[SIPForum-discussion] Offer/Answer Model

[雨 陈]

Hi Vivek,
  What I had mentioned 180/ACK modle is a flow with SDP negociation like this:
 
           User A         User B   
          |                       |              
          |   INVITE F1     |              
          |--------------------> |              
          | 180 [SDP] F2  |   Callee B offer the session discription first           
          |<-------------------- |             
          | 200 [SDP] F3  |   The same SDP Msg from User B .          
          |<-------------------- |              
          | ACK [SDP] F4 |   Caller A answer with his SDP Msg .       
          |--------------------->|              
          |                       | 
          |  RTP Media     |             
          |<======== =>|
  Well, it can be found in the process to create or modify a session. BTW, the User A and User B represent different brand of softswitch. 
   
  Any further dissucion? 
   
  Regards
   
  Nora

Vivek Batra <vivek7683 at gmail.com> 写道：
    Hi Nora,
As the possibilities of SDP negotiation stated by you, how can SDP be negotiated between 180 and ACK? Can you please explore??

--Vivek


  On Thu, Aug 21, 2008 at 6:12 AM, 雨 陈 <chen.yu26 at yahoo.com.cn> wrote:
    Hi,
  According to the practical call flow, it seem the offer/answer model of SDP exchange can be found in INVITE/180, INVITE/200, 180/ACK or 200/ACK, even though the 180 response is provisional and sometimes the followed 200 OK send the same SDP Msg to confirm it.
   
  Regards
   
  Nora
  

vijay kant gupta <vijaykant.it2002 at gmail.com> 写道：
    
      See in Offer Answer Model. if u send invite without SDP at that time ACK has to contain SDP for A party.
But if INVITE conatin SDP then 200 ok is Answer for Invite 
ACK is final ACKNOWLEDGE.
  On Wed, Aug 20, 2008 at 3:54 PM, zabi <mohamed.zabiulla at gmail.com> wrote:
              Dear All,
   
      As per my knoweldge, Offer/Answer can occur in INVITE/2XX/ACK.
   
  Given a Sip message containing SDP how do we differentiate whether it is an OFFER/ANSWER??
   
   
  Regards,
  Zabi
   
   








-- 
why run? you'll only die tired!! 
Zabi.


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