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

Robert Sparks rjsparks at nostrum.com
Fri Jul 13 13:27:03 UTC 2007

The session is the thing being described with the SDP (The Session  
Description Protocol).
It is identified (in each direction) by the session_id in the o= line  
of the offer and the answer.

The SIP working group is arguing right now about whether the  
session_id for the session
related to a given dialog has to remain constant. Its looking like  
the answer will be yes
(and that's what Jonathan says he had in mind).

You should, if you haven't already, read the dialogusage and  
offeranswer drafts in SIPPING.
You'll note that the dialog you're talking about has one session  
usage (a dialog can have at most one
session usage), and that usage has a session (or you could argue a  
pair of sessions, one in
each direction). Streams can be altered or additional streams can be  
added during the lifetime
of that session.


On Jul 13, 2007, at 12:41 AM, chandan kumar anjani wrote:

> Hi,
> 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.
> Regards
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