Subject: [Sip] Comment on draft-ietf-sip-rfc2543bis-05

From: Paul Kyzivat <[email-masked]>
Date: Fri, 26 Oct 2001 16:33:36 -0400

I haven't read the whole draft yet, but I did read
draft-rosenberg-mmusic-sdp-offer-answer-00, and found something there
that needs to be addressed in the bis. I just want to post it before I
forget.

You have now introduced the notion of an offer and an answer, that get
mapped onto SDP via draft-rosenberg-mmusic-sdp-offer-answer-00. However
in splitting the documents I think you have introduced a subtle change.
This has to do with how to determine if the INVITE contains an offer.

Bis-04, section 5.1, says "The caller MAY choose to omit the request
body (i.e., not send a session description) OR SEND A SESSION
DESCRIPTION THAT DOES NOT LIST ANY MEDIA TYPES. This indicates that the
caller does not know its desired media characteristics until the call
has been accepted."

When I read this in the past I concluded that it meant it is permissible
to send an SDP body containing a description without any m lines, and
this should not be considered to be an offer. Now bis-05 (based on a
quick search) no longer says this. In section 13.2.1 it says "The first,
... is that the INVITE contains the offer. ... A second model is that
the INVITE contains no session description, the 2xx response contains
the offer, and the ACK contains the answer." 

This no longer permits an SDP body without m lines, that isn't an offer.
(Not surprising, because it would be difficult to describe this
situation without getting into the details of SDP.)

Personally, I think this change is a considerable *improvement*, and I
am happy to see it made. But it *is* a change, and probably ought to be
discussed, if it hasn't been already.

	Paul Kyzivat

_______________________________________________
Sip mailing list  http://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: Gonzalo Camarillo <[email-masked]>
Date: Mon, 29 Oct 2001 19:25:17 +0200

Hello,

> discussed, if it hasn't been already.

I believe that this has already been discussed for a while. Even in
MMUSIC we had to change considerably the FID draft (3 or 4 IETF meetings
ago) because SIP did not allow three SDPs in the INVITE-200 OK-ACK
hand-shake anymore. I do not think this merits further discussions.

Regards,

Gonzalo
-- 
Gonzalo Camarillo                    Phone :   +1 212 939 71 71
Columbia University                  Mobile:  +358 40 702 35 35
472 Computer Science Building        Fax   :  +358  9 299 30 52
1214 Amsterdam Ave., Mail Code 0401  http://www.hut.fi/~gonzalo
New York, NY 10027                   
USA                              [email-masked]