.TH NETEM 8 "25 November 2011" "iproute2" "Linux"
.SH NAME
NetEm \- Network Emulator
.SH SYNOPSIS
.B "tc qdisc ... dev" 
.IR dev " ] "
.BR "add netem" 
.I OPTIONS

.IR OPTIONS " := [ " LIMIT " ] [ " DELAY " ] [ " LOSS \
" ] [ " CORRUPT " ] [ " DUPLICATION " ] [ " REORDERING " ]"

.IR LIMIT " := "
.B limit
.I packets

.IR DELAY " := "
.BI delay 
.IR TIME " [ " JITTER " [ " CORRELATION " ]]]"
.br
       [ 
.BR distribution " { "uniform " | " normal " | " pareto " |  " paretonormal " } ]"

.IR LOSS " := "
.BR loss " { "
.BI random 
.IR PERCENT " [ " CORRELATION " ]  |"
.br
.RB "               " state
.IR p13 " [ " p31 " [ " p32 " [ " p23 " [ " p14 "]]]] |"
.br
.RB "               " gemodel
.IR p " [ " r " [ " 1-h " [ " 1-k " ]]]"

.IR CORRUPT " := "
.B corrupt
.IR PERCENT " [ " CORRELATION " ]]"

.IR DUPLICATION " := "
.B duplicate
.IR PERCENT " [ " CORRELATION " ]]"

.IR REODERING " := "
.B reorder
.IR PERCENT " [ " CORRELATION " ] [ "
.B gap 
.IR DISTANCE " ]"

.SH 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 build using the existing Quality Of Service (QOS)
and Differentiated Services (diffserv) facilities in the Linux
kernel.

.SH netem OPTIONS
netem has the following options:

.SS limit packets

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

.SS 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.

.SS distribution
allow the 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 severeal delay peaks and a tail.

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

.SS loss state
adds packet losses according to the 4-state Markov using the transition
probabilities as input parameters. The parameters 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.

.SS 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 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.

.SS corrupt
allows the emulate the 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.

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

.SS reorder
there are two ways to use this option:

.B "reorder gap"
.I 5 10
.br
in this first example every 5th (10th, 15th) packet is sent immediately while
other packets are delayed by 10 ms

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

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

.SH SOURCES
.IP " 1. " 4
Hemminger S. , "Network Emulation with NetEm", Open Source Development Lab,
April 2005
(http://devresources.linux-foundation.org/shemminger/netem/LCA2005_paper.pdf)

.IP " 2. " 4
Netem page from Linux foundation, (http://www.linuxfoundation.org/en/Net:Netem)

.IP " 3. " 4
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

.SH SEE ALSO
.BR tc (8),
.BR tc-tbf (8)

.SH 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>