Provided by: ns3-doc_3.17+dfsg-1build1_all 
NAME
ns-3-manual - ns-3 Manual
This is the ns-3 Manual. 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 (this document), and Model Library for the latest release and
development tree
· ns-3 wiki
This document is written in reStructuredText for Sphinx and is maintained in the
doc/manual directory of ns-3's source code.
ORGANIZATION
This chapter describes the overall ns-3 software organization and the corresponding
organization of this manual.
ns-3 is a discrete-event network simulator in which the simulation core and models are
implemented in C++. ns-3 is built as a library which may be statically or dynamically
linked to a C++ main program that defines the simulation topology and starts the
simulator. ns-3 also exports nearly all of its API to Python, allowing Python programs to
import an "ns3" module in much the same way as the ns-3 library is linked by executables
in C++.
[image] Software organization of ns-3.UNINDENT
The source code for ns-3 is mostly organized in the src directory and can be described
by the diagram in software-organization. We will work our way from the bottom up; in
general, modules only have dependencies on modules beneath them in the figure.
We first describe the core of the simulator; those components that are common across all
protocol, hardware, and environmental models. The simulation core is implemented in
src/core. Packets are fundamental objects in a network simulator and are implemented in
src/network. These two simulation modules by themselves are intended to comprise a
generic simulation core that can be used by different kinds of networks, not just
Internet-based networks. The above modules of ns-3 are independent of specific network
and device models, which are covered in subsequent parts of this manual.
In addition to the above ns-3 core, we introduce, also in the initial portion of the
manual, two other modules that supplement the core C++-based API. ns-3 programs may
access all of the API directly or may make use of a so-called helper API that provides
convenient wrappers or encapsulation of low-level API calls. The fact that ns-3 programs
can be written to two APIs (or a combination thereof) is a fundamental aspect of the
simulator. We also describe how Python is supported in ns-3 before moving onto specific
models of relevance to network simulation.
The remainder of the manual is focused on documenting the models and supporting
capabilities. The next part focuses on two fundamental objects in ns-3: the Node and
NetDevice. Two special NetDevice types are designed to support network emulation use
cases, and emulation is described next. The following chapter is devoted to
Internet-related models, including the sockets API used by Internet applications. The
next chapter covers applications, and the following chapter describes additional support
for simulation, such as animators and statistics.
The project maintains a separate manual devoted to testing and validation of ns-3 code
(see the ns-3 Testing and Validation manual).
RANDOM VARIABLES
ns-3 contains a built-in pseudo-random number generator (PRNG). It is important for
serious users of the simulator to understand the functionality, configuration, and usage
of this PRNG, and to decide whether it is sufficient for his or her research use.
Quick Overview
ns-3 random numbers are provided via instances of ns3::RandomVariableStream.
· by default, ns-3 simulations use a fixed seed; if there is any randomness in the
simulation, each run of the program will yield identical results unless the seed and/or
run number is changed.
· in ns-3.3 and earlier, ns-3 simulations used a random seed by default; this marks a
change in policy starting with ns-3.4.
· in ns-3.14 and earlier, ns-3 simulations used a different wrapper class called
ns3::RandomVariable. As of ns-3.15, this class has been replaced by
ns3::RandomVariableStream; the underlying pseudo-random number generator has not
changed.
· to obtain randomness across multiple simulation runs, you must either set the seed
differently or set the run number differently. To set a seed, call
ns3::RngSeedManager::SetSeed() at the beginning of the program; to set a run number with
the same seed, call ns3::RngSeedManager::SetRun() at the beginning of the program; see
seeding-and-independent-replications.
· each RandomVariableStream used in ns-3 has a virtual random number generator associated
with it; all random variables use either a fixed or random seed based on the use of the
global seed (previous bullet);
· if you intend to perform multiple runs of the same scenario, with different random
numbers, please be sure to read the section on how to perform independent replications:
seeding-and-independent-replications.
Read further for more explanation about the random number facility for ns-3.
Background
Simulations use a lot of random numbers; one study found that most network simulations
spend as much as 50% of the CPU generating random numbers. Simulation users need to be
concerned with the quality of the (pseudo) random numbers and the independence between
different streams of random numbers.
Users need to be concerned with a few issues, such as:
· the seeding of the random number generator and whether a simulation outcome is
deterministic or not,
· how to acquire different streams of random numbers that are independent from one
another, and
· how long it takes for streams to cycle
We will introduce a few terms here: a RNG provides a long sequence of (pseudo) random
numbers. The length of this sequence is called the cycle length or period, after which
the RNG will repeat itself. This sequence can be partitioned into disjoint streams. A
stream of a RNG is a contiguous subset or block of the RNG sequence. For instance, if the
RNG period is of length N, and two streams are provided from this RNG, then the first
stream might use the first N/2 values and the second stream might produce the second N/2
values. An important property here is that the two streams are uncorrelated. Likewise,
each stream can be partitioned disjointedly to a number of uncorrelated substreams. The
underlying RNG hopefully produces a pseudo-random sequence of numbers with a very long
cycle length, and partitions this into streams and substreams in an efficient manner.
ns-3 uses the same underlying random number generator as does ns-2: the MRG32k3a
generator from Pierre L'Ecuyer. A detailed description can be found in
http://www.iro.umontreal.ca/~lecuyer/myftp/papers/streams00.pdf. The MRG32k3a generator
provides 1.8x10^{19} independent streams of random numbers, each of which consists of
2.3x10^{15} substreams. Each substream has a period (i.e., the number of random numbers
before overlap) of 7.6x10^{22}. The period of the entire generator is 3.1x10^{57}.
Class ns3::RandomVariableStream is the public interface to this underlying random number
generator. When users create new random variables (such as ns3::UniformRandomVariable,
ns3::ExponentialRandomVariable, etc.), they create an object that uses one of the
distinct, independent streams of the random number generator. Therefore, each object of
type ns3::RandomVariableStream has, conceptually, its own "virtual" RNG. Furthermore,
each ns3::RandomVariableStream can be configured to use one of the set of substreams drawn
from the main stream.
An alternate implementation would be to allow each RandomVariable to have its own
(differently seeded) RNG. However, we cannot guarantee as strongly that the different
sequences would be uncorrelated in such a case; hence, we prefer to use a single RNG and
streams and substreams from it.
Seeding and independent replications
ns-3 simulations can be configured to produce deterministic or random results. If the
ns-3 simulation is configured to use a fixed, deterministic seed with the same run number,
it should give the same output each time it is run.
By default, ns-3 simulations use a fixed seed and run number. These values are stored in
two ns3::GlobalValue instances: g_rngSeed and g_rngRun.
A typical use case is to run a simulation as a sequence of independent trials, so as to
compute statistics on a large number of independent runs. The user can either change the
global seed and rerun the simulation, or can advance the substream state of the RNG, which
is referred to as incrementing the run number.
A class ns3::RngSeedManager provides an API to control the seeding and run number
behavior. This seeding and substream state setting must be called before any random
variables are created; e.g:
RngSeedManager::SetSeed (3); // Changes seed from default of 1 to 3
RngSeedManager::SetRun (7); // Changes run number from default of 1 to 7
// Now, create random variables
Ptr<UniformRandomVariable> x = CreateObject<UniformRandomVariable> ();
Ptr<ExponentialRandomVariable> y = CreateObject<ExponentialRandomVarlable> ();
...
Which is better, setting a new seed or advancing the substream state? There is no
guarantee that the streams produced by two random seeds will not overlap. The only way to
guarantee that two streams do not overlap is to use the substream capability provided by
the RNG implementation. Therefore, use the substream capability to produce multiple
independent runs of the same simulation. In other words, the more statistically rigorous
way to configure multiple independent replications is to use a fixed seed and to advance
the run number. This implementation allows for a maximum of 2.3x10^{15} independent
replications using the substreams.
For ease of use, it is not necessary to control the seed and run number from within the
program; the user can set the NS_GLOBAL_VALUE environment variable as follows:
NS_GLOBAL_VALUE="RngRun=3" ./waf --run program-name
Another way to control this is by passing a command-line argument; since this is an ns-3
GlobalValue instance, it is equivalently done such as follows:
./waf --command-template="%s --RngRun=3" --run program-name
or, if you are running programs directly outside of waf:
./build/optimized/scratch/program-name --RngRun=3
The above command-line variants make it easy to run lots of different runs from a shell
script by just passing a different RngRun index.
Class RandomVariableStream
All random variables should derive from class RandomVariable. This base class provides a
few methods for globally configuring the behavior of the random number generator. Derived
classes provide API for drawing random variates from the particular distribution being
supported.
Each RandomVariableStream created in the simulation is given a generator that is a new
RNGStream from the underlying PRNG. Used in this manner, the L'Ecuyer implementation
allows for a maximum of 1.8x10^19 random variables. Each random variable in a single
replication can produce up to 7.6x10^22 random numbers before overlapping.
Base class public API
Below are excerpted a few public methods of class RandomVariableStream that access the
next value in the substream.:
/**
* \brief Returns a random double from the underlying distribution
* \return A floating point random value
*/
double GetValue (void) const;
/**
* \brief Returns a random integer from the underlying distribution
* \return Integer cast of ::GetValue()
*/
uint32_t GetInteger (void) const;
We have already described the seeding configuration above. Different RandomVariable
subclasses may have additional API.
Types of RandomVariables
The following types of random variables are provided, and are documented in the ns-3
Doxygen or by reading src/core/model/random-variable-stream.h. Users can also create
their own custom random variables by deriving from class RandomVariableStream.
· class UniformRandomVariable
· class ConstantRandomVariable
· class SequentialRandomVariable
· class ExponentialRandomVariable
· class ParetoRandomVariable
· class WeibullRandomVariable
· class NormalRandomVariable
· class LogNormalRandomVariable
· class GammaRandomVariable
· class ErlangRandomVariable
· class TriangularRandomVariable
· class ZipfRandomVariable
· class ZetaRandomVariable
· class DeterministicRandomVariable
· class EmpiricalRandomVariable
Semantics of RandomVariableStream objects
RandomVariableStream objects derive from ns3::Object and are handled by smart pointers.
RandomVariableStream instances can also be used in ns-3 attributes, which means that
values can be set for them through the ns-3 attribute system. An example is in the
propagation models for WifiNetDevice::
TypeId
RandomPropagationDelayModel::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::RandomPropagationDelayModel")
.SetParent<PropagationDelayModel> ()
.AddConstructor<RandomPropagationDelayModel> ()
.AddAttribute ("Variable",
"The random variable which generates random delays (s).",
StringValue ("ns3::UniformRandomVariable"),
MakePointerAccessor (&RandomPropagationDelayModel::m_variable),
MakePointerChecker<RandomVariableStream> ())
;
return tid;
}
Here, the ns-3 user can change the default random variable for this delay model (which is
a UniformRandomVariable ranging from 0 to 1) through the attribute system.
Using other PRNG
There is presently no support for substituting a different underlying random number
generator (e.g., the GNU Scientific Library or the Akaroa package). Patches are welcome.
Setting the stream number
The underlying MRG32k3a generator provides 2^64 independent streams. In ns-3, these are
assigned sequentially starting from the first stream as new RandomVariableStream instances
make their first call to GetValue().
As a result of how these RandomVariableStream objects are assigned to underlying streams,
the assignment is sensitive to perturbations of the simulation configuration. The
consequence is that if any aspect of the simulation configuration is changed, the mapping
of RandomVariables to streams may (or may not) change.
As a concrete example, a user running a comparative study between routing protocols may
find that the act of changing one routing protocol for another will notice that the
underlying mobility pattern also changed.
Starting with ns-3.15, some control has been provided to users to allow users to
optionally fix the assignment of selected RandomVariableStream objects to underlying
streams. This is the Stream attribute, part of the base class RandomVariableStream.
By partitioning the existing sequence of streams from before:
<-------------------------------------------------------------------------->
stream 0 stream (2^64 - 1)
into two equal-sized sets:
<--------------------------------------------------------------------------->
^ ^^ ^
| || |
stream 0 stream (2^63 - 1) stream 2^63 stream (2^64 - 1)
<- automatically assigned -----><-------- assigned by user----------->
The first 2^63 streams continue to be automatically assigned, while the last 2^63 are
given stream indices starting with zero up to 2^63-1.
The assignment of streams to a fixed stream number is optional; instances of
RandomVariableStream that do not have a stream value assigned will be assigned the next
one from the pool of automatic streams.
To fix a RandomVariableStream to a particular underlying stream, assign its Stream
attribute to a non-negative integer (the default value of -1 means that a value will be
automatically allocated).
Publishing your results
When you publish simulation results, a key piece of configuration information that you
should always state is how you used the the random number generator.
· what seeds you used,
· what RNG you used if not the default,
· how were independent runs performed,
· for large simulations, how did you check that you did not cycle.
It is incumbent on the researcher publishing results to include enough information to
allow others to reproduce his or her results. It is also incumbent on the researcher to
convince oneself that the random numbers used were statistically valid, and to state in
the paper why such confidence is assumed.
Summary
Let's review what things you should do when creating a simulation.
· Decide whether you are running with a fixed seed or random seed; a fixed seed is the
default,
· Decide how you are going to manage independent replications, if applicable,
· Convince yourself that you are not drawing more random values than the cycle length, if
you are running a very long simulation, and
· When you publish, follow the guidelines above about documenting your use of the random
number generator.
EVENTS AND SIMULATOR
ns-3 is a discrete-event network simulator. Conceptually, the simulator keeps track of a
number of events that are scheduled to execute at a specified simulation time. The job of
the simulator is to execute the events in sequential time order. Once the completion of
an event occurs, the simulator will move to the next event (or will exit if there are no
more events in the event queue). If, for example, an event scheduled for simulation time
"100 seconds" is executed, and the next event is not scheduled until "200 seconds", the
simulator will immediately jump from 100 seconds to 200 seconds (of simulation time) to
execute the next event. This is what is meant by "discrete-event" simulator.
To make this all happen, the simulator needs a few things:
1. a simulator object that can access an event queue where events are stored and that can
manage the execution of events
2. a scheduler responsible for inserting and removing events from the queue
3. a way to represent simulation time
4. the events themselves
This chapter of the manual describes these fundamental objects (simulator, scheduler,
time, event) and how they are used.
Event
To be completed
Simulator
The Simulator class is the public entry point to access event scheduling facilities. Once
a couple of events have been scheduled to start the simulation, the user can start to
execute them by entering the simulator main loop (call Simulator::Run). Once the main loop
starts running, it will sequentially execute all scheduled events in order from oldest to
most recent until there are either no more events left in the event queue or
Simulator::Stop has been called.
To schedule events for execution by the simulator main loop, the Simulator class provides
the Simulator::Schedule* family of functions.
1. Handling event handlers with different signatures
These functions are declared and implemented as C++ templates to handle automatically the
wide variety of C++ event handler signatures used in the wild. For example, to schedule an
event to execute 10 seconds in the future, and invoke a C++ method or function with
specific arguments, you might write this:
void handler (int arg0, int arg1)
{
std::cout << "handler called with argument arg0=" << arg0 << " and
arg1=" << arg1 << std::endl;
}
Simulator::Schedule(Seconds(10), &handler, 10, 5);
Which will output:
handler called with argument arg0=10 and arg1=5
Of course, these C++ templates can also handle transparently member methods on C++
objects:
To be completed: member method example
Notes:
· the ns-3 Schedule methods recognize automatically functions and methods only if they
take less than 5 arguments. If you need them to support more arguments, please, file a
bug report.
· Readers familiar with the term 'fully-bound functors' will recognize the
Simulator::Schedule methods as a way to automatically construct such objects.
2. Common scheduling operations
The Simulator API was designed to make it really simple to schedule most events. It
provides three variants to do so (ordered from most commonly used to least commonly used):
· Schedule methods which allow you to schedule an event in the future by providing the
delay between the current simulation time and the expiration date of the target event.
· ScheduleNow methods which allow you to schedule an event for the current simulation
time: they will execute _after_ the current event is finished executing but _before_ the
simulation time is changed for the next event.
· ScheduleDestroy methods which allow you to hook in the shutdown process of the Simulator
to cleanup simulation resources: every 'destroy' event is executed when the user calls
the Simulator::Destroy method.
3. Maintaining the simulation context
There are two basic ways to schedule events, with and without context. What does this
mean?
Simulator::Schedule (Time const &time, MEM mem_ptr, OBJ obj);
vs.
Simulator::ScheduleWithContext (uint32_t context, Time const &time, MEM mem_ptr, OBJ obj);
Readers who invest time and effort in developing or using a non-trivial simulation model
will know the value of the ns-3 logging framework to debug simple and complex simulations
alike. One of the important features that is provided by this logging framework is the
automatic display of the network node id associated with the 'currently' running event.
The node id of the currently executing network node is in fact tracked by the Simulator
class. It can be accessed with the Simulator::GetContext method which returns the
'context' (a 32-bit integer) associated and stored in the currently-executing event. In
some rare cases, when an event is not associated with a specific network node, its
'context' is set to 0xffffffff.
To associate a context to each event, the Schedule, and ScheduleNow methods automatically
reuse the context of the currently-executing event as the context of the event scheduled
for execution later.
In some cases, most notably when simulating the transmission of a packet from a node to
another, this behavior is undesirable since the expected context of the reception event is
that of the receiving node, not the sending node. To avoid this problem, the Simulator
class provides a specific schedule method: ScheduleWithContext which allows one to provide
explicitly the node id of the receiving node associated with the receive event.
XXX: code example
In some very rare cases, developers might need to modify or understand how the context
(node id) of the first event is set to that of its associated node. This is accomplished
by the NodeList class: whenever a new node is created, the NodeList class uses
ScheduleWithContext to schedule a 'initialize' event for this node. The 'initialize' event
thus executes with a context set to that of the node id and can use the normal variety of
Schedule methods. It invokes the Node::Initialize method which propagates the 'initialize'
event by calling the DoInitialize method for each object associated with the node. The
DoInitialize method overridden in some of these objects (most notably in the Application
base class) will schedule some events (most notably Application::StartApplication) which
will in turn scheduling traffic generation events which will in turn schedule
network-level events.
Notes:
· Users need to be careful to propagate DoInitialize methods across objects by calling
Initialize explicitely on their member objects
· The context id associated with each ScheduleWithContext method has other uses beyond
logging: it is used by an experimental branch of ns-3 to perform parallel simulation on
multicore systems using multithreading.
The Simulator::* functions do not know what the context is: they merely make sure that
whatever context you specify with ScheduleWithContext is available when the corresponding
event executes with ::GetContext.
It is up to the models implemented on top of Simulator::* to interpret the context value.
In ns-3, the network models interpret the context as the node id of the node which
generated an event. This is why it is important to call ScheduleWithContext in
ns3::Channel subclasses because we are generating an event from node i to node j and we
want to make sure that the event which will run on node j has the right context.
Time
To be completed
Scheduler
To be completed
CALLBACKS
Some new users to ns-3 are unfamiliar with an extensively used programming idiom used
throughout the code: the ns-3 callback. This chapter provides some motivation on the
callback, guidance on how to use it, and details on its implementation.
Callbacks Motivation
Consider that you have two simulation models A and B, and you wish to have them pass
information between them during the simulation. One way that you can do that is that you
can make A and B each explicitly knowledgeable about the other, so that they can invoke
methods on each other:
class A {
public:
void ReceiveInput ( // parameters );
...
}
(in another source file:)
class B {
public:
void DoSomething (void);
...
private:
A* a_instance; // pointer to an A
}
void
B::DoSomething()
{
// Tell a_instance that something happened
a_instance->ReceiveInput ( // parameters);
...
}
This certainly works, but it has the drawback that it introduces a dependency on A and B
to know about the other at compile time (this makes it harder to have independent
compilation units in the simulator) and is not generalized; if in a later usage scenario,
B needs to talk to a completely different C object, the source code for B needs to be
changed to add a c_instance and so forth. It is easy to see that this is a brute force
mechanism of communication that can lead to programming cruft in the models.
This is not to say that objects should not know about one another if there is a hard
dependency between them, but that often the model can be made more flexible if its
interactions are less constrained at compile time.
This is not an abstract problem for network simulation research, but rather it has been a
source of problems in previous simulators, when researchers want to extend or modify the
system to do different things (as they are apt to do in research). Consider, for example,
a user who wants to add an IPsec security protocol sublayer between TCP and IP:
------------ -----------
| TCP | | TCP |
------------ -----------
| becomes -> |
----------- -----------
| IP | | IPsec |
----------- -----------
|
-----------
| IP |
-----------
If the simulator has made assumptions, and hard coded into the code, that IP always talks
to a transport protocol above, the user may be forced to hack the system to get the
desired interconnections. This is clearly not an optimal way to design a generic
simulator.
Callbacks Background
NOTE:
Readers familiar with programming callbacks may skip this tutorial section.
The basic mechanism that allows one to address the problem above is known as a callback.
The ultimate goal is to allow one piece of code to call a function (or method in C++)
without any specific inter-module dependency.
This ultimately means you need some kind of indirection -- you treat the address of the
called function as a variable. This variable is called a pointer-to-function variable.
The relationship between function and pointer-to-function pointer is really no different
that that of object and pointer-to-object.
In C the canonical example of a pointer-to-function is a
pointer-to-function-returning-integer (PFI). For a PFI taking one int parameter, this
could be declared like,:
int (*pfi)(int arg) = 0;
What you get from this is a variable named simply pfi that is initialized to the value 0.
If you want to initialize this pointer to something meaningful, you have to have a
function with a matching signature. In this case:
int MyFunction (int arg) {}
If you have this target, you can initialize the variable to point to your function like:
pfi = MyFunction;
You can then call MyFunction indirectly using the more suggestive form of the call:
int result = (*pfi) (1234);
This is suggestive since it looks like you are dereferencing the function pointer just
like you would dereference any pointer. Typically, however, people take advantage of the
fact that the compiler knows what is going on and will just use a shorter form:
int result = pfi (1234);
Notice that the function pointer obeys value semantics, so you can pass it around like any
other value. Typically, when you use an asynchronous interface you will pass some entity
like this to a function which will perform an action and call back to let you know it
completed. It calls back by following the indirection and executing the provided function.
In C++ you have the added complexity of objects. The analogy with the PFI above means you
have a pointer to a member function returning an int (PMI) instead of the pointer to
function returning an int (PFI).
The declaration of the variable providing the indirection looks only slightly different:
int (MyClass::*pmi) (int arg) = 0;
This declares a variable named pmi just as the previous example declared a variable named
pfi. Since the will be to call a method of an instance of a particular class, one must
declare that method in a class:
class MyClass {
public:
int MyMethod (int arg);
};
Given this class declaration, one would then initialize that variable like this:
pmi = &MyClass::MyMethod;
This assigns the address of the code implementing the method to the variable, completing
the indirection. In order to call a method, the code needs a this pointer. This, in turn,
means there must be an object of MyClass to refer to. A simplistic example of this is just
calling a method indirectly (think virtual function):
int (MyClass::*pmi) (int arg) = 0; // Declare a PMI
pmi = &MyClass::MyMethod; // Point at the implementation code
MyClass myClass; // Need an instance of the class
(myClass.*pmi) (1234); // Call the method with an object ptr
Just like in the C example, you can use this in an asynchronous call to another module
which will call back using a method and an object pointer. The straightforward extension
one might consider is to pass a pointer to the object and the PMI variable. The module
would just do:
(*objectPtr.*pmi) (1234);
to execute the callback on the desired object.
One might ask at this time, what's the point? The called module will have to understand
the concrete type of the calling object in order to properly make the callback. Why not
just accept this, pass the correctly typed object pointer and do object->Method(1234) in
the code instead of the callback? This is precisely the problem described above. What is
needed is a way to decouple the calling function from the called class completely. This
requirement led to the development of the Functor.
A functor is the outgrowth of something invented in the 1960s called a closure. It is
basically just a packaged-up function call, possibly with some state.
A functor has two parts, a specific part and a generic part, related through inheritance.
The calling code (the code that executes the callback) will execute a generic overloaded
operator () of a generic functor to cause the callback to be called. The called code (the
code that wants to be called back) will have to provide a specialized implementation of
the operator () that performs the class-specific work that caused the close-coupling
problem above.
With the specific functor and its overloaded operator () created, the called code then
gives the specialized code to the module that will execute the callback (the calling
code).
The calling code will take a generic functor as a parameter, so an implicit cast is done
in the function call to convert the specific functor to a generic functor. This means
that the calling module just needs to understand the generic functor type. It is decoupled
from the calling code completely.
The information one needs to make a specific functor is the object pointer and the
pointer-to-method address.
The essence of what needs to happen is that the system declares a generic part of the
functor:
template <typename T>
class Functor
{
public:
virtual int operator() (T arg) = 0;
};
The caller defines a specific part of the functor that really is just there to implement
the specific operator() method:
template <typename T, typename ARG>
class SpecificFunctor : public Functor<ARG>
{
public:
SpecificFunctor(T* p, int (T::*_pmi)(ARG arg))
{
m_p = p;
m_pmi = _pmi;
}
virtual int operator() (ARG arg)
{
(*m_p.*m_pmi)(arg);
}
private:
int (T::*m_pmi)(ARG arg);
T* m_p;
};
Here is an example of the usage:
class A
{
public:
A (int a0) : a (a0) {}
int Hello (int b0)
{
std::cout << "Hello from A, a = " << a << " b0 = " << b0 << std::endl;
}
int a;
};
int main()
{
A a(10);
SpecificFunctor<A, int> sf(&a, &A::Hello);
sf(5);
}
NOTE:
The previous code is not real ns-3 code. It is simplistic example code used only to
illustrate the concepts involved and to help you understand the system more. Do not
expect to find this code anywhere in the ns-3 tree.
Notice that there are two variables defined in the class above. The m_p variable is the
object pointer and m_pmi is the variable containing the address of the function to
execute.
Notice that when operator() is called, it in turn calls the method provided with the
object pointer using the C++ PMI syntax.
To use this, one could then declare some model code that takes a generic functor as a
parameter:
void LibraryFunction (Functor functor);
The code that will talk to the model would build a specific functor and pass it to
LibraryFunction:
MyClass myClass;
SpecificFunctor<MyClass, int> functor (&myclass, MyClass::MyMethod);
When LibraryFunction is done, it executes the callback using the operator() on the generic
functor it was passed, and in this particular case, provides the integer argument:
void
LibraryFunction (Functor functor)
{
// Execute the library function
functor(1234);
}
Notice that LibraryFunction is completely decoupled from the specific type of the client.
