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RE: HTTP/2 and TCP CWND

Gabriel Montenegro <Gabriel.Montenegro@microsoft.com> Fri, 12 April 2013 21:55 UTC

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From: Gabriel Montenegro <Gabriel.Montenegro@microsoft.com>
To: Roberto Peon <grmocg@gmail.com>, Robert Collins <robertc@squid-cache.org>
CC: Jitu Padhye <padhye@microsoft.com>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>, "Brian Raymor (MS OPEN TECH)" <Brian.Raymor@microsoft.com>, Rob Trace <Rob.Trace@microsoft.com>, Dave Thaler <dthaler@microsoft.com>, Martin Thomson <martin.thomson@skype.net>, "Eggert, Lars" <lars@netapp.com>, Martin Stiemerling <martin.stiemerling@neclab.eu>
Thread-Topic: HTTP/2 and TCP CWND
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Date: Fri, 12 Apr 2013 21:52:03 +0000
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Subject: RE: HTTP/2 and TCP CWND
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I've opened issue #65 to track what we should do about SETTINGS_CURRENT_CWND:
https://github.com/http2/http2-spec/issues/65

As for my opinion about what to do: I think we should delete this TCP congestion window setting from HTTP/2.0.

This is as out of scope as I've ever seen at the IETF. Modifying TCP (by modifying its contract to upper layers such as HTTP, and by modifying its state machine) is not something that can be done outside of the Transport Area. I'm cc-ing Lars Eggert and Martin Stiemerling (former and current Transport ADs), in case they have additional comments or clarifications.

Besides, as pointed out by Lars Eggert (cc-ed, along with Martin Stiemerling) in an offline exchange, there is a perfectly reasonable alternative progressing in the Transport Area's TCPM working group, namely, the proposal to bump up the TCP's initial congestion window to 10. This has undergone the rigorous review required of such a fundamental change, and is currently in the RFC editor's queue (so it's basically done):

https://datatracker.ietf.org/doc/draft-ietf-tcpm-initcwnd/

That exchange also confirmed my opinion that there is very little chance the IESG would allow SETTINGS_CURRENT_CWND to remain in the HTTP/2.0 spec. In the interest of optimizing community time (HTTPbis, HTTP/2.0 implementors, IESG, etc) I think eliminating this now so it does not appear in the first implementable draft makes sense.

Gabriel

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