[Netem] Netem: Packet-size dependent delay

[Stephen Hemminger]

On Wed, 8 Feb 2006 10:24:39 +0100
"Joachim Fabini" <Joachim.Fabini at tuwien.ac.at> wrote:

> 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?

Yes.

> 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.

No. But patches are always welcome. Often you can easily
create a new feature or option, and I can figure out how
to clean it up for mainline.

> 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
> 


-- 
Stephen Hemminger <shemminger at osdl.org>
OSDL http://developer.osdl.org/~shemminger