[SIPForum-discussion] How does the SDP offer and answer works

[Mark Holloway]

If A is a media gateway and B is a SIP subscriber, usually the gateway will
honor the preferred codec of the subscriber.    Thus meaning A is just
informing B of what he is capable of, but if B responds with rtpmap: 8
(G729) first and 0 (G711) second in the 200 OK, the call will be setup as
G729a (unless B also states annexb=yes, then it will be G729b).  

 

From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of arun kumar
Sent: Thursday, January 17, 2008 2:32 AM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] How does the SDP offer and answer works

 

Hi can any one can guide me in this

 

 

       A---------INVITE/SDP----------> B

 

      The SDP offer  has the following 

                m= audio 49170 RTP/ AVP 0 8

              a= rtpmap: 0 PCMU/8000

             a= rtpmap: 8 PCMA/8000

                   m= video 49172 RTP/AVP 32

                   a= rtpmap: 32 MPV/90000

 

    A<-----------200OK-------B

 

                B also supports all the media and codec types provided in
the SDP offer of A

 

So what will be the SDP answer of B, will it send all the medai and codec
supported by itself ?

 

my question is who will select the media & codec for the Media session
establishment between  A & B, if more than  1 suitable codec matches between
the endpoints which codec is selected and on what basis is it done. 

 

 
 
 
v = 0
 
                      
 
 
                      





-- 


With Regards






Arun Kumar .P 
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