Subject: Re: [Sip] a question about offer/answer model

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 05 Dec 2003 15:53:34 -0500

Setting port numbers to zero rejects a STREAM, not the call per se. As 
such, there would be no bye, the call just proceeds without that 
stream. If none of the streams are acceptable, the answerer would 
reject the invite.

-Jonathan R.

Hu Yijun,BISC R&D SA(BJ) wrote:

> hi all,
>  
> I have a question about the SDP offer/answer model.
>  
> In the section 6 of rfc3264, it claimed that the answerer can reject an 
> offer stream by setting the port number to zero.
>  
> My question is: if an SDP offer, included in INVITE, is reject by the 
> answerer, and the corresponding SDP answer is included in 200 OK, then 
> how to deal with this answer in the offerer(UAC)? Should the UAC treat 
> it as a successful SDP negotiation, or send a BYE immediately after 
> sending the ACK?
> 
> -----------------------------------------------------------------------------
> Best regards,
> Hu Yijun
> BISC, R&D SA
> Tel.:+86-10-64346-660
> E-mail: [email-masked]
> 
>  

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: Paul Kyzivat <[email-masked]>
Date: Fri, 05 Dec 2003 16:05:04 -0500

Jonathan Rosenberg wrote:
> such, there would be no bye, the call just proceeds without that stream. 
> If none of the streams are acceptable, the answerer would reject the 
> invite.

Of course an answerer *could* reject all the streams without rejecting 
the call. This would leave a medialess call. Certainly not a common 
situation, but possible.

The answerer might do that with the thought of initiating a new 
offer/answer that it thinks might be more acceptable.

In such a situation, the initial offerer has multiple possibilities:
- send a BYE to terminate the dialog
- send a new offer (via reINVITE or UPDATE) and hope things go
   better
- just wait with no media and see what happens.

A UA like a phone, that sees this entire possibility as remote and to be 
avoided, should probably just be prepared to send a BYE in this case.

	Paul