tc-netem


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 character-
       istics 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 inter-
       face. The optional parameters allows to introduce a delay variation and
       a  correlation.  Delay and jitter values are expressed in ms while cor-
       relation 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
       if used alone corresponds to the Bernoulli model. The optional  parame-
       ters 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 recep-
       tion 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 proba-
       bility 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 pack-
       ets  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 corre-
       lation of 50%) while the others are delayed by 10 ms.
       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 artifi-
       cial 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 Develop-
           ment    Lab,    April    2005    (http://devresources.linux-founda-
           tion.org/shemminger/netem/LCA2005_paper.pdf)


        2. Netem   page   from   Linux   foundation,  (http://www.linuxfounda-
           tion.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://net-
           group.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>



iproute2                       25 November 2011                       NETEM(8)
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