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

michawe at ifi.uio.no (Michael Welzl) Thu, 19 November 2009 14:06 UTC

From: michawe at ifi.uio.no (Michael Welzl)
Date: Thu, 19 Nov 2009 15:06:47 +0100
Subject: [Tmrg] Now, where were we...?
Message-ID: <BE0E1358-7C27-46A8-AF1E-D8D7CC834A52@ifi.uio.no>


This prompts me to ask a question that I've been pondering
ever since a hallway conversation that I had with Stanislav
Shalunov at the Stockholm IETF:

> 2. How reliable are implicit congestion indicators?  The prevailing
> wisdom in the IETF seems to be that "ECN=loss = congestion, delay =
> noise, nothing else is useful for congestion control".  What criteria
> would "delay" have to satisfy in order to be a useful indicator of
> congestion?  Should we listen to the average delay, the frequency with
> which delay exceeds a threshold, or the jitter?

Can delay ever be worse as a congestion indicator than
loss is? What kinds of misinterpretations can we have,
if we carefully interpret it?   (by which I mean, for instance,
updating "baseRTT" samples every once in a while
in order to account for path changes)

To be a bit more precise with my question, I pick the
"frequency with which delay exceeds a threshold" metric
from above.