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Re: [tsvwg] L4S: Guard DSCP

Jonathan Morton <chromatix99@gmail.com> Mon, 03 May 2021 06:34 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
In-Reply-To: <HE1PR0701MB22999B42745A0881726AD185C25B9@HE1PR0701MB2299.eurprd07.prod.outlook.com>
Date: Mon, 03 May 2021 09:33:47 +0300
Cc: Greg White <g.white@CableLabs.com>, TSVWG <tsvwg@ietf.org>
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To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
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Subject: Re: [tsvwg] L4S: Guard DSCP
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> On 3 May, 2021, at 9:21 am, Ingemar Johansson S <ingemar.s.johansson@ericsson.com> wrote:
> 
> This discussion appears to run in circles and each time it delves into all sorts of problems flow aware AQMs will/may see when L4S experiments are run. The obvious solution would be to fix these issues as already pointed out by Greg earlier in this mail thread but that appears to be completely out of the question. 

No - the discussion goes in circles because you (in the plural) refuse to accept that L4S is the *cause* of the problem.  I have been consistent in pointing that out, however tiresome it becomes to repeat myself, because it is simply and demonstrably true.

Notice, for example, that just plain Codel - without the FQ - is an example of the "single queue RFC-3168 AQM" that is *guaranteed* to have problems with L4S, while there are merely *some* circumstances where fq_codel is unable to supply a workaround.  So FQ is not the villain in this piece.

The fact is that fq_codel and Cake are out there, and together constitute the majority, at this time, of ECN AQM deployment.  That is the environment which L4S must interact appropriately with if it is to deployed on the Internet.  Even if we started changing them to accommodate L4S today, the existing deployments will not be eliminated for many years - by which time L4S will be a forgotten footnote in the annals of abject failure.

 - Jonathan Morton

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