RE: Call for Consensus: Frame size (to address #553)

On Monday,14 July 2014 11:21, phk@phk.freebsd.dk wrote:
> Why should we force applications for whom 256 is plenty to use something
> higher ?  Who gains anything by us doing so ?  And if we insist on some lower
> limit which is onerous for tiny devices, do you think they are going to spend 8
> times more for their microcontroller or ignore what we say ?

I think the issue can be broken down as follows:

1) What, if anything, is required if an endpoint's peer advertises a MAX_FRAME_SIZE *greater* than 16K?
2) What, if anything, is required if an endpoints' peer advertises a MAX_FRAME_SIZE *smaller* than 16K?

For 1), greater than 16K,
I think the answer is obvious.  The endpoint can either ignore the setting from its peer and continue using 16K as a max frame size, or if the endpoint so chooses, use larger frames up to the MAX_FRAME_SIZE declared by its peer.

For 2), smaller than 16K,
the answer is not so obvious.  I brought this up before, but it was ignored.  Is the endpoint allowed to continue using any frame size up to 16K, or is the endpoint *required* to honor MAX_FRAME_SIZE?

Allowing an endpoint to ignore settings below 16K makes the setting symmetric i.e. MAX_FRAME_SIZE is optional either way.  It also allows simple implementations to use a fixed 16K frame buffer and ignore the setting altogether.

On the other hand, resource-constrained implementations (e.g. IoT devices) would benefit, as PHK points out, from being able to use a much smaller frame buffer and force the peer to send frames that small.

-keith


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Received on Monday, 14 July 2014 13:43:00 UTC