Subject: Re: Kicking TCP

From: Vernon Schryver <[email-masked]>
Date: Fri, 10 Mar 2000 12:52:27 -0700 (MST)

> From: Phil Karn <[email-masked]>

> >of my knowledge, there's nothing inherent in the RED scheme that
> >requires randomly choosing a packet currently *in* the queue for
> >dropping. (A minor optimization is to use the arrival of a new
>
> I thought it did, but it's been a while since I read up on it.

The idea behind random drop (or so I think, and my recent words make my
thoughts very suspect) is to make the probability that any stream loses
a packet increase with the number of packets that the stream has in the
queue.  If you follow the easiest and old tactic of always dropping the
newest packet, then greedy bursty streams get an unfair advantage.

It's not very random to always drop the oldest or the newest, and not
much better to choose randomly between the oldest and the newest packet
(unless your queue has depth of 1, but no one cares about that case).

Vernon Schryver    [email-masked]

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From: William D Ivancic <[email-masked]>
Date: Fri, 10 Mar 2000 15:22:54 -0500

Regarding WRED, I believe you randomly drop at the input to the queue.  You
start dropping slowly and randomly at a predefined threshold and continue
dropping more aggressively as the queue gets closer to its high limit at
which point you take some other action (drop, reset precedence, put into
another queue, or whatever else the specification allows and the router is
capable of).

Will Ivancic  [email-masked]