[e2e] TCP friendly with variable packet size

[Joerg Widmer]

Hi Abdelbasset,

> in RFC 3448, the authors indicate that TCP-Friendly rate control 
> mechanism should not be used for applications that vary their packet 
> size instead of their packet rate in response to congestion.
> 
> Is this true for an application that varies the packet size after the 
> estimation of the sending rate and keep this size fixed until the next
> feedback report.

There is a (quite long) technical report about this at 
http://ic2.epfl.ch/publications/documents/IC_TECH_REPORT_200282.pdf

In short: the problem is more with the packet-based measurement of the 
loss event rate. If you send smaller packets at a higher rate, you will 
underestimate the loss event rate as more and more packet drops will get 
aggregated to the same loss event. In the tech report we look at a 
number of solutions to remove the bias. However, they are only 
applicable if it is ok to trade off packet size for packet rate.

Cheers,
   Joerg