specified
in [TS36331], After receiving the handover message, the UE attempts to access the target
cell at the first available RACH occasion according to Random Access resource selection
defined in [TS36321]_, i.e. the handover is asynchronous. Consequently, when allocating
a dedicated preamble for the random access in the target cell, E-UTRA shall ensure it is
available from the first RACH occasion the UE may use. Upon successful completion of the
handover, the UE sends a message used to confirm the handover. Note that the random
access procedure in this case is non-contention based, hence in a real LTE system it
differs slightly from the one used in RRC connection established. Also note that the RA
Preamble ID is signalled via the Handover Command included in the X2 Handover Request
ACK message sent from the target eNB to the source eNB; in particular, the preamble is
included in the RACH-ConfigDedicated IE which is part of MobilityControlInfo.
[image] Sequence diagram of the RRC Connection Reconfiguration procedure for the
handover case.UNINDENT
RRC protocol models
As previously anticipated, we provide two different models for the transmission and
reception of RRC messages: Ideal and Real. Each of them is described in one of the
following subsections.
Ideal RRC protocol model
According to this model, implemented in the classes and LteUeRrcProtocolIdeal and
LteEnbRrcProtocolIdeal, all RRC messages and information elements are transmitted between
the eNB and the UE in an ideal fashion, without consuming radio resources and without
errors. From an implementation point of view, this is achieved by passing the RRC data
structure directly between the UE and eNB RRC entities, without involving the lower layers
(PDCP, RLC, MAC, scheduler).
Real RRC protocol model
This model is implemented in the classes LteUeRrcProtocolReal and LteEnbRrcProtocolReal
and aims at modeling the transmission of RRC PDUs as commonly performed in real LTE
systems. In particular:
· for every RRC message being sent, a real RRC PDUs is created following the ASN.1
encoding of RRC PDUs and information elements (IEs) specified in [TS36331]. Some
simplification are made with respect to the IEs included in the PDU, i.e., only those
IEs that are useful for simulation purposes are included. For a detailed list, please
see the IEs defined in lte-rrc-sap.h and compare with [TS36331].
· the encoded RRC PDUs are sent on Signaling Radio Bearers and are subject to the same
transmission modeling used for data communications, thus including scheduling, radio
resource consumption, channel errors, delays, retransmissions, etc.
Signaling Radio Bearer model
We now describe the Signaling Radio Bearer model that is used for the Real RRC protocol
model.
· SRB0 messages (over CCCH):
· RrcConnectionRequest: in real LTE systems, this is an RLC TM SDU sent over
resources specified in the UL Grant in the RAR (not in UL DCIs); the reason is that
C-RNTI is not known yet at this stage. In the simulator, this is modeled as a real
RLC TM RLC PDU whose UL resources are allocated by the sched upon call to
SCHED_DL_RACH_INFO_REQ.
· RrcConnectionSetup: in the simulator this is implemented as in real LTE systems,
i.e., with an RLC TM SDU sent over resources indicated by a regular UL DCI,
allocated with SCHED_DL_RLC_BUFFER_REQ triggered by the RLC TM instance that is
mapped to LCID 0 (the CCCH).
· SRB1 messages (over DCCH):
· All the SRB1 messages modeled in the simulator (e.g., RrcConnectionCompleted) are
implemented as in real LTE systems, i.e., with a real RLC SDU sent over RLC AM
using DL resources allocated via Buffer Status Reports. See the RLC model
documentation for details.
· SRB2 messages (over DCCH):
· According to [TS36331], "SRB1 is for RRC messages (which may include a
piggybacked NAS message) as well as for NAS messages prior to the establishment
of SRB2, all using DCCH logical channel", whereas "SRB2 is for NAS messages,
using DCCH logical channel" and "SRB2 has a lower-priority than SRB1 and is
always configured by E-UTRAN after security activation". Modeling
security-related aspects is not a requirement of the LTE simulation model,
hence we always use SRB1 and never activate SRB2.
ASN.1 encoding of RRC IE's
The messages defined in RRC SAP, common to all Ue/Enb SAP Users/Providers, are transported
in a transparent container to/from a Ue/Enb. The encoding format for the different
Information Elements are specified in [TS36331], using ASN.1 rules in the unaligned
variant. The implementation in Ns3/Lte has been divided in the following classes:
· Asn1Header : Contains the encoding / decoding of basic ASN types
· RrcAsn1Header : Inherits Asn1Header and contains the encoding / decoding of common
IE's defined in [TS36331]
· Rrc specific messages/IEs classes : A class for each of the messages defined in RRC
SAP header
Asn1Header class - Implementation of base ASN.1 types
This class implements the methods to Serialize / Deserialize the ASN.1 types being used in
[TS36331], according to the packed encoding rules in ITU-T X.691. The types considered
are:
· Boolean : a boolean value uses a single bit (1=true, 0=false).
· Integer : a constrained integer (with min and max values defined) uses the minimum
amount of bits to encode its range (max-min+1).
· Bitstring : a bistring will be copied bit by bit to the serialization buffer.
· Octetstring : not being currently used.
· Sequence : the sequence generates a preamble indicating the presence of optional and
default fields. It also adds a bit indicating the presence of extension marker.
· Sequence...Of : the sequence...of type encodes the number of elements of the sequence
as an integer (the subsequent elements will need to be encoded afterwards).
· Choice : indicates which element among the ones in the choice set is being encoded.
· Enumeration : is serialized as an integer indicating which value is used, among the
ones in the enumeration, with the number of elements in the enumeration as upper
bound.
· Null : the null value is not encoded, although its serialization function is defined
to provide a clearer map between specification and implementation.
The class inherits from ns-3 Header, but Deserialize() function is declared pure virtual,
thus inherited classes having to implement it. The reason is that deserialization will
retrieve the elements in RRC messages, each of them containing different information
elements.
Additionally, it has to be noted that the resulting byte length of a specific type/message
can vary, according to the presence of optional fields, and due to the optimized encoding.
Hence, the serialized bits will be processed using PreSerialize() function, saving the
result in m_serializationResult Buffer. As the methods to read/write in a ns3 buffer are
defined in a byte basis, the serialization bits are stored into m_serializationPendingBits
attribute, until the 8 bits are set and can be written to buffer iterator. Finally, when
invoking Serialize(), the contents of the m_serializationResult attribute will be copied
to Buffer::Iterator parameter
RrcAsn1Header : Common IEs
As some Information Elements are being used for several RRC messages, this class
implements the following common IE's:
· SrbToAddModList
· DrbToAddModList
· LogicalChannelConfig
· RadioResourceConfigDedicated
· PhysicalConfigDedicated
· SystemInformationBlockType1
· SystemInformationBlockType2
· RadioResourceConfigCommonSIB
Rrc specific messages/IEs classes
The following RRC SAP have been implemented:
· RrcConnectionRequest
· RrcConnectionSetup
· RrcConnectionSetupCompleted
· RrcConnectionReconfiguration
· RrcConnectionReconfigurationCompleted
· HandoverPreparationInfo
· RrcConnectionReestablishmentRequest
· RrcConnectionReestablishment
· RrcConnectionReestablishmentComplete
· RrcConnectionReestablishmentReject
· RrcConnectionRelease
NAS
The focus of the LTE-EPC model is on the NAS Active state, which corresponds to EMM
Registered, ECM connected, and RRC connected. Because of this, the following
simplifications are made:
· EMM and ECM are not modeled explicitly; instead, the NAS entity at the UE will
interact directy with the MME to perfom actions that are equivalent (with gross
simplifications) to taking the UE to the states EMM Connected and ECM Connected;
· the NAS also takes care of multiplexing uplink data packets coming from the upper
layers into the appropriate EPS bearer by using the Traffic Flow Template classifier
(TftClassifier).
· the NAS does not support PLMN and CSG selection
· the NAS does not support any location update/paging procedure in idle mode
Figure Sequence diagram of the attach procedure shows how the simplified NAS model
implements the attach procedure. Note that both the default and eventual dedicated EPS
bearers are activated as part of this procedure.
[image] Sequence diagram of the attach procedure.UNINDENT
S1
S1-U
The S1-U interface is modeled in a realistic way by encapsulating data packets over
GTP/UDP/IP, as done in real LTE-EPC systems. The corresponding protocol stack is shown in
Figure LTE-EPC data plane protocol stack. As shown in the figure, there are two different
layers of IP networking. The first one is the end-to-end layer, which provides end-to-end
connectivity to the users; this layers involves the UEs, the PGW and the remote host
(including eventual internet routers and hosts in between), but does not involve the eNB.
By default, UEs are assigned a public IPv4 address in the 7.0.0.0/8 network, and the PGW
gets the address 7.0.0.1, which is used by all UEs as the gateway to reach the internet.
The second layer of IP networking is the EPC local area network. This involves all eNB
nodes and the SGW/PGW node. This network is implemented as a set of point-to-point links
which connect each eNB with the SGW/PGW node; thus, the SGW/PGW has a set of
point-to-point devices, each providing connectivity to a different eNB. By default, a
10.x.y.z/30 subnet is assigned to each point-to-point link (a /30 subnet is the smallest
subnet that allows for two distinct host addresses).
As specified by 3GPP, the end-to-end IP communications is tunneled over the local EPC IP
network using GTP/UDP/IP. In the following, we explain how this tunneling is implemented
in the EPC model. The explanation is done by discussing the end-to-end flow of data
packets.
[image] Data flow in the downlink between the internet and the UE.UNINDENT
To begin with, we consider the case of the downlink, which is depicted in Figure Data
flow in the downlink between the internet and the UE. Downlink Ipv4 packets are
generated from a generic remote host, and addressed to one of the UE device. Internet
routing will take care of forwarding the packet to the generic NetDevice of the SGW/PGW
node which is connected to the internet (this is the Gi interface according to 3GPP
terminology). The SGW/PGW has a VirtualNetDevice which is assigned the gateway IP
address of the UE subnet; hence, static routing rules will cause the incoming packet
from the internet to be routed through this VirtualNetDevice. Such device starts the
GTP/UDP/IP tunneling procedure, by forwarding the packet to a dedicated application in
the SGW/PGW node which is called EpcSgwPgwApplication. This application does the
following operations:
1. it determines the eNB node to which the UE is attached, by looking at the IP
destination address (which is the address of the UE);
2. it classifies the packet using Traffic Flow Templates (TFTs) to identify to which
EPS Bearer it belongs. EPS bearers have a one-to-one mapping to S1-U Bearers, so
this operation returns the GTP-U Tunnel Endpoint Identifier (TEID) to which the
packet belongs;
3. it adds the corresponding GTP-U protocol header to the packet;
4. finally, it sends the packet over an UDP socket to the S1-U point-to-point
NetDevice, addressed to the eNB to which the UE is attached.
As a consequence, the end-to-end IP packet with newly added IP, UDP and GTP headers is
sent through one of the S1 links to the eNB, where it is received and delivered locally
(as the destination address of the outmost IP header matches the eNB IP address). The
local delivery process will forward the packet, via an UDP socket, to a dedicated
application called EpcEnbApplication. This application then performs the following
operations:
1. it removes the GTP header and retrieves the TEID which is contained in it;
2. leveraging on the one-to-one mapping between S1-U bearers and Radio Bearers (which
is a 3GPP requirement), it determines the Bearer ID (BID) to which the packet
belongs;
3. it records the BID in a dedicated tag called EpsBearerTag, which is added to the
packet;
4. it forwards the packet to the LteEnbNetDevice of the eNB node via a raw packet
socket
Note that, at this point, the outmost header of the packet is the end-to-end IP header,
since the IP/UDP/GTP headers of the S1 protocol stack have already been stripped. Upon
reception of the packet from the EpcEnbApplication, the LteEnbNetDevice will retrieve the
BID from the EpsBearerTag, and based on the BID will determine the Radio Bearer instance
(and the corresponding PDCP and RLC protocol instances) which are then used to forward the
packet to the UE over the LTE radio interface. Finally, the LteUeNetDevice of the UE will
receive the packet, and delivery it locally to the IP protocol stack, which will in turn
delivery it to the application of the UE, which is the end point of the downlink
communication.
[image] Data flow in the uplink between the UE and the internet.UNINDENT
The case of the uplink is depicted in Figure Data flow in the uplink between the UE and
the internet. Uplink IP packets are generated by a generic application inside the UE,
and forwarded by the local TCP/IP stack to the LteUeNetDevice of the UE. The
LteUeNetDevice then performs the following operations:
1. it classifies the packet using TFTs and determines the Radio Bearer to which the
packet belongs (and the corresponding RBID);
2. it identifies the corresponding PDCP protocol instance, which is the entry point of
the LTE Radio Protocol stack for this packet;
3. it sends the packet to the eNB over the LTE Radio Protocol stack.
The eNB receives the packet via its LteEnbNetDevice. Since there is a single PDCP and RLC
protocol instance for each Radio Bearer, the LteEnbNetDevice is able to determine the BID
of the packet. This BID is then recorded onto an EpsBearerTag, which is added to the
packet. The LteEnbNetDevice then forwards the packet to the EpcEnbApplication via a raw
packet socket.
Upon receiving the packet, the EpcEnbApplication performs the following operations:
1. it retrieves the BID from the EpsBearerTag in the packet;
2. it determines the corresponding EPS Bearer instance and GTP-U TEID by leveraging on
the one-to-one mapping between S1-U bearers and Radio Bearers;
3. it adds a GTP-U header on the packet, including the TEID determined previously;
4. it sends the packet to the SGW/PGW node via the UDP socket connected to the S1-U
point-to-point net device.
At this point, the packet contains the S1-U IP, UDP and GTP headers in addition to the
original end-to-end IP header. When the packet is received by the corresponding S1-U
point-to-point NetDevice of the SGW/PGW node, it is delivered locally (as the destination
address of the outmost IP header matches the address of the point-to-point net device).
The local delivery process will forward the packet to the EpcSgwPgwApplication via the
correponding UDP socket. The EpcSgwPgwApplication then removes the GTP header and forwards
the packet to the VirtualNetDevice. At this point, the outmost header of the packet is the
end-to-end IP header. Hence, if the destination address within this header is a remote
host on the internet, the packet is sent to the internet via the corresponding NetDevice
of the SGW/PGW. In the event that the packet is addressed to another UE, the IP stack of
the SGW/PGW will redirect the packet again to the VirtualNetDevice, and the packet will go
through the dowlink delivery process in order to reach its destination UE.
Note that the EPS Bearer QoS is not enforced on the S1-U links, it is assumed that the
overprovisioning of the link bandwidth is sufficient to meet the QoS requirements of all
bearers.
S1AP
The S1-AP interface provides control plane interaction between the eNB and the MME. In the
simulator, this interface is modeled in an ideal fashion, with direct interaction between
the eNB and the MME objects, without actually implementing the encoding of S1AP messages
and information elements specified in [TS36413] and without actually transmitting any PDU
on any link.
The S1-AP primitives that are modeled are:
· INITIAL UE MESSAGE
· INITIAL CONTEXT SETUP REQUEST
· INITIAL CONTEXT SETUP RESPONSE
· PATH SWITCH REQUEST
· PATH SWITCH REQUEST ACKNOWLEDGE
X2
The X2 interface interconnects two eNBs [TS36420]. From a logical point of view, the X2
interface is a point-to-point interface between the two eNBs. In a real E-UTRAN, the
logical point-to-point interface should be feasible even in the absence of a physical
direct connection between the two eNBs. In the X2 model implemented in the simulator, the
X2 interface is a point-to-point link between the two eNBs. A point-to-point device is
created in both eNBs and the two point-to-point devices are attached to the point-to-point
link.
For a representation of how the X2 interface fits in the overall architecture of the LENA
simulation model, the reader is referred to the figure Overview of the LTE-EPC simulation
model.
The X2 interface implemented in the simulator provides detailed implementation of the
following elementary procedures of the Mobility Management functionality [TS36423]:
· Handover Request procedure
· Handover Request Acknowledgement procedure
· SN Status Transfer procedure
· UE Context Release procedure
These procedures are involved in the X2-based handover. You can find the detailed
description of the handover in section 10.1.2.1 of [TS36300]. We note that the simulator
model currently supports only the seamless handover as defined in Section 2.6.3.1 of
[Sesia2009]; in particular, lossless handover as described in Section 2.6.3.2 of
[Sesia2009] is not supported at the time of this writing.
Figure Sequence diagram of the X2-based handover below shows the interaction of the
entities of the X2 model in the simulator. The shaded labels indicate the moments when the
UE or eNodeB transition to another RRC state.
[image] Sequence diagram of the X2-based handover.UNINDENT
The figure also shows two timers within the handover procedure: the handover leaving
timer is maintained by the source eNodeB, while the handover joining timer by the target
eNodeB. The duration of the timers can be configured in the
HandoverLeavingTimeoutDuration and HandoverJoiningTimeoutDuration attributes of the
respective LteEnbRrc instances. When one of these timers expire, the handover procedure
is considered as failed.
However, there is no proper handling of handover failure in the current version of LTE
module. Users should tune the simulation properly in order to avoid handover failure,
otherwise unexpected behaviour may occur. Please refer to Section
sec-tuning-handover-simulation of the User Documentation for some tips regarding this
matter.
The X2 model is an entity that uses services from:
· the X2 interfaces,
· They are implemented as Sockets on top of the point-to-point devices.
· They are used to send/receive X2 messages through the X2-C and X2-U interfaces
(i.e. the point-to-point device attached to the point-to-point link) towards the
peer eNB.
· the S1 application.
· Currently, it is the EpcEnbApplication.
· It is used to get some information needed for the Elementary Procedures of the X2
messages.
and it provides services to:
· the RRC entity (X2 SAP)
· to send/receive RRC messages. The X2 entity sends the RRC message as a transparent
container in the X2 message. This RRC message is sent to the UE.
Figure Implementation Model of X2 entity and SAPs shows the implentation model of the X2
entity and its relationship with all the other entities and services in the protocol
stack.
[image] Implementation Model of X2 entity and SAPs.UNINDENT
The RRC entity manages the initiation of the handover procedure. This is done in the
Handover Management submodule of the eNB RRC entity. The target eNB may perform some
Admission Control procedures. This is done in the Admission Control submodule.
Initially, this submodule will accept any handover request.
X2 interfaces
The X2 model contains two interfaces:
· the X2-C interface. It is the control interface and it is used to send the X2-AP PDUs
(i.e. the elementary procedures).
· the X2-U interface. It is used to send the bearer data when there is DL forwarding.
Figure X2 interface protocol stacks shows the protocol stacks of the X2-U interface and
X2-C interface modeled in the simulator.
[image] X2 interface protocol stacks.UNINDENT
X2-C
The X2-C interface is the control part of the X2 interface and it is used to send the
X2-AP PDUs (i.e. the elementary procedures).
In the original X2 interface control plane protocol stack, SCTP is used as the transport
protocol but currently, the SCTP protocol is not modeled in the ns-3 simulator and its
implementation is out-of-scope of the project. The UDP protocol is used as the datagram
oriented protocol instead of the SCTP protocol.
X2-U
The X2-U interface is used to send the bearer data when there is DL forwarding during the
execution of the X2-based handover procedure. Similarly to what done for the S1-U
interface, data packets are encapsulated over GTP/UDP/IP when being sent over this
interface. Note that the EPS Bearer QoS is not enforced on the X2-U links, it is assumed
that the overprovisioning of the link bandwidth is sufficient to meet the QoS requirements
of all bearers.
X2 Service Interface
The X2 service interface is used by the RRC entity to send and receive messages of the X2
procedures. It is divided into two parts:
· the EpcX2SapProvider part is provided by the X2 entity and used by the RRC entity and
· the EpcX2SapUser part is provided by the RRC entity and used by the RRC enity.
The primitives that are supported in our X2-C model are described in the following
subsections.
X2-C primitives for handover execution
The following primitives are used for the X2-based handover:
· HANDOVER REQUEST
· HANDOVER REQUEST ACK
· HANDOVER PREPARATION FAILURE
· SN STATUS STRANSFER
· UE CONTEXT RELEASE
all the above primitives are used by the currently implemented RRC model during the
preparation and execution of the handover procedure. Their usage interacts with the RRC
state machine; therefore, they are not meant to be used for code customization, at least
unless it is desired to modify the RRC state machine.