The connection is made through the Functor polymorphism.
The Callback API in ns-3 implements object-oriented callbacks using the functor mechanism.
This callback API, being based on C++ templates, is type-safe; that is, it performs static
type checks to enforce proper signature compatibility between callers and callees. It is
therefore more type-safe to use than traditional function pointers, but the syntax may
look imposing at first. This section is designed to walk you through the Callback system
so that you can be comfortable using it in ns-3.
Using the Callback API
The Callback API is fairly minimal, providing only two services:
1. callback type declaration: a way to declare a type of callback with a given signature,
and,
2. callback instantiation: a way to instantiate a template-generated forwarding callback
which can forward any calls to another C++ class member method or C++ function.
This is best observed via walking through an example, based on samples/main-callback.cc.
Using the Callback API with static functions
Consider a function:
static double
CbOne (double a, double b)
{
std::cout << "invoke cbOne a=" << a << ", b=" << b << std::endl;
return a;
}
Consider also the following main program snippet:
int main (int argc, char *argv[])
{
// return type: double
// first arg type: double
// second arg type: double
Callback<double, double, double> one;
}
This is an example of a C-style callback -- one which does not include or need a this
pointer. The function template Callback is essentially the declaration of the variable
containing the pointer-to-function. In the example above, we explicitly showed a pointer
to a function that returned an integer and took a single integer as a parameter, The
Callback template function is a generic version of that -- it is used to declare the type
of a callback.
NOTE:
Readers unfamiliar with C++ templates may consult
http://www.cplusplus.com/doc/tutorial/templates/.
The Callback template requires one mandatory argument (the return type of the function to
be assigned to this callback) and up to five optional arguments, which each specify the
type of the arguments (if your particular callback function has more than five arguments,
then this can be handled by extending the callback implementation).
So in the above example, we have a declared a callback named "one" that will eventually
hold a function pointer. The signature of the function that it will hold must return
double and must support two double arguments. If one tries to pass a function whose
signature does not match the declared callback, a compilation error will occur. Also, if
one tries to assign to a callback an incompatible one, compilation will succeed but a
run-time NS_FATAL_ERROR will be raised. The sample program
src/core/examples/main-callback.cc demonstrates both of these error cases at the end of
the main() program.
Now, we need to tie together this callback instance and the actual target function
(CbOne). Notice above that CbOne has the same function signature types as the callback--
this is important. We can pass in any such properly-typed function to this callback.
Let's look at this more closely:
static double CbOne (double a, double b) {}
^ ^ ^
| ---| ------|
| | |
Callback<double, double, double> one;
You can only bind a function to a callback if they have the matching signature. The first
template argument is the return type, and the additional template arguments are the types
of the arguments of the function signature.
Now, let's bind our callback "one" to the function that matches its signature:
// build callback instance which points to cbOne function
one = MakeCallback (&CbOne);
This call to MakeCallback is, in essence, creating one of the specialized functors
mentioned above. The variable declared using the Callback template function is going to
be playing the part of the generic functor. The assignment one = MakeCallback (&CbOne) is
the cast that converts the specialized functor known to the callee to a generic functor
known to the caller.
Then, later in the program, if the callback is needed, it can be used as follows:
NS_ASSERT (!one.IsNull ());
// invoke cbOne function through callback instance
double retOne;
retOne = one (10.0, 20.0);
The check for IsNull() ensures that the callback is not null -- that there is a function
to call behind this callback. Then, one() executes the generic operator() which is really
overloaded with a specific implementation of operator() and returns the same result as if
CbOne() had been called directly.
Using the Callback API with member functions
Generally, you will not be calling static functions but instead public member functions of
an object. In this case, an extra argument is needed to the MakeCallback function, to
tell the system on which object the function should be invoked. Consider this example,
also from main-callback.cc:
class MyCb {
public:
int CbTwo (double a) {
std::cout << "invoke cbTwo a=" << a << std::endl;
return -5;
}
};
int main ()
{
...
// return type: int
// first arg type: double
Callback<int, double> two;
MyCb cb;
// build callback instance which points to MyCb::cbTwo
two = MakeCallback (&MyCb::CbTwo, &cb);
...
}
Here, we pass an additional object pointer to the MakeCallback<> function. Recall from
the background section above that Operator() will use the pointer to member syntax when it
executes on an object:
virtual int operator() (ARG arg)
{
(*m_p.*m_pmi)(arg);
}
And so we needed to provide the two variables (m_p and m_pmi) when we made the specific
functor. The line:
two = MakeCallback (&MyCb::CbTwo, &cb);
does precisely that. In this case, when two () is invoked:
int result = two (1.0);
will result in a call tothe CbTwo member function (method) on the object pointed to by
&cb.
Building Null Callbacks
It is possible for callbacks to be null; hence it may be wise to check before using them.
There is a special construct for a null callback, which is preferable to simply passing
"0" as an argument; it is the MakeNullCallback<> construct:
two = MakeNullCallback<int, double> ();
NS_ASSERT (two.IsNull ());
Invoking a null callback is just like invoking a null function pointer: it will crash at
runtime.
Bound Callbacks
A very useful extension to the functor concept is that of a Bound Callback. Previously it
was mentioned that closures were originally function calls packaged up for later
execution. Notice that in all of the Callback descriptions above, there is no way to
package up any parameters for use later -- when the Callback is called via operator().
All of the parameters are provided by the calling function.
What if it is desired to allow the client function (the one that provides the callback) to
provide some of the parameters? Alexandrescu calls the process of allowing a client to
specify one of the parameters "binding". One of the parameters of operator() has been
bound (fixed) by the client.
Some of our pcap tracing code provides a nice example of this. There is a function that
needs to be called whenever a packet is received. This function calls an object that
actually writes the packet to disk in the pcap file format. The signature of one of these
functions will be:
static void DefaultSink (Ptr<PcapFileWrapper> file, Ptr<const Packet> p);
The static keyword means this is a static function which does not need a this pointer, so
it will be using C-style callbacks. We don't want the calling code to have to know about
anything but the Packet. What we want in the calling code is just a call that looks like:
m_promiscSnifferTrace (m_currentPkt);
What we want to do is to bind the Ptr<PcapFileWriter> file to the specific callback
implementation when it is created and arrange for the operator() of the Callback to
provide that parameter for free.
We provide the MakeBoundCallback template function for that purpose. It takes the same
parameters as the MakeCallback template function but also takes the parameters to be
bound. In the case of the example above:
MakeBoundCallback (&DefaultSink, file);
will create a specific callback implementation that knows to add in the extra bound
arguments. Conceptually, it extends the specific functor described above with one or more
bound arguments:
template <typename T, typename ARG, typename BOUND_ARG>
class SpecificFunctor : public Functor
{
public:
SpecificFunctor(T* p, int (T::*_pmi)(ARG arg), BOUND_ARG boundArg)
{
m_p = p;
m_pmi = pmi;
m_boundArg = boundArg;
}
virtual int operator() (ARG arg)
{
(*m_p.*m_pmi)(m_boundArg, arg);
}
private:
void (T::*m_pmi)(ARG arg);
T* m_p;
BOUND_ARG m_boundArg;
};
You can see that when the specific functor is created, the bound argument is saved in the
functor / callback object itself. When the operator() is invoked with the single
parameter, as in:
m_promiscSnifferTrace (m_currentPkt);
the implementation of operator() adds the bound parameter into the actual function call:
(*m_p.*m_pmi)(m_boundArg, arg);
Traced Callbacks
Placeholder subsection
Callback locations in ns-3
Where are callbacks frequently used in ns-3? Here are some of the more visible ones to
typical users:
· Socket API
· Layer-2/Layer-3 API
· Tracing subsystem
· API between IP and routing subsystems
Implementation details
The code snippets above are simplistic and only designed to illustrate the mechanism
itself. The actual Callback code is quite complicated and very template-intense and a
deep understanding of the code is not required. If interested, expert users may find the
following useful.
The code was originally written based on the techniques described in
http://www.codeproject.com/cpp/TTLFunction.asp. It was subsequently rewritten to follow
the architecture outlined in Modern C++ Design, Generic Programming and Design Patterns
Applied, Alexandrescu, chapter 5, Generalized Functors.
This code uses:
· default template parameters to saves users from having to specify empty parameters when
the number of parameters is smaller than the maximum supported number
· the pimpl idiom: the Callback class is passed around by value and delegates the crux of
the work to its pimpl pointer.
· two pimpl implementations which derive from CallbackImpl FunctorCallbackImpl can be used
with any functor-type while MemPtrCallbackImpl can be used with pointers to member
functions.
· a reference list implementation to implement the Callback's value semantics.
This code most notably departs from the Alexandrescu implementation in that it does not
use type lists to specify and pass around the types of the callback arguments. Of course,
it also does not use copy-destruction semantics and relies on a reference list rather than
autoPtr to hold the pointer.
OBJECT MODEL
ns-3 is fundamentally a C++ object system. Objects can be declared and instantiated as
usual, per C++ rules. ns-3 also adds some features to traditional C++ objects, as
described below, to provide greater functionality and features. This manual chapter is
intended to introduce the reader to the ns-3 object model.
This section describes the C++ class design for ns-3 objects. In brief, several design
patterns in use include classic object-oriented design (polymorphic interfaces and
implementations), separation of interface and implementation, the non-virtual public
interface design pattern, an object aggregation facility, and reference counting for
memory management. Those familiar with component models such as COM or Bonobo will
recognize elements of the design in the ns-3 object aggregation model, although the ns-3
design is not strictly in accordance with either.
Object-oriented behavior
C++ objects, in general, provide common object-oriented capabilities (abstraction,
encapsulation, inheritance, and polymorphism) that are part of classic object-oriented
design. ns-3 objects make use of these properties; for instance::
class Address
{
public:
Address ();
Address (uint8_t type, const uint8_t *buffer, uint8_t len);
Address (const Address & address);
Address &operator = (const Address &address);
...
private:
uint8_t m_type;
uint8_t m_len;
...
};
Object base classes
There are three special base classes used in ns-3. Classes that inherit from these base
classes can instantiate objects with special properties. These base classes are:
· class Object
· class ObjectBase
· class SimpleRefCount
It is not required that ns-3 objects inherit from these class, but those that do get
special properties. Classes deriving from class Object get the following properties.
· the ns-3 type and attribute system (see Attributes)
· an object aggregation system
· a smart-pointer reference counting system (class Ptr)
Classes that derive from class ObjectBase get the first two properties above, but do not
get smart pointers. Classes that derive from class SimpleRefCount: get only the
smart-pointer reference counting system.
In practice, class Object is the variant of the three above that the ns-3 developer will
most commonly encounter.
Memory management and class Ptr
Memory management in a C++ program is a complex process, and is often done incorrectly or
inconsistently. We have settled on a reference counting design described as follows.
All objects using reference counting maintain an internal reference count to determine
when an object can safely delete itself. Each time that a pointer is obtained to an
interface, the object's reference count is incremented by calling Ref(). It is the
obligation of the user of the pointer to explicitly Unref() the pointer when done. When
the reference count falls to zero, the object is deleted.
· When the client code obtains a pointer from the object itself through object creation,
or via GetObject, it does not have to increment the reference count.
· When client code obtains a pointer from another source (e.g., copying a pointer) it must
call Ref() to increment the reference count.
· All users of the object pointer must call Unref() to release the reference.
The burden for calling Unref() is somewhat relieved by the use of the reference counting
smart pointer class described below.
Users using a low-level API who wish to explicitly allocate non-reference-counted objects
on the heap, using operator new, are responsible for deleting such objects.
Reference counting smart pointer (Ptr)
Calling Ref() and Unref() all the time would be cumbersome, so ns-3 provides a smart
pointer class Ptr similar to Boost::intrusive_ptr. This smart-pointer class assumes that
the underlying type provides a pair of Ref and Unref methods that are expected to
increment and decrement the internal refcount of the object instance.
This implementation allows you to manipulate the smart pointer as if it was a normal
pointer: you can compare it with zero, compare it against other pointers, assign zero to
it, etc.
It is possible to extract the raw pointer from this smart pointer with the GetPointer()
and PeekPointer() methods.
If you want to store a newed object into a smart pointer, we recommend you to use the
CreateObject template functions to create the object and store it in a smart pointer to
avoid memory leaks. These functions are really small convenience functions and their goal
is just to save you a small bit of typing.
CreateObject and Create
Objects in C++ may be statically, dynamically, or automatically created. This holds true
for ns-3 also, but some objects in the system have some additional frameworks available.
Specifically, reference counted objects are usually allocated using a templated Create or
CreateObject method, as follows.
For objects deriving from class Object::
Ptr<WifiNetDevice> device = CreateObject<WifiNetDevice> ();
Please do not create such objects using operator new; create them using CreateObject()
instead.
For objects deriving from class SimpleRefCount, or other objects that support usage of the
smart pointer class, a templated helper function is available and recommended to be used::
Ptr<B> b = Create<B> ();
This is simply a wrapper around operator new that correctly handles the reference counting
system.
In summary, use Create<B> if B is not an object but just uses reference counting (e.g.
Packet), and use CreateObject<B> if B derives from ns3::Object.
Aggregation
The ns-3 object aggregation system is motivated in strong part by a recognition that a
common use case for ns-2 has been the use of inheritance and polymorphism to extend
protocol models. For instance, specialized versions of TCP such as RenoTcpAgent derive
from (and override functions from) class TcpAgent.
However, two problems that have arisen in the ns-2 model are downcasts and "weak base
class." Downcasting refers to the procedure of using a base class pointer to an object and
querying it at run time to find out type information, used to explicitly cast the pointer
to a subclass pointer so that the subclass API can be used. Weak base class refers to the
problems that arise when a class cannot be effectively reused (derived from) because it
lacks necessary functionality, leading the developer to have to modify the base class and
causing proliferation of base class API calls, some of which may not be semantically
correct for all subclasses.
ns-3 is using a version of the query interface design pattern to avoid these problems.
This design is based on elements of the Component Object Model and GNOME Bonobo although
full binary-level compatibility of replaceable components is not supported and we have
tried to simplify the syntax and impact on model developers.
Exmaples
Aggregation example
Node is a good example of the use of aggregation in ns-3. Note that there are not derived
classes of Nodes in ns-3 such as class InternetNode. Instead, components (protocols) are
aggregated to a node. Let's look at how some Ipv4 protocols are added to a node.:
static void
AddIpv4Stack(Ptr<Node> node)
{
Ptr<Ipv4L3Protocol> ipv4 = CreateObject<Ipv4L3Protocol> ();
ipv4->SetNode (node);
node->AggregateObject (ipv4);
Ptr<Ipv4Impl> ipv4Impl = CreateObject<Ipv4Impl> ();
ipv4Impl->SetIpv4 (ipv4);
node->AggregateObject (ipv4Impl);
}
Note that the Ipv4 protocols are created using CreateObject(). Then, they are aggregated
to the node. In this manner, the Node base class does not need to be edited to allow users
with a base class Node pointer to access the Ipv4 interface; users may ask the node for a
pointer to its Ipv4 interface at runtime. How the user asks the node is described in the
next subsection.
Note that it is a programming error to aggregate more than one object of the same type to
an ns3::Object. So, for instance, aggregation is not an option for storing all of the
active sockets of a node.
GetObject example
GetObject is a type-safe way to achieve a safe downcasting and to allow interfaces to be
found on an object.
Consider a node pointer m_node that points to a Node object that has an implementation of
IPv4 previously aggregated to it. The client code wishes to configure a default route. To
do so, it must access an object within the node that has an interface to the IP forwarding
configuration. It performs the following::
Ptr<Ipv4> ipv4 = m_node->GetObject<Ipv4> ();
If the node in fact does not have an Ipv4 object aggregated to it, then the method will
return null. Therefore, it is good practice to check the return value from such a function
call. If successful, the user can now use the Ptr to the Ipv4 object that was previously
aggregated to the node.
Another example of how one might use aggregation is to add optional models to objects. For
instance, an existing Node object may have an "Energy Model" object aggregated to it at
run time (without modifying and recompiling the node class). An existing model (such as a
wireless net device) can then later "GetObject" for the energy model and act appropriately
if the interface has been either built in to the underlying Node object or aggregated to
it at run time. However, other nodes need not know anything about energy models.
We hope that this mode of programming will require much less need for developers to modify
the base classes.
Object factories
A common use case is to create lots of similarly configured objects. One can repeatedly
call CreateObject() but there is also a factory design pattern in use in the ns-3 system.
It is heavily used in the "helper" API.
Class ObjectFactory can be used to instantiate objects and to configure the attributes on
those objects:
void SetTypeId (TypeId tid);
void Set (std::string name, const AttributeValue &value);
Ptr<T> Create (void) const;
The first method allows one to use the ns-3 TypeId system to specify the type of objects
created. The second allows one to set attributes on the objects to be created, and the
third allows one to create the objects themselves.
For example:
ObjectFactory factory;
// Make this factory create objects of type FriisPropagationLossModel
factory.SetTypeId ("ns3::FriisPropagationLossModel")
// Make this factory object change a default value of an attribute, for
// subsequently created objects
factory.Set ("SystemLoss", DoubleValue (2.0));
// Create one such object
Ptr<Object> object = factory.Create ();
factory.Set ("SystemLoss", DoubleValue (3.0));
// Create another object with a different SystemLoss
Ptr<Object> object = factory.Create ();
Downcasting
A question that has arisen several times is, "If I have a base class pointer (Ptr) to an
object and I want the derived class pointer, should I downcast (via C++ dynamic cast) to
get the derived pointer, or should I use the object aggregation system to GetObject<> ()
to find a Ptr to the interface to the subclass API?"
The answer to this is that in many situations, both techniques will work. ns-3 provides a
templated function for making the syntax of Object dynamic casting much more user
friendly::
template <typename T1, typename T2>
Ptr<T1>
DynamicCast (Ptr<T2> const&p)
{
return Ptr<T1> (dynamic_cast<T1 *> (PeekPointer (p)));
}
DynamicCast works when the programmer has a base type pointer and is testing against a
subclass pointer. GetObject works when looking for different objects aggregated, but also
works with subclasses, in the same way as DynamicCast. If unsure, the programmer should
use GetObject, as it works in all cases. If the programmer knows the class hierarchy of
the object under consideration, it is more direct to just use DynamicCast.
ATTRIBUTES
In ns-3 simulations, there are two main aspects to configuration:
· the simulation topology and how objects are connected
· the values used by the models instantiated in the topology
This chapter focuses on the second item above: how the many values in use in ns-3 are
organized, documented, and modifiable by ns-3 users. The ns-3 attribute system is also the
underpinning of how traces and statistics are gathered in the simulator.
Before delving into details of the attribute value system, it will help to review some
basic properties of class ns3::Object.
Object Overview
ns-3 is fundamentally a C++ object-based system. By this we mean that new C++ classes
(types) can be declared, defined, and subclassed as usual.
Many ns-3 objects inherit from the ns3::Object base class. These objects have some
additional properties that we exploit for organizing the system and improving the memory
management of our objects:
· a "metadata" system that links the class name to a lot of meta-information about the
object, including the base class of the subclass, the set of accessible constructors in
the subclass, and the set of "attributes" of the subclass
· a reference counting smart pointer implementation, for memory management.
ns-3 objects that use the attribute system derive from either ns3::Object or
ns3::ObjectBase. Most ns-3 objects we will discuss derive from ns3::Object, but a few that
are outside the smart pointer memory management framework derive from ns3::ObjectBase.
Let's review a couple of properties of these objects.
Smart pointers
As introduced in the ns-3 tutorial, ns-3 objects are memory managed by a reference
counting smart pointer implementation, class ns3::Ptr.
Smart pointers are used extensively in the ns-3 APIs, to avoid passing references to
heap-allocated objects that may cause memory leaks. For most basic usage (syntax), treat
a smart pointer like a regular pointer::
Ptr<WifiNetDevice> nd = ...;
nd->CallSomeFunction ();
// etc.
CreateObject
As we discussed above in Memory-management-and-class-Ptr, at the lowest-level API, objects
of type ns3::Object are not instantiated using operator new as usual but instead by a
templated function called CreateObject().
A typical way to create such an object is as follows::
Ptr<WifiNetDevice> nd = CreateObject<WifiNetDevice> ();
You can think of this as being functionally equivalent to::
WifiNetDevice* nd = new WifiNetDevice ();
Objects that derive from ns3::Object must be allocated on the heap using CreateObject().
Those deriving from ns3::ObjectBase, such as ns-3 helper functions and packet headers and
trailers, can be allocated on the stack.
In some scripts, you may not see a lot of CreateObject() calls in the code; this is
because there are some helper objects in effect that are doing the CreateObject()s for
you.
TypeId
ns-3 classes that derive from class ns3::Object can include a metadata class called TypeId
that records meta-information about the class, for use in the object aggregation and
component manager systems:
· a unique string identifying the class
· the base class of the subclass, within the metadata system
· the set of accessible constructors in the subclass
Object Summary
Putting all of these concepts together, let's look at a specific example: class ns3::Node.
The public header file node.h has a declaration that includes a static GetTypeId function
call::
class Node : public Object
{
public:
static TypeId GetTypeId (void);
...
This is defined in the node.cc file as follows::
TypeId
Node::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::Node")
.SetParent<Object> ()
.AddConstructor<Node> ()
.AddAttribute ("DeviceList", "The list of devices associated to this Node.",
ObjectVectorValue (),
MakeObjectVectorAccessor (&Node::m_devices),
MakeObjectVectorChecker<NetDevice> ())
.AddAttribute ("ApplicationList", "The list of applications associated to this Node.",
ObjectVectorValue (),
MakeObjectVectorAccessor (&Node::m_applications),
MakeObjectVectorChecker<Application> ())
.AddAttribute ("Id", "The id (unique integer) of this Node.",
TypeId::ATTR_GET, // allow only getting it.
UintegerValue (0),
MakeUintegerAccessor (&Node::m_id),
MakeUintegerChecker<uint32_t> ())
;
return tid;
}
Consider the TypeId of an ns-3 Object class as an extended form of run time type
information (RTTI). The C++ language includes a simple kind of RTTI in order to support
dynamic_cast and typeid operators.
The ".SetParent<Object> ()" call in the declaration above is used in conjunction with our
object aggregation mechanisms to allow safe up- and down-casting in inheritance trees
during GetObject.
The ".AddConstructor<Node> ()" call is used in conjunction with our abstract object
factory mechanisms to allow us to construct C++ objects without forcing a user to know the
concrete class of the object she is building.
The three calls to ".AddAttribute" associate a given string with a strongly typed value in
the class. Notice that you must provide a help string which may be displayed, for example,
via command line processors. Each Attribute is associated with mechanisms for accessing
the underlying member variable in the object (for example, MakeUintegerAccessor tells the
generic Attribute code how to get to the node ID above). There are also "Checker" methods
which are used to validate values.
When users want to create Nodes, they will usually call some form of CreateObject,:
Ptr<Node> n = CreateObject<Node> ();
or more abstractly, using an object factory, you can create a Node object without even
knowing the concrete C++ type:
ObjectFactory factory;
const std::string typeId = "ns3::Node'';
factory.SetTypeId (typeId);
Ptr<Object> node = factory.Create <Object> ();
Both of these methods result in fully initialized attributes being available in the
resulting Object instances.
We next discuss how attributes (values associated with member variables or functions of
the class) are plumbed into the above TypeId.
Attribute Overview
The goal of the attribute system is to organize the access of internal member objects of a
simulation. This goal arises because, typically in simulation, users will cut and
paste/modify existing simulation scripts, or will use higher-level simulation constructs,
but often will be interested in studying or tracing particular internal variables. For
instance, use cases such as:
· "I want to trace the packets on the wireless interface only on the first access point"
· "I want to trace the value of the TCP congestion window (every time it changes) on a
particular TCP socket"
· "I want a dump of all values that were used in my simulation."
Similarly, users may want fine-grained access to internal variables in the simulation, or
may want to broadly change the initial value used for a particular parameter in all
subsequently created objects. Finally, users may wish to know what variables are settable
and retrievable in a simulation configuration. This is not just for direct simulation
interaction on the command line; consider also a (future) graphical user interface that
would like to be able to provide a feature whereby a user might right-click on an node on
the canvas and see a hierarchical, organized list of parameters that are settable on the
node and its constituent member objects, and help text and default values for each
parameter.
Functional overview
We provide a way for users to access values deep in the system, without having to plumb
accessors (pointers) through the system and walk pointer chains to get to them. Consider a
class DropTailQueue that has a member variable that is an unsigned integer m_maxPackets;
this member variable controls the depth of the queue.
If we look at the declaration of DropTailQueue, we see the following::
class DropTailQueue : public Queue {
public:
static TypeId GetTypeId (void);
...
private:
std::queue<Ptr<Packet> > m_packets;
uint32_t m_maxPackets;
};
Let's consider things that a user may want to do with the value of m_maxPackets:
· Set a default value for the system, such that whenever a new DropTailQueue is created,
this member is initialized to that default.
· Set or get the value on an already instantiated queue.
The above things typically require providing Set() and Get() functions, and some type of
global default value.
In the ns-3 attribute system, these value definitions and accessor functions are moved
into the TypeId class; e.g.::
NS_OBJECT_ENSURE_REGISTERED (DropTailQueue);
TypeId DropTailQueue::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::DropTailQueue")
.SetParent<Queue> ()
.AddConstructor<DropTailQueue> ()
.AddAttribute ("MaxPackets",
"The maximum number of packets accepted by this DropTailQueue.",
UintegerValue (100),
MakeUintegerAccessor (&DropTailQueue::m_maxPackets),
MakeUintegerChecker<uint32_t> ())
;
return tid;
}
The AddAttribute() method is performing a number of things with this value:
· Binding the variable m_maxPackets to a string "MaxPackets"
· Providing a default value (100 packets)
· Providing some help text defining the value
· Providing a "checker" (not used in this example) that can be used to set bounds on the
allowable range of values
The key point is that now the value of this variable and its default value are accessible
in the attribute namespace, which is based on strings such as "MaxPackets" and TypeId
strings. In the next section, we will provide an example script that shows how users may
manipulate these values.
Note that initialization of the attribute relies on the macro NS_OBJECT_ENSURE_REGISTERED
(DropTailQueue) being called; if you leave this out of your new class implementation, your
attributes will not be initialized correctly.
