Re: [aqm] aqm Digest, Vol 1, Issue 7

A problem with ECN is that it does not drain an already flooded queue, and depends (like RED) on the idea that one has a large queue in normal operation.  It is not obvious that sustaining a deep queue is a desirable state, especially when there are highly variable capacities along any path, as is the case where one link is more than 2x slower than the rest of the links.

If the dynamics of user loads are fractal, this will cause draining (and latency reduction) not to work.

If user loads are stationary gaussian and so forth, ECN can "tune" to relatively stable situations, but the queueing delay will be quite long end-to-end.

Since there is lots of evidence that user loads are fractal, dropping packets during sudden bursts will prevent sustained queueing, whereas ECN will not.

So a proper approach (in my opinion) on the "real" Internet (rather than a bunch of competing long-duration FTPs) requires keeping the queues so short that there is no real opportunity to benefit from ECN.

Hence - we need to really see what happens with *real* traffic loads, not simplified simulations.

Real traffic loads are fractal, and fractal loads do not generally obey the Gaussian style "law of large numbers" - multiple fractal flows are *rougher* not smoother than a single one.

So check your mathematical "intuitions" at the door.  Stop writing equations based on tractable analytic models, because actual traffic does not follow those models.

Yeah, the Bell Heads believe in never dropping packets.  So what.  The Internet is not about making them comfortable in their misunderstandings.

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Sent: Tuesday, March 19, 2013 7:43pm
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Subject: aqm Digest, Vol 1, Issue 7

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Today's Topics:

 1. Re: [tcpm] ECN support and usage on the Internet (Yuchung Cheng)
 2. Re: ECN support and usage on the Internet (Fred Baker (fred))
 3. Re: ??: [iccrg] [tcpm] ECN support and usage on the Internet
 (Jim Gettys)
 4. Re: ??: [iccrg] [tcpm] ECN support and usage on the Internet
 (Simon Barber)
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