Subject: FW: [SIP] wg last call on reliable provisional responses

From: "Schroeder, Tim" <[email-masked]>
Date: Wed, 31 May 2000 15:28:25 -0500

James Undery writes:
I think what is being hinted at albeit subtlety is, is the transaction ever
going to end? (The Halting Problem.) Although I can't think of a case off
hand where you'd want to provisionally respond to a PRACK, specifically
allowing it is just asking for trouble between legitimate implementations.
[...] Except it may spawn another PRACK that spawns another PRACK ad
infinitum.

I was going to write in support of reliable provisional responses for PRACK,
but I think this sways me over to the opposition.  One could get one's self
into a fair amount of trouble receiving a PRACK and sending a reliable
provisional response that results in receiving another PRACK, etc.

This would also address my previous comment about mandating Require: 100rel
or Supported: 100rel in a PRACK message, rather than relying on the presence
of PRACK to imply support.  The UAC could of course include the Require or
Supported header if it chose, but it'd be moot because the UAS would not be
allowed to send a reliable provisional response.  The UAS would therefore
not be allowed to put the Require: 100rel in a provisional response to a
PRACK.

Tim Schroeder
[email-masked]
SBC Technology Resources, 9505 Arboretum Blvd., Austin, TX  78759

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