While we have described how to create attributes, we still haven't described how to access
and manage these values. For instance, there is no globals.h header file where these are
stored; attributes are stored with their classes. Questions that naturally arise are how
do users easily learn about all of the attributes of their models, and how does a user
access these attributes, or document their values as part of the record of their
simulation?
Default values and command-line arguments
Let's look at how a user script might access these values. This is based on the script
found at src/point-to-point/examples/main-attribute-value.cc, with some details stripped
out.:
//
// This is a basic example of how to use the attribute system to
// set and get a value in the underlying system; namely, an unsigned
// integer of the maximum number of packets in a queue
//
int
main (int argc, char *argv[])
{
// By default, the MaxPackets attribute has a value of 100 packets
// (this default can be observed in the function DropTailQueue::GetTypeId)
//
// Here, we set it to 80 packets. We could use one of two value types:
// a string-based value or a Uinteger value
Config::SetDefault ("ns3::DropTailQueue::MaxPackets", StringValue ("80"));
// The below function call is redundant
Config::SetDefault ("ns3::DropTailQueue::MaxPackets", UintegerValue (80));
// Allow the user to override any of the defaults and the above
// SetDefaults() at run-time, via command-line arguments
CommandLine cmd;
cmd.Parse (argc, argv);
The main thing to notice in the above are the two calls to Config::SetDefault. This is
how we set the default value for all subsequently instantiated DropTailQueues. We
illustrate that two types of Value classes, a StringValue and a UintegerValue class, can
be used to assign the value to the attribute named by "ns3::DropTailQueue::MaxPackets".
Now, we will create a few objects using the low-level API; here, our newly created queues
will not have a m_maxPackets initialized to 100 packets but to 80 packets, because of what
we did above with default values.:
Ptr<Node> n0 = CreateObject<Node> ();
Ptr<PointToPointNetDevice> net0 = CreateObject<PointToPointNetDevice> ();
n0->AddDevice (net0);
Ptr<Queue> q = CreateObject<DropTailQueue> ();
net0->AddQueue(q);
At this point, we have created a single node (Node 0) and a single PointToPointNetDevice
(NetDevice 0) and added a DropTailQueue to it.
Now, we can manipulate the MaxPackets value of the already instantiated DropTailQueue.
Here are various ways to do that.
Pointer-based access
We assume that a smart pointer (Ptr) to a relevant network device is in hand; in the
current example, it is the net0 pointer.
One way to change the value is to access a pointer to the underlying queue and modify its
attribute.
First, we observe that we can get a pointer to the (base class) queue via the
PointToPointNetDevice attributes, where it is called TxQueue:
PointerValue tmp;
net0->GetAttribute ("TxQueue", tmp);
Ptr<Object> txQueue = tmp.GetObject ();
Using the GetObject function, we can perform a safe downcast to a DropTailQueue, where
MaxPackets is a member:
Ptr<DropTailQueue> dtq = txQueue->GetObject <DropTailQueue> ();
NS_ASSERT (dtq != 0);
Next, we can get the value of an attribute on this queue. We have introduced wrapper
"Value" classes for the underlying data types, similar to Java wrappers around these
types, since the attribute system stores values and not disparate types. Here, the
attribute value is assigned to a UintegerValue, and the Get() method on this value
produces the (unwrapped) uint32_t.:
UintegerValue limit;
dtq->GetAttribute ("MaxPackets", limit);
NS_LOG_INFO ("1. dtq limit: " << limit.Get () << " packets");
Note that the above downcast is not really needed; we could have done the same using the
Ptr<Queue> even though the attribute is a member of the subclass:
txQueue->GetAttribute ("MaxPackets", limit);
NS_LOG_INFO ("2. txQueue limit: " << limit.Get () << " packets");
Now, let's set it to another value (60 packets):
txQueue->SetAttribute("MaxPackets", UintegerValue (60));
txQueue->GetAttribute ("MaxPackets", limit);
NS_LOG_INFO ("3. txQueue limit changed: " << limit.Get () << " packets");
Namespace-based access
An alternative way to get at the attribute is to use the configuration namespace. Here,
this attribute resides on a known path in this namespace; this approach is useful if one
doesn't have access to the underlying pointers and would like to configure a specific
attribute with a single statement.:
Config::Set ("/NodeList/0/DeviceList/0/TxQueue/MaxPackets", UintegerValue (25));
txQueue->GetAttribute ("MaxPackets", limit);
NS_LOG_INFO ("4. txQueue limit changed through namespace: " <<
limit.Get () << " packets");
We could have also used wildcards to set this value for all nodes and all net devices
(which in this simple example has the same effect as the previous Set()):
Config::Set ("/NodeList/*/DeviceList/*/TxQueue/MaxPackets", UintegerValue (15));
txQueue->GetAttribute ("MaxPackets", limit);
NS_LOG_INFO ("5. txQueue limit changed through wildcarded namespace: " <<
limit.Get () << " packets");
Object Name Service-based access
Another way to get at the attribute is to use the object name service facility. Here,
this attribute is found using a name string. This approach is useful if one doesn't have
access to the underlying pointers and it is difficult to determine the required concrete
configuration namespaced path.:
Names::Add ("server", serverNode);
Names::Add ("server/eth0", serverDevice);
...
Config::Set ("/Names/server/eth0/TxQueue/MaxPackets", UintegerValue (25));
Object-names for a fuller treatment of the ns-3 configuration namespace.
Setting through constructors helper classes
Arbitrary combinations of attributes can be set and fetched from the helper and low-level
APIs; either from the constructors themselves::
Ptr<Object> p = CreateObject<MyNewObject> ("n1", v1, "n2", v2, ...);
or from the higher-level helper APIs, such as::
mobility.SetPositionAllocator ("GridPositionAllocator",
"MinX", DoubleValue (-100.0),
"MinY", DoubleValue (-100.0),
"DeltaX", DoubleValue (5.0),
"DeltaY", DoubleValue (20.0),
"GridWidth", UintegerValue (20),
"LayoutType", StringValue ("RowFirst"));
Implementation details
Value classes
Readers will note the new FooValue classes which are subclasses of the AttributeValue base
class. These can be thought of as an intermediate class that can be used to convert from
raw types to the Values that are used by the attribute system. Recall that this database
is holding objects of many types with a single generic type. Conversions to this type can
either be done using an intermediate class (IntegerValue, DoubleValue for "floating
point") or via strings. Direct implicit conversion of types to Value is not really
practical. So in the above, users have a choice of using strings or values::
p->Set ("cwnd", StringValue ("100")); // string-based setter
p->Set ("cwnd", IntegerValue (100)); // integer-based setter
The system provides some macros that help users declare and define new AttributeValue
subclasses for new types that they want to introduce into the attribute system:
· ATTRIBUTE_HELPER_HEADER
· ATTRIBUTE_HELPER_CPP
Initialization order
Attributes in the system must not depend on the state of any other Attribute in this
system. This is because an ordering of Attribute initialization is not specified, nor
enforced, by the system. A specific example of this can be seen in automated configuration
programs such as ns3::ConfigStore. Although a given model may arrange it so that
Attributes are initialized in a particular order, another automatic configurator may
decide independently to change Attributes in, for example, alphabetic order.
Because of this non-specific ordering, no Attribute in the system may have any dependence
on any other Attribute. As a corollary, Attribute setters must never fail due to the state
of another Attribute. No Attribute setter may change (set) any other Attribute value as a
result of changing its value.
This is a very strong restriction and there are cases where Attributes must set
consistently to allow correct operation. To this end we do allow for consistency checking
when the attribute is used (cf. NS_ASSERT_MSG or NS_ABORT_MSG).
In general, the attribute code to assign values to the underlying class member variables
is executed after an object is constructed. But what if you need the values assigned
before the constructor body executes, because you need them in the logic of the
constructor? There is a way to do this, used for example in the class ns3::ConfigStore:
call ObjectBase::ConstructSelf () as follows::
ConfigStore::ConfigStore ()
{
ObjectBase::ConstructSelf (AttributeConstructionList ());
// continue on with constructor.
}
Beware that the object and all its derived classes must also implement a virtual TypeId
GetInstanceTypeId (void) const; method. Otherwise the ObjectBase::ConstructSelf () will
not be able to read the attributes.
Extending attributes
The ns-3 system will place a number of internal values under the attribute system, but
undoubtedly users will want to extend this to pick up ones we have missed, or to add their
own classes to this.
Adding an existing internal variable to the metadata system
Consider this variable in class TcpSocket::
uint32_t m_cWnd; // Congestion window
Suppose that someone working with TCP wanted to get or set the value of that variable
using the metadata system. If it were not already provided by ns-3, the user could declare
the following addition in the runtime metadata system (to the TypeId declaration for
TcpSocket)::
.AddAttribute ("Congestion window",
"Tcp congestion window (bytes)",
UintegerValue (1),
MakeUintegerAccessor (&TcpSocket::m_cWnd),
MakeUintegerChecker<uint16_t> ())
Now, the user with a pointer to the TcpSocket can perform operations such as setting and
getting the value, without having to add these functions explicitly. Furthermore, access
controls can be applied, such as allowing the parameter to be read and not written, or
bounds checking on the permissible values can be applied.
Adding a new TypeId
Here, we discuss the impact on a user who wants to add a new class to ns-3; what
additional things must be done to hook it into this system.
We've already introduced what a TypeId definition looks like::
TypeId
RandomWalk2dMobilityModel::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::RandomWalk2dMobilityModel")
.SetParent<MobilityModel> ()
.SetGroupName ("Mobility")
.AddConstructor<RandomWalk2dMobilityModel> ()
.AddAttribute ("Bounds",
"Bounds of the area to cruise.",
RectangleValue (Rectangle (0.0, 0.0, 100.0, 100.0)),
MakeRectangleAccessor (&RandomWalk2dMobilityModel::m_bounds),
MakeRectangleChecker ())
.AddAttribute ("Time",
"Change current direction and speed after moving for this delay.",
TimeValue (Seconds (1.0)),
MakeTimeAccessor (&RandomWalk2dMobilityModel::m_modeTime),
MakeTimeChecker ())
// etc (more parameters).
;
return tid;
}
The declaration for this in the class declaration is one-line public member method::
public:
static TypeId GetTypeId (void);
Typical mistakes here involve:
· Not calling the SetParent method or calling it with the wrong type
· Not calling the AddConstructor method of calling it with the wrong type
· Introducing a typographical error in the name of the TypeId in its constructor
· Not using the fully-qualified c++ typename of the enclosing c++ class as the name of the
TypeId
None of these mistakes can be detected by the ns-3 codebase so, users are advised to check
carefully multiple times that they got these right.
Adding new class type to the attribute system
From the perspective of the user who writes a new class in the system and wants to hook it
in to the attribute system, there is mainly the matter of writing the conversions to/from
strings and attribute values. Most of this can be copy/pasted with macro-ized code. For
instance, consider class declaration for Rectangle in the src/mobility/model directory:
Header file
/**
* \brief a 2d rectangle
*/
class Rectangle
{
...
double xMin;
double xMax;
double yMin;
double yMax;
};
One macro call and two operators, must be added below the class declaration in order to
turn a Rectangle into a value usable by the Attribute system::
std::ostream &operator << (std::ostream &os, const Rectangle &rectangle);
std::istream &operator >> (std::istream &is, Rectangle &rectangle);
ATTRIBUTE_HELPER_HEADER (Rectangle);
Implementation file
In the class definition (.cc file), the code looks like this::
ATTRIBUTE_HELPER_CPP (Rectangle);
std::ostream &
operator << (std::ostream &os, const Rectangle &rectangle)
{
os << rectangle.xMin << "|" << rectangle.xMax << "|" << rectangle.yMin << "|"
<< rectangle.yMax;
return os;
}
std::istream &
operator >> (std::istream &is, Rectangle &rectangle)
{
char c1, c2, c3;
is >> rectangle.xMin >> c1 >> rectangle.xMax >> c2 >> rectangle.yMin >> c3
>> rectangle.yMax;
if (c1 != '|' ||
c2 != '|' ||
c3 != '|')
{
is.setstate (std::ios_base::failbit);
}
return is;
}
These stream operators simply convert from a string representation of the Rectangle
("xMin|xMax|yMin|yMax") to the underlying Rectangle, and the modeler must specify these
operators and the string syntactical representation of an instance of the new class.
ConfigStore
The ConfigStore is a specialized database for attribute values and default values.
Although it is a separately maintained module in src/config-store/ directory, we document
it here because of its sole dependency on ns-3 core module and attributes.
Values for ns-3 attributes can be stored in an ASCII or XML text file and loaded into a
future simulation. This feature is known as the ns-3 ConfigStore. We can explore this
system by using an example from src/config-store/examples/config-store-save.cc.
First, all users must include the following statement::
#include "ns3/config-store-module.h"
Next, this program adds a sample object A to show how the system is extended::
class A : public Object
{
public:
static TypeId GetTypeId (void) {
static TypeId tid = TypeId ("ns3::A")
.SetParent<Object> ()
.AddAttribute ("TestInt16", "help text",
IntegerValue (-2),
MakeIntegerAccessor (&A::m_int16),
MakeIntegerChecker<int16_t> ())
;
return tid;
}
int16_t m_int16;
};
NS_OBJECT_ENSURE_REGISTERED (A);
Next, we use the Config subsystem to override the defaults in a couple of ways::
Config::SetDefault ("ns3::A::TestInt16", IntegerValue (-5));
Ptr<A> a_obj = CreateObject<A> ();
NS_ABORT_MSG_UNLESS (a_obj->m_int16 == -5, "Cannot set A's integer attribute via Config::SetDefault");
Ptr<A> a2_obj = CreateObject<A> ();
a2_obj->SetAttribute ("TestInt16", IntegerValue (-3));
IntegerValue iv;
a2_obj->GetAttribute ("TestInt16", iv);
NS_ABORT_MSG_UNLESS (iv.Get () == -3, "Cannot set A's integer attribute via SetAttribute");
The next statement is necessary to make sure that (one of) the objects created is rooted
in the configuration namespace as an object instance. This normally happens when you
aggregate objects to ns3::Node or ns3::Channel but here, since we are working at the core
level, we need to create a new root namespace object::
Config::RegisterRootNamespaceObject (a2_obj);
Next, we want to output the configuration store. The examples show how to do it in two
formats, XML and raw text. In practice, one should perform this step just before calling
Simulator::Run (); it will allow the configuration to be saved just before running the
simulation.
There are three attributes that govern the behavior of the ConfigStore: "Mode",
"Filename", and "FileFormat". The Mode (default "None") configures whether ns-3 should
load configuration from a previously saved file (specify "Mode=Load") or save it to a file
(specify "Mode=Save"). The Filename (default "") is where the ConfigStore should store
its output data. The FileFormat (default "RawText") governs whether the ConfigStore
format is Xml or RawText format.
The example shows::
Config::SetDefault ("ns3::ConfigStore::Filename", StringValue ("output-attributes.xml"));
Config::SetDefault ("ns3::ConfigStore::FileFormat", StringValue ("Xml"));
Config::SetDefault ("ns3::ConfigStore::Mode", StringValue ("Save"));
ConfigStore outputConfig;
outputConfig.ConfigureDefaults ();
outputConfig.ConfigureAttributes ();
// Output config store to txt format
Config::SetDefault ("ns3::ConfigStore::Filename", StringValue ("output-attributes.txt"));
Config::SetDefault ("ns3::ConfigStore::FileFormat", StringValue ("RawText"));
Config::SetDefault ("ns3::ConfigStore::Mode", StringValue ("Save"));
ConfigStore outputConfig2;
outputConfig2.ConfigureDefaults ();
outputConfig2.ConfigureAttributes ();
Simulator::Run ();
Simulator::Destroy ();
After running, you can open the output-attributes.txt file and see::
default ns3::RealtimeSimulatorImpl::SynchronizationMode "BestEffort"
default ns3::RealtimeSimulatorImpl::HardLimit "+100000000.0ns"
default ns3::PcapFileWrapper::CaptureSize "65535"
default ns3::PacketSocket::RcvBufSize "131072"
default ns3::ErrorModel::IsEnabled "true"
default ns3::RateErrorModel::ErrorUnit "EU_BYTE"
default ns3::RateErrorModel::ErrorRate "0"
default ns3::RateErrorModel::RanVar "Uniform:0:1"
default ns3::DropTailQueue::Mode "Packets"
default ns3::DropTailQueue::MaxPackets "100"
default ns3::DropTailQueue::MaxBytes "6553500"
default ns3::Application::StartTime "+0.0ns"
default ns3::Application::StopTime "+0.0ns"
default ns3::ConfigStore::Mode "Save"
default ns3::ConfigStore::Filename "output-attributes.txt"
default ns3::ConfigStore::FileFormat "RawText"
default ns3::A::TestInt16 "-5"
global RngSeed "1"
global RngRun "1"
global SimulatorImplementationType "ns3::DefaultSimulatorImpl"
global SchedulerType "ns3::MapScheduler"
global ChecksumEnabled "false"
value /$ns3::A/TestInt16 "-3"
In the above, all of the default values for attributes for the core module are shown.
Then, all the values for the ns-3 global values are recorded. Finally, the value of the
instance of A that was rooted in the configuration namespace is shown. In a real ns-3
program, many more models, attributes, and defaults would be shown.
An XML version also exists in output-attributes.xml::
<?xml version="1.0" encoding="UTF-8"?>
<ns3>
<default name="ns3::RealtimeSimulatorImpl::SynchronizationMode" value="BestEffort"/>
<default name="ns3::RealtimeSimulatorImpl::HardLimit" value="+100000000.0ns"/>
<default name="ns3::PcapFileWrapper::CaptureSize" value="65535"/>
<default name="ns3::PacketSocket::RcvBufSize" value="131072"/>
<default name="ns3::ErrorModel::IsEnabled" value="true"/>
<default name="ns3::RateErrorModel::ErrorUnit" value="EU_BYTE"/>
<default name="ns3::RateErrorModel::ErrorRate" value="0"/>
<default name="ns3::RateErrorModel::RanVar" value="Uniform:0:1"/>
<default name="ns3::DropTailQueue::Mode" value="Packets"/>
<default name="ns3::DropTailQueue::MaxPackets" value="100"/>
<default name="ns3::DropTailQueue::MaxBytes" value="6553500"/>
<default name="ns3::Application::StartTime" value="+0.0ns"/>
<default name="ns3::Application::StopTime" value="+0.0ns"/>
<default name="ns3::ConfigStore::Mode" value="Save"/>
<default name="ns3::ConfigStore::Filename" value="output-attributes.xml"/>
<default name="ns3::ConfigStore::FileFormat" value="Xml"/>
<default name="ns3::A::TestInt16" value="-5"/>
<global name="RngSeed" value="1"/>
<global name="RngRun" value="1"/>
<global name="SimulatorImplementationType" value="ns3::DefaultSimulatorImpl"/>
<global name="SchedulerType" value="ns3::MapScheduler"/>
<global name="ChecksumEnabled" value="false"/>
<value path="/$ns3::A/TestInt16" value="-3"/>
</ns3>
This file can be archived with your simulation script and output data.
While it is possible to generate a sample config file and lightly edit it to change a
couple of values, there are cases where this process will not work because the same value
on the same object can appear multiple times in the same automatically-generated
configuration file under different configuration paths.
As such, the best way to use this class is to use it to generate an initial configuration
file, extract from that configuration file only the strictly necessary elements, and move
these minimal elements to a new configuration file which can then safely be edited and
loaded in a subsequent simulation run.
When the ConfigStore object is instantiated, its attributes Filename, Mode, and FileFormat
must be set, either via command-line or via program statements.
As a more complicated example, let's assume that we want to read in a configuration of
defaults from an input file named "input-defaults.xml", and write out the resulting
attributes to a separate file called "output-attributes.xml". (Note-- to get this input
xml file to begin with, it is sometimes helpful to run the program to generate an output
xml file first, then hand-edit that file and re-input it for the next simulation run).:
#include "ns3/config-store-module.h"
...
int main (...)
{
Config::SetDefault ("ns3::ConfigStore::Filename", StringValue ("input-defaults.xml"));
Config::SetDefault ("ns3::ConfigStore::Mode", StringValue ("Load"));
Config::SetDefault ("ns3::ConfigStore::FileFormat", StringValue ("Xml"));
ConfigStore inputConfig;
inputConfig.ConfigureDefaults ();
//
// Allow the user to override any of the defaults and the above Bind() at
// run-time, via command-line arguments
//
CommandLine cmd;
cmd.Parse (argc, argv);
// setup topology
...
// Invoke just before entering Simulator::Run ()
Config::SetDefault ("ns3::ConfigStore::Filename", StringValue ("output-attributes.xml"));
Config::SetDefault ("ns3::ConfigStore::Mode", StringValue ("Save"));
ConfigStore outputConfig;
outputConfig.ConfigureAttributes ();
Simulator::Run ();
}
GTK-based ConfigStore
There is a GTK-based front end for the ConfigStore. This allows users to use a GUI to
access and change variables. Screenshots of this feature are available in the |ns3|
Overview presentation.
To use this feature, one must install libgtk and libgtk-dev; an example Ubuntu
installation command is::
sudo apt-get install libgtk2.0-0 libgtk2.0-dev
To check whether it is configured or not, check the output of the step::
./waf configure --enable-examples --enable-tests
---- Summary of optional NS-3 features:
Python Bindings : enabled
Python API Scanning Support : enabled
NS-3 Click Integration : enabled
GtkConfigStore : not enabled (library 'gtk+-2.0 >= 2.12' not found)
In the above example, it was not enabled, so it cannot be used until a suitable version is
installed and:
./waf configure --enable-examples --enable-tests
./waf
is rerun.
Usage is almost the same as the non-GTK-based version, but there are no ConfigStore
attributes involved::
// Invoke just before entering Simulator::Run ()
GtkConfigStore config;
config.ConfigureDefaults ();
config.ConfigureAttributes ();
Now, when you run the script, a GUI should pop up, allowing you to open menus of
attributes on different nodes/objects, and then launch the simulation execution when you
are done.
Future work
There are a couple of possible improvements: * save a unique version number with date and
time at start of file * save rng initial seed somewhere. * make each RandomVariable
serialize its own initial seed and re-read it later
OBJECT NAMES
Placeholder chapter
LOGGING
The ns-3 logging facility can be used to monitor or debug the progress of simulation
programs. Logging output can be enabled by program statements in your main() program or
by the use of the NS_LOG environment variable.
Logging statements are not compiled into optimized builds of ns-3. To use logging, one
must build the (default) debug build of ns-3.
The project makes no guarantee about whether logging output will remain the same over
time. Users are cautioned against building simulation output frameworks on top of logging
code, as the output and the way the output is enabled may change over time.
Logging overview
ns-3 logging statements are typically used to log various program execution events, such
as the occurrence of simulation events or the use of a particular function.
For example, this code snippet is from Ipv4L3Protocol::IsDestinationAddress():
if (address == iaddr.GetBroadcast ())
{
NS_LOG_LOGIC ("For me (interface broadcast address)");
return true;
}
If logging has been enabled for the Ipv4L3Protocol component at a level of LOGIC or above
(see below about logging levels), the statement will be printed out; otherwise, it will be
suppressed.
Logging levels
The following levels are defined; each level will enable the levels above it, with the ALL
level being most verbose:
1. LOG_NONE: the default, no logging
2. LOG_ERROR: serious error messages only
3. LOG_WARN: warning messages
4. LOG_DEBUG: for use in debugging
5. LOG_FUNCTION: function tracing
6. LOG_LOGIC: control flow tracing within functions
7. LOG_ALL: print everything
A special logging level will cause logging output to unconditionally appear on std::clog,
regardless of whether the user has explicitly enabled logging. This macro,
NS_LOG_UNCOND(), can be used like a kind of printf() in your code. An example can be
found in scratch/scratch-simulator.cc:
NS_LOG_UNCOND ("Scratch Simulator");
Logging prefixes
This section still needs documentation; bug 1496 is open on this:
$ NS_LOG="*=all|prefix_all" ./waf --run scratch-simulator
Scratch Simulator
ScratchSimulator:main(): [ERROR] error message
ScratchSimulator:main(): [WARN] warn message
ScratchSimulator:main(): [DEBUG] debug message
ScratchSimulator:main(): [INFO] info message
ScratchSimulator:main(function)
ScratchSimulator:main(): [LOGIC] logic message
Enabling logging output
There are two ways that users typically control logging output. The first is by setting
an NS_LOG environment variable; e.g.:
NS_LOG="*" ./waf --run first
will run the first tutorial program with all logging output. This can be made more
granular by selecting individual components:
NS_LOG="Ipv4L3Protocol" ./waf --run first
The second way to enable this is to use explicit statements in your program, such as in
the first tutorial program:
int
main (int argc, char *argv[])
{
LogComponentEnable ("UdpEchoClientApplication", LOG_LEVEL_INFO);
LogComponentEnable ("UdpEchoServerApplication", LOG_LEVEL_INFO);
...
Some helpers have special methods to enable the logging of all components in a module
(across different compilation units, but logically grouped together such as the ns-3 wifi
code:
WifiHelper wifiHelper;
wifiHelper.EnableLogComponents ();
How to add logging to your code
To add logging to your code, please follow the below steps:
1. Put NS_LOG_COMPONENT_DEFINE macro outside of namespace ns3
Create a unique string identifier (usually based on the name of the file and/or class
defined within the file) and register it with a macro call such as follows:
NS_LOG_COMPONENT_DEFINE ("Ipv4L3Protocol");
namespace ns3 {
...
The macro was carefully written to permit inclusion either within or outside of namespace
ns3, and usage will vary across the codebase, but the original intent was to register this
outside of namespace ns3.
2. Add logging statements to your functions and function bodies.
There are a couple of guidelines on this:
· Do not add function logging in operators or explicit copy constructors, since these will
cause infinite recursion and stack overflow.
· Use the NS_LOG_FUNCTION_NOARGS() variant for static methods only. When a non-static
member function has no arguments, it should be logged by NS_LOG_FUNCTION (this) macro.
· Make sure that you test that your logging changes do not break the code; running some
example programs with all log components turned on (e.g. NS_LOG="*") is one way to test
this.
TRACING
The tracing subsystem is one of the most important mechanisms to understand in ns-3. In
most cases, ns-3 users will have a brilliant idea for some new and improved networking
feature. In order to verify that this idea works, the researcher will make changes to an
existing system and then run experiments to see how the new feature behaves by gathering
statistics that capture the behavior of the feature.
