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199 lines
7.0 KiB
199 lines
7.0 KiB
.TH NETEM 8 "25 November 2011" "iproute2" "Linux"
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.SH NAME
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NetEm \- Network Emulator
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.SH SYNOPSIS
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.B "tc qdisc ... dev"
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.IR DEVICE " ] "
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.BR "add netem"
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.I OPTIONS
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.IR OPTIONS " := [ " LIMIT " ] [ " DELAY " ] [ " LOSS \
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" ] [ " CORRUPT " ] [ " DUPLICATION " ] [ " REORDERING " ][ " RATE " ]"
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.IR LIMIT " := "
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.B limit
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.I packets
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.IR DELAY " := "
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.BI delay
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.IR TIME " [ " JITTER " [ " CORRELATION " ]]]"
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.br
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[
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.BR distribution " { "uniform " | " normal " | " pareto " | " paretonormal " } ]"
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.IR LOSS " := "
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.BR loss " { "
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.BI random
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.IR PERCENT " [ " CORRELATION " ] |"
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.br
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.RB " " state
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.IR p13 " [ " p31 " [ " p32 " [ " p23 " [ " p14 "]]]] |"
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.br
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.RB " " gemodel
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.IR p " [ " r " [ " 1-h " [ " 1-k " ]]] } "
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.RB " [ " ecn " ] "
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.IR CORRUPT " := "
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.B corrupt
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.IR PERCENT " [ " CORRELATION " ]]"
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.IR DUPLICATION " := "
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.B duplicate
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.IR PERCENT " [ " CORRELATION " ]]"
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.IR REORDERING " := "
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.B reorder
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.IR PERCENT " [ " CORRELATION " ] [ "
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.B gap
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.IR DISTANCE " ]"
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.IR RATE " := "
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.B rate
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.IR RATE " [ " PACKETOVERHEAD " [ " CELLSIZE " [ " CELLOVERHEAD " ]]]]"
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.SH DESCRIPTION
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NetEm is an enhancement of the Linux traffic control facilities
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that allow to add delay, packet loss, duplication and more other
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characteristics to packets outgoing from a selected network
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interface. NetEm is built using the existing Quality Of Service (QOS)
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and Differentiated Services (diffserv) facilities in the Linux
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kernel.
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.SH netem OPTIONS
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netem has the following options:
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.SS limit packets
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limits the effect of selected options to the indicated number of next packets.
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.SS delay
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adds the chosen delay to the packets outgoing to chosen network interface. The
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optional parameters allows to introduce a delay variation and a correlation.
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Delay and jitter values are expressed in ms while correlation is percentage.
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.SS distribution
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allow the user to choose the delay distribution. If not specified, the default
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distribution is Normal. Additional parameters allow to consider situations in
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which network has variable delays depending on traffic flows concurring on the
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same path, that causes several delay peaks and a tail.
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.SS loss random
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adds an independent loss probability to the packets outgoing from the chosen
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network interface. It is also possible to add a correlation, but this option
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is now deprecated due to the noticed bad behavior.
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.SS loss state
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adds packet losses according to the 4-state Markov using the transition
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probabilities as input parameters. The parameter p13 is mandatory and if used
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alone corresponds to the Bernoulli model. The optional parameters allows to
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extend the model to 2-state (p31), 3-state (p23 and p32) and 4-state (p14).
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State 1 corresponds to good reception, State 4 to independent losses, State 3
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to burst losses and State 2 to good reception within a burst.
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.SS loss gemodel
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adds packet losses according to the Gilbert-Elliot loss model or its special
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cases (Gilbert, Simple Gilbert and Bernoulli). To use the Bernoulli model, the
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only needed parameter is p while the others will be set to the default
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values r=1-p, 1-h=1 and 1-k=0. The parameters needed for the Simple Gilbert
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model are two (p and r), while three parameters (p, r, 1-h) are needed for the
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Gilbert model and four (p, r, 1-h and 1-k) are needed for the Gilbert-Elliot
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model. As known, p and r are the transition probabilities between the bad and
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the good states, 1-h is the loss probability in the bad state and 1-k is the
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loss probability in the good state.