X2-C SON primitives
The following primitives can be used to implement Self-Organized Network (SON)
functionalities:
· LOAD INFORMATION
· RESOURCE STATUS UPDATE
note that the current RRC model does not actually use these primitives, they are included
in the model just to make it possible to develop SON algorithms included in the RRC logic
that make use of them.
As a first example, we show here how the load information primitive can be used. We assume
that the LteEnbRrc has been modified to include the following new member variables:
std::vector<EpcX2Sap::UlInterferenceOverloadIndicationItem>
m_currentUlInterferenceOverloadIndicationList;
std::vector <EpcX2Sap::UlHighInterferenceInformationItem>
m_currentUlHighInterferenceInformationList;
EpcX2Sap::RelativeNarrowbandTxBand m_currentRelativeNarrowbandTxBand;
for a detailed description of the type of these variables, we suggest to consult the file
epc-x2-sap.h, the corresponding doxygen documentation, and the references therein to the
relevant sections of 3GPP TS 36.423. Now, assume that at run time these variables have
been set to meaningful values following the specifications just mentioned. Then, you can
add the following code in the LteEnbRrc class implementation in order to send a load
information primitive:
EpcX2Sap::CellInformationItem cii;
cii.sourceCellId = m_cellId;
cii.ulInterferenceOverloadIndicationList = m_currentUlInterferenceOverloadIndicationList;
cii.ulHighInterferenceInformationList = m_currentUlHighInterferenceInformationList;
cii.relativeNarrowbandTxBand = m_currentRelativeNarrowbandTxBand;
EpcX2Sap::LoadInformationParams params;
params.targetCellId = cellId;
params.cellInformationList.push_back (cii);
m_x2SapProvider->SendLoadInformation (params);
The above code allows the source eNB to send the message. The method
LteEnbRrc::DoRecvLoadInformation will be called when the target eNB receives the message.
The desired processing of the load information should therefore be implemented within that
method.
In the following second example we show how the resource status update primitive is used.
We assume that the LteEnbRrc has been modified to include the following new member
variable:
EpcX2Sap::CellMeasurementResultItem m_cmri;
similarly to before, we refer to epc-x2-sap.h and the references therein for detailed
information about this variable type. Again, we assume that the variable has been already
set to a meaningful value. Then, you can add the following code in order to send a
resource status update:
EpcX2Sap::ResourceStatusUpdateParams params;
params.targetCellId = cellId;
params.cellMeasurementResultList.push_back (m_cmri);
m_x2SapProvider->SendResourceStatusUpdate (params);
The method eEnbRrc::DoRecvResourceStatusUpdate will be called when the target eNB receives
the resource status update message. The desired processing of this message should
therefore be implemented within that method.
Finally, we note that the setting and processing of the appropriate values for the
variable passed to the above described primitives is deemed to be specific of the SON
algorithm being implemented, and hence is not covered by this documentation.
Unsupported primitives
Mobility Robustness Optimization primitives such as Radio Link Failure indication and
Handover Report are not supported at this stage.
S11
The S11 interface provides control plane interaction between the SGW and the MME using the
GTPv2-C protocol specified in [TS29274]. In the simulator, this interface is modeled in an
ideal fashion, with direct interaction between the SGW and the MME objects, without
actually implementing the encoding of the messages and without actually transmitting any
PDU on any link.
The S11 primitives that are modeled are:
· CREATE SESSION REQUEST
· CREATE SESSION RESPONSE
· MODIFY BEARER REQUEST
· MODIFY BEARER RESPONSE
Of these primitives, the first two are used upon initial UE attachment for the
establishment of the S1-U bearers; the other two are used during handover to switch the
S1-U bearers from the source eNB to the target eNB as a consequence of the reception by
the MME of a PATH SWITCH REQUEST S1-AP message.
Power Control
This section describes the ns-3 implementation of Downlink and Uplink Power Control.
Downlink Power Control
Since some of Frequency Reuse Algorithms require Downlink Power Control, this feature was
also implemented in ns-3.
[image] Sequence diagram of Downlink Power Control.UNINDENT
Figure Sequence diagram of Downlink Power Control shows the sequence diagram of setting
downlink P_A value for UE, highlighting the interactions between the RRC and the other
entities. FR algorithm triggers RRC to change P_A values for UE. Then RRC starts
RrcConnectionReconfiguration function to inform UE about new configuration. After
successful RrcConnectionReconfiguration, RRC can set P_A value for UE by calling
function SetPa from CphySap, value is saved in new map m_paMap which contain P_A values
for each UE served by eNb.
When LteEnbPhy starts new subframe, DCI control messages are processed to get vector of
used RBs. Now also GeneratePowerAllocationMap(uint16_t rnti, int rbId) function is also
called. This function check P_A value for UE, generate power for each RB and store it in
m_dlPowerAllocationMap. Then this map is used by
CreateTxPowerSpectralDensityWithPowerAllocation function to create Ptr<SpectrumValue>
txPsd.
PdschConfigDedicated (TS 36.331, 6.3.2 PDSCH-Config) was added in
LteRrcSap::PhysicalConfigDedicated struct, which is used in RrcConnectionReconfiguration
process.
Uplink Power Control
Uplink power control controls the transmit power of the different uplink physical
channels. This functionality is described in 3GPP TS 36.213 section 5.
Uplink Power Control is enabled by default, and can be disabled by attribute system:
Config::SetDefault ("ns3::LteUePhy::EnableUplinkPowerControl", BooleanValue (false));
Two Uplink Power Control mechanisms are implemented:
· Open Loop Uplink Power Control: the UE transmission power depends on estimation of
the downlink path-loss and channel configuration
· Closed Loop Uplink Power Control: as in Open Loop, in addition eNB can control the UE
transmission power by means of explicit Transmit Power Control TPC commands
transmitted in the downlink.
To switch between these two mechanism types, one should change parameter:
Config::SetDefault ("ns3::LteUePowerControl::ClosedLoop", BooleanValue (true));
By default, Closed Loop Power Control is enabled.
Two modes of Closed Loop Uplink Power Control are available:
· Absolute mode: TxPower is computed with absolute TPC values
· Accumulative mode: TxPower is computed with accumulated TPC values
To switch between these two modes, one should change parameter:
Config::SetDefault ("ns3::LteUePowerControl::AccumulationEnabled", BooleanValue (true));
By default, Accumulation Mode is enabled and TPC commands in DL-DCI are set by all
schedulers to 1, what is mapped to value of 0 in Accumulation Mode.
Uplink Power Control for PUSCH
The setting of the UE Transmit power for a Physical Uplink Shared Channel (PUSCH)
transmission is defined as follows:
· If the UE transmits PUSCH without a simultaneous PUCCH for the serving cell c, then
the UE transmit power P_{PUSCH,c}(i) for PUSCH transmission in subframe i for the
serving cell c is given by:
· If the UE transmits PUSCH simultaneous with PUCCH for the serving cell c, then the UE
transmit power P_{PUSCH,c}(i) for the PUSCH transmission in subframe i for the
serving cell c is given by:
Since Uplink Power Control for PUCCH is not implemented, this case is not implemented
as well.
· If the UE is not transmitting PUSCH for the serving cell c, for the accumulation of
TPC command received with DCI format 3/3A for PUSCH, the UE shall assume that the UE
transmit power P_{PUSCH,c}(i) for the PUSCH transmission in subframe i for the
serving cell c is computed by
where:
· P_{CMAX,c}(i) is the configured UE transmit power defined in 3GPP 36.101. Table
6.2.2-1 in subframe i for serving cell c and {P}_{CMAX,c}(i) is the linear value
of P_{CMAX,c}(i). Default value for P_{CMAX,c}(i) is 23 dBm
· M_{PUSCH,c}(i) is the bandwidth of the PUSCH resource assignment expressed in
number of resource blocks valid for subframe i and serving cell c .
· P_{O_PUSCH,c}(j) is a parameter composed of the sum of a component
P_{O_NOMINAL_PUSCH,c}(j) provided from higher layers for j={0,1} and a component
P_{O_UE_PUSCH,c}(j) provided by higher layers for j={0,1} for serving cell c.
SIB2 message needs to be extended to carry these two components, but currently
they can be set via attribute system:
Config::SetDefault ("ns3::LteUePowerControl::PoNominalPusch", IntegerValue (-90));
Config::SetDefault ("ns3::LteUePowerControl::PoUePusch", IntegerValue (7));
· lpha_{c} (j) is a 3-bit parameter provided by higher layers for ightinForelj=2,
For j=0,1, lpha_c in t 0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1
lpha_{c} (j) = 1. This parameter is configurable by attribute system:
Config::SetDefault ("ns3::LteUePowerControl::Alpha", DoubleValue (0.8));
· PL_{c} is the downlink pathloss estimate calculated in the UE for serving cell c
in dB and PL_{c} = referenceSignalPower – higher layer filtered RSRP, where
referenceSignalPower is provided by higher layers and RSRP. referenceSignalPower
is provided in SIB2 message
· and cond case is implemented.
· f_{c}(i) is component of Closed Loop Power Control. It is the current PUSCH power
control adjustment state for serving cell c.
If Accumulation Mode is enabled f_{c}(i) is given by:
where: elta_{PUSCH,c} is a correction value, also referred to as a TPC command
and is included in PDCCH with DCI; elta_{PUSCH,c}(i - K_{PUSCH}) was signalled on
PDCCH/EPDCCH with DCI for serving cell c on subframe (i - K_{PUSCH}); K_{PUSCH} =
4 for FDD.
If UE has reached P_{CMAX,c}(i) for serving cell c, positive TPC commands for
serving cell c are not be accumulated. If UE has reached minimum power, negative
TPC commands are not be accumulated. Minimum UE power is defined in TS36.101
section 6.2.3. Default value is -40 dBm.
If Accumulation Mode is not enabled f_{c}(i) is given by:
where: elta_{PUSCH,c} is a correction value, also referred to as a TPC command
and is included in PDCCH with DCI; elta_{PUSCH,c}(i - K_{PUSCH}) was signalled on
PDCCH/EPDCCH with DCI for serving cell c on subframe (i - K_{PUSCH}); K_{PUSCH} =
4 for FDD.
Mapping of TPC Command Field in DCI format 0/3/4 to absolute and accumulated
elta_{PUSCH,c} values is defined in TS36.231 section 5.1.1.1 Table 5.1.1.1-2
Uplink Power Control for PUCCH
Since all uplink control messages are an ideal messages and do not consume any radio
resources, Uplink Power Control for PUCCH is not needed and it is not implemented.
Uplink Power Control for SRS
The setting of the UE Transmit power P_{SRS} for the SRS transmitted on subframe i for
serving cell c is defined by
where:
· P_{CMAX,c}(i) is the configured UE transmit power defined in 3GPP 36.101. Table
6.2.2-1. Default value for P_{CMAX,c}(i) is 23 dBm
· P_{SRS_OFFSET,c}(m) is semi-statically configured by higher layers for m=0,1 for
serving cell c . For SRS transmission given trigger type 0 then m=0,1 and for SRS
transmission given trigger type 1 then m=1. For K_{s} = 0 P_Srs_Offset_Value is
computed with equation:
This parameter is configurable by attribute system:
Config::SetDefault ("ns3::LteUePowerControl::PsrsOffset", IntegerValue (7));
· M_{SRS,c} is the bandwidth of the SRS transmission in subframe i for serving cell
c expressed in number of resource blocks. In current implementation SRS is sent
over entire UL bandwidth.
· f_{c}(i) is the current PUSCH power control adjustment state for serving cell c,
as defined in Uplink Power Control for PUSCH
· P_{O_PUSCH,c}(j) and lpha_{c}(j) are parameters as defined in Uplink Power
Control for PUSCH, where j = 1 .
Fractional Frequency Reuse
Overview
This section describes the ns-3 support for Fractional Frequency Reuse algorithms. All
implemented algorithms are described in [ASHamza2013]. Currently 7 FR algorithms are
implemented:
· ns3::LteFrNoOpAlgorithm
· ns3::LteFrHardAlgorithm
· ns3::LteFrStrictAlgorithm
· ns3::LteFrSoftAlgorithm
· ns3::LteFfrSoftAlgorithm
· ns3::LteFfrEnhancedAlgorithm
· ns3::LteFfrDistributedAlgorithm
New LteFfrAlgorithm class was created and it is a abstract class for Frequency Reuse
algorithms implementation. Also, two new SAPs between FR-Scheduler and FR-RRC were added.
[image] Sequence diagram of Scheduling with FR algorithm.UNINDENT
Figure Sequence diagram of Scheduling with FR algorithm shows the sequence diagram of
scheduling process with FR algorithm. In the beginning of scheduling process, scheduler
asks FR entity for avaiable RBGs. According to implementation FR returns all RBGs
available in cell or filter them based on its policy. Then when trying to assign some
RBG to UE, scheduler asks FR entity if this RBG is allowed for this UE. When FR returns
true, scheduler can assign this RBG to this UE, if not scheduler is checking another RBG
for this UE. Again, FR response depends on implementation and policy applied to UE.
Supported FR algorithms
No Frequency Reuse
The NoOp FR algorithm (LteFrNoOpAlgorithm class) is implementation of Full Frequency Reuse
scheme, that means no frequency partitioning is performed between eNBs of the same network
(frequency reuse factor, FRF equals 1). eNBs uses entire system bandwidth and transmit
with uniform power over all RBGs. It is the simplest scheme and is the basic way of
operating an LTE network. This scheme allows for achieving the high peak data rate. But
from the other hand, due to heavy interference levels from neighbouring cells, cell-edge
users performance is greatly limited.
Figure Full Frequency Reuse scheme below presents frequency and power plan for Full
Frequency Reuse scheme.
[image] Full Frequency Reuse scheme.UNINDENT
In ns-3, the NoOp FR algorithm always allows scheduler to use full bandwidth and allows
all UEs to use any RBG. It simply does nothing new (i.e. it does not limit eNB
bandwidth, FR algorithm is disabled), it is the simplest implementation of FrAlgorithm
class and is installed in eNb by default.
Hard Frequency Reuse
The Hard Frequency Reuse algorithm provides the simplest scheme which allows to reduce
inter-cell interference level. In this scheme whole frequency bandwidth is divided into
few (typically 3, 4, or 7) disjoint sub-bands. Adjacent eNBs are allocated with different
sub-band. Frequency reuse factor equals the number of sub-bands. This scheme allows to
significanlty reduce ICI at the cell edge, so the performance of cell-users is improved.
But due to the fact, that each eNB uses only one part of whole bandwidth, peak data rate
level is also reduced by the factor equal to the reuse factor.
Figure Hard Frequency Reuse scheme below presents frequency and power plan for Hard
Frequency Reuse scheme.
[image] Hard Frequency Reuse scheme.UNINDENT
In our implementation, the Hard FR algorithm has only vector of RBGs available for eNB
and pass it to MAC Scheduler during scheduling functions. When scheduler ask, if RBG is
allowed for specific UE it allways return true.
Strict Frequency Reuse
Strict Frequency Reuse scheme is combination of Full and Hard Frequency Reuse schemes. It
consists of dividing the system bandwidth into two parts which will have different
frequency reuse. One common sub-band of the system bandwidth is used in each cell interior
(frequency reuse-1), while the other part of the bandwidth is divided among the
neighboring eNBs as in hard frequency reuse (frequency reuse-N, N>1), in order to create
one sub-band with a low inter-cell interference level in each sector. Center UEs will be
granted with the fully-reused frequency chunks, while cell-edge UEs with ortogonal chunks.
It means that interior UEs from one cell do not share any spectrum with edge UEs from
second cell, which reduces interference for both. As can be noticed, Strict FR requires a
total of N + 1 sub-bands, and allows to achieve RFR in the middle between 1 and 3.
Figure Strict Frequency Reuse scheme below presents frequency and power plan for Strict
Frequency Reuse scheme with a cell-edge reuse factor of N = 3.
[image] Strict Frequency Reuse scheme.UNINDENT
In our implementation, Strict FR algorithm has two maps, one for each sub-band. If UE
can be served within private sub-band, its RNTI is added to m_privateSubBandUe map. If
UE can be served within common sub-band, its RNTI is added to m_commonSubBandUe map.
Strict FR algorithm needs to decide within which sub-band UE should be served. It uses
UE measurements provided by RRB and compare them with signal quality threshold (this
parameter can be easily tuned by attribute mechanism). Threshold has influence on
interior to cell radius ratio.
Soft Frequency Reuse
In Soft Frequency Reuse (SFR) scheme each eNb transmits over the entire system bandwidth,
but there are two sub-bands, within UEs are served with different power level. Since
cell-center UEs share the bandwidth with neighboring cells, they usually transmit at lower
power level than the cell-edge UEs. SFR is more bandwidth efficient than Strict FR,
because it uses entire system bandwidth, but it also results in more interference to both
cell interior and edge users.
There are two possible versions of SFR scheme:
· In first version, the sub-band dedicated for the cell-edge UEs may also be used by
the cell-center UEs but with reduced power level and only if it is not occupied by
the cell-edge UEs. Cell-center sub-band is available to the centre UEs only. Figure
Soft Frequency Reuse scheme version 1 below presents frequency and power plan for
this version of Soft Frequency Reuse scheme.
[image] Soft Frequency Reuse scheme version 1.UNINDENT
· In second version, cell-center UEs do not have access to cell-edge sub-band. In
this way, each cell can use the whole system bandwidth while reducing the
interference to the neighbors cells. From the other hand, lower ICI level at the
cell-edge is achieved at the expense of lower spectrum utilization. Figure Soft
Frequency Reuse scheme version 2 below presents frequency and power plan for this
version of Soft Frequency Reuse scheme.
[image] Soft Frequency Reuse scheme version 2.UNINDENT
SFR algorithm maintain two maps. If UE should be served with lower power level, its
RNTI is added to m_lowPowerSubBandUe map. If UE should be served with higher power
level, its RNTI is added to m_highPowerSubBandUe map. To decide with which power level
UE should be served SFR algorithm utilize UE measurements, and compares them to
threshold. Signal quality threshold and PdschConfigDedicated (i.e. P_A value) for inner
and outer area can be configured by attributes system. SFR utilizes Downlink Power
Control described here.
Soft Fractional Frequency Reuse
Soft Fractional Frequency Reuse (SFFR) is an combination of Strict and Soft Frequency
Reuse schemes. While Strict FR do not use the subbands allocated for outer region in the
adjacent cells, soft FFR uses these subbands for the inner UEs with low transmit power. As
a result, the SFFR, like SFR, use the subband with high transmit power level and with low
transmit power level. Unlike the Soft FR and like Strict FR, the Soft FFR uses the common
sub-band which can enhance the throughput of the inner users.
Figure Soft Fractional Fractional Frequency Reuse scheme below presents frequency and
power plan for Soft Fractional Frequency Reuse.
[image] Soft Fractional Fractional Frequency Reuse scheme.UNINDENT
Enhanced Fractional Frequency Reuse
Enhanced Fractional Frequency Reuse (EFFR) described in [ZXie2009] defines 3 cell-types
for directly neighboring cells in a cellular system, and reserves for each cell-type a
part of the whole frequency band named Primary Segment, which among different type cells
should be orthogonal. The remaining subchannels constitute the Secondary Segment. The
Primary Segment of a cell-type is at the same time a part of the Secondary Segments
belonging to the other two cell-types. Each cell can occupy all subchannels of its Primary
Segment at will, whereas only a part of subchannels in the Secondary Segment can be used
by this cell in an interference-aware manner.The Primary Segment of each cell is divided
into a reuse-3 part and reuse-1 part. The reuse-1 part can be reused by all types of cells
in the system, whereas reuse-3 part can only be exclusively reused by other same type
cells( i.e. the reuse-3 subchannels cannot be reused by directly neighboring cells). On
the Secondary Segment cell acts as a guest, and occupying secondary subchannels is
actually reuse the primary subchannels belonging to the directly neighboring cells, thus
reuse on the Secondary Segment by each cell should conform to two rules:
· monitor before use
· resource reuse based on SINR estimation
Each cell listens on every secondary subchannel all the time. And before occupation, it
makes SINR evaluation according to the gathered channel quality information (CQI) and
chooses resources with best estimation values for reuse. If CQI value for RBG is above
configured threshold for some user, transmission for this user can be performed using this
RBG.