In other words, the whole point of running a simulation is to generate output for further
study. In ns-3, the subsystem that enables a researcher to do this is the tracing
subsystem.
Tracing Motivation
There are many ways to get information out of a program. The most straightforward way is
to just directly print the information to the standard output, as in,
#include <iostream>
...
int main ()
{
...
std::cout << "The value of x is " << x << std::endl;
...
}
This is workable in small environments, but as your simulations get more and more
complicated, you end up with more and more prints and the task of parsing and performing
computations on the output begins to get harder and harder.
Another thing to consider is that every time a new tidbit is needed, the software core
must be edited and another print introduced. There is no standardized way to control all
of this output, so the amount of output tends to grow without bounds. Eventually, the
bandwidth required for simply outputting this information begins to limit the running time
of the simulation. The output files grow to enormous sizes and parsing them becomes a
problem.
ns-3 provides a simple mechanism for logging and providing some control over output via
Log Components, but the level of control is not very fine grained at all. The logging
module is a relatively blunt instrument.
It is desirable to have a facility that allows one to reach into the core system and only
get the information required without having to change and recompile the core system. Even
better would be a system that notified the user when an item of interest changed or an
interesting event happened.
The ns-3 tracing system is designed to work along those lines and is well-integrated with
the Attribute and Config substems allowing for relatively simple use scenarios.
Overview
The tracing subsystem relies heavily on the ns-3 Callback and Attribute mechanisms. You
should read and understand the corresponding sections of the manual before attempting to
understand the tracing system.
The ns-3 tracing system is built on the concepts of independent tracing sources and
tracing sinks; along with a uniform mechanism for connecting sources to sinks.
Trace sources are entities that can signal events that happen in a simulation and provide
access to interesting underlying data. For example, a trace source could indicate when a
packet is received by a net device and provide access to the packet contents for
interested trace sinks. A trace source might also indicate when an interesting state
change happens in a model. For example, the congestion window of a TCP model is a prime
candidate for a trace source.
Trace sources are not useful by themselves; they must be connected to other pieces of code
that actually do something useful with the information provided by the source. The
entities that consume trace information are called trace sinks. Trace sources are
generators of events and trace sinks are consumers.
This explicit division allows for large numbers of trace sources to be scattered around
the system in places which model authors believe might be useful. Unless a user connects a
trace sink to one of these sources, nothing is output. This arrangement allows relatively
unsophisticated users to attach new types of sinks to existing tracing sources, without
requiring editing and recompiling the core or models of the simulator.
There can be zero or more consumers of trace events generated by a trace source. One can
think of a trace source as a kind of point-to-multipoint information link.
The "transport protocol" for this conceptual point-to-multipoint link is an ns-3 Callback.
Recall from the Callback Section that callback facility is a way to allow two modules in
the system to communicate via function calls while at the same time decoupling the calling
function from the called class completely. This is the same requirement as outlined above
for the tracing system.
Basically, a trace source is a callback to which multiple functions may be registered.
When a trace sink expresses interest in receiving trace events, it adds a callback to a
list of callbacks held by the trace source. When an interesting event happens, the trace
source invokes its operator() providing zero or more parameters. This tells the source to
go through its list of callbacks invoking each one in turn. In this way, the parameter(s)
are communicated to the trace sinks, which are just functions.
The Simplest Example
It will be useful to go walk a quick example just to reinforce what we've said.:
#include "ns3/object.h"
#include "ns3/uinteger.h"
#include "ns3/traced-value.h""
#include "ns3/trace-source-accessor.h"
#include <iostream>
using namespace ns3;
The first thing to do is include the required files. As mentioned above, the trace system
makes heavy use of the Object and Attribute systems. The first two includes bring in the
declarations for those systems. The file, traced-value.h brings in the required
declarations for tracing data that obeys value semantics.
In general, value semantics just means that you can pass the object around, not an
address. In order to use value semantics at all you have to have an object with an
associated copy constructor and assignment operator available. We extend the requirements
to talk about the set of operators that are pre-defined for plain-old-data (POD) types.
Operator=, operator++, operator--, operator+, operator==, etc.
What this all means is that you will be able to trace changes to an object made using
those operators.:
class MyObject : public Object
{
public:
static TypeId GetTypeId (void)
{
static TypeId tid = TypeId ("MyObject")
.SetParent (Object::GetTypeId ())
.AddConstructor<MyObject> ()
.AddTraceSource ("MyInteger",
"An integer value to trace.",
MakeTraceSourceAccessor (&MyObject::m_myInt))
;
return tid;
}
MyObject () {}
TracedValue<uint32_t> m_myInt;
};
Since the tracing system is integrated with Attributes, and Attributes work with Objects,
there must be an ns-3 Object for the trace source to live in. The two important lines of
code are the .AddTraceSource and the TracedValue declaration.
The .AddTraceSource provides the "hooks" used for connecting the trace source to the
outside world. The TracedValue declaration provides the infrastructure that overloads the
operators mentioned above and drives the callback process.:
void
IntTrace (Int oldValue, Int newValue)
{
std::cout << "Traced " << oldValue << " to " << newValue << std::endl;
}
This is the definition of the trace sink. It corresponds directly to a callback function.
This function will be called whenever one of the operators of the TracedValue is
executed.:
int
main (int argc, char *argv[])
{
Ptr<MyObject> myObject = CreateObject<MyObject> ();
myObject->TraceConnectWithoutContext ("MyInteger", MakeCallback(&IntTrace));
myObject->m_myInt = 1234;
}
In this snippet, the first thing that needs to be done is to create the object in which
the trace source lives.
The next step, the TraceConnectWithoutContext, forms the connection between the trace
source and the trace sink. Notice the MakeCallback template function. Recall from the
Callback section that this creates the specialized functor responsible for providing the
overloaded operator() used to "fire" the callback. The overloaded operators (++, --, etc.)
will use this operator() to actually invoke the callback. The TraceConnectWithoutContext,
takes a string parameter that provides the name of the Attribute assigned to the trace
source. Let's ignore the bit about context for now since it is not important yet.
Finally, the line,:
myObject->m_myInt = 1234;
should be interpreted as an invocation of operator= on the member variable m_myInt with
the integer 1234 passed as a parameter. It turns out that this operator is defined (by
TracedValue) to execute a callback that returns void and takes two integer values as
parameters -- an old value and a new value for the integer in question. That is exactly
the function signature for the callback function we provided -- IntTrace.
To summarize, a trace source is, in essence, a variable that holds a list of callbacks. A
trace sink is a function used as the target of a callback. The Attribute and object type
information systems are used to provide a way to connect trace sources to trace sinks. The
act of "hitting" a trace source is executing an operator on the trace source which fires
callbacks. This results in the trace sink callbacks registering interest in the source
being called with the parameters provided by the source.
Using the Config Subsystem to Connect to Trace Sources
The TraceConnectWithoutContext call shown above in the simple example is actually very
rarely used in the system. More typically, the Config subsystem is used to allow selecting
a trace source in the system using what is called a config path.
For example, one might find something that looks like the following in the system (taken
from examples/tcp-large-transfer.cc):
void CwndTracer (uint32_t oldval, uint32_t newval) {}
...
Config::ConnectWithoutContext (
"/NodeList/0/$ns3::TcpL4Protocol/SocketList/0/CongestionWindow",
MakeCallback (&CwndTracer));
This should look very familiar. It is the same thing as the previous example, except that
a static member function of class Config is being called instead of a method on Object;
and instead of an Attribute name, a path is being provided.
The first thing to do is to read the path backward. The last segment of the path must be
an Attribute of an Object. In fact, if you had a pointer to the Object that has the
"CongestionWindow" Attribute handy (call it theObject), you could write this just like the
previous example::
void CwndTracer (uint32_t oldval, uint32_t newval) {}
...
theObject->TraceConnectWithoutContext ("CongestionWindow", MakeCallback (&CwndTracer));
It turns out that the code for Config::ConnectWithoutContext does exactly that. This
function takes a path that represents a chain of Object pointers and follows them until it
gets to the end of the path and interprets the last segment as an Attribute on the last
object. Let's walk through what happens.
The leading "/" character in the path refers to a so-called namespace. One of the
predefined namespaces in the config system is "NodeList" which is a list of all of the
nodes in the simulation. Items in the list are referred to by indices into the list, so
"/NodeList/0" refers to the zeroth node in the list of nodes created by the simulation.
This node is actually a Ptr<Node> and so is a subclass of an ns3::Object.
As described in the Object-model section, ns-3 supports an object aggregation model. The
next path segment begins with the "$" character which indicates a GetObject call should be
made looking for the type that follows. When a node is initialized by an
InternetStackHelper a number of interfaces are aggregated to the node. One of these is the
TCP level four protocol. The runtime type of this protocol object is "ns3::TcpL4Protocol".
When the GetObject is executed, it returns a pointer to the object of this type.
The TcpL4Protocol class defines an Attribute called "SocketList" which is a list of
sockets. Each socket is actually an ns3::Object with its own Attributes. The items in
the list of sockets are referred to by index just as in the NodeList, so "SocketList/0"
refers to the zeroth socket in the list of sockets on the zeroth node in the NodeList --
the first node constructed in the simulation.
This socket, the type of which turns out to be an ns3::TcpSocketImpl defines an attribute
called "CongestionWindow" which is a TracedValue<uint32_t>. The
Config::ConnectWithoutContext now does a,:
object->TraceConnectWithoutContext ("CongestionWindow", MakeCallback (&CwndTracer));
using the object pointer from "SocketList/0" which makes the connection between the trace
source defined in the socket to the callback -- CwndTracer.
Now, whenever a change is made to the TracedValue<uint32_t> representing the congestion
window in the TCP socket, the registered callback will be executed and the function
CwndTracer will be called printing out the old and new values of the TCP congestion
window.
Using the Tracing API
There are three levels of interaction with the tracing system:
· Beginning user can easily control which objects are participating in tracing;
· Intermediate users can extend the tracing system to modify the output format generated
or use existing trace sources in different ways, without modifying the core of the
simulator;
· Advanced users can modify the simulator core to add new tracing sources and sinks.
Using Trace Helpers
The ns-3 trace helpers provide a rich environment for configuring and selecting different
trace events and writing them to files. In previous sections, primarily "Building
Topologies," we have seen several varieties of the trace helper methods designed for use
inside other (device) helpers.
Perhaps you will recall seeing some of these variations::
pointToPoint.EnablePcapAll ("second");
pointToPoint.EnablePcap ("second", p2pNodes.Get (0)->GetId (), 0);
csma.EnablePcap ("third", csmaDevices.Get (0), true);
pointToPoint.EnableAsciiAll (ascii.CreateFileStream ("myfirst.tr"));
What may not be obvious, though, is that there is a consistent model for all of the
trace-related methods found in the system. We will now take a little time and take a look
at the "big picture".
There are currently two primary use cases of the tracing helpers in ns-3: Device helpers
and protocol helpers. Device helpers look at the problem of specifying which traces should
be enabled through a node, device pair. For example, you may want to specify that pcap
tracing should be enabled on a particular device on a specific node. This follows from the
ns-3 device conceptual model, and also the conceptual models of the various device
helpers. Following naturally from this, the files created follow a
<prefix>-<node>-<device> naming convention.
Protocol helpers look at the problem of specifying which traces should be enabled through
a protocol and interface pair. This follows from the ns-3 protocol stack conceptual model,
and also the conceptual models of internet stack helpers. Naturally, the trace files
should follow a <prefix>-<protocol>-<interface> naming convention.
The trace helpers therefore fall naturally into a two-dimensional taxonomy. There are
subtleties that prevent all four classes from behaving identically, but we do strive to
make them all work as similarly as possible; and whenever possible there are analogs for
all methods in all classes.:
| pcap | ascii |
-----------------+------+-------|
Device Helper | | |
-----------------+------+-------|
Protocol Helper | | |
-----------------+------+-------|
We use an approach called a mixin to add tracing functionality to our helper classes. A
mixin is a class that provides functionality to that is inherited by a subclass.
Inheriting from a mixin is not considered a form of specialization but is really a way to
collect functionality.
Let's take a quick look at all four of these cases and their respective mixins.
Pcap Tracing Device Helpers
The goal of these helpers is to make it easy to add a consistent pcap trace facility to an
ns-3 device. We want all of the various flavors of pcap tracing to work the same across
all devices, so the methods of these helpers are inherited by device helpers. Take a look
at src/network/helper/trace-helper.h if you want to follow the discussion while looking at
real code.
The class PcapHelperForDevice is a mixin provides the high level functionality for using
pcap tracing in an ns-3 device. Every device must implement a single virtual method
inherited from this class.:
virtual void EnablePcapInternal (std::string prefix, Ptr<NetDevice> nd, bool promiscuous) = 0;
The signature of this method reflects the device-centric view of the situation at this
level. All of the public methods inherited from class PcapUserHelperForDevice reduce to
calling this single device-dependent implementation method. For example, the lowest level
pcap method,:
void EnablePcap (std::string prefix, Ptr<NetDevice> nd, bool promiscuous = false, bool explicitFilename = false);
will call the device implementation of EnablePcapInternal directly. All other public pcap
tracing methods build on this implementation to provide additional user-level
functionality. What this means to the user is that all device helpers in the system will
have all of the pcap trace methods available; and these methods will all work in the same
way across devices if the device implements EnablePcapInternal correctly.
Pcap Tracing Device Helper Methods
void EnablePcap (std::string prefix, Ptr<NetDevice> nd, bool promiscuous = false, bool explicitFilename = false);
void EnablePcap (std::string prefix, std::string ndName, bool promiscuous = false, bool explicitFilename = false);
void EnablePcap (std::string prefix, NetDeviceContainer d, bool promiscuous = false);
void EnablePcap (std::string prefix, NodeContainer n, bool promiscuous = false);
void EnablePcap (std::string prefix, uint32_t nodeid, uint32_t deviceid, bool promiscuous = false);
void EnablePcapAll (std::string prefix, bool promiscuous = false);
In each of the methods shown above, there is a default parameter called promiscuous that
defaults to false. This parameter indicates that the trace should not be gathered in
promiscuous mode. If you do want your traces to include all traffic seen by the device
(and if the device supports a promiscuous mode) simply add a true parameter to any of the
calls above. For example,:
Ptr<NetDevice> nd;
...
helper.EnablePcap ("prefix", nd, true);
will enable promiscuous mode captures on the NetDevice specified by nd.
The first two methods also include a default parameter called explicitFilename that will
be discussed below.
You are encouraged to peruse the Doxygen for class PcapHelperForDevice to find the details
of these methods; but to summarize ...
You can enable pcap tracing on a particular node/net-device pair by providing a
Ptr<NetDevice> to an EnablePcap method. The Ptr<Node> is implicit since the net device
must belong to exactly one Node. For example,:
Ptr<NetDevice> nd;
...
helper.EnablePcap ("prefix", nd);
You can enable pcap tracing on a particular node/net-device pair by providing a
std::string representing an object name service string to an EnablePcap method. The
Ptr<NetDevice> is looked up from the name string. Again, the <Node> is implicit since the
named net device must belong to exactly one Node. For example,:
Names::Add ("server" ...);
Names::Add ("server/eth0" ...);
...
helper.EnablePcap ("prefix", "server/ath0");
You can enable pcap tracing on a collection of node/net-device pairs by providing a
NetDeviceContainer. For each NetDevice in the container the type is checked. For each
device of the proper type (the same type as is managed by the device helper), tracing is
enabled. Again, the <Node> is implicit since the found net device must belong to exactly
one Node. For example,:
NetDeviceContainer d = ...;
...
helper.EnablePcap ("prefix", d);
You can enable pcap tracing on a collection of node/net-device pairs by providing a
NodeContainer. For each Node in the NodeContainer its attached NetDevices are iterated.
For each NetDevice attached to each node in the container, the type of that device is
checked. For each device of the proper type (the same type as is managed by the device
helper), tracing is enabled.:
NodeContainer n;
...
helper.EnablePcap ("prefix", n);
You can enable pcap tracing on the basis of node ID and device ID as well as with explicit
Ptr. Each Node in the system has an integer node ID and each device connected to a node
has an integer device ID.:
helper.EnablePcap ("prefix", 21, 1);
Finally, you can enable pcap tracing for all devices in the system, with the same type as
that managed by the device helper.:
helper.EnablePcapAll ("prefix");
Pcap Tracing Device Helper Filename Selection
Implicit in the method descriptions above is the construction of a complete filename by
the implementation method. By convention, pcap traces in the ns-3 system are of the form
<prefix>-<node id>-<device id>.pcap
As previously mentioned, every node in the system will have a system-assigned node id; and
every device will have an interface index (also called a device id) relative to its node.
By default, then, a pcap trace file created as a result of enabling tracing on the first
device of node 21 using the prefix "prefix" would be prefix-21-1.pcap.
You can always use the ns-3 object name service to make this more clear. For example, if
you use the object name service to assign the name "server" to node 21, the resulting pcap
trace file name will automatically become, prefix-server-1.pcap and if you also assign the
name "eth0" to the device, your pcap file name will automatically pick this up and be
called prefix-server-eth0.pcap.
Finally, two of the methods shown above,:
void EnablePcap (std::string prefix, Ptr<NetDevice> nd, bool promiscuous = false, bool explicitFilename = false);
void EnablePcap (std::string prefix, std::string ndName, bool promiscuous = false, bool explicitFilename = false);
have a default parameter called explicitFilename. When set to true, this parameter
disables the automatic filename completion mechanism and allows you to create an explicit
filename. This option is only available in the methods which enable pcap tracing on a
single device.
For example, in order to arrange for a device helper to create a single promiscuous pcap
capture file of a specific name (my-pcap-file.pcap) on a given device, one could::
Ptr<NetDevice> nd;
...
helper.EnablePcap ("my-pcap-file.pcap", nd, true, true);
The first true parameter enables promiscuous mode traces and the second tells the helper
to interpret the prefix parameter as a complete filename.
Ascii Tracing Device Helpers
The behavior of the ascii trace helper mixin is substantially similar to the pcap version.
Take a look at src/network/helper/trace-helper.h if you want to follow the discussion
while looking at real code.
The class AsciiTraceHelperForDevice adds the high level functionality for using ascii
tracing to a device helper class. As in the pcap case, every device must implement a
single virtual method inherited from the ascii trace mixin.:
virtual void EnableAsciiInternal (Ptr<OutputStreamWrapper> stream, std::string prefix, Ptr<NetDevice> nd) = 0;
The signature of this method reflects the device-centric view of the situation at this
level; and also the fact that the helper may be writing to a shared output stream. All of
the public ascii-trace-related methods inherited from class AsciiTraceHelperForDevice
reduce to calling this single device- dependent implementation method. For example, the
lowest level ascii trace methods,:
void EnableAscii (std::string prefix, Ptr<NetDevice> nd);
void EnableAscii (Ptr<OutputStreamWrapper> stream, Ptr<NetDevice> nd);
will call the device implementation of EnableAsciiInternal directly, providing either a
valid prefix or stream. All other public ascii tracing methods will build on these
low-level functions to provide additional user-level functionality. What this means to the
user is that all device helpers in the system will have all of the ascii trace methods
available; and these methods will all work in the same way across devices if the devices
implement EnablAsciiInternal correctly.
Ascii Tracing Device Helper Methods
void EnableAscii (std::string prefix, Ptr<NetDevice> nd);
void EnableAscii (Ptr<OutputStreamWrapper> stream, Ptr<NetDevice> nd);
void EnableAscii (std::string prefix, std::string ndName);
void EnableAscii (Ptr<OutputStreamWrapper> stream, std::string ndName);
void EnableAscii (std::string prefix, NetDeviceContainer d);
void EnableAscii (Ptr<OutputStreamWrapper> stream, NetDeviceContainer d);
void EnableAscii (std::string prefix, NodeContainer n);
void EnableAscii (Ptr<OutputStreamWrapper> stream, NodeContainer n);
void EnableAscii (std::string prefix, uint32_t nodeid, uint32_t deviceid);
void EnableAscii (Ptr<OutputStreamWrapper> stream, uint32_t nodeid, uint32_t deviceid);
void EnableAsciiAll (std::string prefix);
void EnableAsciiAll (Ptr<OutputStreamWrapper> stream);
You are encouraged to peruse the Doxygen for class TraceHelperForDevice to find the
details of these methods; but to summarize ...
There are twice as many methods available for ascii tracing as there were for pcap
tracing. This is because, in addition to the pcap-style model where traces from each
unique node/device pair are written to a unique file, we support a model in which trace
information for many node/device pairs is written to a common file. This means that the
<prefix>-<node>-<device> file name generation mechanism is replaced by a mechanism to
refer to a common file; and the number of API methods is doubled to allow all
combinations.
Just as in pcap tracing, you can enable ascii tracing on a particular node/net-device pair
by providing a Ptr<NetDevice> to an EnableAscii method. The Ptr<Node> is implicit since
the net device must belong to exactly one Node. For example,:
Ptr<NetDevice> nd;
...
helper.EnableAscii ("prefix", nd);
In this case, no trace contexts are written to the ascii trace file since they would be
redundant. The system will pick the file name to be created using the same rules as
described in the pcap section, except that the file will have the suffix ".tr" instead of
".pcap".
If you want to enable ascii tracing on more than one net device and have all traces sent
to a single file, you can do that as well by using an object to refer to a single file::
Ptr<NetDevice> nd1;
Ptr<NetDevice> nd2;
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAscii (stream, nd1);
helper.EnableAscii (stream, nd2);
In this case, trace contexts are written to the ascii trace file since they are required
to disambiguate traces from the two devices. Note that since the user is completely
specifying the file name, the string should include the ".tr" for consistency.
You can enable ascii tracing on a particular node/net-device pair by providing a
std::string representing an object name service string to an EnablePcap method. The
Ptr<NetDevice> is looked up from the name string. Again, the <Node> is implicit since the
named net device must belong to exactly one Node. For example,:
Names::Add ("client" ...);
Names::Add ("client/eth0" ...);
Names::Add ("server" ...);
Names::Add ("server/eth0" ...);
...
helper.EnableAscii ("prefix", "client/eth0");
helper.EnableAscii ("prefix", "server/eth0");
This would result in two files named prefix-client-eth0.tr and prefix-server-eth0.tr with
traces for each device in the respective trace file. Since all of the EnableAscii
functions are overloaded to take a stream wrapper, you can use that form as well::
Names::Add ("client" ...);
Names::Add ("client/eth0" ...);
Names::Add ("server" ...);
Names::Add ("server/eth0" ...);
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAscii (stream, "client/eth0");
helper.EnableAscii (stream, "server/eth0");
This would result in a single trace file called trace-file-name.tr that contains all of
the trace events for both devices. The events would be disambiguated by trace context
strings.
You can enable ascii tracing on a collection of node/net-device pairs by providing a
NetDeviceContainer. For each NetDevice in the container the type is checked. For each
device of the proper type (the same type as is managed by the device helper), tracing is
enabled. Again, the <Node> is implicit since the found net device must belong to exactly
one Node. For example,:
NetDeviceContainer d = ...;
...
helper.EnableAscii ("prefix", d);
This would result in a number of ascii trace files being created, each of which follows
the <prefix>-<node id>-<device id>.tr convention. Combining all of the traces into a
single file is accomplished similarly to the examples above::
NetDeviceContainer d = ...;
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAscii (stream, d);
You can enable ascii tracing on a collection of node/net-device pairs by providing a
NodeContainer. For each Node in the NodeContainer its attached NetDevices are iterated.
For each NetDevice attached to each node in the container, the type of that device is
checked. For each device of the proper type (the same type as is managed by the device
helper), tracing is enabled.:
NodeContainer n;
...
helper.EnableAscii ("prefix", n);
This would result in a number of ascii trace files being created, each of which follows
the <prefix>-<node id>-<device id>.tr convention. Combining all of the traces into a
single file is accomplished similarly to the examples above:
You can enable pcap tracing on the basis of node ID and device ID as well as with explicit
Ptr. Each Node in the system has an integer node ID and each device connected to a node
has an integer device ID.:
helper.EnableAscii ("prefix", 21, 1);
Of course, the traces can be combined into a single file as shown above.
Finally, you can enable pcap tracing for all devices in the system, with the same type as
that managed by the device helper.:
helper.EnableAsciiAll ("prefix");
This would result in a number of ascii trace files being created, one for every device in
the system of the type managed by the helper. All of these files will follow the
<prefix>-<node id>-<device id>.tr convention. Combining all of the traces into a single
file is accomplished similarly to the examples above.
Ascii Tracing Device Helper Filename Selection
Implicit in the prefix-style method descriptions above is the construction of the complete
filenames by the implementation method. By convention, ascii traces in the ns-3 system are
of the form <prefix>-<node id>-<device id>.tr.
As previously mentioned, every node in the system will have a system-assigned node id; and
every device will have an interface index (also called a device id) relative to its node.
By default, then, an ascii trace file created as a result of enabling tracing on the first
device of node 21, using the prefix "prefix", would be prefix-21-1.tr.
You can always use the ns-3 object name service to make this more clear. For example, if
you use the object name service to assign the name "server" to node 21, the resulting
ascii trace file name will automatically become, prefix-server-1.tr and if you also assign
the name "eth0" to the device, your ascii trace file name will automatically pick this up
and be called prefix-server-eth0.tr.
Pcap Tracing Protocol Helpers
The goal of these mixins is to make it easy to add a consistent pcap trace facility to
protocols. We want all of the various flavors of pcap tracing to work the same across all
protocols, so the methods of these helpers are inherited by stack helpers. Take a look at
src/network/helper/trace-helper.h if you want to follow the discussion while looking at
real code.
In this section we will be illustrating the methods as applied to the protocol Ipv4. To
specify traces in similar protocols, just substitute the appropriate type. For example,
use a Ptr<Ipv6> instead of a Ptr<Ipv4> and call EnablePcapIpv6 instead of EnablePcapIpv4.
The class PcapHelperForIpv4 provides the high level functionality for using pcap tracing
in the Ipv4 protocol. Each protocol helper enabling these methods must implement a single
virtual method inherited from this class. There will be a separate implementation for
Ipv6, for example, but the only difference will be in the method names and signatures.
