Subject: Re: [aqm] real traffic, network and highway (was aqm Digest, Vol 1, Issue 16)

From: [email-masked]
Date: Tue, 26 Mar 2013 15:34:00 -0400 (EDT)

A small standing queue of approximately 1/2 packet for the bottleneck link would not work for either ECN or RED, and neither can get close to that - because by the time either one actually signals congestion (bit or drop), there are far more than one packet in the queue.
 
As far as a highway operating at high speed maximizing cars per hour, that's plain wrong.   But here's the mistake I think you are making.  You are assuming all cars are already on the highway, it is infinitely long, and *there are no onramps and offramps*, probably.
 
But *real* traffic in real cities is NEVER in that state (OK, maybe once in a million years by accident).  Several have quoted to me things about traffic that are manifestly *not* true in complex city highway systems at any time of the day as "truth".  Only in a trivial model system - used for teaching simple principles, not reflecting actual traffic.
 
So here's the deal regarding network traffic: you all seem to focus on lots of "steady state" flows, and also assume that the variations are "stationary random processes", typically with Gaussian-family distributions.
 
No computer programs behave like that.  No interactive systems behave like that.  Even YouTube uploads and downloads don't behave like that!  (people don't all start their uploads at 7 pm, and go have dinner - they generally have a very fat-tailed distribution of starts and stops).
 
One might think that "fractal" or non-stationary distributions are the rare case - because that is how elementary probability is *taught*.   But they are the common case (except in casinos, which is the rare exception, not the model system)!
 
So, we can have a conversation about the real world and the real Internet, OR we can have a conversation about "benchmark land"  (the favorite networking hangout of academia, and most IETFers).
 
As an engineer, I prefer to discuss the real world and the real Internet. Whether ECN or RED work well in simplified model systems with stationary random processes (and no applications or humans) is a nice topic for a theoretical PhD thesis.  But a better *engineering* PhD thesis would actually work on the Internet as it is, and those who actually build equipment should only work on such problems.
 
In the old days, ECN might have been OK, because the end-to-end delays due to running on 50 Kb/sec ARPANET were quite long.  But today the end-to-end delays are under 50 msec, so little queues at bottleneck links really, really matter.

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From: [email-masked]
Sent: Tuesday, March 26, 2013 3:00pm
To: [email-masked]
Subject: aqm Digest, Vol 1, Issue 16

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Today's Topics:

 1. Re: aqm Digest, Vol 1, Issue 7 (Mikael Abrahamsson)
 2. Re: aqm Digest, Vol 1, Issue 7 (Scheffenegger, Richard)
 3. Re: [tsvwg] [Bloat] how much of a problem is buffer	bloat
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 4. Re: aqm Digest, Vol 1, Issue 7 (Joe Touch)
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