[SIPForum-discussion] Regarding SDP in 180 and 200

Sword Chen swordchen at posteritytech.com
Tue Dec 18 04:29:18 UTC 2007

Hi, Man,

I don't think so, the 18X is not reliable response, so the UAC will take the 200 SDP when the called party answered.



after get the 180 message the UAC will decode the RTP in G729 format, and that is the same as the 183 message,
once the UAC got the 200 message, it must change the codec from G729 to G723. we ready tested this case.

  ----- Original Message ----- 
  From: Rajesh 
  To: discussion at sipforum.org 
  Sent: Tuesday, December 18, 2007 11:45 AM
  Subject: [SIPForum-discussion] Regarding SDP in 180 and 200

  Hi all,

    If SDP in 180 and 200 responses are different, How UAC should behave? According to RFC 3261 "If the initial offer is in an INVITE, the answer MUST be in a reliable non-failure message from UAS back to UAC which is correlated to that INVITE. For this specification, that is only the final 2xx response to that INVITE. That same exact answer MAY also be placed in any provisional responses sent prior to the answer. The UAC MUST treat the first session description it receives as the answer, and MUST ignore any session descriptions in subsequent responses to the initial INVITE."  


  What I understood from this one means, if SDP in 180 and 200 are different also, UAC will take SDP in 180 as answer. Is it like that? What will happen if 180 with SP is not sending reliably ?


  Thanks in Advance



  Rajesh K R

  Software Engineer

  Huawei Technologies





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