Different method names are required to disambiguate class Ipv4 from Ipv6 which are both
derived from class Object, and methods that share the same signature.:
virtual void EnablePcapIpv4Internal (std::string prefix, Ptr<Ipv4> ipv4, uint32_t interface) = 0;
The signature of this method reflects the protocol and interface-centric view of the
situation at this level. All of the public methods inherited from class PcapHelperForIpv4
reduce to calling this single device-dependent implementation method. For example, the
lowest level pcap method,:
void EnablePcapIpv4 (std::string prefix, Ptr<Ipv4> ipv4, uint32_t interface);
will call the device implementation of EnablePcapIpv4Internal directly. All other public
pcap tracing methods build on this implementation to provide additional user-level
functionality. What this means to the user is that all protocol helpers in the system will
have all of the pcap trace methods available; and these methods will all work in the same
way across protocols if the helper implements EnablePcapIpv4Internal correctly.
Pcap Tracing Protocol Helper Methods
These methods are designed to be in one-to-one correspondence with the Node- and
NetDevice- centric versions of the device versions. Instead of Node and NetDevice pair
constraints, we use protocol and interface constraints.
Note that just like in the device version, there are six methods::
void EnablePcapIpv4 (std::string prefix, Ptr<Ipv4> ipv4, uint32_t interface);
void EnablePcapIpv4 (std::string prefix, std::string ipv4Name, uint32_t interface);
void EnablePcapIpv4 (std::string prefix, Ipv4InterfaceContainer c);
void EnablePcapIpv4 (std::string prefix, NodeContainer n);
void EnablePcapIpv4 (std::string prefix, uint32_t nodeid, uint32_t interface);
void EnablePcapIpv4All (std::string prefix);
You are encouraged to peruse the Doxygen for class PcapHelperForIpv4 to find the details
of these methods; but to summarize ...
You can enable pcap tracing on a particular protocol/interface pair by providing a
Ptr<Ipv4> and interface to an EnablePcap method. For example,:
Ptr<Ipv4> ipv4 = node->GetObject<Ipv4> ();
...
helper.EnablePcapIpv4 ("prefix", ipv4, 0);
You can enable pcap tracing on a particular node/net-device pair by providing a
std::string representing an object name service string to an EnablePcap method. The
Ptr<Ipv4> is looked up from the name string. For example,:
Names::Add ("serverIPv4" ...);
...
helper.EnablePcapIpv4 ("prefix", "serverIpv4", 1);
You can enable pcap tracing on a collection of protocol/interface pairs by providing an
Ipv4InterfaceContainer. For each Ipv4 / interface pair in the container the protocol type
is checked. For each protocol of the proper type (the same type as is managed by the
device helper), tracing is enabled for the corresponding interface. For example,:
NodeContainer nodes;
...
NetDeviceContainer devices = deviceHelper.Install (nodes);
...
Ipv4AddressHelper ipv4;
ipv4.SetBase ("10.1.1.0", "255.255.255.0");
Ipv4InterfaceContainer interfaces = ipv4.Assign (devices);
...
helper.EnablePcapIpv4 ("prefix", interfaces);
You can enable pcap tracing on a collection of protocol/interface pairs by providing a
NodeContainer. For each Node in the NodeContainer the appropriate protocol is found. For
each protocol, its interfaces are enumerated and tracing is enabled on the resulting
pairs. For example,:
NodeContainer n;
...
helper.EnablePcapIpv4 ("prefix", n);
You can enable pcap tracing on the basis of node ID and interface as well. In this case,
the node-id is translated to a Ptr<Node> and the appropriate protocol is looked up in the
node. The resulting protocol and interface are used to specify the resulting trace
source.:
helper.EnablePcapIpv4 ("prefix", 21, 1);
Finally, you can enable pcap tracing for all interfaces in the system, with associated
protocol being the same type as that managed by the device helper.:
helper.EnablePcapIpv4All ("prefix");
Pcap Tracing Protocol Helper Filename Selection
Implicit in all of the method descriptions above is the construction of the complete
filenames by the implementation method. By convention, pcap traces taken for devices in
the ns-3 system are of the form <prefix>-<node id>-<device id>.pcap. In the case of
protocol traces, there is a one-to-one correspondence between protocols and Nodes. This is
because protocol Objects are aggregated to Node Objects. Since there is no global protocol
id in the system, we use the corresponding node id in file naming. Therefore there is a
possibility for file name collisions in automatically chosen trace file names. For this
reason, the file name convention is changed for protocol traces.
As previously mentioned, every node in the system will have a system-assigned node id.
Since there is a one-to-one correspondence between protocol instances and node instances
we use the node id. Each interface has an interface id relative to its protocol. We use
the convention "<prefix>-n<node id>-i<interface id>.pcap" for trace file naming in
protocol helpers.
Therefore, by default, a pcap trace file created as a result of enabling tracing on
interface 1 of the Ipv4 protocol of node 21 using the prefix "prefix" would be
"prefix-n21-i1.pcap".
You can always use the ns-3 object name service to make this more clear. For example, if
you use the object name service to assign the name "serverIpv4" to the Ptr<Ipv4> on node
21, the resulting pcap trace file name will automatically become,
"prefix-nserverIpv4-i1.pcap".
Ascii Tracing Protocol Helpers
The behavior of the ascii trace helpers is substantially similar to the pcap case. Take a
look at src/network/helper/trace-helper.h if you want to follow the discussion while
looking at real code.
In this section we will be illustrating the methods as applied to the protocol Ipv4. To
specify traces in similar protocols, just substitute the appropriate type. For example,
use a Ptr<Ipv6> instead of a Ptr<Ipv4> and call EnableAsciiIpv6 instead of
EnableAsciiIpv4.
The class AsciiTraceHelperForIpv4 adds the high level functionality for using ascii
tracing to a protocol helper. Each protocol that enables these methods must implement a
single virtual method inherited from this class.:
virtual void EnableAsciiIpv4Internal (Ptr<OutputStreamWrapper> stream, std::string prefix,
Ptr<Ipv4> ipv4, uint32_t interface) = 0;
The signature of this method reflects the protocol- and interface-centric view of the
situation at this level; and also the fact that the helper may be writing to a shared
output stream. All of the public methods inherited from class
PcapAndAsciiTraceHelperForIpv4 reduce to calling this single device- dependent
implementation method. For example, the lowest level ascii trace methods,:
void EnableAsciiIpv4 (std::string prefix, Ptr<Ipv4> ipv4, uint32_t interface);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, Ptr<Ipv4> ipv4, uint32_t interface);
will call the device implementation of EnableAsciiIpv4Internal directly, providing either
the prefix or the stream. All other public ascii tracing methods will build on these
low-level functions to provide additional user-level functionality. What this means to the
user is that all device helpers in the system will have all of the ascii trace methods
available; and these methods will all work in the same way across protocols if the
protocols implement EnablAsciiIpv4Internal correctly.
Ascii Tracing Device Helper Methods
void EnableAsciiIpv4 (std::string prefix, Ptr<Ipv4> ipv4, uint32_t interface);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, Ptr<Ipv4> ipv4, uint32_t interface);
void EnableAsciiIpv4 (std::string prefix, std::string ipv4Name, uint32_t interface);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, std::string ipv4Name, uint32_t interface);
void EnableAsciiIpv4 (std::string prefix, Ipv4InterfaceContainer c);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, Ipv4InterfaceContainer c);
void EnableAsciiIpv4 (std::string prefix, NodeContainer n);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, NodeContainer n);
void EnableAsciiIpv4 (std::string prefix, uint32_t nodeid, uint32_t deviceid);
void EnableAsciiIpv4 (Ptr<OutputStreamWrapper> stream, uint32_t nodeid, uint32_t interface);
void EnableAsciiIpv4All (std::string prefix);
void EnableAsciiIpv4All (Ptr<OutputStreamWrapper> stream);
You are encouraged to peruse the Doxygen for class PcapAndAsciiHelperForIpv4 to find the
details of these methods; but to summarize ...
There are twice as many methods available for ascii tracing as there were for pcap
tracing. This is because, in addition to the pcap-style model where traces from each
unique protocol/interface pair are written to a unique file, we support a model in which
trace information for many protocol/interface pairs is written to a common file. This
means that the <prefix>-n<node id>-<interface> file name generation mechanism is replaced
by a mechanism to refer to a common file; and the number of API methods is doubled to
allow all combinations.
Just as in pcap tracing, you can enable ascii tracing on a particular protocol/interface
pair by providing a Ptr<Ipv4> and an interface to an EnableAscii method. For example,:
Ptr<Ipv4> ipv4;
...
helper.EnableAsciiIpv4 ("prefix", ipv4, 1);
In this case, no trace contexts are written to the ascii trace file since they would be
redundant. The system will pick the file name to be created using the same rules as
described in the pcap section, except that the file will have the suffix ".tr" instead of
".pcap".
If you want to enable ascii tracing on more than one interface and have all traces sent to
a single file, you can do that as well by using an object to refer to a single file. We
have already something similar to this in the "cwnd" example above::
Ptr<Ipv4> protocol1 = node1->GetObject<Ipv4> ();
Ptr<Ipv4> protocol2 = node2->GetObject<Ipv4> ();
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAsciiIpv4 (stream, protocol1, 1);
helper.EnableAsciiIpv4 (stream, protocol2, 1);
In this case, trace contexts are written to the ascii trace file since they are required
to disambiguate traces from the two interfaces. Note that since the user is completely
specifying the file name, the string should include the ".tr" for consistency.
You can enable ascii tracing on a particular protocol by providing a std::string
representing an object name service string to an EnablePcap method. The Ptr<Ipv4> is
looked up from the name string. The <Node> in the resulting filenames is implicit since
there is a one-to-one correspondence between protocol instances and nodes, For example,:
Names::Add ("node1Ipv4" ...);
Names::Add ("node2Ipv4" ...);
...
helper.EnableAsciiIpv4 ("prefix", "node1Ipv4", 1);
helper.EnableAsciiIpv4 ("prefix", "node2Ipv4", 1);
This would result in two files named "prefix-nnode1Ipv4-i1.tr" and
"prefix-nnode2Ipv4-i1.tr" with traces for each interface in the respective trace file.
Since all of the EnableAscii functions are overloaded to take a stream wrapper, you can
use that form as well::
Names::Add ("node1Ipv4" ...);
Names::Add ("node2Ipv4" ...);
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAsciiIpv4 (stream, "node1Ipv4", 1);
helper.EnableAsciiIpv4 (stream, "node2Ipv4", 1);
This would result in a single trace file called "trace-file-name.tr" that contains all of
the trace events for both interfaces. The events would be disambiguated by trace context
strings.
You can enable ascii tracing on a collection of protocol/interface pairs by providing an
Ipv4InterfaceContainer. For each protocol of the proper type (the same type as is managed
by the device helper), tracing is enabled for the corresponding interface. Again, the
<Node> is implicit since there is a one-to-one correspondence between each protocol and
its node. For example,:
NodeContainer nodes;
...
NetDeviceContainer devices = deviceHelper.Install (nodes);
...
Ipv4AddressHelper ipv4;
ipv4.SetBase ("10.1.1.0", "255.255.255.0");
Ipv4InterfaceContainer interfaces = ipv4.Assign (devices);
...
...
helper.EnableAsciiIpv4 ("prefix", interfaces);
This would result in a number of ascii trace files being created, each of which follows
the <prefix>-n<node id>-i<interface>.tr convention. Combining all of the traces into a
single file is accomplished similarly to the examples above::
NodeContainer nodes;
...
NetDeviceContainer devices = deviceHelper.Install (nodes);
...
Ipv4AddressHelper ipv4;
ipv4.SetBase ("10.1.1.0", "255.255.255.0");
Ipv4InterfaceContainer interfaces = ipv4.Assign (devices);
...
Ptr<OutputStreamWrapper> stream = asciiTraceHelper.CreateFileStream ("trace-file-name.tr");
...
helper.EnableAsciiIpv4 (stream, interfaces);
You can enable ascii tracing on a collection of protocol/interface pairs by providing a
NodeContainer. For each Node in the NodeContainer the appropriate protocol is found. For
each protocol, its interfaces are enumerated and tracing is enabled on the resulting
pairs. For example,:
NodeContainer n;
...
helper.EnableAsciiIpv4 ("prefix", n);
This would result in a number of ascii trace files being created, each of which follows
the <prefix>-<node id>-<device id>.tr convention. Combining all of the traces into a
single file is accomplished similarly to the examples above:
You can enable pcap tracing on the basis of node ID and device ID as well. In this case,
the node-id is translated to a Ptr<Node> and the appropriate protocol is looked up in the
node. The resulting protocol and interface are used to specify the resulting trace
source.:
helper.EnableAsciiIpv4 ("prefix", 21, 1);
Of course, the traces can be combined into a single file as shown above.
Finally, you can enable ascii tracing for all interfaces in the system, with associated
protocol being the same type as that managed by the device helper.:
helper.EnableAsciiIpv4All ("prefix");
This would result in a number of ascii trace files being created, one for every interface
in the system related to a protocol of the type managed by the helper. All of these files
will follow the <prefix>-n<node id>-i<interface.tr convention. Combining all of the traces
into a single file is accomplished similarly to the examples above.
Ascii Tracing Device Helper Filename Selection
Implicit in the prefix-style method descriptions above is the construction of the complete
filenames by the implementation method. By convention, ascii traces in the ns-3 system are
of the form "<prefix>-<node id>-<device id>.tr."
As previously mentioned, every node in the system will have a system-assigned node id.
Since there is a one-to-one correspondence between protocols and nodes we use to node-id
to identify the protocol identity. Every interface on a given protocol will have an
interface index (also called simply an interface) relative to its protocol. By default,
then, an ascii trace file created as a result of enabling tracing on the first device of
node 21, using the prefix "prefix", would be "prefix-n21-i1.tr". Use the prefix to
disambiguate multiple protocols per node.
You can always use the ns-3 object name service to make this more clear. For example, if
you use the object name service to assign the name "serverIpv4" to the protocol on node
21, and also specify interface one, the resulting ascii trace file name will automatically
become, "prefix-nserverIpv4-1.tr".
Tracing implementation details
REALTIME
ns-3 has been designed for integration into testbed and virtual machine environments. To
integrate with real network stacks and emit/consume packets, a real-time scheduler is
needed to try to lock the simulation clock with the hardware clock. We describe here a
component of this: the RealTime scheduler.
The purpose of the realtime scheduler is to cause the progression of the simulation clock
to occur synchronously with respect to some external time base. Without the presence of
an external time base (wall clock), simulation time jumps instantly from one simulated
time to the next.
Behavior
When using a non-realtime scheduler (the default in ns-3), the simulator advances the
simulation time to the next scheduled event. During event execution, simulation time is
frozen. With the realtime scheduler, the behavior is similar from the perspective of
simulation models (i.e., simulation time is frozen during event execution), but between
events, the simulator will attempt to keep the simulation clock aligned with the machine
clock.
When an event is finished executing, and the scheduler moves to the next event, the
scheduler compares the next event execution time with the machine clock. If the next
event is scheduled for a future time, the simulator sleeps until that realtime is reached
and then executes the next event.
It may happen that, due to the processing inherent in the execution of simulation events,
that the simulator cannot keep up with realtime. In such a case, it is up to the user
configuration what to do. There are two ns-3 attributes that govern the behavior. The
first is ns3::RealTimeSimulatorImpl::SynchronizationMode. The two entries possible for
this attribute are BestEffort (the default) or HardLimit. In "BestEffort" mode, the
simulator will just try to catch up to realtime by executing events until it reaches a
point where the next event is in the (realtime) future, or else the simulation ends. In
BestEffort mode, then, it is possible for the simulation to consume more time than the
wall clock time. The other option "HardLimit" will cause the simulation to abort if the
tolerance threshold is exceeded. This attribute is ns3::RealTimeSimulatorImpl::HardLimit
and the default is 0.1 seconds.
A different mode of operation is one in which simulated time is not frozen during an event
execution. This mode of realtime simulation was implemented but removed from the ns-3 tree
because of questions of whether it would be useful. If users are interested in a realtime
simulator for which simulation time does not freeze during event execution (i.e., every
call to Simulator::Now() returns the current wall clock time, not the time at which the
event started executing), please contact the ns-developers mailing list.
Usage
The usage of the realtime simulator is straightforward, from a scripting perspective.
Users just need to set the attribute SimulatorImplementationType to the Realtime
simulator, such as follows:
GlobalValue::Bind ("SimulatorImplementationType",
StringValue ("ns3::RealtimeSimulatorImpl"));
There is a script in examples/realtime/realtime-udp-echo.cc that has an example of how to
configure the realtime behavior. Try:
./waf --run realtime-udp-echo
Whether the simulator will work in a best effort or hard limit policy fashion is governed
by the attributes explained in the previous section.
Implementation
The implementation is contained in the following files:
· src/core/model/realtime-simulator-impl.{cc,h}
· src/core/model/wall-clock-synchronizer.{cc,h}
In order to create a realtime scheduler, to a first approximation you just want to cause
simulation time jumps to consume real time. We propose doing this using a combination of
sleep- and busy- waits. Sleep-waits cause the calling process (thread) to yield the
processor for some amount of time. Even though this specified amount of time can be passed
to nanosecond resolution, it is actually converted to an OS-specific granularity. In
Linux, the granularity is called a Jiffy. Typically this resolution is insufficient for
our needs (on the order of a ten milliseconds), so we round down and sleep for some
smaller number of Jiffies. The process is then awakened after the specified number of
Jiffies has passed. At this time, we have some residual time to wait. This time is
generally smaller than the minimum sleep time, so we busy-wait for the remainder of the
time. This means that the thread just sits in a for loop consuming cycles until the
desired time arrives. After the combination of sleep- and busy-waits, the elapsed realtime
(wall) clock should agree with the simulation time of the next event and the simulation
proceeds.
HELPERS
The above chapters introduced you to various ns-3 programming concepts such as smart
pointers for reference-counted memory management, attributes, namespaces, callbacks, etc.
Users who work at this low-level API can interconnect ns-3 objects with fine granulariy.
However, a simulation program written entirely using the low-level API would be quite long
and tedious to code. For this reason, a separate so-called "helper API" has been overlaid
on the core ns-3 API. If you have read the ns-3 tutorial, you will already be familiar
with the helper API, since it is the API that new users are typically introduced to first.
In this chapter, we introduce the design philosophy of the helper API and contrast it to
the low-level API. If you become a heavy user of ns-3, you will likely move back and forth
between these APIs even in the same program.
The helper API has a few goals:
1. the rest of src/ has no dependencies on the helper API; anything that can be done with
the helper API can be coded also at the low-level API
2. Containers: Often simulations will need to do a number of identical actions to groups
of objects. The helper API makes heavy use of containers of similar objects to which
similar or identical operations can be performed.
3. The helper API is not generic; it does not strive to maximize code reuse. So,
programming constructs such as polymorphism and templates that achieve code reuse are
not as prevalent. For instance, there are separate CsmaNetDevice helpers and
PointToPointNetDevice helpers but they do not derive from a common NetDevice base
class.
4. The helper API typically works with stack-allocated (vs. heap-allocated) objects. For
some programs, ns-3 users may not need to worry about any low level Object Create or
Ptr handling; they can make do with containers of objects and stack-allocated helpers
that operate on them.
The helper API is really all about making ns-3 programs easier to write and read, without
taking away the power of the low-level interface. The rest of this chapter provides some
examples of the programming conventions of the helper API.
MAKING PLOTS USING THE GNUPLOT CLASS
There are 2 common methods to make a plot using ns-3 and gnuplot (‐
http://www.gnuplot.info):
1. Create a gnuplot control file using ns-3's Gnuplot class.
2. Create a gnuplot data file using values generated by ns-3.
This section is about method 1, i.e. it is about how to make a plot using ns-3's Gnuplot
class. If you are interested in method 2, see the "A Real Example" subsection under the
"Tracing" section in the ns-3 Tutorial.
Creating Plots Using the Gnuplot Class
The following steps must be taken in order to create a plot using ns-3's Gnuplot class:
1. Modify your code so that is uses the Gnuplot class and its functions.
2. Run your code so that it creates a gnuplot control file.
3. Call gnuplot with the name of the gnuplot control file.
4. View the graphics file that was produced in your favorite graphics viewer.
See the code from the example plots that are discussed below for details on step 1.
An Example Program that Uses the Gnuplot Class
An example program that uses ns-3's Gnuplot class can be found here:
src/tools/examples/gnuplot-example.cc
In order to run this example, do the following:
./waf shell
cd build/debug/src/tools/examples
./gnuplot-example
This should produce the following gnuplot control files in the directory where the example
is located:
plot-2d.plt
plot-2d-with-error-bars.plt
plot-3d.plt
In order to process these gnuplot control files, do the following:
gnuplot plot-2d.plt
gnuplot plot-2d-with-error-bars.plt
gnuplot plot-3d.plt
This should produce the following graphics files in the directory where the example is
located:
plot-2d.png
plot-2d-with-error-bars.png
plot-3d.png
You can view these graphics files in your favorite graphics viewer. If you have gimp
installed on your machine, for example, you can do this:
gimp plot-2d.png
gimp plot-2d-with-error-bars.png
gimp plot-3d.png
An Example 2-Dimensional Plot
The following 2-Dimensional plot
[image]
was created using the following code from gnuplot-example.cc:
using namespace std;
string fileNameWithNoExtension = "plot-2d";
string graphicsFileName = fileNameWithNoExtension + ".png";
string plotFileName = fileNameWithNoExtension + ".plt";
string plotTitle = "2-D Plot";
string dataTitle = "2-D Data";
// Instantiate the plot and set its title.
Gnuplot plot (graphicsFileName);
plot.SetTitle (plotTitle);
// Make the graphics file, which the plot file will create when it
// is used with Gnuplot, be a PNG file.
plot.SetTerminal ("png");
// Set the labels for each axis.
plot.SetLegend ("X Values", "Y Values");
// Set the range for the x axis.
plot.AppendExtra ("set xrange [-6:+6]");
// Instantiate the dataset, set its title, and make the points be
// plotted along with connecting lines.
Gnuplot2dDataset dataset;
dataset.SetTitle (dataTitle);
dataset.SetStyle (Gnuplot2dDataset::LINES_POINTS);
double x;
double y;
// Create the 2-D dataset.
for (x = -5.0; x <= +5.0; x += 1.0)
{
// Calculate the 2-D curve
//
// 2
// y = x .
//
y = x * x;
// Add this point.
dataset.Add (x, y);
}
// Add the dataset to the plot.
plot.AddDataset (dataset);
// Open the plot file.
ofstream plotFile (plotFileName.c_str());
// Write the plot file.
plot.GenerateOutput (plotFile);
// Close the plot file.
plotFile.close ();
An Example 2-Dimensional Plot with Error Bars
The following 2-Dimensional plot with error bars in the x and y directions
[image]
was created using the following code from gnuplot-example.cc:
using namespace std;
string fileNameWithNoExtension = "plot-2d-with-error-bars";
string graphicsFileName = fileNameWithNoExtension + ".png";
string plotFileName = fileNameWithNoExtension + ".plt";
string plotTitle = "2-D Plot With Error Bars";
string dataTitle = "2-D Data With Error Bars";
// Instantiate the plot and set its title.
Gnuplot plot (graphicsFileName);
plot.SetTitle (plotTitle);
// Make the graphics file, which the plot file will create when it
// is used with Gnuplot, be a PNG file.
plot.SetTerminal ("png");
// Set the labels for each axis.
plot.SetLegend ("X Values", "Y Values");
// Set the range for the x axis.
plot.AppendExtra ("set xrange [-6:+6]");
// Instantiate the dataset, set its title, and make the points be
// plotted with no connecting lines.
Gnuplot2dDataset dataset;
dataset.SetTitle (dataTitle);
dataset.SetStyle (Gnuplot2dDataset::POINTS);
// Make the dataset have error bars in both the x and y directions.
dataset.SetErrorBars (Gnuplot2dDataset::XY);
double x;
double xErrorDelta;
double y;
double yErrorDelta;
// Create the 2-D dataset.
for (x = -5.0; x <= +5.0; x += 1.0)
{
// Calculate the 2-D curve
//
// 2
// y = x .
//
y = x * x;
// Make the uncertainty in the x direction be constant and make
// the uncertainty in the y direction be a constant fraction of
// y's value.
xErrorDelta = 0.25;
yErrorDelta = 0.1 * y;
// Add this point with uncertainties in both the x and y
// direction.
dataset.Add (x, y, xErrorDelta, yErrorDelta);
}
// Add the dataset to the plot.
plot.AddDataset (dataset);
// Open the plot file.
ofstream plotFile (plotFileName.c_str());
// Write the plot file.
plot.GenerateOutput (plotFile);
// Close the plot file.
plotFile.close ();
An Example 3-Dimensional Plot
The following 3-Dimensional plot
[image]
was created using the following code from gnuplot-example.cc:
using namespace std;
string fileNameWithNoExtension = "plot-3d";
string graphicsFileName = fileNameWithNoExtension + ".png";
string plotFileName = fileNameWithNoExtension + ".plt";
string plotTitle = "3-D Plot";
string dataTitle = "3-D Data";
// Instantiate the plot and set its title.
Gnuplot plot (graphicsFileName);
plot.SetTitle (plotTitle);
// Make the graphics file, which the plot file will create when it
// is used with Gnuplot, be a PNG file.
plot.SetTerminal ("png");
// Rotate the plot 30 degrees around the x axis and then rotate the
// plot 120 degrees around the new z axis.
plot.AppendExtra ("set view 30, 120, 1.0, 1.0");
// Make the zero for the z-axis be in the x-axis and y-axis plane.
plot.AppendExtra ("set ticslevel 0");
// Set the labels for each axis.
plot.AppendExtra ("set xlabel 'X Values'");
plot.AppendExtra ("set ylabel 'Y Values'");
plot.AppendExtra ("set zlabel 'Z Values'");
// Set the ranges for the x and y axis.
plot.AppendExtra ("set xrange [-5:+5]");
plot.AppendExtra ("set yrange [-5:+5]");
// Instantiate the dataset, set its title, and make the points be
// connected by lines.
Gnuplot3dDataset dataset;
dataset.SetTitle (dataTitle);
dataset.SetStyle ("with lines");
double x;
double y;
double z;
// Create the 3-D dataset.
for (x = -5.0; x <= +5.0; x += 1.0)
{
for (y = -5.0; y <= +5.0; y += 1.0)
{
// Calculate the 3-D surface
//
// 2 2
// z = x * y .
