[SIPForum-discussion] A query regarding the session and dialog in SIP

sreekant nair sreekant_nair at yahoo.com
Fri Jul 13 12:54:52 UTC 2007

Hi Chandan, 

Are there some specific references that you can mention where these two terms have been used which is leading to the confusion? That would  make it easier. 

As far as I can explain, they are both synonyms of the same. The dialog is a slightly more technical representation of a session and is specific to the stateful proxy or UA that is trying to establish a session with another agent. So u can see that they essentially the same. 

Another way of looking at it could be with the SDP carried by some of the SIP Messages. The SDP being used to describe the parameters used to set up the actual media session while the SIP messages form the signalling used to convey the SDP. 

A dialog can have multiple transactions (combination of [Request - provisional response - .....- final response] ). For all these requests and responses, as you mentioned the  CallId and Tags remain the same.  

As you mention towards the end, the session is established, when the SDP(also called as OFFER) sent in the INVITE is acknowledged by the SDP (ANSWER) in either the 18X or 200OK message. However, this can be modified by additional SDPs conveyed in subsequent Request-Response pairs (For e.g UPDATE or Re-INVITE). This is termed as modying the established session. 

Not sure if I helped clear the mess or add to it. 


----- Original Message ----
From: chandan kumar anjani <chandan.anjani at gmail.com>
To: discussion at sipforum.org
Sent: Friday, July 13, 2007 1:41:10 AM
Subject: [SIPForum-discussion] A query regarding the session and dialog in SIP



I had a query like what is the difference b/w session and a dialog.

like a session can have multiple dialog or a dialog can have multiple session.


As i know a dialog is identified by CALL-ID,To_tag,From_tag


and i a particular call all the three remains the same.


And abt the session , a session is termed to be established when we receive 200OK for the INVITE.




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