In [ZXie2009] scheduling process is described, it consist of three steps and two
scheduling polices. Since none of currently implemented schedulers allow for this
behaviour, some simplification were applied. In our implementation reuse-1 subchannels can
be used only by cell center users. Reuse-3 subchannels can be used by edge users, and only
if there is no edge user, transmission for cell center users can be served in reuse-3
subchannels.
Figure Enhanced Fractional Fractional Frequency Reuse scheme below presents frequency and
power plan for Enhanced Fractional Frequency Reuse.
[image] Enhanced Fractional Fractional Frequency Reuse scheme.UNINDENT
Distributed Fractional Frequency Reuse
This Distributed Fractional Frequency Reuse Algorithm was presented in [DKimura2012]. It
automatically optimizes cell-edge sub-bands by focusing on user distribution (in
particular, receive-power distribution). This algorithm adaptively selects RBs for
cell-edge sub-band on basis of coordination information from adjecent cells and notifies
the base stations of the adjacent cells, which RBs it selected to use in edge sub-band.
The base station of each cell uses the received information and the following equation to
compute cell-edge-band metric A_{k} for each RB.
where J is a set of neighbor cells, X_{j,k}=0,1 is the RNTP from the j-th neighbor cell.
It takes a value of 1 when the k-th RB in the j-th neighbor cell is used as a cell-edge
sub-band and 0 otherwise. The symbol w_{j} denotes weight with respect to adjacent cell j,
that is, the number of users for which the difference between the power of the signal
received from the serving cell i and the power of the signal received from the adjacent
cell j is less than a threshold value (i.e., the number of users near the cell edge in the
service cell). A large received power difference means that cell-edge users in the i-th
cell suffer strong interference from the j-th cell.
The RB for which metric A_{k} is smallest is considered to be least affected by
interference from another cell. Serving cell selects a configured number of RBs as
cell-edge sub-band in ascending order of A_{k}. As a result, the RBs in which a small
number of cell-edge users receive high interference from adjacent base stations are
selected.
The updated RNTP is then sent to all the neighbor cells. In order to avoid the meaningless
oscillation of cell-edge-band selection, a base station ignores an RNTP from another base
station that has larger cell ID than the base station.
Repeating this process across all cells enables the allocation of RBs to cell-edge areas
to be optimized over the system and to be adjusted with changes in user distribution.
Figure Sequence diagram of Distributed Frequency Reuse Scheme below presents sequence
diagram of Distributed Fractional Frequency Reuse Scheme.
[image] Sequence diagram of Distributed Frequency Reuse Scheme.UNINDENT
Helpers
Two helper objects are use to setup simulations and configure the various components.
These objects are:
· LteHelper, which takes care of the configuration of the LTE radio access network, as
well as of coordinating the setup and release of EPS bearers. The LteHelper class
provides both the API definition and its implementation.
· EpcHelper, which takes care of the configuration of the Evolved Packet Core. The
EpcHelper class is an abstract base class which only provides the API definition; the
implementation is delegated to child classes in order to allow for different EPC
network models.
It is possible to create a simple LTE-only simulations by using LteHelper alone, or to
create complete LTE-EPC simulations by using both LteHelper and EpcHelper. When both
helpers are used, they interact in a master-slave fashion, with LteHelper being the Master
that interacts directly with the user program, and EpcHelper working "under the hood" to
configure the EPC upon explicit methods called by LteHelper. The exact interactions are
displayed in the Figure Sequence diagram of the interaction between LteHelper and
EpcHelper.
[image] Sequence diagram of the interaction between LteHelper and EpcHelper.UNINDENT
User Documentation
Background
We assume the reader is already familiar with how to use the ns-3 simulator to run generic
simulation programs. If this is not the case, we strongly recommend the reader to consult
[ns3tutorial].
Usage Overview
The ns-3 LTE model is a software library that allows the simulation of LTE networks,
optionally including the Evolved Packet Core (EPC). The process of performing such
simulations typically involves the following steps:
1. Define the scenario to be simulated
2. Write a simulation program that recreates the desired scenario
topology/architecture. This is done accessing the ns-3 LTE model library using the
ns3::LteHelper API defined in src/lte/helper/lte-helper.h.
3. Specify configuration parameters of the objects that are being used for the
simulation. This can be done using input files (via the ns3::ConfigStore) or
directly within the simulation program.
4. Configure the desired output to be produced by the simulator
5. Run the simulation.
All these aspects will be explained in the following sections by means of practical
examples.
Basic simulation program
Here is the minimal simulation program that is needed to do an LTE-only simulation
(without EPC).
1. Initial boilerplate:
#include <ns3/core-module.h>
#include <ns3/network-module.h>
#include <ns3/mobility-module.h>
#include <ns3/lte-module.h>
using namespace ns3;
int main (int argc, char *argv[])
{
// the rest of the simulation program follows
2. Create an LteHelper object:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
This will instantiate some common objects (e.g., the Channel object) and provide the
methods to add eNBs and UEs and configure them.
3. Create Node objects for the eNB(s) and the UEs:
NodeContainer enbNodes;
enbNodes.Create (1);
NodeContainer ueNodes;
ueNodes.Create (2);
Note that the above Node instances at this point still don't have an LTE protocol
stack installed; they're just empty nodes.
4. Configure the Mobility model for all the nodes:
MobilityHelper mobility;
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
mobility.Install (enbNodes);
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
mobility.Install (ueNodes);
The above will place all nodes at the coordinates (0,0,0). Please refer to the
documentation of the ns-3 mobility model for how to set your own position or configure
node movement.
5. Install an LTE protocol stack on the eNB(s):
NetDeviceContainer enbDevs;
enbDevs = lteHelper->InstallEnbDevice (enbNodes);
6. Install an LTE protocol stack on the UEs:
NetDeviceContainer ueDevs;
ueDevs = lteHelper->InstallUeDevice (ueNodes);
7. Attach the UEs to an eNB. This will configure each UE according to the eNB
configuration, and create an RRC connection between them:
lteHelper->Attach (ueDevs, enbDevs.Get (0));
8. Activate a data radio bearer between each UE and the eNB it is attached to:
enum EpsBearer::Qci q = EpsBearer::GBR_CONV_VOICE;
EpsBearer bearer (q);
lteHelper->ActivateDataRadioBearer (ueDevs, bearer);
this method will also activate two saturation traffic generators for that bearer, one
in uplink and one in downlink.
9. Set the stop time:
Simulator::Stop (Seconds (0.005));
This is needed otherwise the simulation will last forever, because (among others) the
start-of-subframe event is scheduled repeatedly, and the ns-3 simulator scheduler will
hence never run out of events.
10. Run the simulation:
Simulator::Run ();
11. Cleanup and exit:
Simulator::Destroy ();
return 0;
}
For how to compile and run simulation programs, please refer to [ns3tutorial].
Configuration of LTE model parameters
All the relevant LTE model parameters are managed through the ns-3 attribute system.
Please refer to the [ns3tutorial] and [ns3manual] for detailed information on all the
possible methods to do it (environmental variables, C++ API, GtkConfigStore...).
In the following, we just briefly summarize how to do it using input files together with
the ns-3 ConfigStore. First of all, you need to put the following in your simulation
program, right after main () starts:
CommandLine cmd;
cmd.Parse (argc, argv);
ConfigStore inputConfig;
inputConfig.ConfigureDefaults ();
// parse again so you can override default values from the command line
cmd.Parse (argc, argv);
for the above to work, make sure you also #include "ns3/config-store.h". Now create a
text file named (for example) input-defaults.txt specifying the new default values that
you want to use for some attributes:
default ns3::LteHelper::Scheduler "ns3::PfFfMacScheduler"
default ns3::LteHelper::PathlossModel "ns3::FriisSpectrumPropagationLossModel"
default ns3::LteEnbNetDevice::UlBandwidth "25"
default ns3::LteEnbNetDevice::DlBandwidth "25"
default ns3::LteEnbNetDevice::DlEarfcn "100"
default ns3::LteEnbNetDevice::UlEarfcn "18100"
default ns3::LteUePhy::TxPower "10"
default ns3::LteUePhy::NoiseFigure "9"
default ns3::LteEnbPhy::TxPower "30"
default ns3::LteEnbPhy::NoiseFigure "5"
Supposing your simulation program is called src/lte/examples/lte-sim-with-input, you can
now pass these settings to the simulation program in the following way:
./waf --command-template="%s --ns3::ConfigStore::Filename=input-defaults.txt --ns3::ConfigStore::Mode=Load --ns3::ConfigStore::FileFormat=RawText" --run src/lte/examples/lte-sim-with-input
Furthermore, you can generate a template input file with the following command:
./waf --command-template="%s --ns3::ConfigStore::Filename=input-defaults.txt --ns3::ConfigStore::Mode=Save --ns3::ConfigStore::FileFormat=RawText" --run src/lte/examples/lte-sim-with-input
note that the above will put in the file input-defaults.txt all the default values that
are registered in your particular build of the simulator, including lots of non-LTE
attributes.
Configure LTE MAC Scheduler
There are several types of LTE MAC scheduler user can choose here. User can use following
codes to define scheduler type:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetSchedulerType ("ns3::FdMtFfMacScheduler"); // FD-MT scheduler
lteHelper->SetSchedulerType ("ns3::TdMtFfMacScheduler"); // TD-MT scheduler
lteHelper->SetSchedulerType ("ns3::TtaFfMacScheduler"); // TTA scheduler
lteHelper->SetSchedulerType ("ns3::FdBetFfMacScheduler"); // FD-BET scheduler
lteHelper->SetSchedulerType ("ns3::TdBetFfMacScheduler"); // TD-BET scheduler
lteHelper->SetSchedulerType ("ns3::FdTbfqFfMacScheduler"); // FD-TBFQ scheduler
lteHelper->SetSchedulerType ("ns3::TdTbfqFfMacScheduler"); // TD-TBFQ scheduler
lteHelper->SetSchedulerType ("ns3::PssFfMacScheduler"); //PSS scheduler
TBFQ and PSS have more parameters than other schedulers. Users can define those parameters
in following way:
* TBFQ scheduler::
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetSchedulerAttribute("DebtLimit", IntegerValue(yourvalue)); // default value -625000 bytes (-5Mb)
lteHelper->SetSchedulerAttribute("CreditLimit", UintegerValue(yourvalue)); // default value 625000 bytes (5Mb)
lteHelper->SetSchedulerAttribute("TokenPoolSize", UintegerValue(yourvalue)); // default value 1 byte
lteHelper->SetSchedulerAttribute("CreditableThreshold", UintegerValue(yourvalue)); // default value 0
* PSS scheduler::
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetSchedulerAttribute("nMux", UIntegerValue(yourvalue)); // the maximum number of UE selected by TD scheduler
lteHelper->SetSchedulerAttribute("PssFdSchedulerType", StringValue("CoItA")); // PF scheduler type in PSS
In TBFQ, default values of debt limit and credit limit are set to -5Mb and 5Mb
respectively based on paper [FABokhari2009]. Current implementation does not consider
credit threshold (C = 0). In PSS, if user does not define nMux, PSS will set this value to
half of total UE. The default FD scheduler is PFsch.
In addition, token generation rate in TBFQ and target bit rate in PSS need to be
configured by Guarantee Bit Rate (GBR) or Maximum Bit Rate (MBR) in epc bearer QoS
parameters. Users can use following codes to define GBR and MBR in both downlink and
uplink:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
enum EpsBearer::Qci q = EpsBearer::yourvalue; // define Qci type
GbrQosInformation qos;
qos.gbrDl = yourvalue; // Downlink GBR
qos.gbrUl = yourvalue; // Uplink GBR
qos.mbrDl = yourvalue; // Downlink MBR
qos.mbrUl = yourvalue; // Uplink MBR
EpsBearer bearer (q, qos);
lteHelper->ActivateDedicatedEpsBearer (ueDevs, bearer, EpcTft::Default ());
In PSS, TBR is obtained from GBR in bearer level QoS parameters. In TBFQ, token generation
rate is obtained from the MBR setting in bearer level QoS parameters, which therefore
needs to be configured consistently. For constant bit rate (CBR) traffic, it is suggested
to set MBR to GBR. For variance bit rate (VBR) traffic, it is suggested to set MBR k times
larger than GBR in order to cover the peak traffic rate. In current implementation, k is
set to three based on paper [FABokhari2009]. In addition, current version of TBFQ does not
consider RLC header and PDCP header length in MBR and GBR. Another parameter in TBFQ is
packet arrival rate. This parameter is calculated within scheduler and equals to the past
average throughput which is used in PF scheduler.
Many useful attributes of the LTE-EPC model will be described in the following
subsections. Still, there are many attributes which are not explicitly mentioned in the
design or user documentation, but which are clearly documented using the ns-3 attribute
system. You can easily print a list of the attributes of a given object together with
their description and default value passing --PrintAttributes= to a simulation program,
like this:
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::LteHelper"
You can try also with other LTE and EPC objects, like this:
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::LteEnbNetDevice"
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::LteEnbMac"
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::LteEnbPhy"
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::LteUePhy"
./waf --run lena-simple --command-template="%s --PrintAttributes=ns3::PointToPointEpcHelper"
Simulation Output
The ns-3 LTE model currently supports the output to file of PHY, MAC, RLC and PDCP level
Key Performance Indicators (KPIs). You can enable it in the following way:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
// configure all the simulation scenario here...
lteHelper->EnablePhyTraces ();
lteHelper->EnableMacTraces ();
lteHelper->EnableRlcTraces ();
lteHelper->EnablePdcpTraces ();
Simulator::Run ();
RLC and PDCP KPIs are calculated over a time interval and stored on ASCII files, two for
RLC KPIs and two for PDCP KPIs, in each case one for uplink and one for downlink. The time
interval duration can be controlled using the attribute
ns3::RadioBearerStatsCalculator::EpochDuration.
The columns of the RLC KPI files is the following (the same for uplink and downlink):
1. start time of measurement interval in seconds since the start of simulation
2. end time of measurement interval in seconds since the start of simulation
3. Cell ID
4. unique UE ID (IMSI)
5. cell-specific UE ID (RNTI)
6. Logical Channel ID
7. Number of transmitted RLC PDUs
8. Total bytes transmitted.
9. Number of received RLC PDUs
10. Total bytes received
11. Average RLC PDU delay in seconds
12. Standard deviation of the RLC PDU delay
13. Minimum value of the RLC PDU delay
14. Maximum value of the RLC PDU delay
15. Average RLC PDU size, in bytes
16. Standard deviation of the RLC PDU size
17. Minimum RLC PDU size
18. Maximum RLC PDU size
Similarly, the columns of the PDCP KPI files is the following (again, the same for uplink
and downlink):
1. start time of measurement interval in seconds since the start of simulation
2. end time of measurement interval in seconds since the start of simulation
3. Cell ID
4. unique UE ID (IMSI)
5. cell-specific UE ID (RNTI)
6. Logical Channel ID
7. Number of transmitted PDCP PDUs
8. Total bytes transmitted.
9. Number of received PDCP PDUs
10. Total bytes received
11. Average PDCP PDU delay in seconds
12. Standard deviation of the PDCP PDU delay
13. Minimum value of the PDCP PDU delay
14. Maximum value of the PDCP PDU delay
15. Average PDCP PDU size, in bytes
16. Standard deviation of the PDCP PDU size
17. Minimum PDCP PDU size
18. Maximum PDCP PDU size
MAC KPIs are basically a trace of the resource allocation reported by the scheduler upon
the start of every subframe. They are stored in ASCII files. For downlink MAC KPIs the
format is the following:
1. Simulation time in seconds at which the allocation is indicated by the scheduler
2. Cell ID
3. unique UE ID (IMSI)
4. Frame number
5. Subframe number
6. cell-specific UE ID (RNTI)
7. MCS of TB 1
8. size of TB 1
9. MCS of TB 2 (0 if not present)
10. size of TB 2 (0 if not present)
while for uplink MAC KPIs the format is:
1. Simulation time in seconds at which the allocation is indicated by the scheduler
2. Cell ID
3. unique UE ID (IMSI)
4. Frame number
5. Subframe number
6. cell-specific UE ID (RNTI)
7. MCS of TB
8. size of TB
The names of the files used for MAC KPI output can be customized via the ns-3 attributes
ns3::MacStatsCalculator::DlOutputFilename and ns3::MacStatsCalculator::UlOutputFilename.
PHY KPIs are distributed in seven different files, configurable through the attributes
1. ns3::PhyStatsCalculator::DlRsrpSinrFilename
2. ns3::PhyStatsCalculator::UeSinrFilename
3. ns3::PhyStatsCalculator::InterferenceFilename
4. ns3::PhyStatsCalculator::DlTxOutputFilename
5. ns3::PhyStatsCalculator::UlTxOutputFilename
6. ns3::PhyStatsCalculator::DlRxOutputFilename
7. ns3::PhyStatsCalculator::UlRxOutputFilename
In the RSRP/SINR file, the following content is available:
1. Simulation time in seconds at which the allocation is indicated by the scheduler
2. Cell ID
3. unique UE ID (IMSI)
4. RSRP
5. Linear average over all RBs of the downlink SINR in linear units
The contents in the UE SINR file are:
1. Simulation time in seconds at which the allocation is indicated by the scheduler
2. Cell ID
3. unique UE ID (IMSI)
4. uplink SINR in linear units for the UE
In the interference filename the content is:
1. Simulation time in seconds at which the allocation is indicated by the scheduler
2. Cell ID
3. List of interference values per RB
In UL and DL transmission files the parameters included are:
1. Simulation time in milliseconds
2. Cell ID
3. unique UE ID (IMSI)
4. RNTI
5. Layer of transmission
6. MCS
7. size of the TB
8. Redundancy version
9. New Data Indicator flag
And finally, in UL and DL reception files the parameters included are:
1. Simulation time in milliseconds
2. Cell ID
3. unique UE ID (IMSI)
4. RNTI
5. Transmission Mode
6. Layer of transmission
7. MCS
8. size of the TB
9. Redundancy version
10. New Data Indicator flag
11. Correctness in the reception of the TB
Fading Trace Usage
In this section we will describe how to use fading traces within LTE simulations.
Fading Traces Generation
It is possible to generate fading traces by using a dedicated matlab script provided with
the code (/lte/model/fading-traces/fading-trace-generator.m). This script already includes
the typical taps configurations for three 3GPP scenarios (i.e., pedestrian, vehicular and
urban as defined in Annex B.2 of [TS36104]); however users can also introduce their
specific configurations. The list of the configurable parameters is provided in the
following:
· fc : the frequency in use (it affects the computation of the doppler speed).
· v_km_h : the speed of the users
· traceDuration : the duration in seconds of the total length of the trace.
· numRBs : the number of the resource block to be evaluated.
· tag : the tag to be applied to the file generated.
The file generated contains ASCII-formatted real values organized in a matrix fashion:
every row corresponds to a different RB, and every column correspond to a different
temporal fading trace sample.
It has to be noted that the ns-3 LTE module is able to work with any fading trace file
that complies with the above described ASCII format. Hence, other external tools can be
used to generate custom fading traces, such as for example other simulators or
experimental devices.
Fading Traces Usage
When using a fading trace, it is of paramount importance to specify correctly the trace
parameters in the simulation, so that the fading model can load and use it correcly. The
parameters to be configured are:
· TraceFilename : the name of the trace to be loaded (absolute path, or relative path
w.r.t. the path from where the simulation program is executed);
· TraceLength : the trace duration in seconds;
· SamplesNum : the number of samples;
· WindowSize : the size of the fading sampling window in seconds;
It is important to highlight that the sampling interval of the fading trace has to be 1 ms
or greater, and in the latter case it has to be an integer multiple of 1 ms in order to be
correctly processed by the fading module.
