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Re: [tsvwg] new tests of L4S RTT fairness and intra-flow latency

Jonathan Morton <chromatix99@gmail.com> Sun, 15 November 2020 13:24 UTC

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From: Jonathan Morton <chromatix99@gmail.com>
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Date: Sun, 15 Nov 2020 15:23:32 +0200
Cc: tsvwg IETF list <tsvwg@ietf.org>, Pete Heist <pete@heistp.net>
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To: "alex.burr@ealdwulf.org.uk" <alex.burr@ealdwulf.org.uk>
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Subject: Re: [tsvwg] new tests of L4S RTT fairness and intra-flow latency
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> On 15 Nov, 2020, at 3:06 pm, alex.burr@ealdwulf.org.uk wrote:
> 
> Maybe I've missed it, but I don't see whether these tests were run against a version of TCP-Prague having the RTT-independence workaround mentioned during interim-2020-tsvwg-01 [1], and if so what its mode was. Can you clarify that?

We're using the latest version of the L4S kernel, with any TCP Prague-specific parameters left at the default setting.  Looking at the code, the default appears to disable the 15ms RTT bias embedded in TCP Prague, which as you note was proposed to counter the bias imposed by DualPI2.

But even if that were enabled, it's a nasty workaround which addresses only one aspect of the unfairness we show in our results.

 - Jonathan Morton

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