AW: [e2e] Queue size of routers
David P. Reed
dpreed at reed.com
Mon Jan 20 06:56:18 PST 2003
At 11:46 AM 1/20/2003 +0100, Sebastian Zimmermann wrote:
>Doesn't RED allow us to define a "target" buffer size that is larger
If you just think about Little's theorem, the impact of RED is not to
stabilize the system around a "target buffer size".
Little's theorem says that when arrival rate grows, queue size grows
non-linearly, getting to infinity at the point where arrival rate = queue
size. This leads to a phase transition that propagates towards the
congestion sources, filling all the intervening buffers back from the point
What RED does is apply gradually increasing pressure to the arrival rate,
via drops, so that the congestion sources get the message more quickly,
while still allowing the system to absorb burstiness in its buffers.
ECN works even faster, because the simulated drops propagate faster. (in
fact, thinking about it, I wonder if flagging packets with ECN from the
front of their queue (rather than the tail) would provide a faster
congestion notification that would be worthwhile trying...).
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