The default configuration of the matlab script provides a trace 10 seconds long, made of
10,000 samples (i.e., 1 sample per TTI=1ms) and used with a windows size of 0.5 seconds
amplitude. These are also the default values of the parameters above used in the
simulator; therefore their settage can be avoided in case the fading trace respects them.
In order to activate the fading module (which is not active by default) the following code
should be included in the simulation program:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetFadingModel("ns3::TraceFadingLossModel");
And for setting the parameters:
lteHelper->SetFadingModelAttribute ("TraceFilename", StringValue ("src/lte/model/fading-traces/fading_trace_EPA_3kmph.fad"));
lteHelper->SetFadingModelAttribute ("TraceLength", TimeValue (Seconds (10.0)));
lteHelper->SetFadingModelAttribute ("SamplesNum", UintegerValue (10000));
lteHelper->SetFadingModelAttribute ("WindowSize", TimeValue (Seconds (0.5)));
lteHelper->SetFadingModelAttribute ("RbNum", UintegerValue (100));
It has to be noted that, TraceFilename does not have a default value, therefore is has to
be always set explicitly.
The simulator provide natively three fading traces generated according to the
configurations defined in in Annex B.2 of [TS36104]. These traces are available in the
folder src/lte/model/fading-traces/). An excerpt from these traces is represented in the
following figures.
[image: Fading trace 3 kmph] [image] Excerpt of the fading trace included in the
simulator for a pedestrian scenario (speed of 3 kmph)..UNINDENT
[image: Fading trace 60 kmph] [image] Excerpt of the fading trace included in the
simulator for a vehicular scenario (speed of 60 kmph)..UNINDENT
[image: Fading trace 3 kmph] [image] Excerpt of the fading trace included in the
simulator for an urban scenario (speed of 3 kmph)..UNINDENT
Mobility Model with Buildings
We now explain by examples how to use the buildings model (in particular, the
MobilityBuildingInfo and the BuildingPropagationModel classes) in an ns-3 simulation
program to setup an LTE simulation scenario that includes buildings and indoor nodes.
1. Header files to be included:
#include <ns3/mobility-building-info.h>
#include <ns3/buildings-propagation-loss-model.h>
#include <ns3/building.h>
2. Pathloss model selection:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetAttribute ("PathlossModel", StringValue ("ns3::BuildingsPropagationLossModel"));
3. EUTRA Band Selection
The selection of the working frequency of the propagation model has to be done with the
standard ns-3 attribute system as described in the correspond section ("Configuration of
LTE model parameters") by means of the DlEarfcn and UlEarfcn parameters, for instance:
lteHelper->SetEnbDeviceAttribute ("DlEarfcn", UintegerValue (100));
lteHelper->SetEnbDeviceAttribute ("UlEarfcn", UintegerValue (18100));
It is to be noted that using other means to configure the frequency used by the
propagation model (i.e., configuring the corresponding BuildingsPropagationLossModel
attributes directly) might generates conflicts in the frequencies definition in the
modules during the simulation, and is therefore not advised.
1. Mobility model selection:
MobilityHelper mobility;
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
It is to be noted that any mobility model can be used.
2. Building creation:
double x_min = 0.0;
double x_max = 10.0;
double y_min = 0.0;
double y_max = 20.0;
double z_min = 0.0;
double z_max = 10.0;
Ptr<Building> b = CreateObject <Building> ();
b->SetBoundaries (Box (x_min, x_max, y_min, y_max, z_min, z_max));
b->SetBuildingType (Building::Residential);
b->SetExtWallsType (Building::ConcreteWithWindows);
b->SetNFloors (3);
b->SetNRoomsX (3);
b->SetNRoomsY (2);
This will instantiate a residential building with base of 10 x 20 meters and height of
10 meters whose external walls are of concrete with windows; the building has three
floors and has an internal 3 x 2 grid of rooms of equal size.
3. Node creation and positioning:
ueNodes.Create (2);
mobility.Install (ueNodes);
BuildingsHelper::Install (ueNodes);
NetDeviceContainer ueDevs;
ueDevs = lteHelper->InstallUeDevice (ueNodes);
Ptr<ConstantPositionMobilityModel> mm0 = enbNodes.Get (0)->GetObject<ConstantPositionMobilityModel> ();
Ptr<ConstantPositionMobilityModel> mm1 = enbNodes.Get (1)->GetObject<ConstantPositionMobilityModel> ();
mm0->SetPosition (Vector (5.0, 5.0, 1.5));
mm1->SetPosition (Vector (30.0, 40.0, 1.5));
4. Finalize the building and mobility model configuration:
BuildingsHelper::MakeMobilityModelConsistent ();
See the documentation of the buildings module for more detailed information.
PHY Error Model
The Physical error model consists of the data error model and the downlink control error
model, both of them active by default. It is possible to deactivate them with the ns3
attribute system, in detail:
Config::SetDefault ("ns3::LteSpectrumPhy::CtrlErrorModelEnabled", BooleanValue (false));
Config::SetDefault ("ns3::LteSpectrumPhy::DataErrorModelEnabled", BooleanValue (false));
MIMO Model
Is this subsection we illustrate how to configure the MIMO parameters. LTE defines 7 types
of transmission modes:
· Transmission Mode 1: SISO.
· Transmission Mode 2: MIMO Tx Diversity.
· Transmission Mode 3: MIMO Spatial Multiplexity Open Loop.
· Transmission Mode 4: MIMO Spatial Multiplexity Closed Loop.
· Transmission Mode 5: MIMO Multi-User.
· Transmission Mode 6: Closer loop single layer precoding.
· Transmission Mode 7: Single antenna port 5.
According to model implemented, the simulator includes the first three transmission modes
types. The default one is the Transmission Mode 1 (SISO). In order to change the default
Transmission Mode to be used, the attribute DefaultTransmissionMode of the LteEnbRrc can
be used, as shown in the following:
Config::SetDefault ("ns3::LteEnbRrc::DefaultTransmissionMode", UintegerValue (0)); // SISO
Config::SetDefault ("ns3::LteEnbRrc::DefaultTransmissionMode", UintegerValue (1)); // MIMO Tx diversity (1 layer)
Config::SetDefault ("ns3::LteEnbRrc::DefaultTransmissionMode", UintegerValue (2)); // MIMO Spatial Multiplexity (2 layers)
For changing the transmission mode of a certain user during the simulation a specific
interface has been implemented in both standard schedulers:
void TransmissionModeConfigurationUpdate (uint16_t rnti, uint8_t txMode);
This method can be used both for developing transmission mode decision engine (i.e., for
optimizing the transmission mode according to channel condition and/or user's
requirements) and for manual switching from simulation script. In the latter case, the
switching can be done as shown in the following:
Ptr<LteEnbNetDevice> lteEnbDev = enbDevs.Get (0)->GetObject<LteEnbNetDevice> ();
PointerValue ptrval;
enbNetDev->GetAttribute ("FfMacScheduler", ptrval);
Ptr<RrFfMacScheduler> rrsched = ptrval.Get<RrFfMacScheduler> ();
Simulator::Schedule (Seconds (0.2), &RrFfMacScheduler::TransmissionModeConfigurationUpdate, rrsched, rnti, 1);
Finally, the model implemented can be reconfigured according to different MIMO models by
updating the gain values (the only constraints is that the gain has to be constant during
simulation run-time and common for the layers). The gain of each Transmission Mode can be
changed according to the standard ns3 attribute system, where the attributes are:
TxMode1Gain, TxMode2Gain, TxMode3Gain, TxMode4Gain, TxMode5Gain, TxMode6Gain and
TxMode7Gain. By default only TxMode1Gain, TxMode2Gain and TxMode3Gain have a meaningful
value, that are the ones derived by _[CatreuxMIMO] (i.e., respectively 0.0, 4.2 and -2.8
dB).
Use of AntennaModel
We now show how associate a particular AntennaModel with an eNB device in order to model a
sector of a macro eNB. For this purpose, it is convenient to use the CosineAntennaModel
provided by the ns-3 antenna module. The configuration of the eNB is to be done via the
LteHelper instance right before the creation of the EnbNetDevice, as shown in the
following:
lteHelper->SetEnbAntennaModelType ("ns3::CosineAntennaModel");
lteHelper->SetEnbAntennaModelAttribute ("Orientation", DoubleValue (0));
lteHelper->SetEnbAntennaModelAttribute ("Beamwidth", DoubleValue (60);
lteHelper->SetEnbAntennaModelAttribute ("MaxGain", DoubleValue (0.0));
the above code will generate an antenna model with a 60 degrees beamwidth pointing along
the X axis. The orientation is measured in degrees from the X axis, e.g., an orientation
of 90 would point along the Y axis, and an orientation of -90 would point in the negative
direction along the Y axis. The beamwidth is the -3 dB beamwidth, e.g, for a 60 degree
beamwidth the antenna gain at an angle of m
30 degrees from the direction of orientation is -3 dB.
To create a multi-sector site, you need to create different ns-3 nodes placed at the same
position, and to configure separate EnbNetDevice with different antenna orientations to be
installed on each node.
Radio Environment Maps
By using the class RadioEnvironmentMapHelper it is possible to output to a file a Radio
Environment Map (REM), i.e., a uniform 2D grid of values that represent the
Signal-to-noise ratio in the downlink with respect to the eNB that has the strongest
signal at each point. It is possible to specify if REM should be generated for data or
control channel. Also user can set the RbId, for which REM will be generated. Default RbId
is -1, what means that REM will generated with averaged Signal-to-noise ratio from all
RBs.
To do this, you just need to add the following code to your simulation program towards the
end, right before the call to Simulator::Run ():
Ptr<RadioEnvironmentMapHelper> remHelper = CreateObject<RadioEnvironmentMapHelper> ();
remHelper->SetAttribute ("ChannelPath", StringValue ("/ChannelList/0"));
remHelper->SetAttribute ("OutputFile", StringValue ("rem.out"));
remHelper->SetAttribute ("XMin", DoubleValue (-400.0));
remHelper->SetAttribute ("XMax", DoubleValue (400.0));
remHelper->SetAttribute ("XRes", UintegerValue (100));
remHelper->SetAttribute ("YMin", DoubleValue (-300.0));
remHelper->SetAttribute ("YMax", DoubleValue (300.0));
remHelper->SetAttribute ("YRes", UintegerValue (75));
remHelper->SetAttribute ("Z", DoubleValue (0.0));
remHelper->SetAttribute ("UseDataChannel", BooleanValue (true));
remHelper->SetAttribute ("RbId", IntegerValue (10));
remHelper->Install ();
By configuring the attributes of the RadioEnvironmentMapHelper object as shown above, you
can tune the parameters of the REM to be generated. Note that each
RadioEnvironmentMapHelper instance can generate only one REM; if you want to generate more
REMs, you need to create one separate instance for each REM.
Note that the REM generation is very demanding, in particular:
· the run-time memory consumption is approximately 5KB per pixel. For example, a REM
with a resolution of 500x500 would need about 1.25 GB of memory, and a resolution of
1000x1000 would need needs about 5 GB (too much for a regular PC at the time of this
writing). To overcome this issue, the REM is generated at successive steps, with each
step evaluating at most a number of pixels determined by the value of the the
attribute RadioEnvironmentMapHelper::MaxPointsPerIteration.
· if you generate a REM at the beginning of a simulation, it will slow down the
execution of the rest of the simulation. If you want to generate a REM for a program
and also use the same program to get simulation result, it is recommended to add a
command-line switch that allows to either generate the REM or run the complete
simulation. For this purpose, note that there is an attribute
RadioEnvironmentMapHelper::StopWhenDone (default: true) that will force the
simulation to stop right after the REM has been generated.
The REM is stored in an ASCII file in the following format:
· column 1 is the x coordinate
· column 2 is the y coordinate
· column 3 is the z coordinate
· column 4 is the SINR in linear units
A minimal gnuplot script that allows you to plot the REM is given below:
set view map;
set xlabel "X"
set ylabel "Y"
set cblabel "SINR (dB)"
unset key
plot "rem.out" using ($1):($2):(10*log10($4)) with image
As an example, here is the REM that can be obtained with the example program
lena-dual-stripe, which shows a three-sector LTE macrocell in a co-channel deployment with
some residential femtocells randomly deployed in two blocks of apartments.
[image] REM obtained from the lena-dual-stripe example.UNINDENT
Note that the lena-dual-stripe example program also generate gnuplot-compatible output
files containing information about the positions of the UE and eNB nodes as well as of
the buildings, respectively in the files ues.txt, enbs.txt and buildings.txt. These can
be easily included when using gnuplot. For example, assuming that your gnuplot script
(e.g., the minimal gnuplot script described above) is saved in a file named
my_plot_script, running the following command would plot the location of UEs, eNBs and
buildings on top of the REM:
gnuplot -p enbs.txt ues.txt buildings.txt my_plot_script
AMC Model and CQI Calculation
The simulator provides two possible schemes for what concerns the selection of the MCSs
and correspondly the generation of the CQIs. The first one is based on the GSoC module
[Piro2011] and works per RB basis. This model can be activated with the ns3 attribute
system, as presented in the following:
Config::SetDefault ("ns3::LteAmc::AmcModel", EnumValue (LteAmc::PiroEW2010));
While, the solution based on the physical error model can be controlled with:
Config::SetDefault ("ns3::LteAmc::AmcModel", EnumValue (LteAmc::MiErrorModel));
Finally, the required efficiency of the PiroEW2010 AMC module can be tuned thanks to the
Ber attribute (), for instance:
Config::SetDefault ("ns3::LteAmc::Ber", DoubleValue (0.00005));
Evolved Packet Core (EPC)
We now explain how to write a simulation program that allows to simulate the EPC in
addition to the LTE radio access network. The use of EPC allows to use IPv4 networking
with LTE devices. In other words, you will be able to use the regular ns-3 applications
and sockets over IPv4 over LTE, and also to connect an LTE network to any other IPv4
network you might have in your simulation.
First of all, in addition to LteHelper that we already introduced in Basic simulation
program, you need to use an additional EpcHelper class, which will take care of creating
the EPC entities and network topology. Note that you can't use EpcHelper directly, as it
is an abstract base class; instead, you need to use one of its child classes, which
provide different EPC topology implementations. In this example we will consider
PointToPointEpcHelper, which implements an EPC based on point-to-point links. To use it,
you need first to insert this code in your simulation program:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
Ptr<PointToPointEpcHelper> epcHelper = CreateObject<PointToPointEpcHelper> ();
Then, you need to tell the LTE helper that the EPC will be used:
lteHelper->SetEpcHelper (epcHelper);
the above step is necessary so that the LTE helper will trigger the appropriate EPC
configuration in correspondance with some important configuration, such as when a new eNB
or UE is added to the simulation, or an EPS bearer is created. The EPC helper will
automatically take care of the necessary setup, such as S1 link creation and S1 bearer
setup. All this will be done without the intervention of the user.
Calling lteHelper->SetEpcHelper (epcHelper) enables the use of EPC, and has the side
effect that any new LteEnbRrc that is created will have the EpsBearerToRlcMapping
attribute set to RLC_UM_ALWAYS instead of RLC_SM_ALWAYS if the latter was the default;
otherwise, the attribute won't be changed (e.g., if you changed the default to
RLC_AM_ALWAYS, it won't be touched).
It is to be noted that the EpcHelper will also automatically create the PGW node and
configure it so that it can properly handle traffic from/to the LTE radio access network.
Still, you need to add some explicit code to connect the PGW to other IPv4 networks (e.g.,
the internet). Here is a very simple example about how to connect a single remote host to
the PGW via a point-to-point link:
Ptr<Node> pgw = epcHelper->GetPgwNode ();
// Create a single RemoteHost
NodeContainer remoteHostContainer;
remoteHostContainer.Create (1);
Ptr<Node> remoteHost = remoteHostContainer.Get (0);
InternetStackHelper internet;
internet.Install (remoteHostContainer);
// Create the internet
PointToPointHelper p2ph;
p2ph.SetDeviceAttribute ("DataRate", DataRateValue (DataRate ("100Gb/s")));
p2ph.SetDeviceAttribute ("Mtu", UintegerValue (1500));
p2ph.SetChannelAttribute ("Delay", TimeValue (Seconds (0.010)));
NetDeviceContainer internetDevices = p2ph.Install (pgw, remoteHost);
Ipv4AddressHelper ipv4h;
ipv4h.SetBase ("1.0.0.0", "255.0.0.0");
Ipv4InterfaceContainer internetIpIfaces = ipv4h.Assign (internetDevices);
// interface 0 is localhost, 1 is the p2p device
Ipv4Address remoteHostAddr = internetIpIfaces.GetAddress (1);
It's important to specify routes so that the remote host can reach LTE UEs. One way of
doing this is by exploiting the fact that the PointToPointEpcHelper will by default assign
to LTE UEs an IP address in the 7.0.0.0 network. With this in mind, it suffices to do:
Ipv4StaticRoutingHelper ipv4RoutingHelper;
Ptr<Ipv4StaticRouting> remoteHostStaticRouting = ipv4RoutingHelper.GetStaticRouting (remoteHost->GetObject<Ipv4> ());
remoteHostStaticRouting->AddNetworkRouteTo (Ipv4Address ("7.0.0.0"), Ipv4Mask ("255.0.0.0"), 1);
Now, you should go on and create LTE eNBs and UEs as explained in the previous sections.
You can of course configure other LTE aspects such as pathloss and fading models. Right
after you created the UEs, you should also configure them for IP networking. This is done
as follows. We assume you have a container for UE and eNodeB nodes like this:
NodeContainer ueNodes;
NodeContainer enbNodes;
to configure an LTE-only simulation, you would then normally do something like this:
NetDeviceContainer ueLteDevs = lteHelper->InstallUeDevice (ueNodes);
lteHelper->Attach (ueLteDevs, enbLteDevs.Get (0));
in order to configure the UEs for IP networking, you just need to additionally do like
this:
// we install the IP stack on the UEs
InternetStackHelper internet;
internet.Install (ueNodes);
// assign IP address to UEs
for (uint32_t u = 0; u < ueNodes.GetN (); ++u)
{
Ptr<Node> ue = ueNodes.Get (u);
Ptr<NetDevice> ueLteDevice = ueLteDevs.Get (u);
Ipv4InterfaceContainer ueIpIface = epcHelper->AssignUeIpv4Address (NetDeviceContainer (ueLteDevice));
// set the default gateway for the UE
Ptr<Ipv4StaticRouting> ueStaticRouting = ipv4RoutingHelper.GetStaticRouting (ue->GetObject<Ipv4> ());
ueStaticRouting->SetDefaultRoute (epcHelper->GetUeDefaultGatewayAddress (), 1);
}
The activation of bearers is done in a slightly different way with respect to what done
for an LTE-only simulation. First, the method ActivateDataRadioBearer is not to be used
when the EPC is used. Second, when EPC is used, the default EPS bearer will be activated
automatically when you call LteHelper::Attach (). Third, if you want to setup dedicated
EPS bearer, you can do so using the method LteHelper::ActivateDedicatedEpsBearer (). This
method takes as a parameter the Traffic Flow Template (TFT), which is a struct that
identifies the type of traffic that will be mapped to the dedicated EPS bearer. Here is an
example for how to setup a dedicated bearer for an application at the UE communicating on
port 1234:
Ptr<EpcTft> tft = Create<EpcTft> ();
EpcTft::PacketFilter pf;
pf.localPortStart = 1234;
pf.localPortEnd = 1234;
tft->Add (pf);
lteHelper->ActivateDedicatedEpsBearer (ueLteDevs, EpsBearer (EpsBearer::NGBR_VIDEO_TCP_DEFAULT), tft);
you can of course use custom EpsBearer and EpcTft configurations, please refer to the
doxygen documentation for how to do it.
Finally, you can install applications on the LTE UE nodes that communicate with remote
applications over the internet. This is done following the usual ns-3 procedures.
