NAME

       NetEm - Network Emulator

SYNOPSIS

       tc qdisc ... dev DEVICE ] add netem OPTIONS

       OPTIONS := [ LIMIT ] [ DELAY ] [ LOSS ] [ CORRUPT ] [ DUPLICATION ] [ REORDERING ][ RATE ]

       LIMIT := limit packets

       DELAY := delay TIME [ JITTER [ CORRELATION ]]]
              [ distribution { uniform | normal | pareto |  paretonormal } ]

       LOSS := loss { random PERCENT [ CORRELATION ]  |
                      state p13 [ p31 [ p32 [ p23 [ p14]]]] |
                      gemodel p [ r [ 1-h [ 1-k ]]] }  [ ecn ]

       CORRUPT := corrupt PERCENT [ CORRELATION ]]

       DUPLICATION := duplicate PERCENT [ CORRELATION ]]

       REORDERING := reorder PERCENT [ CORRELATION ] [ gap DISTANCE ]

       RATE := rate RATE [ PACKETOVERHEAD [ CELLSIZE [ CELLOVERHEAD ]]]]

DESCRIPTION

       NetEm  is  an  enhancement  of the Linux traffic control facilities that allow to add delay, packet loss,
       duplication and more other characteristics to packets outgoing from a selected network  interface.  NetEm
       is built using the existing Quality Of Service (QOS) and Differentiated Services (diffserv) facilities in
       the Linux kernel.

netem OPTIONS

       netem has the following options:

   limit packets
       limits the effect of selected options to the indicated number of next packets.

   delay
       adds the chosen delay to the packets outgoing to chosen network interface. The optional parameters allows
       to  introduce  a  delay  variation  and a correlation.  Delay and jitter values are expressed in ms while
       correlation is percentage.

   distribution
       allow the user to choose the delay distribution. If not specified, the default  distribution  is  Normal.
       Additional  parameters  allow  to  consider  situations in which network has variable delays depending on
       traffic flows concurring on the same path, that causes several delay peaks and a tail.

   loss random
       adds an independent loss probability to the packets outgoing from the chosen  network  interface.  It  is
       also possible to add a correlation, but this option is now deprecated due to the noticed bad behavior.

   loss state
       adds  packet  losses  according  to  the  4-state  Markov  using  the  transition  probabilities as input
       parameters. The parameter p13 is mandatory and if used alone corresponds  to  the  Bernoulli  model.  The
       optional parameters allows to extend the model to 2-state (p31), 3-state (p23 and p32) and 4-state (p14).
       State 1 corresponds to good reception, State 4 to independent losses, State 3 to burst losses and State 2
       to good reception within a burst.

   loss gemodel
       adds  packet  losses  according  to  the  Gilbert-Elliot loss model or its special cases (Gilbert, Simple
       Gilbert and Bernoulli). To use the Bernoulli model, the only needed parameter is p while the others  will
       be  set  to the default values r=1-p, 1-h=1 and 1-k=0. The parameters needed for the Simple Gilbert model
       are two (p and r), while three parameters (p, r, 1-h) are needed for the Gilbert model and  four  (p,  r,
       1-h  and 1-k) are needed for the Gilbert-Elliot model. As known, p and r are the transition probabilities
       between the bad and the good states, 1-h is the loss probability in the bad state and  1-k  is  the  loss
       probability in the good state.

   ecn
       can  be used optionally to mark packets instead of dropping them. A loss model has to be used for this to
       be enabled.

   corrupt
       allows the emulation of random noise introducing an error in a random position for a  chosen  percent  of
       packets. It is also possible to add a correlation through the proper parameter.

   duplicate
       using this option the chosen percent of packets is duplicated before queuing them. It is also possible to
       add a correlation through the proper parameter.

   reorder
       to use reordering, a delay option must be specified. There are two ways  to  use  this  option  (assuming
       'delay 10ms' in the options list).

       reorder 25% 50% gap 5
       in  this first example, the first 4 (gap - 1) packets are delayed by 10ms and subsequent packets are sent
       immediately with a probability of 0.25 (with correlation of 50% ) or delayed with a probability of  0.75.
       After  a  packet  is  reordered,  the process restarts i.e. the next 4 packets are delayed and subsequent
       packets are sent immediately or delayed based on reordering probability. To cause  a  repeatable  pattern
       where every 5th packet is reordered reliably, a reorder probability of 100% can be used.

       reorder 25% 50%
       in this second example 25% of packets are sent immediately (with correlation of 50%) while the others are
       delayed by 10 ms.

   rate
       delay packets based on packet size and is a replacement for TBF.  Rate can be specified in  common  units
       (e.g.  100kbit). Optional PACKETOVERHEAD (in bytes) specify an per packet overhead and can be negative. A
       positive value can be used to simulate additional link layer headers. A negative value  can  be  used  to
       artificial  strip  the Ethernet header (e.g. -14) and/or simulate a link layer header compression scheme.
       The third parameter - an unsigned value - specify the cellsize. Cellsize can be  used  to  simulate  link
       layer  schemes.  ATM  for  example  has  an payload cellsize of 48 bytes and 5 byte per cell header. If a
       packet is 50 byte then ATM must use two cells: 2 * 48 bytes payload including 2 *  5  byte  header,  thus
       consume  106  byte  on  the  wire.   The last optional value CELLOVERHEAD can be used to specify per cell
       overhead - for our ATM example 5.  CELLOVERHEAD can be negative, but use negative values with caution.

       Note that rate throttling is limited by several factors: the kernel clock  granularity  avoid  a  perfect
       shaping  at  a  specific  level.  This will show up in an artificial packet compression (bursts). Another
       influence factor are network adapter buffers which can also add artificial delay.

LIMITATIONS

       The main known limitation of Netem are related to timer granularity,  since  Linux  is  not  a  real-time
       operating system.

EXAMPLES

       tc qdisc add dev eth0 root netem rate 5kbit 20 100 5
           delay  all  outgoing packets on device eth0 with a rate of 5kbit, a per packet overhead of 20 byte, a
           cellsize of 100 byte and a per celloverhead of 5 byte:

SOURCES

        1. Hemminger  S.  ,  "Network  Emulation  with  NetEm",  Open  Source  Development   Lab,   April   2005
           (http://devresources.linux-foundation.org/shemminger/netem/LCA2005_paper.pdf)

        2. Netem page from Linux foundation, (http://www.linuxfoundation.org/en/Net:Netem)

        3. Salsano  S.,  Ludovici  F.,  Ordine  A., "Definition of a general and intuitive loss model for packet
           networks  and  its  implementation  in  the  Netem  module  in  the  Linux  kernel",   available   at
           http://netgroup.uniroma2.it/NetemCLG

SEE ALSO

       tc(8), tc-tbf(8)

AUTHOR

       Netem  was  written  by  Stephen Hemminger at Linux foundation and is based on NISTnet.  This manpage was
       created by Fabio Ludovici <fabio.ludovici at yahoo dot it> and Hagen Paul Pfeifer <hagen@jauu.net>