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Re: [tsvwg] plan for L4S issue #29

Jonathan Morton <chromatix99@gmail.com> Thu, 01 October 2020 13:25 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Thu, 01 Oct 2020 16:24:57 +0300
Cc: Mikael Abrahamsson <swmike=40swm.pp.se@dmarc.ietf.org>, Gorry Fairhurst <gorry@erg.abdn.ac.uk>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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References: <202009291549.08TFnvFV068509@gndrsh.dnsmgr.net> <c7080365-233c-5f1e-ef5c-1f42c969042a@erg.abdn.ac.uk> <73562E45-3EE7-43D4-B26B-76478AE19AF8@cablelabs.com> <ae5eb008118ab1b88d65e7712a5e3c54b4207e52.camel@heistp.net> <28cd9795-5b04-4ecb-6e8c-2e12e476f034@erg.abdn.ac.uk> <alpine.DEB.2.20.2010011436510.15604@uplift.swm.pp.se> <D19117FC-24F5-477C-8431-0CFCBCA6FE04@gmail.com> <B64A9A8E-9664-4EC6-8D5E-26C8AA464BB1@gmx.de>
To: Sebastian Moeller <moeller0@gmx.de>
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Subject: Re: [tsvwg] plan for L4S issue #29
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> On 1 Oct, 2020, at 4:16 pm, Sebastian Moeller <moeller0@gmx.de> wrote:
> 
> This seems driven by the fact that according to the RFC the dual queue coupled AQ actually is set up with a 1:16 or 1:15 worst case split between the L4S and the non-L4S queue. The idea seems to be to have that as a backstop to avoid "starvation", but only for very peculiar definition of starvation. IMHO differences >= 1:8 over the expected equitable share are clear cut cases of starvation and need to be avoided. 

I suppose we also have to distinguish between the behaviour when the bottleneck is L4S enabled, and when it is not L4S enabled but is ECN enabled, and also when neither L4S nor ECN are enabled.  A robust solution would be one that behaves well in all three cases.

Presently, the 1:16 ratio approximately applies in both the first two cases (but for different reasons) when the baseline path length is short, and is only avoided in the last one where both conventional and L4S flows exhibit an AIMD response to losses.

 - Jonathan Morton

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