Subject: Re: [Sip] Last Call - draft-ietf-sip-manyfolks-resource-02.txt

From: William Marshall <[email-masked]>
Date: Thu, 25 Oct 2001 10:17:34 -0400 (EDT)

Miguel wrote:
> Manyfolks should clearly state that the SDP returned in the 200 OK for the 
> INVITE MUST NOT be used to change the "agreed" SDP negotiated in the INVITE,
> 183 (and PRACK) process. The SDP in the 200 OK MUST be sent to allow backward
> compatibility of middle proxies, but not to change the SDP itself.

This principle will be incorporated in the next revision of the draft.
The same principle holds for the SDP contained in the COMET, and the
SDP contained in the ACK (if necessary).

One item we may need to address is what the behavior of the UA should be
if the other endpoint does not follow this requirement (the general rule
about strict adherence in what you send, generous about what you receive).

For example, if a UAC includes SDP in the INVITE, gets SDP back in 183,
but then gets a completely different SDP in the 200OK, what error recovery
can it take?  Anything better than BYE?  MUST the UAC examine the SDP
in the 200OK in the first place, or is that just a SHOULD?

Bill Marshall
[email-masked]

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---

From: "Miguel A. Garcia" <[email-masked]>
Date: Thu, 25 Oct 2001 17:31:21 +0300

> in the 200OK in the first place, or is that just a SHOULD?

If a UA changes the SDP when it is not allowed, it is definitely a protocol
violation. Perhaps we don't need to specify the action, the same as we don't
specify any other possible violations in the 2543bis. 

However, if there is some action to do, I would say that the SDP should be
ignored in that case, and the call should be established according to the 
agreed SDP.

/Miguel

-- 
Miguel-Angel Garcia                     Oy LM Ericsson AB
                                        Jorvas, Finland
mailto:[email-masked]     Phone:  +358 9 299 3553
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