[e2e] Interpretation of ECN as a less severe congestion signal

Michael Welzl michael.welzl at uibk.ac.at
Mon Jul 1 00:06:56 PDT 2002

Hi all,

Just out of curiosity:

Why is it that the semantics of an ECN flag were not defined
as a LESS severe congestion signal than a dropped packet?
For example, a sender could reduce the rate by 1/4 instead
of 1/2 in response to an ECN flag; this way, ECN would provide
MORE instead of complementary information.

Router behaviour would then be:
minThresh <= queue length < maxThresh: mark packet
maxThresh <= queue length: drop packet

I assume that this can't be changed now because the behaviour
in routers needs to be uniform - but I like the idea ... it's
simple, and it should be better ... it's well known that the
rate reduction factor (beta) could be higher than 1/2 and the
AIMD idea would still be preserved.

I've seen this idea in the Multilevel ECN proposal by Arjan
Durresi, Jain et al (somewhere on Raj Jain's publications site).


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