Re: [tsvwg] [Ecn-sane] Comments on L4S drafts

Sebastian Moeller <> Fri, 19 July 2019 22:04 UTC

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From: Sebastian Moeller <>
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Date: Sat, 20 Jul 2019 00:03:57 +0200
Cc: "Black, David" <>, "" <>, "" <>, Dave Taht <>, "De Schepper, Koen (Nokia - BE/Antwerp)" <>
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To: Jonathan Morton <>
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Subject: Re: [tsvwg] [Ecn-sane] Comments on L4S drafts
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Hi Jonathan,

> On Jul 19, 2019, at 22:44, Jonathan Morton <> wrote:
>> On 19 Jul, 2019, at 4:06 pm, Black, David <> wrote:
>> To be clear on what I have in mind:
>> 	o Unacceptable: All traffic marked with ECT(1) goes into the L4S queue, independent of what DSCP it is marked with.
>> 	o Acceptable:  There's an operator-configurable list of DSCPs that support an L4S service - traffic marked with ECT(1) goes into the L4S queue if and only if that traffic is also marked with a DSCP that is on the operator's DSCPs-for-L4S list.
> I take it, in the latter case, that this increases the cases in which L4S endpoints would need to detect that they are not receiving L4S signals, but RFC-3168 signals.  The current lack of such a mechanism therefore remains concerning.  For comparison, SCE inherently retains such a mechanism by putting the RFC-3168 and high-fidelity signals on different ECN codepoints.
> So I'm pleased to hear that the L4S team will be at the hackathon with a demo setup.  Hopefully we will be able to obtain comparative test results, using the same test scripts as we use on SCE, and also insert an RFC-3168 single queue AQM into their network to demonstrate what actually happens in that case.  I think that the results will be illuminating for all concerned.

	What I really would like to see, how L4S endpoints will deal with post-bottleneck ingress shaping by an RFC3168 -compliant FQ-AQM. I know the experts here deems this not even a theoretical concern, but I really really want to see data, that L4S flows will not crowd out the more reactive RFC3168 flows in that situation. This is the set-up quite a number of latency sensitive end-users actually use to "debloat" the internet and it would be nice to have real data showing that this is not a concern.

Best Regards

> - Jonathan Morton
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