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

Dave Taht <dave@taht.net> Sat, 20 July 2019 21:03 UTC

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From: Dave Taht <dave@taht.net>
To: Sebastian Moeller <moeller0@gmx.de>
Cc: Jonathan Morton <chromatix99@gmail.com>, "Black\, David" <David.Black@dell.com>, "tsvwg\@ietf.org" <tsvwg@ietf.org>, "ecn-sane\@lists.bufferbloat.net" <ecn-sane@lists.bufferbloat.net>, "De Schepper\, Koen \(Nokia - BE\/Antwerp\)" <koen.de_schepper@nokia-bell-labs.com>
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Date: Sat, 20 Jul 2019 14:02:48 -0700
In-Reply-To: <0079BC6B-4792-48ED-90D3-D9A69407F316@gmx.de> (Sebastian Moeller's message of "Sat, 20 Jul 2019 00:03:57 +0200")
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Subject: Re: [tsvwg] [Ecn-sane] Comments on L4S drafts
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Sebastian Moeller <moeller0@gmx.de> writes:

> Hi Jonathan,
>
>
>
>> On Jul 19, 2019, at 22:44, Jonathan Morton <chromatix99@gmail.com> wrote:
>> 
>>> On 19 Jul, 2019, at 4:06 pm, Black, David <David.Black@dell.com> 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.

+10

>
> Best Regards
> 	Sebastian
>
>
>
>> 
>> - Jonathan Morton
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