Following our simple example with a single remoteHost, here is how to setup downlink
communication, with an UdpClient application on the remote host, and a PacketSink on the
LTE UE (using the same variable names of the previous code snippets)
uint16_t dlPort = 1234;
PacketSinkHelper packetSinkHelper ("ns3::UdpSocketFactory",
InetSocketAddress (Ipv4Address::GetAny (), dlPort));
ApplicationContainer serverApps = packetSinkHelper.Install (ue);
serverApps.Start (Seconds (0.01));
UdpClientHelper client (ueIpIface.GetAddress (0), dlPort);
ApplicationContainer clientApps = client.Install (remoteHost);
clientApps.Start (Seconds (0.01));
That's all! You can now start your simulation as usual:
Simulator::Stop (Seconds (10.0));
Simulator::Run ();
Using the EPC with emulation mode
In the previous section we used PointToPoint links for the connection between the eNBs and
the SGW (S1-U interface) and among eNBs (X2-U and X2-C interfaces). The LTE module
supports using emulated links instead of PointToPoint links. This is achieved by just
replacing the creation of LteHelper and EpcHelper with the following code:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
Ptr<EmuEpcHelper> epcHelper = CreateObject<EmuEpcHelper> ();
lteHelper->SetEpcHelper (epcHelper);
epcHelper->Initialize ();
The attributes ns3::EmuEpcHelper::sgwDeviceName and ns3::EmuEpcHelper::enbDeviceName are
used to set the name of the devices used for transporting the S1-U, X2-U and X2-C
interfaces at the SGW and eNB, respectively. We will now show how this is done in an
example where we execute the example program lena-simple-epc-emu using two virtual
ethernet interfaces.
First of all we build ns-3 appropriately:
# configure
./waf configure --enable-sudo --enable-modules=lte,fd-net-device --enable-examples
# build
./waf
Then we setup two virtual ethernet interfaces, and start wireshark to look at the traffic
going through:
# note: you need to be root
# create two paired veth devices
ip link add name veth0 type veth peer name veth1
ip link show
# enable promiscuous mode
ip link set veth0 promisc on
ip link set veth1 promisc on
# bring interfaces up
ip link set veth0 up
ip link set veth1 up
# start wireshark and capture on veth0
wireshark &
We can now run the example program with the simulated clock:
./waf --run lena-simple-epc-emu --command="%s --ns3::EmuEpcHelper::sgwDeviceName=veth0 --ns3::EmuEpcHelper::enbDeviceName=veth1"
Using wireshark, you should see ARP resolution first, then some GTP packets exchanged both
in uplink and downlink.
The default setting of the example program is 1 eNB and 1UE. You can change this via
command line parameters, e.g.:
./waf --run lena-simple-epc-emu --command="%s --ns3::EmuEpcHelper::sgwDeviceName=veth0 --ns3::EmuEpcHelper::enbDeviceName=veth1 --nEnbs=2 --nUesPerEnb=2"
To get a list of the available parameters:
./waf --run lena-simple-epc-emu --command="%s --PrintHelp"
To run with the realtime clock: it turns out that the default debug build is too slow for
realtime. Softening the real time constraints with the BestEffort mode is not a good idea:
something can go wrong (e.g., ARP can fail) and, if so, you won't get any data packets
out. So you need a decent hardware and the optimized build with statically linked
modules:
./waf configure -d optimized --enable-static --enable-modules=lte --enable-examples --enable-sudo
Then run the example program like this:
./waf --run lena-simple-epc-emu --command="%s --ns3::EmuEpcHelper::sgwDeviceName=veth0 --ns3::EmuEpcHelper::enbDeviceName=veth1 --simulatorImplementationType=ns3::RealtimeSimulatorImpl --ns3::RealtimeSimulatorImpl::SynchronizationMode=HardLimit"
note the HardLimit setting, which will cause the program to terminate if it cannot keep up
with real time.
The approach described in this section can be used with any type of net device. For
instance, [Baldo2014] describes how it was used to run an emulated LTE-EPC network over a
real multi-layer packet-optical transport network.
Network Attachment
As shown in the basic example in section Basic simulation program, attaching a UE to an
eNodeB is done by calling LteHelper::Attach function.
There are 2 possible ways of network attachment. The first method is the "manual" one,
while the second one has a more "automatic" sense on it. Each of them will be covered in
this section.
Manual attachment
This method uses the LteHelper::Attach function mentioned above. It has been the only
available network attachment method in earlier versions of LTE module. It is typically
invoked before the simulation begins:
lteHelper->Attach (ueDevs, enbDev); // attach one or more UEs to a single eNodeB
LteHelper::InstallEnbDevice and LteHelper::InstallUeDevice functions must have been called
before attaching. In an EPC-enabled simulation, it is also required to have IPv4 properly
pre-installed in the UE.
This method is very simple, but requires you to know exactly which UE belongs to to which
eNodeB before the simulation begins. This can be difficult when the UE initial position is
randomly determined by the simulation script.
One may choose the distance between the UE and the eNodeB as a criterion for selecting the
appropriate cell. It is quite simple (at least from the simulator's point of view) and
sometimes practical. But it is important to note that sometimes distance does not make a
single correct criterion. For instance, the eNodeB antenna directivity should be
considered as well. Besides that, one should also take into account the channel condition,
which might be fluctuating if there is fading or shadowing in effect. In these kind of
cases, network attachment should not be based on distance alone.
In real life, UE will automatically evaluate certain criteria and select the best cell to
attach to, without manual intervention from the user. Obviously this is not the case in
this LteHelper::Attach function. The other network attachment method uses more "automatic"
approach to network attachment, as will be described next.
Automatic attachment using Idle mode cell selection procedure
The strength of the received signal is the standard criterion used for selecting the best
cell to attach to. The use of this criterion is implemented in the initial cell selection
process, which can be invoked by calling another version of the LteHelper::Attach
function, as shown below:
lteHelper->Attach (ueDevs); // attach one or more UEs to a strongest cell
The difference with the manual method is that the destination eNodeB is not specified. The
procedure will find the best cell for the UEs, based on several criteria, including the
strength of the received signal (RSRP).
After the method is called, the UE will spend some time to measure the neighbouring cells,
and then attempt to attach to the best one. More details can be found in section
sec-initial-cell-selection of the Design Documentation.
It is important to note that this method only works in EPC-enabled simulations. LTE-only
simulations must resort to manual attachment method.
Closed Subscriber Group
An interesting use case of the initial cell selection process is to setup a simulation
environment with Closed Subscriber Group (CSG).
For example, a certain eNodeB, typically a smaller version such as femtocell, might belong
to a private owner (e.g. a household or business), allowing access only to some UEs which
have been previously registered by the owner. The eNodeB and the registered UEs altogether
form a CSG.
The access restriction can be simulated by "labeling" the CSG members with the same CSG
ID. This is done through the attributes in both eNodeB and UE, for example using the
following LteHelper functions:
// label the following eNodeBs with CSG identity of 1 and CSG indication enabled
lteHelper->SetEnbDeviceAttribute ("CsgId", UintegerValue (1));
lteHelper->SetEnbDeviceAttribute ("CsgIndication", BooleanValue (true));
// label one or more UEs with CSG identity of 1
lteHelper->SetUeDeviceAttribute ("CsgId", UintegerValue (1));
// install the eNodeBs and UEs
NetDeviceContainer csgEnbDevs = lteHelper->InstallEnbDevice (csgEnbNodes);
NetDeviceContainer csgUeDevs = lteHelper->InstallUeDevice (csgUeNodes);
Then enable the initial cell selection procedure on the UEs:
lteHelper->Attach (csgUeDevs);
This is necessary because the CSG restriction only works with automatic method of network
attachment, but not in the manual method.
Note that setting the CSG indication of an eNodeB as false (the default value) will
disable the restriction, i.e., any UEs can connect to this eNodeB.
Configure UE measurements
The active UE measurement configuration in a simulation is dictated by the selected so
called "consumers", such as handover algorithm. Users may add their own configuration into
action, and there are several ways to do so:
1. direct configuration in eNodeB RRC entity;
2. configuring existing handover algorithm; and
3. developing a new handover algorithm.
This section will cover the first method only. The second method is covered in Automatic
handover trigger, while the third method is explained in length in Section
sec-handover-algorithm of the Design Documentation.
Direct configuration in eNodeB RRC works as follows. User begins by creating a new
LteRrcSap::ReportConfigEutra instance and pass it to the LteEnbRrc::AddUeMeasReportConfig
function. The function will return the measId (measurement identity) which is a unique
reference of the configuration in the eNodeB instance. This function must be called before
the simulation begins. The measurement configuration will be active in all UEs attached to
the eNodeB throughout the duration of the simulation. During the simulation, user can
capture the measurement reports produced by the UEs by listening to the existing
LteEnbRrc::RecvMeasurementReport trace source.
The structure ReportConfigEutra is in accord with 3GPP specification. Definition of the
structure and each member field can be found in Section 6.3.5 of [TS36331].
The code sample below configures Event A1 RSRP measurement to every eNodeB within the
container devs:
LteRrcSap::ReportConfigEutra config;
config.eventId = LteRrcSap::ReportConfigEutra::EVENT_A1;
config.threshold1.choice = LteRrcSap::ThresholdEutra::THRESHOLD_RSRP;
config.threshold1.range = 41;
config.triggerQuantity = LteRrcSap::ReportConfigEutra::RSRP;
config.reportInterval = LteRrcSap::ReportConfigEutra::MS480;
std::vector<uint8_t> measIdList;
NetDeviceContainer::Iterator it;
for (it = devs.Begin (); it != devs.End (); it++)
{
Ptr<NetDevice> dev = *it;
Ptr<LteEnbNetDevice> enbDev = dev->GetObject<LteEnbNetDevice> ();
Ptr<LteEnbRrc> enbRrc = enbDev->GetRrc ();
uint8_t measId = enbRrc->AddUeMeasReportConfig (config);
measIdList.push_back (measId); // remember the measId created
enbRrc->TraceConnect ("RecvMeasurementReport",
"context",
MakeCallback (&RecvMeasurementReportCallback));
}
Note that thresholds are expressed as range. In the example above, the range 41 for RSRP
corresponds to -100 dBm. The conversion from and to the range format is due to Section
9.1.4 and 9.1.7 of [TS36133]. The EutranMeasurementMapping class has several static
functions that can be used for this purpose.
The corresponding callback function would have a definition similar as below:
void
RecvMeasurementReportCallback (std::string context,
uint64_t imsi,
uint16_t cellId,
uint16_t rnti,
LteRrcSap::MeasurementReport measReport);
This method will register the callback function as a consumer of UE measurements. In the
case where there are more than one consumers in the simulation (e.g. handover algorithm),
the measurements intended for other consumers will also be captured by this callback
function. Users may utilize the the measId field, contained within the
LteRrcSap::MeasurementReport argument of the callback function, to tell which measurement
configuration has triggered the report.
In general, this mechanism prevents one consumer to unknowingly intervene with another
consumer's reporting configuration.
Note that only the reporting configuration part (i.e. LteRrcSap::ReportConfigEutra) of
the UE measurements parameter is open for consumers to configure, while the other parts
are kept hidden. The intra-frequency limitation is the main motivation behind this API
implementation decision:
· there is only one, unambiguous and definitive measurement object, thus there is no
need to configure it;
· measurement identities are kept hidden because of the fact that there is one-to-one
mapping between reporting configuration and measurement identity, thus a new
measurement identity is set up automatically when a new reporting configuration is
created;
· quantity configuration is configured elsewhere, see sec-performing-measurements; and
· measurement gaps are not supported, because it is only applicable for inter-frequency
settings;
X2-based handover
As defined by 3GPP, handover is a procedure for changing the serving cell of a UE in
CONNECTED mode. The two eNodeBs involved in the process are typically called the source
eNodeB and the target eNodeB.
In order to enable the execution of X2-based handover in simulation, there are two
requirements that must be met. Firstly, EPC must be enabled in the simulation (see Evolved
Packet Core (EPC)).
Secondly, an X2 interface must be configured between the two eNodeBs, which needs to be
done explicitly within the simulation program:
lteHelper->AddX2Interface (enbNodes);
where enbNodes is a NodeContainer that contains the two eNodeBs between which the X2
interface is to be configured. If the container has more than two eNodeBs, the function
will create an X2 interface between every pair of eNodeBs in the container.
Lastly, the target eNodeB must be configured as "open" to X2 HANDOVER REQUEST. Every
eNodeB is open by default, so no extra instruction is needed in most cases. However, users
may set the eNodeB to "closed" by setting the boolean attribute
LteEnbRrc::AdmitHandoverRequest to false. As an example, you can run the lena-x2-handover
program and setting the attribute in this way:
NS_LOG=EpcX2:LteEnbRrc ./waf --run lena-x2-handover --command="%s --ns3::LteEnbRrc::AdmitHandoverRequest=false"
After the above three requirements are fulfilled, the handover procedure can be triggered
manually or automatically. Each will be presented in the following subsections.
Manual handover trigger
Handover event can be triggered "manually" within the simulation program by scheduling an
explicit handover event. The LteHelper object provides a convenient method for the
scheduling of a handover event. As an example, let us assume that ueLteDevs is a
NetDeviceContainer that contains the UE that is to be handed over, and that enbLteDevs is
another NetDeviceContainer that contains the source and the target eNB. Then, a handover
at 0.1s can be scheduled like this:
lteHelper->HandoverRequest (Seconds (0.100),
ueLteDevs.Get (0),
enbLteDevs.Get (0),
enbLteDevs.Get (1));
Note that the UE needs to be already connected to the source eNB, otherwise the simulation
will terminate with an error message.
For an example with full source code, please refer to the lena-x2-handover example
program.
Automatic handover trigger
Handover procedure can also be triggered "automatically" by the serving eNodeB of the UE.
The logic behind the trigger depends on the handover algorithm currently active in the
eNodeB RRC entity. Users may select and configure the handover algorithm that will be used
in the simulation, which will be explained shortly in this section. Users may also opt to
write their own implementation of handover algorithm, as described in Section
sec-handover-algorithm of the Design Documentation.
Selecting a handover algorithm is done via the LteHelper object and its
SetHandoverAlgorithmType method as shown below:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetHandoverAlgorithmType ("ns3::A2A4RsrqHandoverAlgorithm");
The selected handover algorithm may also provide several configurable attributes, which
can be set as follows:
lteHelper->SetHandoverAlgorithmAttribute ("ServingCellThreshold",
UintegerValue (30));
lteHelper->SetHandoverAlgorithmAttribute ("NeighbourCellOffset",
UintegerValue (1));
Three options of handover algorithm are included in the LTE module. The A2-A4-RSRQ
handover algorithm (named as ns3::A2A4RsrqHandoverAlgorithm) is the default option, and
the usage has already been shown above.
Another option is the strongest cell handover algorithm (named as
ns3::A3RsrpHandoverAlgorithm), which can be selected and configured by the following code:
lteHelper->SetHandoverAlgorithmType ("ns3::A3RsrpHandoverAlgorithm");
lteHelper->SetHandoverAlgorithmAttribute ("Hysteresis",
DoubleValue (3.0));
lteHelper->SetHandoverAlgorithmAttribute ("TimeToTrigger",
TimeValue (MilliSeconds (256)));
The last option is a special one, called the no-op handover algorithm, which basically
disables automatic handover trigger. This is useful for example in cases where manual
handover trigger need an exclusive control of all handover decision. It does not have any
configurable attributes. The usage is as follows:
lteHelper->SetHandoverAlgorithmType ("ns3::NoOpHandoverAlgorithm");
For more information on each handover algorithm's decision policy and their attributes,
please refer to their respective subsections in Section sec-handover-algorithm of the
Design Documentation.
Finally, the InstallEnbDevice function of LteHelper will instantiate one instance of the
selected handover algorithm for each eNodeB device. In other words, make sure to select
the right handover algorithm before finalizing it in the following line of code:
NetDeviceContainer enbLteDevs = lteHelper->InstallEnbDevice (enbNodes);
Example with full source code of using automatic handover trigger can be found in the
lena-x2-handover-measures example program.
Tuning simulation with handover
As mentioned in the Design Documentation, the current implementation of handover model may
produce unpredicted behaviour when handover failure occurs. This subsection will focus on
the steps that should be taken into account by users if they plan to use handover in their
simulations.
The major cause of handover failure that we will tackle is the error in transmitting
handover-related signaling messages during the execution of a handover procedure. As
apparent from the Figure fig-x2-based-handover-seq-diagram from the Design Documentation,
there are many of them and they use different interfaces and protocols. For the sake of
simplicity, we can safely assume that the X2 interface (between the source eNodeB and the
target eNodeB) and the S1 interface (between the target eNodeB and the SGW/PGW) are quite
stable. Therefore we will focus our attention to the RRC protocol (between the UE and the
eNodeBs) and the Random Access procedure, which are normally transmitted through the air
and susceptible to degradation of channel condition.
A general tips to reduce transmission error is to ensure high enough SINR level in every
UE. This can be done by a proper planning of the network topology that minimizes network
coverage hole. If the topology has a known coverage hole, then the UE should be configured
not to venture to that area.
Another approach to keep in mind is to avoid too-late handovers. In other words, handover
should happen before the UE's SINR becomes too low, otherwise the UE may fail to receive
the handover command from the source eNodeB. Handover algorithms have the means to control
how early or late a handover decision is made. For example, A2-A4-RSRQ handover algorithm
can be configured with a higher threshold to make it decide a handover earlier. Similarly,
smaller hysteresis and/or shorter time-to-trigger in the strongest cell handover algorithm
typically results in earlier handovers. In order to find the right values for these
parameters, one of the factors that should be considered is the UE movement speed.
Generally, a faster moving UE requires the handover to be executed earlier. Some research
work have suggested recommended values, such as in [Lee2010].
The above tips should be enough in normal simulation uses, but in the case some special
needs arise then an extreme measure can be taken into consideration. For instance, users
may consider disabling the channel error models. This will ensure that all
handover-related signaling messages will be transmitted successfully, regardless of
distance and channel condition. However, it will also affect all other data or control
packets not related to handover, which may be an unwanted side effect. Otherwise, it can
be done as follows:
Config::SetDefault ("ns3::LteSpectrumPhy::CtrlErrorModelEnabled", BooleanValue (false));
Config::SetDefault ("ns3::LteSpectrumPhy::DataErrorModelEnabled", BooleanValue (false));
By using the above code, we disable the error model in both control and data channels and
in both directions (downlink and uplink). This is necessary because handover-related
signaling messages are transmitted using these channels. An exception is when the
simulation uses the ideal RRC protocol. In this case, only the Random Access procedure is
left to be considered. The procedure consists of control messages, therefore we only need
to disable the control channel's error model.