//
z = x * x * y * y;
// Add this point.
dataset.Add (x, y, z);
}
// The blank line is necessary at the end of each x value's data
// points for the 3-D surface grid to work.
dataset.AddEmptyLine ();
}
// Add the dataset to the plot.
plot.AddDataset (dataset);
// Open the plot file.
ofstream plotFile (plotFileName.c_str());
// Write the plot file.
plot.GenerateOutput (plotFile);
// Close the plot file.
plotFile.close ();
USING PYTHON TO RUN NS-3
Python bindings allow the C++ code in ns-3 to be called from Python.
This chapter shows you how to create a Python script that can run ns-3 and also the
process of creating Python bindings for a C++ ns-3 module.
Introduction
The goal of Python bindings for ns-3 are two fold:
1. Allow the programmer to write complete simulation scripts in Python (‐
http://www.python.org);
2. Prototype new models (e.g. routing protocols).
For the time being, the primary focus of the bindings is the first goal, but the second
goal will eventually be supported as well. Python bindings for ns-3 are being developed
using a new tool called PyBindGen (http://code.google.com/p/pybindgen).
An Example Python Script that Runs ns-3
Here is some example code that is written in Python and that runs ns-3, which is written
in C++. This Python example can be found in examples/tutorial/first.py:
import ns.applications
import ns.core
import ns.internet
import ns.network
import ns.point_to_point
ns.core.LogComponentEnable("UdpEchoClientApplication", ns.core.LOG_LEVEL_INFO)
ns.core.LogComponentEnable("UdpEchoServerApplication", ns.core.LOG_LEVEL_INFO)
nodes = ns.network.NodeContainer()
nodes.Create(2)
pointToPoint = ns.point_to_point.PointToPointHelper()
pointToPoint.SetDeviceAttribute("DataRate", ns.core.StringValue("5Mbps"))
pointToPoint.SetChannelAttribute("Delay", ns.core.StringValue("2ms"))
devices = pointToPoint.Install(nodes)
stack = ns.internet.InternetStackHelper()
stack.Install(nodes)
address = ns.internet.Ipv4AddressHelper()
address.SetBase(ns.network.Ipv4Address("10.1.1.0"), ns.network.Ipv4Mask("255.255.255.0"))
interfaces = address.Assign (devices);
echoServer = ns.applications.UdpEchoServerHelper(9)
serverApps = echoServer.Install(nodes.Get(1))
serverApps.Start(ns.core.Seconds(1.0))
serverApps.Stop(ns.core.Seconds(10.0))
echoClient = ns.applications.UdpEchoClientHelper(interfaces.GetAddress(1), 9)
echoClient.SetAttribute("MaxPackets", ns.core.UintegerValue(1))
echoClient.SetAttribute("Interval", ns.core.TimeValue(ns.core.Seconds (1.0)))
echoClient.SetAttribute("PacketSize", ns.core.UintegerValue(1024))
clientApps = echoClient.Install(nodes.Get(0))
clientApps.Start(ns.core.Seconds(2.0))
clientApps.Stop(ns.core.Seconds(10.0))
ns.core.Simulator.Run()
ns.core.Simulator.Destroy()
Running Python Scripts
waf contains some options that automatically update the python path to find the ns3
module. To run example programs, there are two ways to use waf to take care of this. One
is to run a waf shell; e.g.:
./waf --shell
python examples/mixed-wireless.py
and the other is to use the --pyrun option to waf:
./waf --pyrun examples/mixed-wireless.py
To run a python script under the C debugger:
./waf --shell
gdb --args python examples/mixed-wireless.py
To run your own Python script that calls ns-3 and that has this path,
/path/to/your/example/my-script.py, do the following:
./waf --shell
python /path/to/your/example/my-script.py
Caveats
Python bindings for ns-3 are a work in progress, and some limitations are known by
developers. Some of these limitations (not all) are listed here.
Incomplete Coverage
First of all, keep in mind that not 100% of the API is supported in Python. Some of the
reasons are:
1. some of the APIs involve pointers, which require knowledge of what kind of memory
passing semantics (who owns what memory). Such knowledge is not part of the function
signatures, and is either documented or sometimes not even documented. Annotations are
needed to bind those functions;
2. Sometimes a unusual fundamental data type or C++ construct is used which is not yet
supported by PyBindGen;
3. GCC-XML does not report template based classes unless they are instantiated.
Most of the missing APIs can be wrapped, given enough time, patience, and expertise, and
will likely be wrapped if bug reports are submitted. However, don't file a bug report
saying "bindings are incomplete", because we do not have manpower to complete 100% of the
bindings.
Conversion Constructors
Conversion constructors (‐
http://publib.boulder.ibm.com/infocenter/compbgpl/v9v111/topic/com.ibm.xlcpp9.bg.doc/language_ref/cplr384.htm)
are not fully supported yet by PyBindGen, and they always act as explicit constructors
when translating an API into Python. For example, in C++ you can do this:
Ipv4AddressHelper ipAddrs;
ipAddrs.SetBase ("192.168.0.0", "255.255.255.0");
ipAddrs.Assign (backboneDevices);
In Python, for the time being you have to do:
ipAddrs = ns3.Ipv4AddressHelper()
ipAddrs.SetBase(ns3.Ipv4Address("192.168.0.0"), ns3.Ipv4Mask("255.255.255.0"))
ipAddrs.Assign(backboneDevices)
CommandLine
CommandLine::AddValue() works differently in Python than it does in ns-3. In Python, the
first parameter is a string that represents the command-line option name. When the option
is set, an attribute with the same name as the option name is set on the CommandLine()
object. Example:
NUM_NODES_SIDE_DEFAULT = 3
cmd = ns3.CommandLine()
cmd.NumNodesSide = None
cmd.AddValue("NumNodesSide", "Grid side number of nodes (total number of nodes will be this number squared)")
cmd.Parse(argv)
[...]
if cmd.NumNodesSide is None:
num_nodes_side = NUM_NODES_SIDE_DEFAULT
else:
num_nodes_side = int(cmd.NumNodesSide)
Tracing
Callback based tracing is not yet properly supported for Python, as new ns-3 API needs to
be provided for this to be supported.
Pcap file writing is supported via the normal API.
Ascii tracing is supported since ns-3.4 via the normal C++ API translated to Python.
However, ascii tracing requires the creation of an ostream object to pass into the ascii
tracing methods. In Python, the C++ std::ofstream has been minimally wrapped to allow
this. For example:
ascii = ns3.ofstream("wifi-ap.tr") # create the file
ns3.YansWifiPhyHelper.EnableAsciiAll(ascii)
ns3.Simulator.Run()
ns3.Simulator.Destroy()
ascii.close() # close the file
There is one caveat: you must not allow the file object to be garbage collected while ns-3
is still using it. That means that the 'ascii' variable above must not be allowed to go
out of scope or else the program will crash.
Cygwin limitation
Python bindings do not work on Cygwin. This is due to a gccxml bug.
You might get away with it by re-scanning API definitions from within the cygwin
environment (./waf --python-scan). However the most likely solution will probably have to
be that we disable python bindings in CygWin.
If you really care about Python bindings on Windows, try building with mingw and native
python instead. Or else, to build without python bindings, disable python bindings in the
configuration stage:
./waf configure --disable-python
Working with Python Bindings
There are currently two kinds of Python bindings in ns-3:
1. Monolithic bindings contain API definitions for all of the modules and can be found in
a single directory, bindings/python.
2. Modular bindings contain API definitions for a single module and can be found in each
module's bindings directory.
Python Bindings Workflow
The process by which Python bindings are handled is the following:
1. Periodically a developer uses a GCC-XML (http://www.gccxml.org) based API scanning
script, which saves the scanned API definition as bindings/python/ns3_module_*.py files
or as Python files in each modules' bindings directory. These files are kept under
version control in the main ns-3 repository;
2. Other developers clone the repository and use the already scanned API definitions;
3. When configuring ns-3, pybindgen will be automatically downloaded if not already
installed. Released ns-3 tarballs will ship a copy of pybindgen.
If something goes wrong with compiling Python bindings and you just want to ignore them
and move on with C++, you can disable Python with:
./waf --disable-python
Instructions for Handling New Files or Changed API's
So you have been changing existing ns-3 APIs and Python bindings no longer compile? Do
not despair, you can rescan the bindings to create new bindings that reflect the changes
to the ns-3 API.
Depending on if you are using monolithic or modular bindings, see the discussions below to
learn how to rescan your Python bindings.
Monolithic Python Bindings
Scanning the Monolithic Python Bindings
To scan the monolithic Python bindings do the following:
./waf --python-scan
Organization of the Monolithic Python Bindings
The monolithic Python API definitions are organized as follows. For each ns-3 module
<name>, the file bindings/python/ns3_module_<name>.py describes its API. Each of those
files have 3 toplevel functions:
1. def register_types(module)(): this function takes care of registering new types (e.g.
C++ classes, enums) that are defined in tha module;
2. def register_methods(module)(): this function calls, for each class <name>, another
function register_methods_Ns3<name>(module). These latter functions add method
definitions for each class;
3. def register_functions(module)(): this function registers ns-3 functions that belong to
that module.
Modular Python Bindings
Overview
Since ns 3.11, the modular bindings are being added, in parallel to the old monolithic
bindings.
The new python bindings are generated into an 'ns' namespace, instead of 'ns3' for the old
bindings. Example:
from ns.network import Node
n1 = Node()
With modular Python bindings:
1. There is one separate Python extension module for each ns-3 module;
2. Scanning API definitions (apidefs) is done on a per ns- module basis;
3. Each module's apidefs files are stored in a 'bindings' subdirectory of the module
directory;
Scanning the Modular Python Bindings
To scan the modular Python bindings for the core module, for example, do the following:
./waf --apiscan=core
To scan the modular Python bindings for all of the modules, do the following:
./waf --apiscan=all
Creating a New Module
If you are adding a new module, Python bindings will continue to compile but will not
cover the new module.
To cover a new module, you have to create a bindings/python/ns3_module_<name>.py file,
similar to the what is described in the previous sections, and register it in the variable
LOCAL_MODULES() in bindings/python/ns3modulegen.py
Adding Modular Bindings To A Existing Module
To add support for modular bindings to an existing ns-3 module, simply add the following
line to its wscript build() function:
bld.ns3_python_bindings()
Organization of the Modular Python Bindings
The src/<module>/bindings directory may contain the following files, some of them
optional:
· callbacks_list.py: this is a scanned file, DO NOT TOUCH. Contains a list of
Callback<...> template instances found in the scanned headers;
· modulegen__gcc_LP64.py: this is a scanned file, DO NOT TOUCH. Scanned API definitions
for the GCC, LP64 architecture (64-bit)
· modulegen__gcc_ILP32.py: this is a scanned file, DO NOT TOUCH. Scanned API definitions
for the GCC, ILP32 architecture (32-bit)
· modulegen_customizations.py: you may optionally add this file in order to customize the
pybindgen code generation
· scan-header.h: you may optionally add this file to customize what header file is scanned
for the module. Basically this file is scanned instead of ns3/<module>-module.h.
Typically, the first statement is #include "ns3/<module>-module.h", plus some other
stuff to force template instantiations;
· module_helpers.cc: you may add additional files, such as this, to be linked to python
extension module, but they have to be registered in the wscript. Look at
src/core/wscript for an example of how to do so;
· <module>.py: if this file exists, it becomes the "frontend" python module for the ns3
module, and the extension module (.so file) becomes _<module>.so instead of <module>.so.
The <module>.py file has to import all symbols from the module _<module> (this is more
tricky than it sounds, see src/core/bindings/core.py for an example), and then can add
some additional pure-python definitions.
More Information for Developers
If you are a developer and need more information on ns-3's Python bindings, please see the
Python Bindings wiki page at http://www.nsnam.org/wiki/index.php/NS-3_Python_Bindings.
TESTS
Overview
This document is concerned with the testing and validation of ns-3 software.
This document provides
· background about terminology and software testing (Chapter 2);
· a description of the ns-3 testing framework (Chapter 3);
· a guide to model developers or new model contributors for how to write tests (Chapter
4);
In brief, the first three chapters should be read by ns developers and contributors who
need to understand how to contribute test code and validated programs, and the remainder
of the document provides space for people to report on what aspects of selected models
have been validated.
Background
This chapter may be skipped by readers familiar with the basics of software testing.
Writing defect-free software is a difficult proposition. There are many dimensions to the
problem and there is much confusion regarding what is meant by different terms in
different contexts. We have found it worthwhile to spend a little time reviewing the
subject and defining some terms.
Software testing may be loosely defined as the process of executing a program with the
intent of finding errors. When one enters a discussion regarding software testing, it
quickly becomes apparent that there are many distinct mind-sets with which one can
approach the subject.
For example, one could break the process into broad functional categories like
''correctness testing,'' ''performance testing,'' ''robustness testing'' and ''security
testing.'' Another way to look at the problem is by life-cycle: ''requirements testing,''
''design testing,'' ''acceptance testing,'' and ''maintenance testing.'' Yet another view
is by the scope of the tested system. In this case one may speak of ''unit testing,''
''component testing,'' ''integration testing,'' and ''system testing.'' These terms are
also not standardized in any way, and so ''maintenance testing'' and ''regression
testing'' may be heard interchangeably. Additionally, these terms are often misused.
There are also a number of different philosophical approaches to software testing. For
example, some organizations advocate writing test programs before actually implementing
the desired software, yielding ''test-driven development.'' Some organizations advocate
testing from a customer perspective as soon as possible, following a parallel with the
agile development process: ''test early and test often.'' This is sometimes called
''agile testing.'' It seems that there is at least one approach to testing for every
development methodology.
The ns-3 project is not in the business of advocating for any one of these processes, but
the project as a whole has requirements that help inform the test process.
Like all major software products, ns-3 has a number of qualities that must be present for
the product to succeed. From a testing perspective, some of these qualities that must be
addressed are that ns-3 must be ''correct,'' ''robust,'' ''performant'' and
''maintainable.'' Ideally there should be metrics for each of these dimensions that are
checked by the tests to identify when the product fails to meet its expectations /
requirements.
Correctness
The essential purpose of testing is to determine that a piece of software behaves
''correctly.'' For ns-3 this means that if we simulate something, the simulation should
faithfully represent some physical entity or process to a specified accuracy and
precision.
It turns out that there are two perspectives from which one can view correctness.
Verifying that a particular model is implemented according to its specification is
generically called verification. The process of deciding that the model is correct for
its intended use is generically called validation.
Validation and Verification
A computer model is a mathematical or logical representation of something. It can
represent a vehicle, an elephant (see David Harel's talk about modeling an elephant at
SIMUTools 2009, or a networking card. Models can also represent processes such as global
warming, freeway traffic flow or a specification of a networking protocol. Models can be
completely faithful representations of a logical process specification, but they
necessarily can never completely simulate a physical object or process. In most cases, a
number of simplifications are made to the model to make simulation computationally
tractable.
Every model has a target system that it is attempting to simulate. The first step in
creating a simulation model is to identify this target system and the level of detail and
accuracy that the simulation is desired to reproduce. In the case of a logical process,
the target system may be identified as ''TCP as defined by RFC 793.'' In this case, it
will probably be desirable to create a model that completely and faithfully reproduces RFC
793. In the case of a physical process this will not be possible. If, for example, you
would like to simulate a wireless networking card, you may determine that you need, ''an
accurate MAC-level implementation of the 802.11 specification and [...] a not-so-slow
PHY-level model of the 802.11a specification.''
Once this is done, one can develop an abstract model of the target system. This is
typically an exercise in managing the tradeoffs between complexity, resource requirements
and accuracy. The process of developing an abstract model has been called model
qualification in the literature. In the case of a TCP protocol, this process results in a
design for a collection of objects, interactions and behaviors that will fully implement
RFC 793 in ns-3. In the case of the wireless card, this process results in a number of
tradeoffs to allow the physical layer to be simulated and the design of a network device
and channel for ns-3, along with the desired objects, interactions and behaviors.
This abstract model is then developed into an ns-3 model that implements the abstract
model as a computer program. The process of getting the implementation to agree with the
abstract model is called model verification in the literature.
The process so far is open loop. What remains is to make a determination that a given ns-3
model has some connection to some reality -- that a model is an accurate representation of
a real system, whether a logical process or a physical entity.
If one is going to use a simulation model to try and predict how some real system is going
to behave, there must be some reason to believe your results -- i.e., can one trust that
an inference made from the model translates into a correct prediction for the real system.
The process of getting the ns-3 model behavior to agree with the desired target system
behavior as defined by the model qualification process is called model validation in the
literature. In the case of a TCP implementation, you may want to compare the behavior of
your ns-3 TCP model to some reference implementation in order to validate your model. In
the case of a wireless physical layer simulation, you may want to compare the behavior of
your model to that of real hardware in a controlled setting,
The ns-3 testing environment provides tools to allow for both model validation and
testing, and encourages the publication of validation results.
Robustness
Robustness is the quality of being able to withstand stresses, or changes in environments,
inputs or calculations, etc. A system or design is ''robust'' if it can deal with such
changes with minimal loss of functionality.
This kind of testing is usually done with a particular focus. For example, the system as
a whole can be run on many different system configurations to demonstrate that it can
perform correctly in a large number of environments.
The system can be also be stressed by operating close to or beyond capacity by generating
or simulating resource exhaustion of various kinds. This genre of testing is called
''stress testing.''
The system and its components may be exposed to so-called ''clean tests'' that demonstrate
a positive result -- that is that the system operates correctly in response to a large
variation of expected configurations.
The system and its components may also be exposed to ''dirty tests'' which provide inputs
outside the expected range. For example, if a module expects a zero-terminated string
representation of an integer, a dirty test might provide an unterminated string of random
characters to verify that the system does not crash as a result of this unexpected input.
Unfortunately, detecting such ''dirty'' input and taking preventive measures to ensure the
system does not fail catastrophically can require a huge amount of development overhead.
In order to reduce development time, a decision was taken early on in the project to
minimize the amount of parameter validation and error handling in the ns-3 codebase. For
this reason, we do not spend much time on dirty testing -- it would just uncover the
results of the design decision we know we took.
We do want to demonstrate that ns-3 software does work across some set of conditions. We
borrow a couple of definitions to narrow this down a bit. The domain of applicability is
a set of prescribed conditions for which the model has been tested, compared against
reality to the extent possible, and judged suitable for use. The range of accuracy is an
agreement between the computerized model and reality within a domain of applicability.
The ns-3 testing environment provides tools to allow for setting up and running test
environments over multiple systems (buildbot) and provides classes to encourage clean
tests to verify the operation of the system over the expected ''domain of applicability''
and ''range of accuracy.''
Performant
Okay, ''performant'' isn't a real English word. It is, however, a very concise neologism
that is quite often used to describe what we want ns-3 to be: powerful and fast enough to
get the job done.
This is really about the broad subject of software performance testing. One of the key
things that is done is to compare two systems to find which performs better (cf
benchmarks). This is used to demonstrate that, for example, ns-3 can perform a basic kind
of simulation at least as fast as a competing tool, or can be used to identify parts of
the system that perform badly.
In the ns-3 test framework, we provide support for timing various kinds of tests.
Maintainability
A software product must be maintainable. This is, again, a very broad statement, but a
testing framework can help with the task. Once a model has been developed, validated and
verified, we can repeatedly execute the suite of tests for the entire system to ensure
that it remains valid and verified over its lifetime.
When a feature stops functioning as intended after some kind of change to the system is
integrated, it is called generically a regression. Originally the term regression
referred to a change that caused a previously fixed bug to reappear, but the term has
evolved to describe any kind of change that breaks existing functionality. There are many
kinds of regressions that may occur in practice.
A local regression is one in which a change affects the changed component directly. For
example, if a component is modified to allocate and free memory but stale pointers are
used, the component itself fails.
A remote regression is one in which a change to one component breaks functionality in
another component. This reflects violation of an implied but possibly unrecognized
contract between components.
An unmasked regression is one that creates a situation where a previously existing bug
that had no affect is suddenly exposed in the system. This may be as simple as exercising
a code path for the first time.
A performance regression is one that causes the performance requirements of the system to
be violated. For example, doing some work in a low level function that may be repeated
large numbers of times may suddenly render the system unusable from certain perspectives.
The ns-3 testing framework provides tools for automating the process used to validate and
verify the code in nightly test suites to help quickly identify possible regressions.
Testing framework
ns-3 consists of a simulation core engine, a set of models, example programs, and tests.
Over time, new contributors contribute models, tests, and examples. A Python test program
test.py serves as the test execution manager; test.py can run test code and examples to
look for regressions, can output the results into a number of forms, and can manage code
coverage analysis tools. On top of this, we layer Buildbots that are automated build
robots that perform robustness testing by running the test framework on different systems
and with different configuration options.
BuildBots
At the highest level of ns-3 testing are the buildbots (build robots). If you are
unfamiliar with this system look at http://djmitche.github.com/buildbot/docs/0.7.11/.
This is an open-source automated system that allows ns-3 to be rebuilt and tested each
time something has changed. By running the buildbots on a number of different systems we
can ensure that ns-3 builds and executes properly on all of its supported systems.
Users (and developers) typically will not interact with the buildbot system other than to
read its messages regarding test results. If a failure is detected in one of the
automated build and test jobs, the buildbot will send an email to the ns-developers
mailing list. This email will look something like:
The Buildbot has detected a new failure of osx-ppc-g++-4.2 on NsNam.
Full details are available at:
http://ns-regression.ee.washington.edu:8010/builders/osx-ppc-g%2B%2B-4.2/builds/0
Buildbot URL: http://ns-regression.ee.washington.edu:8010/
Buildslave for this Build: darwin-ppc
Build Reason: The web-page 'force build' button was pressed by 'ww': ww
Build Source Stamp: HEAD
Blamelist:
BUILD FAILED: failed shell_5 shell_6 shell_7 shell_8 shell_9 shell_10 shell_11 shell_12
sincerely,
-The Buildbot
In the full details URL shown in the email, one can search for the keyword failed and
select the stdio link for the corresponding step to see the reason for the failure.
The buildbot will do its job quietly if there are no errors, and the system will undergo
build and test cycles every day to verify that all is well.
Test.py
The buildbots use a Python program, test.py, that is responsible for running all of the
tests and collecting the resulting reports into a human- readable form. This program is
also available for use by users and developers as well.
test.py is very flexible in allowing the user to specify the number and kind of tests to
run; and also the amount and kind of output to generate.
Before running test.py, make sure that ns3's examples and tests have been built by doing
the following
./waf configure --enable-examples --enable-tests
./waf
By default, test.py will run all available tests and report status back in a very concise
form. Running the command
./test.py
will result in a number of PASS, FAIL, CRASH or SKIP indications followed by the kind of
test that was run and its display name.
Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
Waf: Leaving directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
'build' finished successfully (0.939s)
FAIL: TestSuite ns3-wifi-propagation-loss-models
PASS: TestSuite object-name-service
PASS: TestSuite pcap-file-object
PASS: TestSuite ns3-tcp-cwnd
...
PASS: TestSuite ns3-tcp-interoperability
PASS: Example csma-broadcast
PASS: Example csma-multicast
This mode is intended to be used by users who are interested in determining if their
distribution is working correctly, and by developers who are interested in determining if
changes they have made have caused any regressions.
There are a number of options available to control the behavior of test.py. if you run
test.py --help you should see a command summary like:
Usage: test.py [options]
Options:
-h, --help show this help message and exit
-b BUILDPATH, --buildpath=BUILDPATH
specify the path where ns-3 was built (defaults to the
build directory for the current variant)
-c KIND, --constrain=KIND
constrain the test-runner by kind of test
-e EXAMPLE, --example=EXAMPLE
specify a single example to run (no relative path is
needed)
-g, --grind run the test suites and examples using valgrind
-k, --kinds print the kinds of tests available
-l, --list print the list of known tests
-m, --multiple report multiple failures from test suites and test
cases
-n, --nowaf do not run waf before starting testing
-p PYEXAMPLE, --pyexample=PYEXAMPLE
specify a single python example to run (with relative
path)
-r, --retain retain all temporary files (which are normally
deleted)
-s TEST-SUITE, --suite=TEST-SUITE
specify a single test suite to run
-t TEXT-FILE, --text=TEXT-FILE
write detailed test results into TEXT-FILE.txt
-v, --verbose print progress and informational messages
-w HTML-FILE, --web=HTML-FILE, --html=HTML-FILE
write detailed test results into HTML-FILE.html
-x XML-FILE, --xml=XML-FILE
write detailed test results into XML-FILE.xml
If one specifies an optional output style, one can generate detailed descriptions of the
tests and status. Available styles are text and HTML. The buildbots will select the HTML
option to generate HTML test reports for the nightly builds using
./test.py --html=nightly.html
In this case, an HTML file named ''nightly.html'' would be created with a pretty summary
of the testing done. A ''human readable'' format is available for users interested in the
details.
./test.py --text=results.txt
In the example above, the test suite checking the ns-3 wireless device propagation loss
models failed. By default no further information is provided.
To further explore the failure, test.py allows a single test suite to be specified.
Running the command
./test.py --suite=ns3-wifi-propagation-loss-models
or equivalently
./test.py -s ns3-wifi-propagation-loss-models
results in that single test suite being run.
FAIL: TestSuite ns3-wifi-propagation-loss-models
To find detailed information regarding the failure, one must specify the kind of output
desired. For example, most people will probably be interested in a text file:
./test.py --suite=ns3-wifi-propagation-loss-models --text=results.txt
This will result in that single test suite being run with the test status written to the
file ''results.txt''.
You should find something similar to the following in that file:
FAIL: Test Suite ''ns3-wifi-propagation-loss-models'' (real 0.02 user 0.01 system 0.00)
PASS: Test Case "Check ... Friis ... model ..." (real 0.01 user 0.00 system 0.00)
FAIL: Test Case "Check ... Log Distance ... model" (real 0.01 user 0.01 system 0.00)
Details:
Message: Got unexpected SNR value
Condition: [long description of what actually failed]
Actual: 176.395
Limit: 176.407 +- 0.0005
File: ../src/test/ns3wifi/propagation-loss-models-test-suite.cc
Line: 360
Notice that the Test Suite is composed of two Test Cases. The first test case checked the
Friis propagation loss model and passed. The second test case failed checking the Log
Distance propagation model. In this case, an SNR of 176.395 was found, and the test
expected a value of 176.407 correct to three decimal places. The file which implemented
the failing test is listed as well as the line of code which triggered the failure.
