[SIPForum-discussion] Is the preference codec 0 ?

[Stewart Bunce]

Nora,
 
The 200 OK from User B would seem to indicate that the re-INVITE from User A was sucessfull, meaning that the media was correctly re-negotiated (if it had failed I would have expected a 488 response). In practical terms this means that PCMU would be used in both directions for the RTP as it is the only common codec present.
.
Stew

-----Original Message-----
From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org]On Behalf Of chen.yu26 at yahoo.com.cn
Sent: 27 August 2008 10:54
To: group SIP
Subject: [SIPForum-discussion] Is the preference codec 0 ?


Hi All, 
there is a call flow of modifying session between two different softswitch:
User A           User B    
|  RTP Established   |
|<=============>|     
                   |  INVITE [SDP]       |  the offer SDP m= audio 9256 RTP/ATP 8 0 97          
                   |------------------------>|            
                   |             100               |
                   |<------------------------|          
                   |                                   |
                   |       200 [SDP]          |  the answer SDP m= audio 10054 RTP/AVP 0
                   |<------------------------|            
                   |            ACK             |  
                   |------------------------>|    
 
Well, according to RFC3264, the preference codec should be present at first. So, the User A would like to choose PT=8 (PCMA), while the User B just afford PT=0 (PCMU). 
 
MY QUESTION IS:  Did they modify the session sucessfully? and if so, is the audio codec they  had negotiated  PT=0 (PCMU) ?  
 
 
Thanks & Regards
 
Nora



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