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Re: [tsvwg] L4S DSCP (was: L4S drafts: Next Steps)

Jonathan Morton <chromatix99@gmail.com> Tue, 30 March 2021 17:47 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
In-Reply-To: <352bf0e9-aa72-127f-a3ff-8c4d3eea821d@bobbriscoe.net>
Date: Tue, 30 Mar 2021 20:47:00 +0300
Cc: Sebastian Moeller <moeller0@gmx.de>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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To: Bob Briscoe <in@bobbriscoe.net>
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Subject: Re: [tsvwg] L4S DSCP (was: L4S drafts: Next Steps)
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> On 30 Mar, 2021, at 11:21 am, Bob Briscoe <in@bobbriscoe.net> wrote:
> 
> L4S does not involve a DSCP, so there is no need to discuss DSCPs in l4sops.

Okay, so what mechanism do you propose to contain the L4S experiment to the participating networks?

> The tunnel issue was central to the choice of the L4S identifier - you will find it mentioned all over the ecn-l4s-id draft.

Yes, you've gone to a lot of trouble to make sure that L4S traffic is identified to the network in many different situations.  But the problems all have to do with networks that don't know to look for that identifier, even though it is present and correct on the traffic in question.  That's why the experiment has to be contained to networks that do.

Ultimately the problems arise because the network does not identify to the receiver what type of congestion signal it is producing.  You can only detect that indirectly through heuristics and probing, and (so far) not at all reliably.  We have been waiting for a solution to that deficiency since it was formally raised at Montreal.

Focus on these problems, and we might get somewhere.  Dismiss them, and you will fail.

 - Jonathan Morton

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