Re: [tcpm] WGLC for draft-ietf-tcpm-hystartplusplus-04

Neal Cardwell <ncardwell@google.com> Mon, 02 May 2022 15:00 UTC

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From: Neal Cardwell <ncardwell@google.com>
Date: Mon, 2 May 2022 11:00:17 -0400
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To: Michael Tuexen <tuexen@fh-muenster.de>
Cc: tcpm IETF list <tcpm@ietf.org>, Randall Stewart <rrs@netflix.com>
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Subject: Re: [tcpm] WGLC for draft-ietf-tcpm-hystartplusplus-04
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On Wed, Apr 13, 2022 at 4:19 PM Michael Tuexen <tuexen@fh-muenster.de> wrote:
>
> Dear all,
>
> this e-mail starts the working group last call for draft-ietf-tcpm-hystartplusplus-04.
>
> The WGLC runs until Friday, May 6th 2022.
>
> Please send any comments, including indications to support this document,
> to the TCMP mailing list by then.
>
> The ID is available at
> https://www.ietf.org/archive/id/draft-ietf-tcpm-hystartplusplus-04.html
>
> Best regards
> Michael

I am generally supportive of this draft advancing, but do want to put
a word in about the application-limited issue Randall mentioned again
earlier in this thread. After the algorithm exits slow start, it seems
like it is likely to oscillate between:

(a) application-limited periods that cause low RTT samples and a
re-entry into slow start ("if current round's minRTT drops below
baseline indicating that HyStart exit was spurious"), and then

(b) non-application-limited periods that will cause a re-exit of
slow-start and re-entry into CSS.

It seems like the algorithm should either be adjusted to avoid this,
or this expected oscillation dynamic should be documented.

best regards,
neal