Handover traces
The RRC model, in particular the LteEnbRrc and LteUeRrc objects, provide some useful
traces which can be hooked up to some custom functions so that they are called upon start
and end of the handover execution phase at both the UE and eNB side. As an example, in
your simulation program you can declare the following methods:
void
NotifyHandoverStartUe (std::string context,
uint64_t imsi,
uint16_t cellId,
uint16_t rnti,
uint16_t targetCellId)
{
std::cout << Simulator::Now ().GetSeconds () << " " << context
<< " UE IMSI " << imsi
<< ": previously connected to CellId " << cellId
<< " with RNTI " << rnti
<< ", doing handover to CellId " << targetCellId
<< std::endl;
}
void
NotifyHandoverEndOkUe (std::string context,
uint64_t imsi,
uint16_t cellId,
uint16_t rnti)
{
std::cout << Simulator::Now ().GetSeconds () << " " << context
<< " UE IMSI " << imsi
<< ": successful handover to CellId " << cellId
<< " with RNTI " << rnti
<< std::endl;
}
void
NotifyHandoverStartEnb (std::string context,
uint64_t imsi,
uint16_t cellId,
uint16_t rnti,
uint16_t targetCellId)
{
std::cout << Simulator::Now ().GetSeconds () << " " << context
<< " eNB CellId " << cellId
<< ": start handover of UE with IMSI " << imsi
<< " RNTI " << rnti
<< " to CellId " << targetCellId
<< std::endl;
}
void
NotifyHandoverEndOkEnb (std::string context,
uint64_t imsi,
uint16_t cellId,
uint16_t rnti)
{
std::cout << Simulator::Now ().GetSeconds () << " " << context
<< " eNB CellId " << cellId
<< ": completed handover of UE with IMSI " << imsi
<< " RNTI " << rnti
<< std::endl;
}
Then, you can hook up these methods to the corresponding trace sources like this:
Config::Connect ("/NodeList/*/DeviceList/*/LteEnbRrc/HandoverStart",
MakeCallback (&NotifyHandoverStartEnb));
Config::Connect ("/NodeList/*/DeviceList/*/LteUeRrc/HandoverStart",
MakeCallback (&NotifyHandoverStartUe));
Config::Connect ("/NodeList/*/DeviceList/*/LteEnbRrc/HandoverEndOk",
MakeCallback (&NotifyHandoverEndOkEnb));
Config::Connect ("/NodeList/*/DeviceList/*/LteUeRrc/HandoverEndOk",
MakeCallback (&NotifyHandoverEndOkUe));
The example program src/lte/examples/lena-x2-handover.cc illustrates how the all above
instructions can be integrated in a simulation program. You can run the program like this:
./waf --run lena-x2-handover
and it will output the messages printed by the custom handover trace hooks. In order
additionally visualize some meaningful logging information, you can run the program like
this:
NS_LOG=LteEnbRrc:LteUeRrc:EpcX2 ./waf --run lena-x2-handover
Frequency Reuse Algorithms
In this section we will describe how to use Frequency Reuse Algorithms in eNb within LTE
simulations. There are two possible ways of configuration. The first approach is the
"manual" one, it requires more parameters to be configured, but allow user to configure FR
algorithm as he/she needs. The second approach is more "automatic". It is very convenient,
because is the same for each FR algorithm, so user can switch FR algorithm very quickly by
changing only type of FR algorithm. One drawback is that "automatic" approach uses only
limited set of configurations for each algorithm, what make it less flexible, but is
sufficient for most of cases.
These two approaches will be described more in following sub-section.
If user do not configure Frequency Reuse algorithm, default one (i.e. LteFrNoOpAlgorithm)
is installed in eNb. It acts as if FR algorithm was disabled.
One thing that should be mentioned is that most of implemented FR algorithms work with
cell bandwidth greater or equal than 15 RBs. This limitation is caused by requirement that
at least three continuous RBs have to be assigned to UE for transmission.
Manual configuration
Frequency reuse algorithm can be configured "manually" within the simulation program by
setting type of FR algorithm and all its attributes. Currently, seven FR algorithms are
implemented:
· ns3::LteFrNoOpAlgorithm
· ns3::LteFrHardAlgorithm
· ns3::LteFrStrictAlgorithm
· ns3::LteFrSoftAlgorithm
· ns3::LteFfrSoftAlgorithm
· ns3::LteFfrEnhancedAlgorithm
· ns3::LteFfrDistributedAlgorithm
Selecting a FR algorithm is done via the LteHelper object and its SetFfrAlgorithmType
method as shown below:
Ptr<LteHelper> lteHelper = CreateObject<LteHelper> ();
lteHelper->SetFfrAlgorithmType ("ns3::LteFrHardAlgorithm");
Each implemented FR algorithm provide several configurable attributes. Users do not have
to care about UL and DL bandwidth configuration, because it is done automatically during
cell configuration. To change bandwidth for FR algorithm, configure required values for
LteEnbNetDevice:
uint8_t bandwidth = 100;
lteHelper->SetEnbDeviceAttribute ("DlBandwidth", UintegerValue (bandwidth));
lteHelper->SetEnbDeviceAttribute ("UlBandwidth", UintegerValue (bandwidth));
Now, each FR algorithms configuration will be described.
Hard Frequency Reuse Algorithm
As described in Section sec-fr-hard-algorithm of the Design Documentation
ns3::LteFrHardAlgorithm uses one sub-band. To configure this sub-band user need to specify
offset and bandwidth for DL and UL in number of RBs.
Hard Frequency Reuse Algorithm provides following attributes:
· DlSubBandOffset: Downlink Offset in number of Resource Block Groups
· DlSubBandwidth: Downlink Transmission SubBandwidth Configuration in number of
Resource Block Groups
· UlSubBandOffset: Uplink Offset in number of Resource Block Groups
· UlSubBandwidth: Uplink Transmission SubBandwidth Configuration in number of Resource
Block Groups
Example configuration of LteFrHardAlgorithm can be done in following way:
lteHelper->SetFfrAlgorithmType ("ns3::LteFrHardAlgorithm");
lteHelper->SetFfrAlgorithmAttribute ("DlSubBandOffset", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("DlSubBandwidth", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("UlSubBandOffset", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("UlSubBandwidth", UintegerValue (8));
NetDeviceContainer enbDevs = lteHelper->InstallEnbDevice (enbNodes.Get(0));
Above example allow eNB to use only RBs from 8 to 16 in DL and UL, while entire cell
bandwidth is 25.
Strict Frequency Reuse Algorithm
Strict Frequency Reuse Algorithm uses two sub-bands: one common for each cell and one
private. There is also RSRQ threshold, which is needed to decide within which sub-band UE
should be served. Moreover the power transmission in these sub-bands can be different.
Strict Frequency Reuse Algorithm provides following attributes:
· UlCommonSubBandwidth: Uplink Common SubBandwidth Configuration in number of Resource
Block Groups
· UlEdgeSubBandOffset: Uplink Edge SubBand Offset in number of Resource Block Groups
· UlEdgeSubBandwidth: Uplink Edge SubBandwidth Configuration in number of Resource
Block Groups
· DlCommonSubBandwidth: Downlink Common SubBandwidth Configuration in number of
Resource Block Groups
· DlEdgeSubBandOffset: Downlink Edge SubBand Offset in number of Resource Block Groups
· DlEdgeSubBandwidth: Downlink Edge SubBandwidth Configuration in number of Resource
Block Groups
· RsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served in
edge sub-band
· CenterPowerOffset: PdschConfigDedicated::Pa value for center sub-band, default value
dB0
· EdgePowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value dB0
· CenterAreaTpc: TPC value which will be set in DL-DCI for UEs in center area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· EdgeAreaTpc: TPC value which will be set in DL-DCI for UEs in edge area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
Example below allow eNB to use RBs from 0 to 6 as common sub-band and from 12 to 18 as
private sub-band in DL and UL, RSRQ threshold is 20 dB, power in center area equals
LteEnbPhy::TxPower - 3dB, power in edge area equals LteEnbPhy::TxPower + 3dB:
lteHelper->SetFfrAlgorithmType ("ns3::LteFrStrictAlgorithm");
lteHelper->SetFfrAlgorithmAttribute ("DlCommonSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("UlCommonSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandOffset", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandOffset", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("RsrqThreshold", UintegerValue (20));
lteHelper->SetFfrAlgorithmAttribute ("CenterPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB_3));
lteHelper->SetFfrAlgorithmAttribute ("EdgePowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB3));
lteHelper->SetFfrAlgorithmAttribute ("CenterAreaTpc", UintegerValue (1));
lteHelper->SetFfrAlgorithmAttribute ("EdgeAreaTpc", UintegerValue (2));
NetDeviceContainer enbDevs = lteHelper->InstallEnbDevice (enbNodes.Get(0));
Soft Frequency Reuse Algorithm
With Soft Frequency Reuse Algorithm, eNb uses entire cell bandwidth, but there are two
sub-bands, within UEs are served with different power level.
Soft Frequency Reuse Algorithm provides following attributes:
· UlEdgeSubBandOffset: Uplink Edge SubBand Offset in number of Resource Block Groups
· UlEdgeSubBandwidth: Uplink Edge SubBandwidth Configuration in number of Resource
Block Groups
· DlEdgeSubBandOffset: Downlink Edge SubBand Offset in number of Resource Block Groups
· DlEdgeSubBandwidth: Downlink Edge SubBandwidth Configuration in number of Resource
Block Groups
· AllowCenterUeUseEdgeSubBand: If true center UEs can receive on edge sub-band RBGs,
otherwise edge sub-band is allowed only for edge UEs, default value is true
· RsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served in
edge sub-band
· CenterPowerOffset: PdschConfigDedicated::Pa value for center sub-band, default value
dB0
· EdgePowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value dB0
· CenterAreaTpc: TPC value which will be set in DL-DCI for UEs in center area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· EdgeAreaTpc: TPC value which will be set in DL-DCI for UEs in edge area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
Example below configures RBs from 8 to 16 to be used by cell edge UEs and this sub-band is
not available for cell center users. RSRQ threshold is 20 dB, power in center area equals
LteEnbPhy::TxPower, power in edge area equals LteEnbPhy::TxPower + 3dB:
lteHelper->SetFfrAlgorithmType ("ns3::LteFrSoftAlgorithm");
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandOffset", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandwidth", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandOffset", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandwidth", UintegerValue (8));
lteHelper->SetFfrAlgorithmAttribute ("AllowCenterUeUseEdgeSubBand", BooleanValue (false));
lteHelper->SetFfrAlgorithmAttribute ("RsrqThreshold", UintegerValue (20));
lteHelper->SetFfrAlgorithmAttribute ("CenterPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB0));
lteHelper->SetFfrAlgorithmAttribute ("EdgePowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB3));
NetDeviceContainer enbDevs = lteHelper->InstallEnbDevice (enbNodes.Get(0));
Soft Fractional Frequency Reuse Algorithm
Soft Fractional Frequency Reuse (SFFR) uses three sub-bands: center, medium (common) and
edge. User have to configure only two of them: common and edge. Center sub-band will be
composed from the remaining bandwidth. Each sub-band can be served with different
transmission power. Since there are three sub-bands, two RSRQ thresholds needs to be
configured.
Soft Fractional Frequency Reuse Algorithm provides following attributes:
· UlCommonSubBandwidth: Uplink Common SubBandwidth Configuration in number of Resource
Block Groups
· UlEdgeSubBandOffset: Uplink Edge SubBand Offset in number of Resource Block Groups
· UlEdgeSubBandwidth: Uplink Edge SubBandwidth Configuration in number of Resource
Block Groups
· DlCommonSubBandwidth: Downlink Common SubBandwidth Configuration in number of
Resource Block Groups
· DlEdgeSubBandOffset: Downlink Edge SubBand Offset in number of Resource Block Groups
· DlEdgeSubBandwidth: Downlink Edge SubBandwidth Configuration in number of Resource
Block Groups
· CenterRsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served
in medium sub-band
· EdgeRsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served
in edge sub-band
· CenterAreaPowerOffset: PdschConfigDedicated::Pa value for center sub-band, default
value dB0
· MediumAreaPowerOffset: PdschConfigDedicated::Pa value for medium sub-band, default
value dB0
· EdgeAreaPowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value
dB0
· CenterAreaTpc: TPC value which will be set in DL-DCI for UEs in center area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· MediumAreaTpc: TPC value which will be set in DL-DCI for UEs in medium area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· EdgeAreaTpc: TPC value which will be set in DL-DCI for UEs in edge area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
In example below RBs from 0 to 6 will be used as common (medium) sub-band, RBs from 6 to
12 will be used as edge sub-band and RBs from 12 to 24 will be used as center sub-band (it
is composed with remaining RBs). RSRQ threshold between center and medium area is 28 dB,
RSRQ threshold between medium and edge area is 18 dB. Power in center area equals
LteEnbPhy::TxPower - 3dB, power in medium area equals LteEnbPhy::TxPower + 3dB, power in
edge area equals LteEnbPhy::TxPower + 3dB:
lteHelper->SetFfrAlgorithmType ("ns3::LteFfrSoftAlgorithm");
lteHelper->SetFfrAlgorithmAttribute ("UlCommonSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("DlCommonSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandOffset", UintegerValue (0));
lteHelper->SetFfrAlgorithmAttribute ("DlEdgeSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandOffset", UintegerValue (0));
lteHelper->SetFfrAlgorithmAttribute ("UlEdgeSubBandwidth", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("CenterRsrqThreshold", UintegerValue (28));
lteHelper->SetFfrAlgorithmAttribute ("EdgeRsrqThreshold", UintegerValue (18));
lteHelper->SetFfrAlgorithmAttribute ("CenterAreaPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB_3));
lteHelper->SetFfrAlgorithmAttribute ("MediumAreaPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB0));
lteHelper->SetFfrAlgorithmAttribute ("EdgeAreaPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB3));
NetDeviceContainer enbDevs = lteHelper->InstallEnbDevice (enbNodes.Get(0));
Enhanced Fractional Frequency Reuse Algorithm
Enhanced Fractional Frequency Reuse (EFFR) reserve part of system bandwidth for each cell
(typically there are 3 cell types and each one gets 1/3 of system bandwidth). Then part of
this subbandwidth it used as Primary Segment with reuse factor 3 and as Secondary Segment
with reuse factor 1. User has to configure (for DL and UL) offset of the cell subbandwidth
in number of RB, number of RB which will be used as Primary Segment and number of RB which
will be used as Secondary Segment. Primary Segment is used by cell at will, but RBs from
Secondary Segment can be assigned to UE only is CQI feedback from this UE have higher
value than configured CQI threshold. UE is considered as edge UE when its RSRQ is lower
than RsrqThreshold.
Since each eNb needs to know where are Primary and Secondary of other cell types, it will
calculate them assuming configuration is the same for each cell and only subbandwidth
offsets are different. So it is important to divide available system bandwidth equally to
each cell and apply the same configuration of Primary and Secondary Segments to them.
Enhanced Fractional Frequency Reuse Algorithm provides following attributes:
· UlSubBandOffset: Uplink SubBand Offset for this cell in number of Resource Block
Groups
· UlReuse3SubBandwidth: Uplink Reuse 3 SubBandwidth Configuration in number of Resource
Block Groups
· UlReuse1SubBandwidth: Uplink Reuse 1 SubBandwidth Configuration in number of Resource
Block Groups
· DlSubBandOffset: Downlink SubBand Offset for this cell in number of Resource Block
Groups
· DlReuse3SubBandwidth: Downlink Reuse 3 SubBandwidth Configuration in number of
Resource Block Groups
· DlReuse1SubBandwidth: Downlink Reuse 1 SubBandwidth Configuration in number of
Resource Block Groups
· RsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served in
edge sub-band
· CenterAreaPowerOffset: PdschConfigDedicated::Pa value for center sub-band, default
value dB0
· EdgeAreaPowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value
dB0
· DlCqiThreshold: If the DL-CQI for RBG of is higher than this threshold, transmission
on RBG is possible
· UlCqiThreshold: If the UL-CQI for RBG of is higher than this threshold, transmission
on RBG is possible
· CenterAreaTpc: TPC value which will be set in DL-DCI for UEs in center area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· EdgeAreaTpc: TPC value which will be set in DL-DCI for UEs in edge area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
In example below offset in DL and UL is 0 RB, 4 RB will be used in Primary Segment and
Secondary Segment. RSRQ threshold between center and edge area is 25 dB. DL and UL CQI
thresholds are set to value of 10. Power in center area equals LteEnbPhy::TxPower - 6dB,
power in edge area equals LteEnbPhy::TxPower + 0dB:
lteHelper->SetFfrAlgorithmType("ns3::LteFfrEnhancedAlgorithm");
lteHelper->SetFfrAlgorithmAttribute("RsrqThreshold", UintegerValue (25));
lteHelper->SetFfrAlgorithmAttribute("DlCqiThreshold", UintegerValue (10));
lteHelper->SetFfrAlgorithmAttribute("UlCqiThreshold", UintegerValue (10));
lteHelper->SetFfrAlgorithmAttribute("CenterAreaPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB_6));
lteHelper->SetFfrAlgorithmAttribute("EdgeAreaPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB0));
lteHelper->SetFfrAlgorithmAttribute("UlSubBandOffset", UintegerValue (0));
lteHelper->SetFfrAlgorithmAttribute("UlReuse3SubBandwidth", UintegerValue (4));
lteHelper->SetFfrAlgorithmAttribute("UlReuse1SubBandwidth", UintegerValue (4));
lteHelper->SetFfrAlgorithmAttribute("DlSubBandOffset", UintegerValue (0));
lteHelper->SetFfrAlgorithmAttribute("DlReuse3SubBandwidth", UintegerValue (4));
lteHelper->SetFfrAlgorithmAttribute("DlReuse1SubBandwidth", UintegerValue (4));
Distributed Fractional Frequency Reuse Algorithm
Distributed Fractional Frequency Reuse requires X2 interface between all eNB to be
installed. X2 interfaces can be installed only when EPC is configured, so this FFR scheme
can be used only with EPC scenarios.
With Distributed Fractional Frequency Reuse Algorithm, eNb uses entire cell bandwidth and
there can be two sub-bands: center sub-band and edge sub-band . Within these sub-bands UEs
can be served with different power level. Algorithm adaptively selects RBs for cell-edge
sub-band on basis of coordination information (i.e. RNTP) from adjecent cells and notifies
the base stations of the adjacent cells, which RBs it selected to use in edge sub-band. If
there are no UE classified as edge UE in cell, eNB will not use any RBs as edge sub-band.
Distributed Fractional Frequency Reuse Algorithm provides following attributes:
· CalculationInterval: Time interval between calculation of Edge sub-band, Default
value 1 second
· RsrqThreshold: If the RSRQ of is worse than this threshold, UE should be served in
edge sub-band
· RsrpDifferenceThreshold: If the difference between the power of the signal received
by UE from the serving cell and the power of the signal received from the adjacent
cell is less than a RsrpDifferenceThreshold value, the cell weight is incremented
· CenterPowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value
dB0
· EdgePowerOffset: PdschConfigDedicated::Pa value for edge sub-band, default value dB0
· EdgeRbNum: Number of RB that can be used in edge sub-band
· CenterAreaTpc: TPC value which will be set in DL-DCI for UEs in center area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
· EdgeAreaTpc: TPC value which will be set in DL-DCI for UEs in edge area, Absolute
mode is used, default value 1 is mapped to -1 according to TS36.213 Table 5.1.1.1-2
In example below calculation interval is 500 ms. RSRQ threshold between center and edge
area is 25. RSRP Difference Threshold is set to be 5. In DL and UL 6 RB will be used by
each cell in edge sub-band. Power in center area equals LteEnbPhy::TxPower - 0dB, power
in edge area equals LteEnbPhy::TxPower + 3dB:
lteHelper->SetFfrAlgorithmType("ns3::LteFfrDistributedAlgorithm");
lteHelper->SetFfrAlgorithmAttribute("CalculationInterval", TimeValue(MilliSeconds(500)));
lteHelper->SetFfrAlgorithmAttribute ("RsrqThreshold", UintegerValue (25));
lteHelper->SetFfrAlgorithmAttribute ("RsrpDifferenceThreshold", UintegerValue (5));
lteHelper->SetFfrAlgorithmAttribute ("EdgeRbNum", UintegerValue (6));
lteHelper->SetFfrAlgorithmAttribute ("CenterPowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB0));
lteHelper->SetFfrAlgorithmAttribute ("EdgePowerOffset",
UintegerValue (LteRrcSap::PdschConfigDedicated::dB3));
Automatic configuration
Frequency Reuse algorithms can also be configured in more “automatic” way by setting only
the bandwidth and FrCellTypeId. During initialization of FR instance, configuration for
set bandwidth and FrCellTypeId will be taken from configuration table. It is important
that only sub-bands will be configured, thresholds and transmission power will be set to
default values. If one wants, he/she can change thresholds and transmission power as show
in previous sub-section.
There are three FrCellTypeId : 1, 2, 3, which correspond to three different configurations
for each bandwidth. Three configurations allow to have different configurations in
neighbouring cells in hexagonal eNB layout. If user needs to have more different
configuration for neighbouring cells, he/she need to use manual configuration.
Example below show automatic FR algorithm configuration:
lteHelper->SetFfrAlgorithmType("ns3::LteFfrSoftAlgorithm");
lteHelper->SetFfrAlgorithmAttribute("FrCellTypeId", UintegerValue (1));
NetDeviceContainer enbDevs = lteHelper->InstallEnbDevice (enbNodes.Get(0));
Uplink Power Control
Uplink Power Control functionality is enabled by default. User can disable it by setting
the boolean attribute ns3::LteUePhy::EnableUplinkPowerControl to true.
