Manpages - tc-netem.8

maximum number of packets the qdisc may hold queued at a time.

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.

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.

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.

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.

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.

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

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.

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.

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.

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

defer delivering accumulated packets to within a slot. Each available slot can be configured with a minimum delay to acquire, and an optional maximum delay. Alternatively it can be configured with the distribution similar to distribution for delay option. Slot delays can be specified in nanoseconds, microseconds, milliseconds or seconds (e.g. 800us). Values for the optional parameters BYTES will limit the number of bytes delivered per slot, and/or PACKETS will limit the number of packets delivered per slot.

These slot options can provide a crude approximation of bursty MACs such as DOCSIS, WiFi, and LTE.

Note that slotting is limited by several factors: the kernel clock granularity, as with a rate, and attempts to deliver many packets within a slot will be smeared by the timer resolution, and by the underlying native bandwidth also.

It is possible to combine slotting with a rate, in which case complex behaviors where either the rate, or the slot limits on bytes or packets per slot, govern the actual delivered rate.