If you desire, you could just as easily have written an HTML file using the --html option
as described above.
Typically a user will run all tests at least once after downloading ns-3 to ensure that
his or her environment has been built correctly and is generating correct results
according to the test suites. Developers will typically run the test suites before and
after making a change to ensure that they have not introduced a regression with their
changes. In this case, developers may not want to run all tests, but only a subset. For
example, the developer might only want to run the unit tests periodically while making
changes to a repository. In this case, test.py can be told to constrain the types of
tests being run to a particular class of tests. The following command will result in only
the unit tests being run:
./test.py --constrain=unit
Similarly, the following command will result in only the example smoke tests being run:
./test.py --constrain=unit
To see a quick list of the legal kinds of constraints, you can ask for them to be listed.
The following command
./test.py --kinds
will result in the following list being displayed:
Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
Waf: Leaving directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
'build' finished successfully (0.939s)Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
bvt: Build Verification Tests (to see if build completed successfully)
core: Run all TestSuite-based tests (exclude examples)
example: Examples (to see if example programs run successfully)
performance: Performance Tests (check to see if the system is as fast as expected)
system: System Tests (spans modules to check integration of modules)
unit: Unit Tests (within modules to check basic functionality)
Any of these kinds of test can be provided as a constraint using the --constraint option.
To see a quick list of all of the test suites available, you can ask for them to be
listed. The following command,
./test.py --list
will result in a list of the test suite being displayed, similar to:
Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
Waf: Leaving directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
'build' finished successfully (0.939s)
histogram
ns3-wifi-interference
ns3-tcp-cwnd
ns3-tcp-interoperability
sample
devices-mesh-flame
devices-mesh-dot11s
devices-mesh
...
object-name-service
callback
attributes
config
global-value
command-line
basic-random-number
object
Any of these listed suites can be selected to be run by itself using the --suite option as
shown above.
Similarly to test suites, one can run a single C++ example program using the --example
option. Note that the relative path for the example does not need to be included and that
the executables built for C++ examples do not have extensions. Entering
./test.py --example=udp-echo
results in that single example being run.
PASS: Example examples/udp/udp-echo
You can specify the directory where ns-3 was built using the --buildpath option as
follows.
./test.py --buildpath=/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build/debug --example=wifi-simple-adhoc
One can run a single Python example program using the --pyexample option. Note that the
relative path for the example must be included and that Python examples do need their
extensions. Entering
./test.py --pyexample=examples/tutorial/first.py
results in that single example being run.
PASS: Example examples/tutorial/first.py
Because Python examples are not built, you do not need to specify the directory where ns-3
was built to run them.
Normally when example programs are executed, they write a large amount of trace file data.
This is normally saved to the base directory of the distribution (e.g.,
/home/user/ns-3-dev). When test.py runs an example, it really is completely unconcerned
with the trace files. It just wants to to determine if the example can be built and run
without error. Since this is the case, the trace files are written into a
/tmp/unchecked-traces directory. If you run the above example, you should be able to find
the associated udp-echo.tr and udp-echo-n-1.pcap files there.
The list of available examples is defined by the contents of the ''examples'' directory in
the distribution. If you select an example for execution using the --example option,
test.py will not make any attempt to decide if the example has been configured or not, it
will just try to run it and report the result of the attempt.
When test.py runs, by default it will first ensure that the system has been completely
built. This can be defeated by selecting the --nowaf option.
./test.py --list --nowaf
will result in a list of the currently built test suites being displayed, similar to:
ns3-wifi-propagation-loss-models
ns3-tcp-cwnd
ns3-tcp-interoperability
pcap-file-object
object-name-service
random-number-generators
Note the absence of the Waf build messages.
test.py also supports running the test suites and examples under valgrind. Valgrind is a
flexible program for debugging and profiling Linux executables. By default, valgrind runs
a tool called memcheck, which performs a range of memory- checking functions, including
detecting accesses to uninitialised memory, misuse of allocated memory (double frees,
access after free, etc.) and detecting memory leaks. This can be selected by using the
--grind option.
./test.py --grind
As it runs, test.py and the programs that it runs indirectly, generate large numbers of
temporary files. Usually, the content of these files is not interesting, however in some
cases it can be useful (for debugging purposes) to view these files. test.py provides a
--retain option which will cause these temporary files to be kept after the run is
completed. The files are saved in a directory named testpy-output under a subdirectory
named according to the current Coordinated Universal Time (also known as Greenwich Mean
Time).
./test.py --retain
Finally, test.py provides a --verbose option which will print large amounts of information
about its progress. It is not expected that this will be terribly useful unless there is
an error. In this case, you can get access to the standard output and standard error
reported by running test suites and examples. Select verbose in the following way:
./test.py --verbose
All of these options can be mixed and matched. For example, to run all of the ns-3 core
test suites under valgrind, in verbose mode, while generating an HTML output file, one
would do:
./test.py --verbose --grind --constrain=core --html=results.html
TestTaxonomy
As mentioned above, tests are grouped into a number of broadly defined classifications to
allow users to selectively run tests to address the different kinds of testing that need
to be done.
· Build Verification Tests
· Unit Tests
· System Tests
· Examples
· Performance Tests
BuildVerificationTests
These are relatively simple tests that are built along with the distribution and are used
to make sure that the build is pretty much working. Our current unit tests live in the
source files of the code they test and are built into the ns-3 modules; and so fit the
description of BVTs. BVTs live in the same source code that is built into the ns-3 code.
Our current tests are examples of this kind of test.
Unit Tests
Unit tests are more involved tests that go into detail to make sure that a piece of code
works as advertised in isolation. There is really no reason for this kind of test to be
built into an ns-3 module. It turns out, for example, that the unit tests for the object
name service are about the same size as the object name service code itself. Unit tests
are tests that check a single bit of functionality that are not built into the ns-3 code,
but live in the same directory as the code it tests. It is possible that these tests
check integration of multiple implementation files in a module as well. The file
src/core/test/names-test-suite.cc is an example of this kind of test. The file
src/network/test/pcap-file-test-suite.cc is another example that uses a known good pcap
file as a test vector file. This file is stored locally in the src/network directory.
System Tests
System tests are those that involve more than one module in the system. We have lots of
this kind of test running in our current regression framework, but they are typically
overloaded examples. We provide a new place for this kind of test in the directory
src/test. The file src/test/ns3tcp/ns3-interop-test-suite.cc is an example of this kind
of test. It uses NSC TCP to test the ns-3 TCP implementation. Often there will be test
vectors required for this kind of test, and they are stored in the directory where the
test lives. For example, ns3tcp-interop-response-vectors.pcap is a file consisting of a
number of TCP headers that are used as the expected responses of the ns-3 TCP under test
to a stimulus generated by the NSC TCP which is used as a ''known good'' implementation.
Examples
The examples are tested by the framework to make sure they built and will run. Nothing is
checked, and currently the pcap files are just written off into /tmp to be discarded. If
the examples run (don't crash) they pass this smoke test.
Performance Tests
Performance tests are those which exercise a particular part of the system and determine
if the tests have executed to completion in a reasonable time.
Running Tests
Tests are typically run using the high level test.py program. To get a list of the
available command-line options, run test.py --help
The test program test.py will run both tests and those examples that have been added to
the list to check. The difference between tests and examples is as follows. Tests
generally check that specific simulation output or events conforms to expected behavior.
In contrast, the output of examples is not checked, and the test program merely checks the
exit status of the example program to make sure that it runs without error.
Briefly, to run all tests, first one must configure tests during configuration stage, and
also (optionally) examples if examples are to be checked:
./waf --configure --enable-examples --enable-tests
Then, build ns-3, and after it is built, just run test.py. test.py -h will show a number
of configuration options that modify the behavior of test.py.
The program test.py invokes, for C++ tests and examples, a lower-level C++ program called
test-runner to actually run the tests. As discussed below, this test-runner can be a
helpful way to debug tests.
Debugging Tests
The debugging of the test programs is best performed running the low-level test-runner
program. The test-runner is the bridge from generic Python code to ns-3 code. It is
written in C++ and uses the automatic test discovery process in the ns-3 code to find and
allow execution of all of the various tests.
The main reason why test.py is not suitable for debugging is that it is not allowed for
logging to be turned on using the NS_LOG environmental variable when test.py runs. This
limitation does not apply to the test-runner executable. Hence, if you want to see logging
output from your tests, you have to run them using the test-runner directly.
In order to execute the test-runner, you run it like any other ns-3 executable -- using
waf. To get a list of available options, you can type:
./waf --run "test-runner --help"
You should see something like the following:
Waf: Entering directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
Waf: Leaving directory `/home/craigdo/repos/ns-3-allinone-test/ns-3-dev/build'
'build' finished successfully (0.353s)
--assert: Tell tests to segfault (like assert) if an error is detected
--basedir=dir: Set the base directory (where to find src) to ''dir''
--tempdir=dir: Set the temporary directory (where to find data files) to ''dir''
--constrain=test-type: Constrain checks to test suites of type ''test-type''
--help: Print this message
--kinds: List all of the available kinds of tests
--list: List all of the test suites (optionally constrained by test-type)
--out=file-name: Set the test status output file to ''file-name''
--suite=suite-name: Run the test suite named ''suite-name''
--verbose: Turn on messages in the run test suites
There are a number of things available to you which will be familiar to you if you have
looked at test.py. This should be expected since the test- runner is just an interface
between test.py and ns-3. You may notice that example-related commands are missing here.
That is because the examples are really not ns-3 tests. test.py runs them as if they were
to present a unified testing environment, but they are really completely different and not
to be found here.
The first new option that appears here, but not in test.py is the --assert option. This
option is useful when debugging a test case when running under a debugger like gdb. When
selected, this option tells the underlying test case to cause a segmentation violation if
an error is detected. This has the nice side-effect of causing program execution to stop
(break into the debugger) when an error is detected. If you are using gdb, you could use
this option something like,
./waf shell
cd build/debug/utils
gdb test-runner
run --suite=global-value --assert
If an error is then found in the global-value test suite, a segfault would be generated
and the (source level) debugger would stop at the NS_TEST_ASSERT_MSG that detected the
error.
Another new option that appears here is the --basedir option. It turns out that some
tests may need to reference the source directory of the ns-3 distribution to find local
data, so a base directory is always required to run a test.
If you run a test from test.py, the Python program will provide the basedir option for
you. To run one of the tests directly from the test-runner using waf, you will need to
specify the test suite to run along with the base directory. So you could use the shell
and do:
./waf --run "test-runner --basedir=`pwd` --suite=pcap-file-object"
Note the ''backward'' quotation marks on the pwd command.
If you are running the test suite out of a debugger, it can be quite painful to remember
and constantly type the absolute path of the distribution base directory. Because of
this, if you omit the basedir, the test-runner will try to figure one out for you. It
begins in the current working directory and walks up the directory tree looking for a
directory file with files named VERSION and LICENSE. If it finds one, it assumes that
must be the basedir and provides it for you.
Test output
Many test suites need to write temporary files (such as pcap files) in the process of
running the tests. The tests then need a temporary directory to write to. The Python
test utility (test.py) will provide a temporary file automatically, but if run stand-alone
this temporary directory must be provided. Just as in the basedir case, it can be
annoying to continually have to provide a --tempdir, so the test runner will figure one
out for you if you don't provide one. It first looks for environment variables named TMP
and TEMP and uses those. If neither TMP nor TEMP are defined it picks /tmp. The code
then tacks on an identifier indicating what created the directory (ns-3) then the time
(hh.mm.ss) followed by a large random number. The test runner creates a directory of that
name to be used as the temporary directory. Temporary files then go into a directory that
will be named something like
/tmp/ns-3.10.25.37.61537845
The time is provided as a hint so that you can relatively easily reconstruct what
directory was used if you need to go back and look at the files that were placed in that
directory.
Another class of output is test output like pcap traces that are generated to compare to
reference output. The test program will typically delete these after the test suites all
run. To disable the deletion of test output, run test.py with the "retain" option:
./test.py -r
and test output can be found in the testpy-output/ directory.
Reporting of test failures
When you run a test suite using the test-runner it will run the test quietly by default.
The only indication that you will get that the test passed is the absence of a message
from waf saying that the program returned something other than a zero exit code. To get
some output from the test, you need to specify an output file to which the tests will
write their XML status using the --out option. You need to be careful interpreting the
results because the test suites will append results onto this file. Try,
./waf --run "test-runner --basedir=`pwd` --suite=pcap-file-object --out=myfile.xml"
If you look at the file myfile.xml you should see something like,
<TestSuite>
<SuiteName>pcap-file-object</SuiteName>
<TestCase>
<CaseName>Check to see that PcapFile::Open with mode ''w'' works</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<TestCase>
<CaseName>Check to see that PcapFile::Open with mode ''r'' works</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<TestCase>
<CaseName>Check to see that PcapFile::Open with mode ''a'' works</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<TestCase>
<CaseName>Check to see that PcapFileHeader is managed correctly</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<TestCase>
<CaseName>Check to see that PcapRecordHeader is managed correctly</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<TestCase>
<CaseName>Check to see that PcapFile can read out a known good pcap file</CaseName>
<CaseResult>PASS</CaseResult>
<CaseTime>real 0.00 user 0.00 system 0.00</CaseTime>
</TestCase>
<SuiteResult>PASS</SuiteResult>
<SuiteTime>real 0.00 user 0.00 system 0.00</SuiteTime>
</TestSuite>
If you are familiar with XML this should be fairly self-explanatory. It is also not a
complete XML file since test suites are designed to have their output appended to a master
XML status file as described in the test.py section.
Debugging test suite failures
To debug test crashes, such as:
CRASH: TestSuite ns3-wifi-interference
You can access the underlying test-runner program via gdb as follows, and then pass the
"--basedir=`pwd`" argument to run (you can also pass other arguments as needed, but
basedir is the minimum needed):
./waf --command-template="gdb %s" --run "test-runner"
Waf: Entering directory `/home/tomh/hg/sep09/ns-3-allinone/ns-3-dev-678/build'
Waf: Leaving directory `/home/tomh/hg/sep09/ns-3-allinone/ns-3-dev-678/build'
'build' finished successfully (0.380s)
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
L cense GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu"...
(gdb) r --basedir=`pwd`
Starting program: <..>/build/debug/utils/test-runner --basedir=`pwd`
[Thread debugging using libthread_db enabled]
assert failed. file=../src/core/model/type-id.cc, line=138, cond="uid <= m_information.size () && uid != 0"
...
Here is another example of how to use valgrind to debug a memory problem such as:
VALGR: TestSuite devices-mesh-dot11s-regression
./waf --command-template="valgrind %s --basedir=`pwd` --suite=devices-mesh-dot11s-regression" --run test-runner
Class TestRunner
The executables that run dedicated test programs use a TestRunner class. This class
provides for automatic test registration and listing, as well as a way to execute the
individual tests. Individual test suites use C++ global constructors to add themselves to
a collection of test suites managed by the test runner. The test runner is used to list
all of the available tests and to select a test to be run. This is a quite simple class
that provides three static methods to provide or Adding and Getting test suites to a
collection of tests. See the doxygen for class ns3::TestRunner for details.
Test Suite
All ns-3 tests are classified into Test Suites and Test Cases. A test suite is a
collection of test cases that completely exercise a given kind of functionality. As
described above, test suites can be classified as,
· Build Verification Tests
· Unit Tests
· System Tests
· Examples
· Performance Tests
This classification is exported from the TestSuite class. This class is quite simple,
existing only as a place to export this type and to accumulate test cases. From a user
perspective, in order to create a new TestSuite in the system one only has to define a new
class that inherits from class TestSuite and perform these two duties.
The following code will define a new class that can be run by test.py as a ''unit'' test
with the display name, my-test-suite-name.
class MySuite : public TestSuite
{
public:
MyTestSuite ();
};
MyTestSuite::MyTestSuite ()
: TestSuite ("my-test-suite-name", UNIT)
{
AddTestCase (new MyTestCase);
}
MyTestSuite myTestSuite;
The base class takes care of all of the registration and reporting required to be a good
citizen in the test framework.
Test Case
Individual tests are created using a TestCase class. Common models for the use of a test
case include "one test case per feature", and "one test case per method." Mixtures of
these models may be used.
In order to create a new test case in the system, all one has to do is to inherit from the
TestCase base class, override the constructor to give the test case a name and override
the DoRun method to run the test.
class MyTestCase : public TestCase
{
MyTestCase ();
virtual void DoRun (void);
};
MyTestCase::MyTestCase ()
: TestCase ("Check some bit of functionality")
{
}
void
MyTestCase::DoRun (void)
{
NS_TEST_ASSERT_MSG_EQ (true, true, "Some failure message");
}
Utilities
There are a number of utilities of various kinds that are also part of the testing
framework. Examples include a generalized pcap file useful for storing test vectors; a
generic container useful for transient storage of test vectors during test execution; and
tools for generating presentations based on validation and verification testing results.
These utilities are not documented here, but for example, please see how the TCP tests
found in src/test/ns3tcp/ use pcap files and reference output.
How to write tests
A primary goal of the ns-3 project is to help users to improve the validity and
credibility of their results. There are many elements to obtaining valid models and
simulations, and testing is a major component. If you contribute models or examples to
ns-3, you may be asked to contribute test code. Models that you contribute will be used
for many years by other people, who probably have no idea upon first glance whether the
model is correct. The test code that you write for your model will help to avoid future
regressions in the output and will aid future users in understanding the verification and
bounds of applicability of your models.
There are many ways to verify the correctness of a model's implementation. In this
section, we hope to cover some common cases that can be used as a guide to writing new
tests.
Sample TestSuite skeleton
When starting from scratch (i.e. not adding a TestCase to an existing TestSuite), these
things need to be decided up front:
· What the test suite will be called
· What type of test it will be (Build Verification Test, Unit Test, System Test, or
Performance Test)
· Where the test code will live (either in an existing ns-3 module or separately in
src/test/ directory). You will have to edit the wscript file in that directory to
compile your new code, if it is a new file.
A program called src/create-module.py is a good starting point. This program can be
invoked such as create-module.py router for a hypothetical new module called router. Once
you do this, you will see a router directory, and a test/router-test-suite.cc test suite.
This file can be a starting point for your initial test. This is a working test suite,
although the actual tests performed are trivial. Copy it over to your module's test
directory, and do a global substitution of "Router" in that file for something pertaining
to the model that you want to test. You can also edit things such as a more descriptive
test case name.
You also need to add a block into your wscript to get this test to compile:
module_test.source = [
'test/router-test-suite.cc',
]
Before you actually start making this do useful things, it may help to try to run the
skeleton. Make sure that ns-3 has been configured with the "--enable-tests" option.
Let's assume that your new test suite is called "router" such as here:
RouterTestSuite::RouterTestSuite ()
: TestSuite ("router", UNIT)
Try this command:
./test.py -s router
Output such as below should be produced:
PASS: TestSuite router
1 of 1 tests passed (1 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
See src/lte/test/test-lte-antenna.cc for a worked example.
Test macros
There are a number of macros available for checking test program output with expected
output. These macros are defined in src/core/model/test.h.
The main set of macros that are used include the following:
NS_TEST_ASSERT_MSG_EQ(actual, limit, msg)
NS_TEST_ASSERT_MSG_NE(actual, limit, msg)
NS_TEST_ASSERT_MSG_LT(actual, limit, msg)
NS_TEST_ASSERT_MSG_GT(actual, limit, msg)
NS_TEST_ASSERT_MSG_EQ_TOL(actual, limit, tol, msg)
The first argument actual is the value under test, the second value limit is the expected
value (or the value to test against), and the last argument msg is the error message to
print out if the test fails.
The first four macros above test for equality, inequality, less than, or greater than,
respectively. The fifth macro above tests for equality, but within a certain tolerance.
This variant is useful when testing floating point numbers for equality against a limit,
where you want to avoid a test failure due to rounding errors.
Finally, there are variants of the above where the keyword ASSERT is replaced by EXPECT.
These variants are designed specially for use in methods (especially callbacks) returning
void. Reserve their use for callbacks that you use in your test programs; otherwise, use
the ASSERT variants.
How to add an example program to the test suite
One can "smoke test" that examples compile and run successfully to completion (without
memory leaks) using the examples-to-run.py script located in your module's test directory.
Briefly, by including an instance of this file in your test directory, you can cause the
test runner to execute the examples listed. It is usually best to make sure that you
select examples that have reasonably short run times so as to not bog down the tests. See
the example in src/lte/test/ directory.
Testing for boolean outcomes
Testing outcomes when randomness is involved
Testing output data against a known distribution
Providing non-trivial input vectors of data
Storing and referencing non-trivial output data
Presenting your output test data
SUPPORT
Creating a new ns-3 model
This chapter walks through the design process of an ns-3 model. In many research cases,
users will not be satisfied to merely adapt existing models, but may want to extend the
core of the simulator in a novel way. We will use the example of adding an ErrorModel to a
simple ns-3 link as a motivating example of how one might approach this problem and
proceed through a design and implementation.
Design-approach
Consider how you want it to work; what should it do. Think about these things:
· functionality: What functionality should it have? What attributes or configuration is
exposed to the user?
· reusability: How much should others be able to reuse my design? Can I reuse code from
ns-2 to get started? How does a user integrate the model with the rest of another
simulation?
· dependencies: How can I reduce the introduction of outside dependencies on my new code
as much as possible (to make it more modular)? For instance, should I avoid any
dependence on IPv4 if I want it to also be used by IPv6? Should I avoid any dependency
on IP at all?
Do not be hesitant to contact the ns-3-users or ns-developers list if you have questions.
In particular, it is important to think about the public API of your new model and ask for
feedback. It also helps to let others know of your work in case you are interested in
collaborators.
Example: ErrorModel
An error model exists in ns-2. It allows packets to be passed to a stateful object that
determines, based on a random variable, whether the packet is corrupted. The caller can
then decide what to do with the packet (drop it, etc.).
The main API of the error model is a function to pass a packet to, and the return value of
this function is a boolean that tells the caller whether any corruption occurred. Note
that depending on the error model, the packet data buffer may or may not be corrupted.
Let's call this function "IsCorrupt()".
So far, in our design, we have::
class ErrorModel
{
public:
/**
* \returns true if the Packet is to be considered as errored/corrupted
* \param pkt Packet to apply error model to
*/
bool IsCorrupt (Ptr<Packet> pkt);
};
Note that we do not pass a const pointer, thereby allowing the function to modify the
packet if IsCorrupt() returns true. Not all error models will actually modify the packet;
whether or not the packet data buffer is corrupted should be documented.
We may also want specialized versions of this, such as in ns-2, so although it is not the
only design choice for polymorphism, we assume that we will subclass a base class
ErrorModel for specialized classes, such as RateErrorModel, ListErrorModel, etc, such as
is done in ns-2.
You may be thinking at this point, "Why not make IsCorrupt() a virtual method?". That is
one approach; the other is to make the public non-virtual function indirect through a
private virtual function (this in C++ is known as the non virtual interface idiom and is
adopted in the ns-3 ErrorModel class).
Next, should this device have any dependencies on IP or other protocols? We do not want
to create dependencies on Internet protocols (the error model should be applicable to
non-Internet protocols too), so we'll keep that in mind later.
Another consideration is how objects will include this error model. We envision putting
an explicit setter in certain NetDevice implementations, for example.:
/**
* Attach a receive ErrorModel to the PointToPointNetDevice.
*
* The PointToPointNetDevice may optionally include an ErrorModel in
* the packet receive chain.
*
* @see ErrorModel
* @param em Ptr to the ErrorModel.
*/
void PointToPointNetDevice::SetReceiveErrorModel(Ptr<ErrorModel> em);
Again, this is not the only choice we have (error models could be aggregated to lots of
other objects), but it satisfies our primary use case, which is to allow a user to force
errors on otherwise successful packet transmissions, at the NetDevice level.
After some thinking and looking at existing ns-2 code, here is a sample API of a base
class and first subclass that could be posted for initial review::
class ErrorModel
{
public:
ErrorModel ();
virtual ~ErrorModel ();
bool IsCorrupt (Ptr<Packet> pkt);
void Reset (void);
void Enable (void);
void Disable (void);
bool IsEnabled (void) const;
private:
virtual bool DoCorrupt (Ptr<Packet> pkt) = 0;
virtual void DoReset (void) = 0;
};
enum ErrorUnit
{
EU_BIT,
EU_BYTE,
EU_PKT
};
// Determine which packets are errored corresponding to an underlying
// random variable distribution, an error rate, and unit for the rate.
class RateErrorModel : public ErrorModel
{
public:
RateErrorModel ();
virtual ~RateErrorModel ();
enum ErrorUnit GetUnit (void) const;
void SetUnit (enum ErrorUnit error_unit);
double GetRate (void) const;
void SetRate (double rate);
void SetRandomVariable (const RandomVariable &ranvar);
private:
virtual bool DoCorrupt (Ptr<Packet> pkt);
virtual void DoReset (void);
};
Scaffolding
Let's say that you are ready to start implementing; you have a fairly clear picture of
what you want to build, and you may have solicited some initial review or suggestions from
the list. One way to approach the next step (implementation) is to create scaffolding and
fill in the details as the design matures.
This section walks through many of the steps you should consider to define scaffolding, or
a non-functional skeleton of what your model will eventually implement. It is usually good
practice to not wait to get these details integrated at the end, but instead to plumb a
skeleton of your model into the system early and then add functions later once the API and
integration seems about right.
Note that you will want to modify a few things in the below presentation for your model
since if you follow the error model verbatim, the code you produce will collide with the
existing error model. The below is just an outline of how ErrorModel was built that you
can adapt to other models.
Review the ns-3 coding style document
At this point, you may want to pause and read the ns-3 coding style document, especially
if you are considering to contribute your code back to the project. The coding style
document is linked off the main project page: ns-3 coding style.
Decide where in the source tree the model will reside in
All of the ns-3 model source code is in the directory src/. You will need to choose which
subdirectory it resides in. If it is new model code of some sort, it makes sense to put it
into the src/ directory somewhere, particularly for ease of integrating with the build
system.
In the case of the error model, it is very related to the packet class, so it makes sense
to implement this in the src/network/ module where ns-3 packets are implemented.
waf and wscript
ns-3 uses the Waf build system. You will want to integrate your new ns-3 uses the Waf
build system. You will want to integrate your new source files into this system. This
requires that you add your files to the wscript file found in each directory.
