[Tmrg] Now, where were we...?

[d.wischik at cs.ucl.ac.uk (Damon Wischik)]

Michael Welzl wrote:
> Can delay ever be worse as a congestion indicator than
> loss is? What kinds of misinterpretations can we have,
> if we carefully interpret it?

Delay is not a reliable indicator in the case of large multiplexers with 
small buffers. For example, Appenzeller et al. suggested that buffer 
size should be bandwidth*delay/sqrt(num flows). Under this 
recommendation, if the number of flows is very large then the maximum 
possible queueing delay is very small, and it may be small enough to be 
swamped by things like timer granularity. Packet loss should simply be 
(x-C)/x where x is the total load and C is the link speed, assuming that 
there are many flows and they are desynchronized, and this should 
continue to be a reliable indicator of congestion no matter how many 
flows there are.

What I've written only applies to large multiplexers with small buffers. 
It doesn't apply to access links, where I can well believe that delay is 
an appropriate congestion indicator.

Damon.