User can switch between Open Loop Power Control and Closed Loop Power Control mechanisms
by setting the boolean attribute ns3::LteUePowerControl::ClosedLoop. By default Closed
Loop Power Control with Accumulation Mode is enabled.
Path-loss is key component of Uplink Power Control. It is computed as difference between
filtered RSRP and ReferenceSignalPower parameter. ReferenceSignalPower is sent with SIB2.
Attributes available in Uplink Power Control:
· ClosedLoop: if true Closed Loop Uplink Power Control mode is enabled and Open Loop
Power Control otherwise, default value is false
· AccumulationEnabled: if true Accumulation Mode is enabled and Absolute mode
otherwise, default value is false
· Alpha: the path loss compensation factor, default value is 1.0
· Pcmin: minimal UE TxPower, default value is -40 dBm
· Pcmax: maximal UE TxPower, default value is 23 dBm
· PoNominalPusch: this parameter should be set by higher layers, but currently it needs
to be configured by attribute system, possible values are integers in range (-126 ...
24), Default value is -80
· PoUePusch: this parameter should be set by higher layers, but currently it needs to
be configured by attribute system, possible values are integers in range (-8 ... 7),
Default value is 0
· PsrsOffset: this parameter should be set by higher layers, but currently it needs to
be configured by attribute system, possible values are integers in range (0 ... 15),
Default value is 7, what gives P_Srs_Offset_Value = 0
Traced values in Uplink Power Control:
· ReportPuschTxPower: Current UE TxPower for PUSCH
· ReportPucchTxPower: Current UE TxPower for PUCCH
· ReportSrsTxPower: Current UE TxPower for SRS
Example configuration is presented below:
Config::SetDefault ("ns3::LteUePhy::EnableUplinkPowerControl", BooleanValue (true));
Config::SetDefault ("ns3::LteEnbPhy::TxPower", DoubleValue (30));
Config::SetDefault ("ns3::LteUePowerControl::ClosedLoop", BooleanValue (true));
Config::SetDefault ("ns3::LteUePowerControl::AccumulationEnabled", BooleanValue (true));
As an example, user can take a look and run the lena-uplink-power-control program.
Examples Programs
The directory src/lte/examples/ contains some example simulation programs that show how to
simulate different LTE scenarios.
Reference scenarios
There is a vast amount of reference LTE simulation scenarios which can be found in the
literature. Here we list some of them:
· The system simulation scenarios mentioned in section A.2 of [TR36814].
· The dual stripe model [R4-092042], which is partially implemented in the example
program src/lte/examples/lena-dual-stripe.cc. This example program features a lot of
configurable parameters which can be customized by changing the corresponding global
variables. To get a list of all these global variables, you can run this command:
./waf --run lena-dual-stripe --command-template="%s --PrintGlobals"
The following subsection presents an example of running a simulation campaign using
this example program.
Handover simulation campaign
In this subsection, we will demonstrate an example of running a simulation campaign using
the LTE module of ns-3. The objective of the campaign is to compare the effect of each
built-in handover algorithm of the LTE module.
The campaign will use the lena-dual-stripe example program. First, we have to modify the
example program to produce the output that we need. In this occassion, we want to produce
the number of handovers, user average throughput, and average SINR.
The number of handovers can be obtained by counting the number of times the HandoverEndOk
Handover traces is fired. Then the user average throughput can be obtained by enabling the
RLC Simulation Output. Finally, SINR can be obtained by enabling the PHY simulation
output. The following sample code snippet shows one possible way to obtain the above:
void
NotifyHandoverEndOkUe (std::string context, uint64_t imsi,
uint16_t cellId, uint16_t rnti)
{
std::cout << "Handover IMSI " << imsi << std::endl;
}
int
main (int argc, char *argv[])
{
/*** SNIP ***/
Config::Connect ("/NodeList/*/DeviceList/*/LteUeRrc/HandoverEndOk",
MakeCallback (&NotifyHandoverEndOkUe));
lteHelper->EnablePhyTraces ();
lteHelper->EnableRlcTraces ();
Ptr<RadioBearerStatsCalculator> rlcStats = lteHelper->GetRlcStats ();
rlcStats->SetAttribute ("StartTime", TimeValue (Seconds (0)));
rlcStats->SetAttribute ("EpochDuration", TimeValue (Seconds (simTime)));
Simulator::Run ();
Simulator::Destroy ();
return 0;
}
Then we have to configure the parameters of the program to suit our simulation needs. We
are looking for the following assumptions in our simulation:
· 7 sites of tri-sectored macro eNodeBs (i.e. 21 macrocells) deployed in hexagonal
layout with 500 m inter-site distance.
· Although lena-dual-stripe is originally intended for a two-tier (macrocell and
femtocell) simulation, we will simplify our simulation to one-tier (macrocell)
simulation only.
· UEs are randomly distributed around the sites and attach to the network automatically
using Idle mode cell selection. After that, UE will roam the simulation environment
with 60 kmph movement speed.
· 50 seconds simulation duration, so UEs would have traveled far enough to trigger some
handovers.
· 46 dBm macrocell Tx power and 10 dBm UE Tx power.
· EPC mode will be used because the X2 handover procedure requires it to be enabled.
· Full-buffer downlink and uplink traffic, both in 5 MHz bandwidth, using TCP protocol
and Proportional Fair scheduler.
· Ideal RRC protocol.
Table lena-dual-stripe parameter configuration for handover campaign below shows how we
configure the parameters of lena-dual-stripe to achieve the above assumptions.
lena-dual-stripe parameter configuration for handover campaign
┌───────────────────┬─────────┬──────────────────────────┐
│Parameter name │ Value │ Description │
├───────────────────┼─────────┼──────────────────────────┤
│simTime │ 50 │ 50 seconds simulation │
│ │ │ duration │
├───────────────────┼─────────┼──────────────────────────┤
│nBlocks │ 0 │ Disabling apartment │
│ │ │ buildings and femtocells │
├───────────────────┼─────────┼──────────────────────────┤
│nMacroEnbSites │ 7 │ Number of macrocell │
│ │ │ sites (each site has 3 │
│ │ │ cells) │
├───────────────────┼─────────┼──────────────────────────┤
│nMacroEnbSitesX │ 2 │ The macrocell sites will │
│ │ │ be positioned in a 2-3-2 │
│ │ │ formation │
├───────────────────┼─────────┼──────────────────────────┤
│interSiteDistance │ 500 │ 500 m distance between │
│ │ │ adjacent macrocell sites │
├───────────────────┼─────────┼──────────────────────────┤
│macroEnbTxPowerDbm │ 46 │ 46 dBm Tx power for each │
│ │ │ macrocell │
├───────────────────┼─────────┼──────────────────────────┤
│epc │ 1 │ Enable EPC mode │
└───────────────────┴─────────┴──────────────────────────┘
│epcDl │ 1 │ Enable full-buffer DL │
│ │ │ traffic │
├───────────────────┼─────────┼──────────────────────────┤
│epcUl │ 1 │ Enable full-buffer UL │
│ │ │ traffic │
├───────────────────┼─────────┼──────────────────────────┤
│useUdp │ 0 │ Disable UDP traffic and │
│ │ │ enable TCP instead │
├───────────────────┼─────────┼──────────────────────────┤
│macroUeDensity │ 0.00002 │ Determines number of UEs │
│ │ │ (translates to 48 UEs in │
│ │ │ our simulation) │
├───────────────────┼─────────┼──────────────────────────┤
│outdoorUeMinSpeed │ 16.6667 │ Minimum UE movement │
│ │ │ speed in m/s (60 kmph) │
├───────────────────┼─────────┼──────────────────────────┤
│outdoorUeMaxSpeed │ 16.6667 │ Maximum UE movement │
│ │ │ speed in m/s (60 kmph) │
├───────────────────┼─────────┼──────────────────────────┤
│macroEnbBandwidth │ 25 │ 5 MHz DL and UL │
│ │ │ bandwidth │
├───────────────────┼─────────┼──────────────────────────┤
│generateRem │ 1 │ (Optional) For plotting │
│ │ │ the Radio Environment │
│ │ │ Map │
└───────────────────┴─────────┴──────────────────────────┘
Some of the required assumptions are not available as parameters of lena-dual-stripe. In
this case, we override the default attributes, as shown in Table Overriding default
attributes for handover campaign below.
Overriding default attributes for handover campaign
┌─────────────────────────────────────────────────────┬────────────────────────────────┬──────────────────────────┐
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::LteHelper::HandoverAlgorithm │ ns3::NoOpHandoverAlgorithm, │ Choice of handover │
│ │ ns3::A3RsrpHandoverAlgorithm, │ algorithm │
│ │ ns3::A2A4RsrqHandoverAlgorithm │ │
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::LteHelper::Scheduler │ ns3::PfFfMacScheduler │ Proportional Fair │
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::RadioBearerStatsCalculator::DlRlcOutputFilename │ <run>-DlRlcStats.txt │ File name for DL RLC │
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::RadioBearerStatsCalculator::UlRlcOutputFilename │ <run>-UlRlcStats.txt │ File name for UL RLC │
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::PhyStatsCalculator::DlRsrpSinrFilename │ <run>-DlRsrpSinrStats.txt │ File name for DL PHY │
├─────────────────────────────────────────────────────┼────────────────────────────────┼──────────────────────────┤
│ns3::PhyStatsCalculator::UlSinrFilename │ <run>-UlSinrStats.txt │ File name for UL PHY │
└─────────────────────────────────────────────────────┴────────────────────────────────┴──────────────────────────┘
ns-3 provides many ways for passing configuration values into a simulation. In this
example, we will use the command line arguments. It is basically done by appending the
parameters and their values to the waf call when starting each individual simulation. So
the waf calls for invoking our 3 simulations would look as below:
$ ./waf --run="lena-dual-stripe
--simTime=50 --nBlocks=0 --nMacroEnbSites=7 --nMacroEnbSitesX=2
--epc=1 --useUdp=0 --outdoorUeMinSpeed=16.6667 --outdoorUeMaxSpeed=16.6667
--ns3::LteHelper::HandoverAlgorithm=ns3::NoOpHandoverAlgorithm
--ns3::RadioBearerStatsCalculator::DlRlcOutputFilename=no-op-DlRlcStats.txt
--ns3::RadioBearerStatsCalculator::UlRlcOutputFilename=no-op-UlRlcStats.txt
--ns3::PhyStatsCalculator::DlRsrpSinrFilename=no-op-DlRsrpSinrStats.txt
--ns3::PhyStatsCalculator::UlSinrFilename=no-op-UlSinrStats.txt
--RngRun=1" > no-op.txt
$ ./waf --run="lena-dual-stripe
--simTime=50 --nBlocks=0 --nMacroEnbSites=7 --nMacroEnbSitesX=2
--epc=1 --useUdp=0 --outdoorUeMinSpeed=16.6667 --outdoorUeMaxSpeed=16.6667
--ns3::LteHelper::HandoverAlgorithm=ns3::A3RsrpHandoverAlgorithm
--ns3::RadioBearerStatsCalculator::DlRlcOutputFilename=a3-rsrp-DlRlcStats.txt
--ns3::RadioBearerStatsCalculator::UlRlcOutputFilename=a3-rsrp-UlRlcStats.txt
--ns3::PhyStatsCalculator::DlRsrpSinrFilename=a3-rsrp-DlRsrpSinrStats.txt
--ns3::PhyStatsCalculator::UlSinrFilename=a3-rsrp-UlSinrStats.txt
--RngRun=1" > a3-rsrp.txt
$ ./waf --run="lena-dual-stripe
--simTime=50 --nBlocks=0 --nMacroEnbSites=7 --nMacroEnbSitesX=2
--epc=1 --useUdp=0 --outdoorUeMinSpeed=16.6667 --outdoorUeMaxSpeed=16.6667
--ns3::LteHelper::HandoverAlgorithm=ns3::A2A4RsrqHandoverAlgorithm
--ns3::RadioBearerStatsCalculator::DlRlcOutputFilename=a2-a4-rsrq-DlRlcStats.txt
--ns3::RadioBearerStatsCalculator::UlRlcOutputFilename=a2-a4-rsrq-UlRlcStats.txt
--ns3::PhyStatsCalculator::DlRsrpSinrFilename=a2-a4-rsrq-DlRsrpSinrStats.txt
--ns3::PhyStatsCalculator::UlSinrFilename=a2-a4-rsrq-UlSinrStats.txt
--RngRun=1" > a2-a4-rsrq.txt
Some notes on the execution:
· Notice that some arguments are not specified because they are already the same as the
default values. We also keep the handover algorithms on each own default settings.
· Note the file names of simulation output, e.g. RLC traces and PHY traces, because we
have to make sure that they are not overwritten by the next simulation run. In this
example, we specify the names one by one using the command line arguments.
· The --RngRun=1 argument at the end is used for setting the run number used by the
random number generator used in the simulation. We re-run the same simulations with
different RngRun values, hence creating several independent replications of the same
simulations. Then we average the results obtained from these replications to achieve
some statistical confidence.
· We can add a --generateRem=1 argument to generate the files necessary for generating
the Radio Environment Map (REM) of the simulation. The result is Figure REM obtained
from a simulation in handover campaign below, which can be produced by following the
steps described in Section Radio Environment Maps. This figure also shows the
position of eNodeBs and UEs at the beginning of a simulation using RngRun = 1. Other
values of RngRun may produce different UE position.
[image] REM obtained from a simulation in handover campaign.UNINDENT
After hours of running, the simulation campaign will eventually end. Next we will
perform some post-processing on the produced simulation output to obtain meaningful
information out of it.
In this example, we use GNU Octave to assist the processing of throughput and SINR data,
as demonstrated in a sample GNU Octave script below:
% RxBytes is the 10th column
DlRxBytes = load ("no-op-DlRlcStats.txt") (:,10);
DlAverageThroughputKbps = sum (DlRxBytes) * 8 / 1000 / 50
% RxBytes is the 10th column
UlRxBytes = load ("no-op-UlRlcStats.txt") (:,10);
UlAverageThroughputKbps = sum (UlRxBytes) * 8 / 1000 / 50
% Sinr is the 6th column
DlSinr = load ("no-op-DlRsrpSinrStats.txt") (:,6);
% eliminate NaN values
idx = isnan (DlSinr);
DlSinr (idx) = 0;
DlAverageSinrDb = 10 * log10 (mean (DlSinr)) % convert to dB
% Sinr is the 5th column
UlSinr = load ("no-op-UlSinrStats.txt") (:,5);
% eliminate NaN values
idx = isnan (UlSinr);
UlSinr (idx) = 0;
UlAverageSinrDb = 10 * log10 (mean (UlSinr)) % convert to dB
As for the number of handovers, we can use simple shell scripting to count the number of
occurrences of string "Handover" in the log file:
$ grep "Handover" no-op.txt | wc -l
Table Results of handover campaign below shows the complete statistics after we are done
with post-processing on every individual simulation run. The values shown are the average
of the results obtained from RngRun of 1, 2, 3, and 4.
Results of handover campaign
┌────────────────────┬────────────┬─────────────┬────────────────┐
│Statistics │ No-op │ A2-A4-RSRQ │ Strongest cell │
├────────────────────┼────────────┼─────────────┼────────────────┤
│Average DL system │ 6 615 kbps │ 20 509 kbps │ 19 709 kbps │
│throughput │ │ │ │
├────────────────────┼────────────┼─────────────┼────────────────┤
│Average UL system │ 4 095 kbps │ 5 705 kbps │ 6 627 kbps │
│throughput │ │ │ │
├────────────────────┼────────────┼─────────────┼────────────────┤
│Average DL SINR │ -0.10 dB │ 5.19 dB │ 5.24 dB │
├────────────────────┼────────────┼─────────────┼────────────────┤
│Average UL SINR │ 9.54 dB │ 81.57 dB │ 79.65 dB │
├────────────────────┼────────────┼─────────────┼────────────────┤
│Number of handovers │ 0 │ 0.05694 │ 0.04771 │
│per UE per second │ │ │ │
└────────────────────┴────────────┴─────────────┴────────────────┘
The results show that having a handover algorithm in a mobility simulation improves both
user throughput and SINR significantly. There is little difference between the two
handover algorithms in this campaign scenario. It would be interesting to see their
performance in different scenarios, such as scenarios with home eNodeBs deployment.
Frequency Reuse examples
There are two examples showing Frequency Reuse Algorithms functionality.
lena-frequency-reuse is simple example with 3 eNBs in triangle layout. There are 3 cell
edge UEs, which are located in the center of this triangle and 3 cell center UEs (one near
each eNB). User can also specify the number of randomly located UEs. FR algorithm is
installed in eNBs and each eNB has different FrCellTypeId, what means each eNB uses
different FR configuration. User can run lena-frequency-reuse with 6 different FR
algorithms: NoOp, Hard FR, Strict FR, Soft FR, Soft FFR and Enhanced FFR. To run scenario
with Distributed FFR algorithm, user should use lena-distributed-ffr. These two examples
are very similar, but they were splitted because Distributed FFR requires EPC to be used,
and other algorihtms do not.
To run lena-frequency-reuse with different Frequency Reuse algorithms, user needs to
specify FR algorithm by overriding the default attribute ns3::LteHelper::FfrAlgorithm.
Example command to run lena-frequency-reuse with Soft FR algorithm is presented below:
$ ./waf --run "lena-frequency-reuse --ns3::LteHelper::FfrAlgorithm=ns3::LteFrSoftAlgorithm"
In these examples functionality to generate REM and spectrum analyzer trace was added.
User can enable generation of it by setting generateRem and generateSpectrumTrace
attributes.
Command to generate REM for RB 1 in data channel from lena-frequency-reuse scenario with
Soft FR algorithm is presented below:
$ ./waf --run "lena-frequency-reuse --ns3::LteHelper::FfrAlgorithm=ns3::LteFrSoftAlgorithm
--generateRem=true --remRbId=1"
Radio Environment Map for Soft FR is presented in Figure REM for RB 1 obtained from
lena-frequency-reuse example with Soft FR algorithm enabled.
[image] REM for RB 1 obtained from lena-frequency-reuse example with Soft FR algorithm
enabled.UNINDENT
Command to generate spectrum trace from lena-frequency-reuse scenario with Soft FFR
algorithm is presented below (Spectrum Analyzer position needs to be configured inside
script):
$ ./waf --run "lena-frequency-reuse --ns3::LteHelper::FfrAlgorithm=ns3::LteFfrSoftAlgorithm
--generateSpectrumTrace=true"
Example spectrum analyzer trace is presented in figure Spectrum Analyzer trace obtained
from lena-frequency-reuse example with Soft FFR algorithm enabled. Spectrum Analyzer was
located need eNB with FrCellTypeId 2.. As can be seen, different data channel subbands
are sent with different power level (according to configuration), while control channel is
transmitted with uniform power along entire system bandwidth.
