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Re: proposed WINDOW_UPDATE text for session flow control windows

From: Mark Nottingham <mnot@mnot.net>
Date: Tue, 26 Feb 2013 12:00:41 +1100
Cc: Roberto Peon <grmocg@gmail.com>, William Chan (ι™ˆζ™Ίζ˜Œ) <willchan@chromium.org>, Patrick McManus <mcmanus@ducksong.com>, HTTP Working Group <ietf-http-wg@w3.org>
Message-Id: <A89944B3-8BB6-4B09-AF80-4F2C683A14EF@mnot.net>
To: Martin Thomson <martin.thomson@gmail.com>
Opening as:
  https://github.com/http2/http2-spec/issues/44
... and marking as ready for the editors to have a kick at it.

Regards,


On 21/02/2013, at 10:00 AM, Martin Thomson <martin.thomson@gmail.com> wrote:

> On 20 February 2013 14:52, Roberto Peon <grmocg@gmail.com> wrote:
>> I'm afraid of simply sending a large window size, because I suspect that
>> simple implementations will mess it up for objects > 31 bits in size.
> 
> Yes. Absolutely.
> 
>> If we don't have a SETTINGS thing, then we're requiring flow control for the
>> first RT for any stream.
> 
> Yes, that's the implication.  Though a client is always able to
> disable flow control without consequence, because it speaks first,
> before the server sends anything.  It's only servers that need to
> worry about having it on briefly.  The consequences are minimal - they
> just don't receive as many packets as they possibly could - but then
> that is always true for two reasons: TCP INIT CWD and the time it
> takes to send the WINDOW_UPDATE.
> 
>> I like the flag solely because it is difficult to do by accident, unlike
>> using zero (which is technically fine otherwise)
> 
> I don't believe in accidents, but I see your point.
> 
>> The other thing to consider is when, if ever, one can transition from
>> flow-control disabled to requiring its use again.
>> Even if we don't allow this, it will require text explaining it.
> 
> I thought about this.  The obvious choice is to start again from zero
> when a WINDOW_UPDATE comes in.  The problem is knowing (at the
> receiver end) when counting started.  Once you stop counting, that's
> the real difficulty.  I believe that once it's off, flow control will
> need to stay off.

--
Mark Nottingham   http://www.mnot.net/
Received on Tuesday, 26 February 2013 01:03:27 GMT

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