Subject: Re: [Sip] Difference between dialog and session in SIP?

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 03 Apr 2003 04:41:24 -0500

Patrick Lam wrote:
> Dear all:
> 
> I am a little confused about the concept of a dialog.  What exactly is
> the difference between a dialog and a session? 

A dialog is a sip relationship. A session is a media relationship.

> Does dialog mean a "call
> has already been setup" in the signaling sense, while a session mean the
> "media has already been setup" in the media sense?

Thats pretty much right.

> 
> Also, what does "part of a dialog" mean?  Are "INVITE", "ACK" and the
> responses considered "part of a dialog"?

Dialog represents state, which includes sequence numbers, route sets, 
and URIs. A request sent as part of a dialog means that it includes 
route headers from the route set of the dialog, and uses the next 
highest sequence number in the dialog.'

> 
> What does "outside the dialog" mean then?  Is a request is outside the
> dialog, does it still affect or change anything "inside the dialog"
> then?

Outside the dialog means that it is not within the context of a dialog. 
It doesnt use the callid, cseq, or route sets of any existing dialogs, 
and when such a reuqest is set, it has no impact on the state of an 
existing dialog.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Scientist                             Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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