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Re: [tsvwg] explanation of option 3 choice

Jonathan Morton <chromatix99@gmail.com> Sun, 17 May 2020 21:53 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Mon, 18 May 2020 00:53:48 +0300
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To: Tom Henderson <tomh@tomh.org>
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Subject: Re: [tsvwg] explanation of option 3 choice
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> On 17 May, 2020, at 8:06 pm, Tom Henderson <tomh@tomh.org> wrote:
> 
> For SCE, the reliance on DSCP-based classification will cause legacy/classic and low latency flows to end up more often in the same queue, and SCE-enabled flows could end up with worse performance than legacy/classic flows.  Can SCE results be presented that show the performance of competing flows (legacy/classic and SCE) in shared queues, but with the SCE classification disabled?

To immediately address one of your points, SCE does not rely on a DSCP to obtain congestion safety; it is only our suggested mechanism for achieving the "ultra low latency" that L4S touts, on those relatively few networks and applications that can genuinely benefit from it.

I do appreciate your healthy skepticism over this matter.  However, we have indeed presented some results that show SCE and non-SCE flows competing in a single queue, both with SCE signalling enabled, and on a legacy network:




Note that even through the first plot above says "Twin-CodelAF", this run on an 80ms path omitted the DSCP classifier, which was only applied to the SCE flow in the run on a 20ms path.  Both of the above plots are taken from the report we published immediately prior to the virtual meeting, but show results that we also presented at the earlier virtual meeting in March.

CodelAF is a system that we plan to improve further, to hopefully eliminate the 2:1 throughput ratio currently seen.  Nevertheless, the above is what we are able to demonstrate right now.

 - Jonathan Morton

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