Subject: [AVT] Is "congestion collapse" misleading?

From: Eddie Kohler <[email-masked]>
Date: Tue, 02 Dec 2003 16:21:19 -0800

There was a discussion earlier about whether "congestion collapse" is a
fair description of the situation when nonresponsive UDP flows cause TCP
bandwidth to suffer.

Well, the *situation* is a problem, and local administration cannot correct
it.

Say that S is sending a nonresponsive flow to R.  At the same time A is
sending a responsive flow to B.  S-R and A-B share parts of a path.

    S ------+----------+-----> R
            |          |
            |          v
            A          B

S-R experiences a high loss rate, say somewhere between A and R.  Sure, R's
administrator can take steps to prevent other flows from/to R from
degrading.  But the A-B flow is affected too; and depending on loss rates
and bandwidths, the A-B flow might "collapse", since S-R doesn't respond to
loss rates.

The user at R might or might not stop the flow.  Anyway, we can't count on
them.

The Internet architecture should support this kind of topology, which isn't
entirely unusual in practice.

Eddie

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