[SIPForum-discussion] thanks!&&other queation about invite transaction

[雨 陈]

Herve,
  THANKS A LOT ! I am very pleasure that you answer my question so exactly.
   
  As you mentioned, I read the RFC3261 (13.3.1.4“The INVITE is Accepted”) again. The UAS do not use any timer ,but rather a retransmission mechanism for 200 OK before a ACK for this response is received. I got it.
   
  However, there are still some related puzzle about the invite transaction:
  1, the difference between session and dialogue. 
  Well, the end of the 13.3.1.4 points out: “If the server retransmits the 2xx response for 64*T1 seconds without receiving an ACK, the dialog is confirmed, but the session SHOULD be terminated.”
   
  I wonder why there are different treatment of 200 between session and dialog ?
  In my opinion, the session means one caller with many callees, more than two participants. While the dialogue is just point to point, two joiners. Is that right?  
   
  2. the terminating remark of invite transactions 
  the 3261 states that when the invite server transaction transmit the 200 response, it will move to the "Terminated" state. And the client transaction also enter to the same state since it receive the 200. 
   
  So, it seems to me that the ACK has no effect on the invite transactions (both client and server).Put it other way, the connection still can be built up , even if without the reception of ACK.
   
  Waiting for your kindly reply!
   
  Your sincerely
  Nora


       
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