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Re: Questions on Frame Size

From: Shigeki Ohtsu <ohtsu@iij.ad.jp>
Date: Fri, 21 Jun 2013 07:29:18 +0900
Message-ID: <51C3823E.7010706@iij.ad.jp>
To: ietf-http-wg@w3.org
Sorry, I replied this only to James.  Re-sent it to WG again.

(2013/06/21 1:29), James M Snell wrote:
> My understanding is...
> When PUSH_PROMISE is used for HTTP, then yes, it would be limited to 16k.
> When PUSH_PROMISE is used for any protocol other than HTTP, it could
> be up to 64k.
> We are defining the Framing Layer separately from the HTTP Layer in
> order to allow other protocols to be built on top of the framing layer
> at some point.

The spec would be applied to other protocols like SPDY but we should not
discuss it here because in "1.1 Document Organization" it says that

"While some of the framing layer concepts are isolated from HTTP, building
a generic framing layer has not been a goal. The framing layer is tailored
to the needs of the HTTP protocol and server push. "


"However, the ability to reuse the HTTP/2.0 framing layer is a non goal. "
in "5.1 Separation of Framing Layer and Application Layer "

We should start discussion at first whether we change them or not.

> On Wed, Jun 19, 2013 at 10:32 PM, Shigeki Ohtsu <ohtsu@iij.ad.jp> wrote:
>> Hi,
>> The issues about frame size were discussed and might had some
>> agreements at SF interium but please let me ask some questions on the
>> current spec of "3.3.2 Frame Size" which is updated by
>> https://github.com/http2/http2-spec/commit/fd703b572cfc527582c0716e59f2c4044ae195a8
>> 1. "For instance, individual DATA and HEADERS frames used to express
>> HTTP request and response messages (see Section 4) are not permitted
>> to exceed 16,383 octets of payload."
>> PUSH_PROMISE is not listed.
>> Is the data size of PUSH_PROMISE also limited to 16K or is it exceptional
>> for some reason?
>> 2. "The absolute maximum amount of payload data any individual frame
>>   can contain is 65,535 octets. All implementations SHOULD be capable
>>   of receiving and minimally processing frames up to this size."
>> If PUSH_PROMISE has a 16K limit, the max frame size is still 64K,
>> however, any other frames besides DATA, HEADERS and PUSH_PROMISE
>> are only several octets at most.
>> Is it for the future extension not to change the frame length to 14bit?
>> If so, why the spec requires all implementations to support the 64K frame
>>   size only for the future extension?
>> Regards,
Received on Thursday, 20 June 2013 22:29:46 UTC

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