[tsvwg] L4S/3168 Coexistence

Martin Duke <martin.h.duke@gmail.com> Mon, 10 May 2021 16:49 UTC

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From: Martin Duke <martin.h.duke@gmail.com>
Date: Mon, 10 May 2021 09:49:41 -0700
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Subject: [tsvwg] L4S/3168 Coexistence
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(As an individual)

I have not been able to follow these threads as well as I'd like. Assuming
I'm not the only one, I would like to confirm that the current state of the
coexistence discussion is that L4S will create problems for "classic flows"
under the following conditions:

(1) There are 3168 routers in the path (order of 1%)
(2) These 3168 routers implement shared queues (no known examples, but it
might happen), AND
(3) The heuristics result in a false negative (<<1%?)

On the face of it (1% * 1%? * <<1%?) seems to be a small price to pay in
the aggregate. I hope we'd agree on that! So the argument against, ISTM,
would rest on two things:

(A) These failures are not uniformly distributed, and there is some
non-negligible use case that will suffer grievously. It would be very
helpful to me if someone could *concisely state* what this use case is and
where it exists. Nothing in the congestion control space is provably
optimal across all parameters and generalized fear that bad parameters
might exist somewhere is IMO not constructive.

(B) Because you can't have a vague MUST, we aren't REQUIRING any particular
limit to false negatives. If experiment participants are going to agree to
do something, I wonder if we can't converge on some words here that prevent
really dumb stuff?

Maybe I have this wrong! The debate is quite hard to follow.

Martin