[Netem] Netem: Packet-size dependent delay

Joachim Fabini Joachim.Fabini at tuwien.ac.at
Wed Feb 8 01:24:39 PST 2006


Hello,

a newbie question: according to my search in the netem
mailing list archives, netem does support distribution 
functions for packet delay. But it treats packets in a
uniformous way and does NOT support variable delay 
depending on the specific packet/payload size. Is this 
correct?

If yes: is there any ongoing work to implement packet-
size-specific delay for netem? This feature is imho 
required to model the behavior of radio networks. While
packet size can be safely ignored in fixed networks 
(the delay variation caused by the packet size is much 
less than the netem timer resolution), this is not the
case in radio networks. If we compare the delay, e.g., 
for GPRS, we see that 100 byte packets are delayed
around 600ms while 1400 byte payload result in almost 
four times this delay.

Without having looked at the sources, a question to the 
developers: Is such a feature compatible with the netem
architecture and do you see major difficulties in the 
implementation of this feature? The question is just 
on the feasibility of the implementation. 
Our practical tests show that the delay because of payload 
size is approximately linear, so we can approximate the 
delay function by interpolating between two points/pairs 
(size,delay).

Any comments warmly welcome,

thanks in advance,
best regards
--Joachim




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