Questions like this belong on the sip-implementors list.  If you wish to
have multiple media streams setup with one Invite, you include these
together in the SDP.  The Invite is bound for one UAS, and only that UAS may
respond with one final response (forking is another story).  Multiple OKs
from different UAS's to the UAC for specific media streams is not valid.
For User B to do what you show, it would probabally have to act as some sort
of B2BUA, and consolidate the response from User C with it's own when
sending a final response to User A.  This behavior is not covered in any
standard.

John Hearty
Level3

-----Original Message-----
From: Purcell Michael-QA3001 [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, December 05, 2001 8:49 AM
To: '[EMAIL PROTECTED]'
Cc: Purcell Michael-QA3001
Subject: [Sip] Multi-Media SIP Scenario


I cannot discover from the existing standards or drafts if the following
Multi-Media Scenario is to the SIP Standard:


Successful SIP to SIP with two Media

   User A          Proxy 1/User B    User C
     |                |                | 
     | INVITE(M1,M2)  |                | 
     |--------------->|    User B      |
     |                |--| Setup       |
     |                |<-|  M1         |
     |     OK(M1)     |                | 
     |<---------------|  INVITE(M2)    |
     |     ACK(M1)    |--------------->|    User C
     |--------------->|                |--| Setup       
     | RTP Media M1   |                |<-|  M2
     |<==============>|    OK(M2)      | 
     |     OK(M2)     |<---------------|
     |<---------------|                |        
     |     ACK(M2)    |                |
     |-------------------------------->|
     |                |                |
     |        RTP Media M2             |
     |<===============================>|
     

In this scenario, there are two media streams (M1, M2) connecting User A to
from two separate sources User B and User C. From User As perspective, both
media streams could be originating from the same source. 
  So the INVITE goes out asking for both media streams. The Proxy and User B
are co-located. User B forwards an INVITE for M2 to User C through it's
proxy interface and returns the OK for just M1. A Separate OK message for M2
is returned from User C to User A. The ACK for the second media stream (M2)
bypasses the proxy.

                Thanks Mike Purcell

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