[image] Spectrum Analyzer trace obtained from lena-frequency-reuse example with Soft FFR
algorithm enabled. Spectrum Analyzer was located need eNB with FrCellTypeId 2..UNINDENT
lena-dual-stripe can be also run with Frequency Reuse algorithms installed in all macro
eNB. User needs to specify FR algorithm by overriding the default attribute
ns3::LteHelper::FfrAlgorithm. Example command to run lena-dual-stripe with Hard FR
algorithm is presented below:
$ ./waf --run="lena-dual-stripe
--simTime=50 --nBlocks=0 --nMacroEnbSites=7 --nMacroEnbSitesX=2
--epc=1 --useUdp=0 --outdoorUeMinSpeed=16.6667 --outdoorUeMaxSpeed=16.6667
--ns3::LteHelper::HandoverAlgorithm=ns3::NoOpHandoverAlgorithm
--ns3::LteHelper::FfrAlgorithm=ns3::LteFrHardAlgorithm
--ns3::RadioBearerStatsCalculator::DlRlcOutputFilename=no-op-DlRlcStats.txt
--ns3::RadioBearerStatsCalculator::UlRlcOutputFilename=no-op-UlRlcStats.txt
--ns3::PhyStatsCalculator::DlRsrpSinrFilename=no-op-DlRsrpSinrStats.txt
--ns3::PhyStatsCalculator::UlSinrFilename=no-op-UlSinrStats.txt
--RngRun=1" > no-op.txt
Example command to generate REM for RB 1 in data channel from lena-dual-stripe scenario
with Hard FR algorithm is presented below:
$ ./waf --run="lena-dual-stripe
--simTime=50 --nBlocks=0 --nMacroEnbSites=7 --nMacroEnbSitesX=2
--epc=0 --useUdp=0 --outdoorUeMinSpeed=16.6667 --outdoorUeMaxSpeed=16.6667
--ns3::LteHelper::HandoverAlgorithm=ns3::NoOpHandoverAlgorithm
--ns3::LteHelper::FfrAlgorithm=ns3::LteFrHardAlgorithm
--ns3::RadioBearerStatsCalculator::DlRlcOutputFilename=no-op-DlRlcStats.txt
--ns3::RadioBearerStatsCalculator::UlRlcOutputFilename=no-op-UlRlcStats.txt
--ns3::PhyStatsCalculator::DlRsrpSinrFilename=no-op-DlRsrpSinrStats.txt
--ns3::PhyStatsCalculator::UlSinrFilename=no-op-UlSinrStats.txt
--RngRun=1 --generateRem=true --remRbId=1" > no-op.txt
Radio Environment Maps for RB 1, 10 and 20 generated from lena-dual-stripe scenario with
Hard Frequency Reuse algorithm are presented in the figures below. These RB were selected
because each one is used by different FR cell type.
[image] REM for RB 1 obtained from lena-dual-stripe simulation with Hard FR algorithm
enabled.UNINDENT
[image] REM for RB 10 obtained from lena-dual-stripe simulation with Hard FR algorithm
enabled.UNINDENT
[image] REM for RB 20 obtained from lena-dual-stripe simulation with Hard FR algorithm
enabled.UNINDENT
Troubleshooting and debugging tips
Many users post on the ns-3-users mailing list asking, for example, why they don't get any
traffic in their simulation, or maybe only uplink but no downlink traffic, etc. In most of
the cases, it's a bug in the user simulation program. Here are some tips to debug the
program and find out the cause of the problem.
The general approach is to selectively and incrementally enable the logging of relevant
LTE module components, veryfing upon each activation that the output is as expected. In
detail:
· first check the control plane, in particular the RRC connection establishment
procedure, by enabling the log components LteUeRrc and LteEnbRrc
· then check packet transmissions on the data plane, starting by enabling the log
componbents LteUeNetDevice and the EpcSgwPgwApplication, then EpcEnbApplication, then
moving down the LTE radio stack (PDCP, RLC, MAC, and finally PHY). All this until you
find where packets stop being processed / forwarded.
Testing Documentation
Overview
To test and validate the ns-3 LTE module, several test suites are provided which are
integrated with the ns-3 test framework. To run them, you need to have configured the
build of the simulator in this way:
$ ./waf configure --enable-tests --enable-modules=lte --enable-examples
$ ./test.py
The above will run not only the test suites belonging to the LTE module, but also those
belonging to all the other ns-3 modules on which the LTE module depends. See the ns-3
manual for generic information on the testing framework.
You can get a more detailed report in HTML format in this way:
$ ./test.py -w results.html
After the above command has run, you can view the detailed result for each test by opening
the file results.html with a web browser.
You can run each test suite separately using this command:
$ ./test.py -s test-suite-name
For more details about test.py and the ns-3 testing framework, please refer to the ns-3
manual.
Description of the test suites
Unit Tests
SINR calculation in the Downlink
The test suite lte-downlink-sinr checks that the SINR calculation in downlink is performed
correctly. The SINR in the downlink is calculated for each RB assigned to data
transmissions by dividing the power of the intended signal from the considered eNB by the
sum of the noise power plus all the transmissions on the same RB coming from other eNBs
(the interference signals):
In general, different signals can be active during different periods of time. We define a
chunk as the time interval between any two events of type either start or end of a
waveform. In other words, a chunk identifies a time interval during which the set of
active waveforms does not change. Let i be the generic chunk, T_i its duration and
thrm{SINR_i} its SINR, calculated with the above equation. The calculation of the average
SINR riemeSINR calculation in the Uplink
The test suite lte-uplink-sinr checks that the SINR calculation in uplink is performed
correctly. This test suite is identical to lte-downlink-sinr described in the previous
section, with the difference than both the signal and the interference now refer to
transmissions by the UEs, and reception is performed by the eNB. This test suite
recreates a number of random transmitted signals and interference signals to mimic a
scenario where an eNB is trying to decode the signal from several UEs simultaneously (the
ones in the cell of the eNB) while facing interference from other UEs (the ones belonging
to other cells).
The test vectors are obtained by a dedicated Octave script. The test passes if the
calculated values are equal to the test vector within a tolerance of 10^{-7} which, as for
the downlink SINR test, deals with floating point arithmetic approximation issues.
E-UTRA Absolute Radio Frequency Channel Number (EARFCN)
The test suite lte-earfcn checks that the carrier frequency used by the
LteSpectrumValueHelper class (which implements the LTE spectrum model) is done in
compliance with [TS36101], where the E-UTRA Absolute Radio Frequency Channel Number
(EARFCN) is defined. The test vector for this test suite comprises a set of EARFCN values
and the corresponding carrier frequency calculated by hand following the specification of
[TS36101]. The test passes if the carrier frequency returned by LteSpectrumValueHelper is
the same as the known value for each element in the test vector.
System Tests
Dedicated Bearer Deactivation Tests
The test suite ‘lte-test-deactivate-bearer’ creates test case with single EnodeB and Three
UE’s. Each UE consists of one Default and one Dedicated EPS bearer with same bearer
specification but with different ARP. Test Case Flow is as follows: Attach UE -> Create
Default+Dedicated Bearer -> Deactivate one of the Dedicated bearer
Test case further deactivates dedicated bearer having bearer ID 2(LCID=BearerId+2) of
First UE (UE_ID=1) User can schedule bearer deactivation after specific time delay using
Simulator::Schedule () method.
Once the test case execution ends it will create DlRlcStats.txt and UlRlcStats.txt. Key
fields that need to be checked in statistics are:
|
Start | end | Cell ID | IMSI | RNTI | LCID | TxBytes | RxBytes |
Test case executes in three epoch’s. 1) In first Epoch (0.04s-1.04s) All UE’s and
corresponding bearers gets attached
and packet flow over the dedicated bearers activated.
2. In second Epoch (1.04s-2.04s), bearer deactivation is instantiated, hence User can see
relatively less number of TxBytes on UE_ID=1 and LCID=4 as compared to other bearers.
3. In third Epoch (2.04s-3.04s) since bearer deactivation of UE_ID=1 and LCID=4 is
completed, user will not see any logging related to LCID=4.
Test case passes if and only if 1) IMSI=1 and LCID=4 completely removed in third epoch 2)
No packets seen in TxBytes and RxBytes corresponding to IMSI=1 and LCID=4 If above
criterion does not match test case considered to be failed
Adaptive Modulation and Coding Tests
The test suite lte-link-adaptation provides system tests recreating a scenario with a
single eNB and a single UE. Different test cases are created corresponding to different
SNR values perceived by the UE. The aim of the test is to check that in each test case the
chosen MCS corresponds to some known reference values. These reference values are obtained
by re-implementing in Octave (see src/lte/test/reference/lte_amc.m) the model described in
Section sec-lte-amc for the calculation of the spectral efficiency, and determining the
corresponding MCS index by manually looking up the tables in [R1-081483]. The resulting
test vector is represented in Figure Test vector for Adaptive Modulation and Coding.
The MCS which is used by the simulator is measured by obtaining the tracing output
produced by the scheduler after 4ms (this is needed to account for the initial delay in
CQI reporting). The SINR which is calcualted by the simulator is also obtained using the
LteChunkProcessor interface. The test passes if both the following conditions are
satisfied:
1. the SINR calculated by the simulator correspond to the SNR of the test vector within
an absolute tolerance of 10^{-7};
2. the MCS index used by the simulator exactly corresponds to the one in the test
vector.
[image] Test vector for Adaptive Modulation and Coding.UNINDENT
Inter-cell Interference Tests
The test suite lte-interference provides system tests recreating an inter-cell
interference scenario with two eNBs, each having a single UE attached to it and employing
Adaptive Modulation and Coding both in the downlink and in the uplink. The topology of the
scenario is depicted in Figure Topology for the inter-cell interference test. The d_1
parameter represents the distance of each UE to the eNB it is attached to, whereas the d_2
parameter represent the interferer distance. We note that the scenario topology is such
that the interferer distance is the same for uplink and downlink; still, the actual
interference power perceived will be different, because of the different propagation loss
in the uplink and downlink bands. Different test cases are obtained by varying the d_1 and
d_2 parameters.
[image] Topology for the inter-cell interference test.UNINDENT
The test vectors are obtained by use of a dedicated octave script (available in
src/lte/test/reference/lte_link_budget_interference.m), which does the link budget
calculations (including interference) corresponding to the topology of each test case,
and outputs the resulting SINR and spectral efficiency. The latter is then used to
determine (using the same procedure adopted for Adaptive Modulation and Coding Tests. We
note that the test vector contains separate values for uplink and downlink.
UE Measurements Tests
The test suite lte-ue-measurements provides system tests recreating an inter-cell
interference scenario identical of the one defined for lte-interference test-suite.
However, in this test the quantities to be tested are represented by RSRP and RSRQ
measurements performed by the UE in two different points of the stack: the source, which
is UE PHY layer, and the destination, that is the eNB RRC.
The test vectors are obtained by the use of a dedicated octave script (available in
src/lte/test/reference/lte-ue-measurements.m), which does the link budget calculations
(including interference) corresponding to the topology of each test case, and outputs the
resulting RSRP and RSRQ. The obtained values are then used for checking the correctness of
the UE Measurements at PHY layer. After that, they have to be converted according to 3GPP
formatting for the purpose of checking their correctness at eNB RRC level.
UE measurement configuration tests
Besides the previously mentioned test suite, there are 3 other test suites for testing UE
measurements: lte-ue-measurements-piecewise-1, lte-ue-measurements-piecewise-2, and
lte-ue-measurements-handover. These test suites are more focused on the reporting trigger
procedure, i.e. the correctness of the implementation of the event-based triggering
criteria is verified here.
In more specific, the tests verify the timing and the content of each measurement reports
received by eNodeB. Each test case is an stand-alone LTE simulation and the test case will
pass if measurement report(s) only occurs at the prescribed time and shows the correct
level of RSRP (RSRQ is not verified at the moment).
Piecewise configuration
The piecewise configuration aims to test a particular UE measurements configuration. The
simulation script will setup the corresponding measurements configuration to the UE, which
will be active throughout the simulation.
Since the reference values are precalculated by hands, several assumptions are made to
simplify the simulation. Firstly, the channel is only affected by path loss model (in this
case, Friis model is used). Secondly, the ideal RRC protocol is used, and layer 3
filtering is disabled. Finally, the UE moves in a predefined motion pattern between 4
distinct spots, as depicted in Figure UE movement trace throughout the simulation in
piecewise configuration below. Therefore the fluctuation of the measured RSRP can be
determined more easily.
[image] UE movement trace throughout the simulation in piecewise configuration.UNINDENT
The motivation behind the "teleport" between the predefined spots is to introduce
drastic change of RSRP level, which will guarantee the triggering of entering or leaving
condition of the tested event. By performing drastic changes, the test can be run within
shorter amount of time.
Figure Measured RSRP trace of an example Event A1 test case in piecewise configuration
below shows the measured RSRP after layer 1 filtering by the PHY layer during the
simulation with a piecewise configuration. Because layer 3 filtering is disabled, these
are the exact values used by the UE RRC instance to evaluate reporting trigger
procedure. Notice that the values are refreshed every 200 ms, which is the default
filtering period of PHY layer measurements report. The figure also shows the time when
entering and leaving conditions of an example instance of Event A1 (serving cell becomes
better than threshold) occur during the simulation.
[image] Measured RSRP trace of an example Event A1 test case in piecewise
configuration.UNINDENT
Each reporting criterion is tested several times with different threshold/offset
parameters. Some test scenarios also take hysteresis and time-to-trigger into account.
Figure Measured RSRP trace of an example Event A1 with hysteresis test case in piecewise
configuration depicts the effect of hysteresis in another example of Event A1 test.
[image] Measured RSRP trace of an example Event A1 with hysteresis test case in
piecewise configuration.UNINDENT
Piecewise configuration is used in two test suites of UE measurements. The first one is
lte-ue-measurements-piecewise-1, henceforth Piecewise test #1, which simulates 1 UE and
1 eNodeB. The other one is lte-ue-measurements-piecewise-2, which has 1 UE and 2 eNodeBs
in the simulation.
Piecewise test #1 is intended to test the event-based criteria which are not dependent
on the existence of a neighbouring cell. These criteria include Event A1 and A2. The
other events are also briefly tested to verify that they are still working correctly
(albeit not reporting anything) in the absence of any neighbouring cell. Table UE
measurements test scenarios using piecewise configuration #1 below lists the scenarios
tested in piecewise test #1.
UE measurements test scenarios using piecewise configuration #1
┌───────┬───────────┬──────────────────┬────────────┬─────────────────┐
│Test # │ Reporting │ Threshold/Offset │ Hysteresis │ Time-to-Trigger │
│ │ Criteria │ │ │ │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│1 │ Event A1 │ Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│2 │ Event A1 │ Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│3 │ Event A1 │ Normal │ No │ Short │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│4 │ Event A1 │ Normal │ No │ Long │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│5 │ Event A1 │ Normal │ No │ Super │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│6 │ Event A1 │ Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│7 │ Event A1 │ High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│8 │ Event A2 │ Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│9 │ Event A2 │ Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│10 │ Event A2 │ Normal │ No │ Short │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│11 │ Event A2 │ Normal │ No │ Long │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│12 │ Event A2 │ Normal │ No │ Super │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│13 │ Event A2 │ Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│14 │ Event A2 │ High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│15 │ Event A3 │ Zero │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│16 │ Event A4 │ Normal │ No │ No │
└───────┴───────────┴──────────────────┴────────────┴─────────────────┘
│17 │ Event A5 │ Normal-Normal │ No │ No │
└───────┴───────────┴──────────────────┴────────────┴─────────────────┘
Other events such as Event A3, A4, and A5 depend on measurements of neighbouring cell, so
they are more thoroughly tested in Piecewise test #2. The simulation places the nodes on a
straight line and instruct the UE to "jump" in a similar manner as in Piecewise test #1.
Handover is disabled in the simulation, so the role of serving and neighbouring cells do
not switch during the simulation. Table UE measurements test scenarios using piecewise
configuration #2 below lists the scenarios tested in Piecewise test #2.
UE measurements test scenarios using piecewise configuration #2
┌───────┬───────────┬──────────────────┬────────────┬─────────────────┐
│Test # │ Reporting │ Threshold/Offset │ Hysteresis │ Time-to-Trigger │
│ │ Criteria │ │ │ │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│1 │ Event A1 │ Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│2 │ Event A1 │ Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│3 │ Event A1 │ Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│4 │ Event A1 │ High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│5 │ Event A2 │ Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│6 │ Event A2 │ Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│7 │ Event A2 │ Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│8 │ Event A2 │ High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│9 │ Event A3 │ Positive │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│10 │ Event A3 │ Zero │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│11 │ Event A3 │ Zero │ No │ Short │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│12 │ Event A3 │ Zero │ No │ Super │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│13 │ Event A3 │ Zero │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│14 │ Event A3 │ Negative │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│15 │ Event A4 │ Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│16 │ Event A4 │ Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│17 │ Event A4 │ Normal │ No │ Short │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│18 │ Event A4 │ Normal │ No │ Super │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│19 │ Event A4 │ Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│20 │ Event A4 │ High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│21 │ Event A5 │ Low-Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│22 │ Event A5 │ Low-Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│23 │ Event A5 │ Low-High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│24 │ Event A5 │ Normal-Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│25 │ Event A5 │ Normal-Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│26 │ Event A5 │ Normal-Normal │ No │ Short │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│27 │ Event A5 │ Normal-Normal │ No │ Super │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│28 │ Event A5 │ Normal-Normal │ Yes │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│29 │ Event A5 │ Normal-High │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│30 │ Event A5 │ High-Low │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│31 │ Event A5 │ High-Normal │ No │ No │
├───────┼───────────┼──────────────────┼────────────┼─────────────────┤
│32 │ Event A5 │ High-High │ No │ No │
└───────┴───────────┴──────────────────┴────────────┴─────────────────┘
One note about the tests with time-to-trigger, they are tested using 3 different values of
time-to-trigger: short (shorter than report interval), long (shorter than the filter
measurement period of 200 ms), and super (longer than 200 ms). The first two ensure that
time-to-trigger evaluation always use the latest measurement reports received from PHY
layer. While the last one is responsible for verifying time-to-trigger cancellation, for
example when a measurement report from PHY shows that the entering/leaving condition is no
longer true before the first trigger is fired.
Handover configuration
The purpose of the handover configuration is to verify whether UE measurement
configuration is updated properly after a succesful handover takes place. For this
purpose, the simulation will construct 2 eNodeBs with different UE measurement
configuration, and the UE will perform handover from one cell to another. The UE will be
located on a straight line between the 2 eNodeBs, and the handover will be invoked
manually. The duration of each simulation is 2 seconds (except the last test case) and the
handover is triggered exactly at halfway of simulation.
The lte-ue-measurements-handover test suite covers various types of configuration
differences. The first one is the difference in report interval, e.g. the first eNodeB is
configured with 480 ms report interval, while the second eNodeB is configured with 240 ms
report interval. Therefore, when the UE performed handover to the second cell, the new
report interval must take effect. As in piecewise configuration, the timing and the
content of each measurement report received by the eNodeB will be verified.
Other types of differences covered by the test suite are differences in event and
differences in threshold/offset. Table UE measurements test scenarios using handover
configuration below lists the tested scenarios.
UE measurements test scenarios using handover configuration
────────────────────────────────────────────────────────────────────────
Test # Test Subject Initial Post-Handover
Configuration Configuration
────────────────────────────────────────────────────────────────────────
1 Report interval 480 ms 240 ms
────────────────────────────────────────────────────────────────────────
2 Report interval 120 ms 640 ms
────────────────────────────────────────────────────────────────────────
3 Event Event A1 Event A2
────────────────────────────────────────────────────────────────────────
4 Event Event A2 Event A1
────────────────────────────────────────────────────────────────────────
5 Event Event A3 Event A4
────────────────────────────────────────────────────────────────────────
6 Event Event A4 Event A3
────────────────────────────────────────────────────────────────────────
7 Event Event A2 Event A3
────────────────────────────────────────────────────────────────────────
8 Event Event A3 Event A2
────────────────────────────────────────────────────────────────────────
9 Event Event A4 Event A5
────────────────────────────────────────────────────────────────────────
10 Event Event A5 Event A4
────────────────────────────────────────────────────────────────────────
11 Threshold/offset RSRP range 52 RSRP range 56
(Event A1) (Event A1)
────────────────────────────────────────────────────────────────────────
12 Threshold/offset RSRP range 52 RSRP range 56
(Event A2) (Event A2)
────────────────────────────────────────────────────────────────────────
13 Threshold/offset A3 offset -30 A3 offset +30
(Event A3) (Event A3)
────────────────────────────────────────────────────────────────────────
14 Threshold/offset RSRP range 52 RSRP range 56
(Event A4) (Event A4)
────────────────────────────────────────────────────────────────────────
15 Threshold/offset RSRP range 52-52 RSRP range 56-56
(Event A5) (Event A5)
────────────────────────────────────────────────────────────────────────
16 Time-to-trigger 1024 ms 100 ms
────────────────────────────────────────────────────────────────────────
17 Time-to-trigger 1024 ms 640 ms
┌───────┬──────────────────┬─────────────────────┬─────────────────────┐
│ │ │ │ │
Binary file (standard input) matches