Subject: RE: [Sip] Open Issue #58: Rejected mid-call SDP in 2xx

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 28 Aug 2001 16:45:24 -0400

> -----Original Message-----
> From: Bert Culpepper [mailto:[email-masked]]
> Sent: Thursday, August 23, 2001 3:11 PM
> To: 'Kim Liu'; 'Jonathan Rosenberg'
> Cc: [email-masked]
> Subject: RE: [Sip] Open Issue #58: Rejected mid-call SDP in 2xx
> 
> 
> How can it happen that B provides an offer that is not acceptable to A
> provided the UA complies with the first paragraph of B.4 in 
> bis-04?  If
> B does want to change, it should issue the re-INVITE. 

Well, the text does allow it to change. I suspect people might change the IP
address and port, just to allow differentiation of media sent from the far
side before and after the re-invite. In principal, that should not warrant a
rejection.

It may very well be that the simplest solution to this problem is simply to
change this SHOULD to a MUST; i.e., in a mid-call re-INVITE w/o SDP, the 2xx
MUST contain the "same" SDP as last provided to the peer, with the exception
of being able to change the IP address/port if so desired. 

I'm quite happy to do that, and would propose this as probably the best and
easiest solution. Objections?

(I'll admit, I don't know of a scenario off 
> hand where
> a UA would re-INVITE without SDP to see what the other side 
> will respond
> with.)

Its a classic third party call control scenario, and arises quite
frequently, actually, in order to connect the user to different media
sources during a call.

-Jonathan R.

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

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---

From: "Bert Culpepper" <[email-masked]>
Date: Tue, 28 Aug 2001 17:24:25 -0400

comments inline...

> From: Jonathan Rosenberg [mailto:[email-masked]]
> Sent: Tuesday, August 28, 2001 4:45 PM
> To: 'Bert Culpepper'; 'Kim Liu'; Jonathan Rosenberg
> Cc: [email-masked]

I agree, changing media destination should not cause a rejection.  And I
realize SHOULD is currently specified in the text.

> easiest solution. Objections?

I myself would like to see MUST, and agree that changing IP address/port
is OK.

> frequently, actually, in order to connect the user to different media

In these cases (3pcc), as the controller I would recommend a more
"assertive" behavior.  That is, send the desired SDP in the re-INVITE.
Re-INTIVEing with no SDP (without the above restrictions) is asking for
trouble in my opinion.  (Just to be clear, I can see INVITE w/o SDP
being very useful, but not re-INVITE.)

regards,
Bert