Subject: RE: [Sip] solving early media, HERFP, and unifying manyfolks

From: William Marshall <[email-masked]>
Date: Wed, 30 Jan 2002 18:04:24 -0500 (EST)

I'm in favor of adding text to bis to allow the offer/answer to take
place outside of the INVITE/200/ACK, as defined by extensions.

One problem identified in the previous manyfolks draft is that the
answer SDP, which appears in the 183, needed to be repeated in the
200 in order to comply with bis.  That leaves open the question
of handling it if it is different.  Text in manyfolks-03 stated that
further SDP MUST NOT change the agreed media definitions, and Rohan
pointed out problems with this statement in early media cases.
Removing the requirement that it be repeated is a far better solution.

This has implications for proxies (that want to know the final media
SDP) needing to understand the extensions.  I believe this can
be avoided with a restriction on extensions that the 'most recent' 
SDP within a dialog is 'most valid', and that such a proxy needs to 
Record-Route to guarantee seeing the final offer&answer.

Bill Marshall
[email-masked]

-----original message-----
Date: Wed, 30 Jan 2002 15:33:52 -0600
From: Alan Johnston <[email-masked]>
Subject: RE: [Sip] solving early media, HERFP, and unifying manyfolks
To: "'Jonathan Rosenberg'" <[email-masked]>,
        "'Sanjoy Sen'" <[email-masked]>
Cc: [email-masked]

Jonathan,

I'd like to try to focus the discussion on the issue of the moment
(literally) relating to bis.

While more discussion is needed before we can reach consensus on your
proposal, we need to agree right now if we want to make the one change
to bis to allow the possibility of this proposal.

Right now, bis says that a 200 OK MUST have SDP, either an answer if the
INVITE had an offer, or an offer if the INVITE did not, in which case
the answer will be in the ACK.

We would need to change bis to allow for the offer/answer to take place
outside of the INVITE/200/ACK exchange in an extension to SIP.  

I think it would be good to make this change, keeping the existing
offer/answer model but adding a statement that extensions may define new
ways of making offers or answers which could take the place of the bis
discussion.  Perhaps this change is needed even for manyfolks COMET not
to contradict bis?

Can we come to consensus on the list to agree to this change?

Thanks,
Alan Johnston
WorldCom
sip:[email-masked]

_______________________________________________
Sip mailing list  https://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: Jonathan Rosenberg <[email-masked]>
Date: Thu, 31 Jan 2002 01:17:22 -0500

William Marshall wrote:
> 200 in order to comply with bis. 

That would no longer be the case with the unify proposal. SDP could be
present in the 200 OK, but that would mean its an offer, with an answer
expected in ACK.

> That leaves open the question

Right; as I say above, you could put it there. It can be the same (O/A
allows you to send an offer that is the same as previous), or can be
different, but an answer would come in ACK in either case.

> Record-Route to guarantee seeing the final offer&answer.

Of course; thats not a change. If a proxy with rfc2543 wanted to see
media information, it would need to record-route, since it could always
change in a re-invite. There is no such thing as the "final" sdp, and
there never was.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
Chief Scientist                         First Floor
dynamicsoft                             East Hanover, NJ 07936
[email-masked]                 FAX: (973) 952-5050
http://www.jdrosen.net                  PH:  (973) 952-5000
http://www.dynamicsoft.com