Let's start with empty files error-model.h and error-model.cc, and add this to
src/network/wscript. It is really just a matter of adding the .cc file to the rest of the
source files, and the .h file to the list of the header files.
Now, pop up to the top level directory and type "./test.py". You shouldn't have broken
anything by this operation.
include guards
Next, let's add some include guards in our header file.:
#ifndef ERROR_MODEL_H
#define ERROR_MODEL_H
...
#endif
namespace ns3
ns-3 uses the ns-3 namespace to isolate its symbols from other namespaces. Typically, a
user will next put an ns-3 namespace block in both the cc and h file.:
namespace ns3 {
...
}
At this point, we have some skeletal files in which we can start defining our new classes.
The header file looks like this::
#ifndef ERROR_MODEL_H
#define ERROR_MODEL_H
namespace ns3 {
} // namespace ns3
#endif
while the error-model.cc file simply looks like this::
#include "error-model.h"
namespace ns3 {
} // namespace ns3
These files should compile since they don't really have any contents. We're now ready to
start adding classes.
Initial Implementation
At this point, we're still working on some scaffolding, but we can begin to define our
classes, with the functionality to be added later.
use of class Object?
This is an important design step; whether to use class Object as a base class for your new
classes.
As described in the chapter on the ns-3 Object-model, classes that inherit from class
Object get special properties:
· the ns-3 type and attribute system (see Attributes)
· an object aggregation system
· a smart-pointer reference counting system (class Ptr)
Classes that derive from class ObjectBase} get the first two properties above, but do not
get smart pointers. Classes that derive from class RefCountBase get only the smart-pointer
reference counting system.
In practice, class Object is the variant of the three above that the ns-3 developer will
most commonly encounter.
In our case, we want to make use of the attribute system, and we will be passing instances
of this object across the ns-3 public API, so class Object is appropriate for us.
initial classes
One way to proceed is to start by defining the bare minimum functions and see if they will
compile. Let's review what all is needed to implement when we derive from class Object.:
#ifndef ERROR_MODEL_H
#define ERROR_MODEL_H
#include "ns3/object.h"
namespace ns3 {
class ErrorModel : public Object
{
public:
static TypeId GetTypeId (void);
ErrorModel ();
virtual ~ErrorModel ();
};
class RateErrorModel : public ErrorModel
{
public:
static TypeId GetTypeId (void);
RateErrorModel ();
virtual ~RateErrorModel ();
};
#endif
A few things to note here. We need to include object.h. The convention in ns-3 is that if
the header file is co-located in the same directory, it may be included without any path
prefix. Therefore, if we were implementing ErrorModel in src/core/model directory, we
could have just said "#include "object.h"". But we are in src/network/model, so we must
include it as "#include "ns3/object.h"". Note also that this goes outside the namespace
declaration.
Second, each class must implement a static public member function called GetTypeId (void).
Third, it is a good idea to implement constructors and destructors rather than to let the
compiler generate them, and to make the destructor virtual. In C++, note also that copy
assignment operator and copy constructors are auto-generated if they are not defined, so
if you do not want those, you should implement those as private members. This aspect of
C++ is discussed in Scott Meyers' Effective C++ book. item 45.
Let's now look at some corresponding skeletal implementation code in the .cc file.:
#include "error-model.h"
namespace ns3 {
NS_OBJECT_ENSURE_REGISTERED (ErrorModel);
TypeId ErrorModel::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::ErrorModel")
.SetParent<Object> ()
;
return tid;
}
ErrorModel::ErrorModel ()
{
}
ErrorModel::~ErrorModel ()
{
}
NS_OBJECT_ENSURE_REGISTERED (RateErrorModel);
TypeId RateErrorModel::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::RateErrorModel")
.SetParent<ErrorModel> ()
.AddConstructor<RateErrorModel> ()
;
return tid;
}
RateErrorModel::RateErrorModel ()
{
}
RateErrorModel::~RateErrorModel ()
{
}
What is the GetTypeId (void) function? This function does a few things. It registers a
unique string into the TypeId system. It establishes the hierarchy of objects in the
attribute system (via SetParent). It also declares that certain objects can be created via
the object creation framework (AddConstructor).
The macro NS_OBJECT_ENSURE_REGISTERED (classname) is needed also once for every class that
defines a new GetTypeId method, and it does the actual registration of the class into the
system. The Object-model chapter discusses this in more detail.
how to include files from elsewhere
log component
Here, write a bit about adding |ns3| logging macros. Note that LOG_COMPONENT_DEFINE is
done outside the namespace ns3
constructor, empty function prototypes
key variables (default values, attributes)
test program 1
Object Framework
Adding-a-sample-script
At this point, one may want to try to take the basic scaffolding defined above and add it
into the system. Performing this step now allows one to use a simpler model when plumbing
into the system and may also reveal whether any design or API modifications need to be
made. Once this is done, we will return to building out the functionality of the
ErrorModels themselves.
Add basic support in the class
point-to-point-net-device.h
class ErrorModel;
/**
* Error model for receive packet events
*/
Ptr<ErrorModel> m_receiveErrorModel;
Add Accessor
void
PointToPointNetDevice::SetReceiveErrorModel (Ptr<ErrorModel> em)
{
NS_LOG_FUNCTION (this << em);
m_receiveErrorModel = em;
}
.AddAttribute ("ReceiveErrorModel",
"The receiver error model used to simulate packet loss",
PointerValue (),
MakePointerAccessor (&PointToPointNetDevice::m_receiveErrorModel),
MakePointerChecker<ErrorModel> ())
Plumb into the system
void PointToPointNetDevice::Receive (Ptr<Packet> packet)
{
NS_LOG_FUNCTION (this << packet);
uint16_t protocol = 0;
if (m_receiveErrorModel && m_receiveErrorModel->IsCorrupt (packet) )
{
//
// If we have an error model and it indicates that it is time to lose a
// corrupted packet, don't forward this packet up, let it go.
//
m_dropTrace (packet);
}
else
{
//
// Hit the receive trace hook, strip off the point-to-point protocol header
// and forward this packet up the protocol stack.
//
m_rxTrace (packet);
ProcessHeader(packet, protocol);
m_rxCallback (this, packet, protocol, GetRemote ());
if (!m_promiscCallback.IsNull ())
{ m_promiscCallback (this, packet, protocol, GetRemote (),
GetAddress (), NetDevice::PACKET_HOST);
}
}
}
Create null functional script
simple-error-model.cc
// Error model
// We want to add an error model to node 3's NetDevice
// We can obtain a handle to the NetDevice via the channel and node
// pointers
Ptr<PointToPointNetDevice> nd3 = PointToPointTopology::GetNetDevice
(n3, channel2);
Ptr<ErrorModel> em = Create<ErrorModel> ();
nd3->SetReceiveErrorModel (em);
bool
ErrorModel::DoCorrupt (Packet& p)
{
NS_LOG_FUNCTION;
NS_LOG_UNCOND("Corrupt!");
return false;
}
At this point, we can run the program with our trivial ErrorModel plumbed into the receive
path of the PointToPointNetDevice. It prints out the string "Corrupt!" for each packet
received at node n3. Next, we return to the error model to add in a subclass that performs
more interesting error modeling.
Add subclass
The trivial base class ErrorModel does not do anything interesting, but it provides a
useful base class interface (Corrupt () and Reset ()), forwarded to virtual functions that
can be subclassed. Let's next consider what we call a BasicErrorModel which is based on
the ns-2 ErrorModel class (in ns-2/queue/errmodel.{cc,h}).
What properties do we want this to have, from a user interface perspective? We would like
for the user to be able to trivially swap out the type of ErrorModel used in the
NetDevice. We would also like the capability to set configurable parameters.
Here are a few simple requirements we will consider:
· Ability to set the random variable that governs the losses (default is UniformVariable)
· Ability to set the unit (bit, byte, packet, time) of granularity over which errors are
applied.
· Ability to set the rate of errors (e.g. 10^-3) corresponding to the above unit of
granularity.
· Ability to enable/disable (default is enabled)
How to subclass
We declare BasicErrorModel to be a subclass of ErrorModel as follows,:
class BasicErrorModel : public ErrorModel
{
public:
static TypeId GetTypeId (void);
...
private:
// Implement base class pure virtual functions
virtual bool DoCorrupt (Ptr<Packet> p);
virtual bool DoReset (void);
...
}
and configure the subclass GetTypeId function by setting a unique TypeId string and
setting the Parent to ErrorModel::
TypeId RateErrorModel::GetTypeId (void)
{
static TypeId tid = TypeId ("ns3::RateErrorModel")
.SetParent<ErrorModel> ()
.AddConstructor<RateErrorModel> ()
...
Build-core-functions-and-unit-tests
assert macros
Writing unit tests
Adding a New Module to ns-3
When you have created a group of related classes, examples, and tests, they can be
combined together into an ns-3 module so that they can be used with existing ns-3 modules
and by other researchers.
This chapter walks you through the steps necessary to add a new module to ns-3.
Step 1 - Familiarize yourself with the module layout
All modules can be found in the src directory. Each module can be found in a directory
that has the same name as the module. For example, the spectrum module can be found here:
src/spectrum
A prototypical module has the following directory structure and required files:
src/
module-name/
bindings/
doc/
examples/
wscript
helper/
model/
test/
examples-to-run.py
wscript
Not all directories will be present in each module.
Step 2 - Create your new module based on the template module
A python program is provided in the source directory that will create a skeleton for a new
module
src/create-module.py
For the purposes of this discussion we will assume that your new module is called
"new-module". From the src directory, do the following to create the new module:
./create-module.py new-module
Next, cd into new-module; you will find this directory layout:
examples helper model test wscript
We next walk through how to customize this module. All ns-3 modules depend on the 'core'
module and usually on other modules. This dependency is specified in the wscript file.
Let's assume that 'new-module' depends on the internet, mobility, and aodv modules. Then
the call to the function that will create this module should look like this before
editing:
def build(bld):
module = bld.create_ns3_module('new-module', ['core'])
and after editing:
def build(bld):
module = bld.create_ns3_module('new-module', ['internet', 'mobility', 'aodv'])
Your module will most likely have model source files. Initial skeletons (which will
compile successfully) are created in model/new-module.cc and model/new-module.h.
If your module will have helper source files, then they will go into the helper/
directory; again, initial skeletons are created in that directory.
Finally, it is good practice to write tests. A skeleton test suite and test case is
created in the test/ directory. The below constructor specifies that it will be a unit
test named 'new-module':
New-moduleTestSuite::New-moduleTestSuite ()
: TestSuite ("new-module", UNIT)
{
AddTestCase (new New-moduleTestCase1);
}
Step 3 - Adding to your module's source files
If your new module has model and/or helper source files, then they must be specified in
your
src/new-module/wscript
file by modifying it with your text editor.
As an example, the source files for the spectrum module are specified in
src/spectrum/wscript
with the following list of source files:
module.source = [
'model/spectrum-model.cc',
'model/spectrum-value.cc',
.
.
.
'model/microwave-oven-spectrum-value-helper.cc',
'helper/spectrum-helper.cc',
'helper/adhoc-aloha-noack-ideal-phy-helper.cc',
'helper/waveform-generator-helper.cc',
'helper/spectrum-analyzer-helper.cc',
]
Step 4 - Specify your module's header files
If your new module has model and/or helper header files, then they must be specified in
your
src/new-module/wscript
file by modifying it with your text editor.
As an example, the header files for the spectrum module are specified in
src/spectrum/wscript
with the following function call, module name, and list of header files. Note that the
argument for the function new_task_gen() tells waf to install this module's headers with
the other ns-3 headers:
headers = bld.new_task_gen(features=['ns3header'])
headers.module = 'spectrum'
headers.source = [
'model/spectrum-model.h',
'model/spectrum-value.h',
.
.
.
'model/microwave-oven-spectrum-value-helper.h',
'helper/spectrum-helper.h',
'helper/adhoc-aloha-noack-ideal-phy-helper.h',
'helper/waveform-generator-helper.h',
'helper/spectrum-analyzer-helper.h',
]
Step 5 - Specify your module's tests
If your new module has tests, then they must be specified in your
src/new-module/wscript
file by modifying it with your text editor.
As an example, the tests for the spectrum module are specified in
src/spectrum/wscript
with the following function call and list of test suites:
module_test = bld.create_ns3_module_test_library('spectrum')
module_test.source = [
'test/spectrum-interference-test.cc',
'test/spectrum-value-test.cc',
]
Step 6 - Specify your module's examples
If your new module has examples, then they must be specified in your
src/new-module/examples/wscript
file by modifying it with your text editor.
As an example, the examples for the core module are specified in
src/core/examples/wscript
The core module's C++ examples are specified using the following function calls and source
file names. Note that the second argument for the function create_ns3_program() is the
list of modules that the program being created depends on:
obj = bld.create_ns3_program('main-callback', ['core'])
obj.source = 'main-callback.cc'
obj = bld.create_ns3_program('sample-simulator', ['core'])
obj.source = 'sample-simulator.cc'
The core module's Python examples are specified using the following function call. Note
that the second argument for the function register_ns3_script() is the list of modules
that the Python example depends on:
bld.register_ns3_script('sample-simulator.py', ['core'])
Step 7 - Specify which of your module's examples should be run as tests
The test framework can also be instrumented to run example programs to try to catch
regressions in the examples. However, not all examples are suitable for regression tests.
A file called examples-to-run.py that exists in each module's test directory can control
the invocation of the examples when the test framework runs.
As an example, the examples that are run by test.py for the core module are specified in
src/core/test/examples-to-run.py
using the following two lists of C++ and Python examples:
# A list of C++ examples to run in order to ensure that they remain
# buildable and runnable over time. Each tuple in the list contains
#
# (example_name, do_run, do_valgrind_run).
#
# See test.py for more information.
cpp_examples = [
("main-attribute-value", "True", "True"),
("main-callback", "True", "True"),
("sample-simulator", "True", "True"),
("main-ptr", "True", "True"),
("main-random-variable", "True", "True"),
("sample-random-variable", "True", "True"),
]
# A list of Python examples to run in order to ensure that they remain
# runnable over time. Each tuple in the list contains
#
# (example_name, do_run).
#
# See test.py for more information.
python_examples = [
("sample-simulator.py", "True"),
]
Each tuple in the C++ list of examples to run contains
(example_name, do_run, do_valgrind_run)
where example_name is the executable to be run, do_run is a condition under which to run
the example, and do_valgrind_run is a condition under which to run the example under
valgrind. This is needed because NSC causes illegal instruction crashes with some tests
when they are run under valgrind.
Note that the two conditions are Python statements that can depend on waf configuration
variables. For example,
("tcp-nsc-lfn", "NSC_ENABLED == True", "NSC_ENABLED == False"),
Each tuple in the Python list of examples to run contains
(example_name, do_run)
where example_name is the Python script to be run and do_run is a condition under which to
run the example.
Note that the condition is a Python statement that can depend on waf configuration
variables. For example,
("realtime-udp-echo.py", "ENABLE_REAL_TIME == False"),
If your new module has examples, then you must specify which of them should be run in your
src/new-module/test/examples-to-run.py
file by modifying it with your text editor. These examples are run by test.py.
Step 8 - Build and test your new module
You can now build and test your module as normal:
./waf configure --enable-examples --enable-tests
./waf build
./test.py
and look for your new module's test suite (and example programs, if enabled) in the test
output.
Enabling Subsets of ns-3 Modules
As with most software projects, ns-3 is ever growing larger in terms of number of modules,
lines of code, and memory footprint. Users, however, may only use a few of those modules
at a time. For this reason, users may want to explicitly enable only the subset of the
possible ns-3 modules that they actually need for their research.
This chapter discusses how to enable only the ns-3 modules that you are intersted in
using.
How to enable a subset of ns-3's modules
If shared libraries are being built, then enabling a module will cause at least one
library to be built:
libns3-modulename.so
If the module has a test library and test libraries are being built, then
libns3-modulename-test.so
will be built, too. Other modules that the module depends on and their test libraries
will also be built.
By default, all modules are built in ns-3. There are two ways to enable a subset of these
modules:
1. Using waf's --enable-modules option
2. Using the ns-3 configuration file
Enable modules using waf's --enable-modules option
To enable only the core module with example and tests, for example, try these commands:
./waf clean
./waf configure --enable-examples --enable-tests --enable-modules=core
./waf build
cd build/debug/
ls
and the following libraries should be present:
bindings libns3-core.so ns3 scratch utils
examples libns3-core-test.so samples src
Note the ./waf clean step is done here only to make it more obvious which module libraries
were built. You don't have to do ./waf clean in order to enable subsets of modules.
Running test.py will cause only those tests that depend on module core to be run:
24 of 24 tests passed (24 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Repeat the above steps for the "network" module instead of the "core" module, and the
following will be built, since network depends on core:
bindings libns3-core.so libns3-network.so ns3 scratch utils
examples libns3-core-test.so libns3-network-test.so samples src
Running test.py will cause those tests that depend on only the core and network modules to
be run:
31 of 31 tests passed (31 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Enable modules using the ns-3 configuration file
A configuration file, .ns3rc, has been added to ns-3 that allows users to specify which
modules are to be included in the build.
When enabling a subset of ns-3 modules, the precedence rules are as follows:
1. the --enable-modules configure string overrides any .ns3rc file
2. the .ns3rc file in the top level ns-3 directory is next consulted, if present
3. the system searches for ~/.ns3rc if the above two are unspecified
If none of the above limits the modules to be built, all modules that waf knows about will
be built.
The maintained version of the .ns3rc file in the ns-3 source code repository resides in
the utils directory. The reason for this is if it were in the top-level directory of the
repository, it would be prone to accidental checkins from maintainers that enable the
modules they want to use. Therefore, users need to manually copy the .ns3rc from the
utils directory to their preferred place (top level directory or their home directory) to
enable persistent modular build configuration.
Assuming that you are in the top level ns-3 directory, you can get a copy of the .ns3rc
file that is in the utils directory as follows:
cp utils/.ns3rc .
The .ns3rc file should now be in your top level ns-3 directory, and it contains the
following:
#! /usr/bin/env python
# A list of the modules that will be enabled when ns-3 is run.
# Modules that depend on the listed modules will be enabled also.
#
# All modules can be enabled by choosing 'all_modules'.
modules_enabled = ['all_modules']
# Set this equal to true if you want examples to be run.
examples_enabled = False
# Set this equal to true if you want tests to be run.
tests_enabled = False
Use your favorite editor to modify the .ns3rc file to only enable the core module with
examples and tests like this:
#! /usr/bin/env python
# A list of the modules that will be enabled when ns-3 is run.
# Modules that depend on the listed modules will be enabled also.
#
# All modules can be enabled by choosing 'all_modules'.
modules_enabled = ['core']
# Set this equal to true if you want examples to be run.
examples_enabled = True
# Set this equal to true if you want tests to be run.
tests_enabled = True
Only the core module will be enabled now if you try these commands:
./waf clean
./waf configure
./waf build
cd build/debug/
ls
and the following libraries should be present:
bindings libns3-core.so ns3 scratch utils
examples libns3-core-test.so samples src
Note the ./waf clean step is done here only to make it more obvious which module libraries
were built. You don't have to do ./waf clean in order to enable subsets of modules.
Running test.py will cause only those tests that depend on module core to be run:
24 of 24 tests passed (24 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Repeat the above steps for the "network" module instead of the "core" module, and the
following will be built, since network depends on core:
bindings libns3-core.so libns3-network.so ns3 scratch utils
examples libns3-core-test.so libns3-network-test.so samples src
Running test.py will cause those tests that depend on only the core and network modules to
be run:
31 of 31 tests passed (31 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Enabling/disabling ns-3 Tests and Examples
The ns-3 distribution includes many examples and tests that are used to validate the ns-3
system. Users, however, may not always want these examples and tests to be run for their
installation of ns-3.
This chapter discusses how to build ns-3 with or without its examples and tests.
How to enable/disable examples and tests in ns-3
There are 3 ways to enable/disable examples and tests in ns-3:
1. Using build.py when ns-3 is built for the first time
2. Using waf once ns-3 has been built
3. Using the ns-3 configuration file once ns-3 has been built
Enable/disable examples and tests using build.py
You can use build.py to enable/disable examples and tests when ns-3 is built for the first
time.
By default, examples and tests are not built in ns-3.
From the ns-3-allinone directory, you can build ns-3 without any examples or tests simply
by doing:
./build.py
Running test.py in the top level ns-3 directory now will cause no examples or tests to be
run:
0 of 0 tests passed (0 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
If you would like build ns-3 with examples and tests, then do the following from the
ns-3-allinone directory:
./build.py --enable-examples --enable-tests
Running test.py in the top level ns-3 directory will cause all of the examples and tests
to be run:
170 of 170 tests passed (170 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Enable/disable examples and tests using waf
You can use waf to enable/disable examples and tests once ns-3 has been built.
By default, examples and tests are not built in ns-3.
From the top level ns-3 directory, you can build ns-3 without any examples or tests simply
by doing:
./waf configure
./waf build
Running test.py now will cause no examples or tests to be run:
0 of 0 tests passed (0 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
If you would like build ns-3 with examples and tests, then do the following from the top
level ns-3 directory:
./waf configure --enable-examples --enable-tests
./waf build
Running test.py will cause all of the examples and tests to be run:
170 of 170 tests passed (170 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Enable/disable examples and tests using the ns-3 configuration file
A configuration file, .ns3rc, has been added to ns-3 that allows users to specify whether
examples and tests should be built or not. You can use this file to enable/disable
examples and tests once ns-3 has been built.
When enabling disabling examples and tests, the precedence rules are as follows:
1. the --enable-examples/--disable-examples configure strings override any .ns3rc file
2. the --enable-tests/--disable-tests configure strings override any .ns3rc file
3. the .ns3rc file in the top level ns-3 directory is next consulted, if present
4. the system searches for ~/.ns3rc if the .ns3rc file was not found in the previous step
If none of the above exists, then examples and tests will not be built.
The maintained version of the .ns3rc file in the ns-3 source code repository resides in
the utils directory. The reason for this is if it were in the top-level directory of the
repository, it would be prone to accidental checkins from maintainers that enable the
modules they want to use. Therefore, users need to manually copy the .ns3rc from the
utils directory to their preferred place (top level directory or their home directory) to
enable persistent enabling of examples and tests.
Assuming that you are in the top level ns-3 directory, you can get a copy of the .ns3rc
file that is in the utils directory as follows:
cp utils/.ns3rc .
The .ns3rc file should now be in your top level ns-3 directory, and it contains the
following:
#! /usr/bin/env python
# A list of the modules that will be enabled when ns-3 is run.
# Modules that depend on the listed modules will be enabled also.
#
# All modules can be enabled by choosing 'all_modules'.
modules_enabled = ['all_modules']
# Set this equal to true if you want examples to be run.
examples_enabled = False
# Set this equal to true if you want tests to be run.
tests_enabled = False
From the top level ns-3 directory, you can build ns-3 without any examples or tests simply
by doing:
./waf configure
./waf build
Running test.py now will cause no examples or tests to be run:
0 of 0 tests passed (0 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
If you would like build ns-3 with examples and tests, use your favorite editor to change
the values in the .ns3rc file for examples_enabled and tests_enabled file to be True:
#! /usr/bin/env python
# A list of the modules that will be enabled when ns-3 is run.
# Modules that depend on the listed modules will be enabled also.
#
# All modules can be enabled by choosing 'all_modules'.
modules_enabled = ['all_modules']
# Set this equal to true if you want examples to be run.
examples_enabled = True
# Set this equal to true if you want tests to be run.
tests_enabled = True
From the top level ns-3 directory, you can build ns-3 with examples and tests simply by
doing:
./waf configure
./waf build
Running test.py will cause all of the examples and tests to be run:
170 of 170 tests passed (170 passed, 0 skipped, 0 failed, 0 crashed, 0 valgrind errors)
Troubleshooting
This chapter posts some information about possibly common errors in building or running
ns-3 programs.
Please note that the wiki (http://www.nsnam.org/wiki/index.php/Troubleshooting) may have
contributed items.
Build errors
Run-time errors
Sometimes, errors can occur with a program after a successful build. These are run-time
errors, and can commonly occur when memory is corrupted or pointer values are unexpectedly
null.
Here is an example of what might occur::
ns-old:~/ns-3-nsc$ ./waf --run tcp-point-to-point
Entering directory `/home/tomh/ns-3-nsc/build'
Compilation finished successfully
Command ['/home/tomh/ns-3-nsc/build/debug/examples/tcp-point-to-point'] exited with code -11
The error message says that the program terminated unsuccessfully, but it is not clear
from this information what might be wrong. To examine more closely, try running it under
the gdb debugger::
ns-old:~/ns-3-nsc$ ./waf --run tcp-point-to-point --command-template="gdb %s"
Entering directory `/home/tomh/ns-3-nsc/build'
Compilation finished successfully
GNU gdb Red Hat Linux (6.3.0.0-1.134.fc5rh)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux-gnu"...Using host libthread_db
library "/lib/libthread_db.so.1".
(gdb) run
Starting program: /home/tomh/ns-3-nsc/build/debug/examples/tcp-point-to-point
Reading symbols from shared object read from target memory...done.
Loaded system supplied DSO at 0xf5c000
Program received signal SIGSEGV, Segmentation fault.
0x0804aa12 in main (argc=1, argv=0xbfdfefa4)
at ../examples/tcp-point-to-point.cc:136
136 Ptr<Socket> localSocket = socketFactory->CreateSocket ();
(gdb) p localSocket
$1 = {m_ptr = 0x3c5d65}
(gdb) p socketFactory
$2 = {m_ptr = 0x0}
(gdb) quit
The program is running. Exit anyway? (y or n) y
Note first the way the program was invoked-- pass the command to run as an argument to the
command template "gdb %s".
This tells us that there was an attempt to dereference a null pointer socketFactory.
Let's look around line 136 of tcp-point-to-point, as gdb suggests::
Ptr<SocketFactory> socketFactory = n2->GetObject<SocketFactory> (Tcp::iid);
Ptr<Socket> localSocket = socketFactory->CreateSocket ();
localSocket->Bind ();
The culprit here is that the return value of GetObject is not being checked and may be
null.
Sometimes you may need to use the valgrind memory checker for more subtle errors. Again,
you invoke the use of valgrind similarly::
ns-old:~/ns-3-nsc$ ./waf --run tcp-point-to-point --command-template="valgrind %s"
AUTHOR
ns-3 project
COPYRIGHT
2010, ns-3 project