Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs

Jonathan Morton <> Thu, 07 November 2019 17:00 UTC

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From: Jonathan Morton <>
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Date: Thu, 7 Nov 2019 19:00:38 +0200
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To: Sebastian Moeller <>
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Subject: Re: [tsvwg] L4S status: #17 Interaction w/ FQ AQMs
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> On 7 Nov, 2019, at 6:47 pm, Sebastian Moeller <> wrote:
> [SM] I guess it is worth repeating that the obvious solution to all of these challenges would be to fix the actual root cause of the issue, instead of trying to paper over the symptoms. If L4S would not try to make the ECT(1) and the CE codepoint do the work that would require 2 independent bits neither issue 16 nor 17 would exist in the first place. I wonder how, after having eloquently argued for the requirement of strict isolation/separation between tcp-friendly and dctcp-style traffic, one could have converged on this clearly sub-optimal approach. 

> I have read the discussion of the alternatives in the L4S draft and while clearly none of the options is perfect, most have less undesirable side effects on normal traffic than the admittedly clever 'overload ECN codepoints' variant that currently is being pushed.

I'm reasonably sure that most if not all of L4S' purported goals can be met, without the need for these complex workarounds, by switching to SCE-type signalling.  If it is then still desired to implement a distinct traffic class for L4S traffic, that can be done by defining a PHB and assigning a DSCP to it.

This isn't exactly rocket surgery; the KISS principle applies.

 - Jonathan Morton