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.SS ecn
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can be used optionally to mark packets instead of dropping them. A loss model
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has to be used for this to be enabled.
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.SS corrupt
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allows the emulation of random noise introducing an error in a random position
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for a chosen percent of packets. It is also possible to add a correlation
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through the proper parameter.
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.SS duplicate
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using this option the chosen percent of packets is duplicated before queuing
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them. It is also possible to add a correlation through the proper parameter.
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.SS reorder
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to use reordering, a delay option must be specified. There are two ways to use
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this option (assuming 'delay 10ms' in the options list).
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.B "reorder "
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.I 25% 50%
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.B "gap"
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.I 5
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.br
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in this first example, the first 4 (gap - 1) packets are delayed by 10ms and
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subsequent packets are sent immediately with a probability of 0.25 (with
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correlation of 50% ) or delayed with a probability of 0.75. After a packet is
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reordered, the process restarts i.e. the next 4 packets are delayed and
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subsequent packets are sent immediately or delayed based on reordering
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probability. To cause a repeatable pattern where every 5th packet is reordered
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reliably, a reorder probability of 100% can be used.
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.B reorder
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.I 25% 50%
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.br
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in this second example 25% of packets are sent immediately (with correlation of
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50%) while the others are delayed by 10 ms.
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.SS rate
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delay packets based on packet size and is a replacement for
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.IR TBF .
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Rate can be
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specified in common units (e.g. 100kbit). Optional
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.I PACKETOVERHEAD
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(in bytes) specify an per packet overhead and can be negative. A positive value can be
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used to simulate additional link layer headers. A negative value can be used to
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artificial strip the Ethernet header (e.g. -14) and/or simulate a link layer
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header compression scheme. The third parameter - an unsigned value - specify
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the cellsize. Cellsize can be used to simulate link layer schemes. ATM for
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example has an payload cellsize of 48 bytes and 5 byte per cell header. If a
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packet is 50 byte then ATM must use two cells: 2 * 48 bytes payload including 2
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* 5 byte header, thus consume 106 byte on the wire. The last optional value
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.I CELLOVERHEAD
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can be used to specify per cell overhead - for our ATM example 5.
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.I CELLOVERHEAD
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can be negative, but use negative values with caution.
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Note that rate throttling is limited by several factors: the kernel clock
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granularity avoid a perfect shaping at a specific level. This will show up in
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an artificial packet compression (bursts). Another influence factor are network
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adapter buffers which can also add artificial delay.
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.SH LIMITATIONS
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The main known limitation of Netem are related to timer granularity, since
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Linux is not a real-time operating system.
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.SH EXAMPLES
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.PP
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tc qdisc add dev eth0 root netem rate 5kbit 20 100 5
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.RS 4
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delay all outgoing packets on device eth0 with a rate of 5kbit, a per packet
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overhead of 20 byte, a cellsize of 100 byte and a per celloverhead of 5 byte:
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.RE
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.SH SOURCES
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.IP " 1. " 4
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Hemminger S. , "Network Emulation with NetEm", Open Source Development Lab,
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April 2005
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(http://devresources.linux-foundation.org/shemminger/netem/LCA2005_paper.pdf)
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.IP " 2. " 4
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Netem page from Linux foundation, (http://www.linuxfoundation.org/en/Net:Netem)
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.IP " 3. " 4
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Salsano S., Ludovici F., Ordine A., "Definition of a general and intuitive loss
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model for packet networks and its implementation in the Netem module in the
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Linux kernel", available at http://netgroup.uniroma2.it/NetemCLG
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.SH SEE ALSO
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.BR tc (8),
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.BR tc-tbf (8)
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.SH AUTHOR
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Netem was written by Stephen Hemminger at Linux foundation and is based on NISTnet.
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This manpage was created by Fabio Ludovici <fabio.ludovici at yahoo dot it> and
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Hagen Paul Pfeifer <hagen@jauu.net>
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