Subject: Re: [bmwg] [Sip] What's the difference between session and dialog in SIP?

From: "Vijay K. Gurbani" <[email-masked]>
Date: Thu, 24 Apr 2008 09:00:48 -0500

There is some work progressing in the BMWG WG to create performance
metrics around SIP.  One of the first tasks in such an endeavor
is to define the notion of dialogs and sessions.  Please see
Section 3.1.1 of
https://svn.resiprocate.org/rep/ietf-drafts/gurbani/bmwg-sip-bench-term/draft-ietf-bmwg-sip-term-00.txt
of the above draft for some insight.

Ëï×Ú¾ý wrote:
> Hi, Lincoln
> 
> thanks for your instructions.
> 
> I know that dialog can exist without session since SUBSCRIBE/REFER can
> create dialog and without any media between communication peers.
> 
> What I want to know is the relationship of dialog and session when
> they both exist in one communication activity. Take a example, when
> there are 2 person participating talks with voice, we say there is a
> dialog and a session.
> 
> But when one caller invites another callee and gets five 200 final
> responses from 5 UA every of which has its own session description. We
> can say that there are 5 dialogs between caller and the other 5
> callees, right? And then what is the exact number of session in this
> scenario? One session or five session? That is what I want to know.
> 
> Dialog is determined by dialogID (call-id, from/to tag) and session id
> is determined by session id given in the SDP message.  My answer is
> there are 5 dialog and one session now, right?

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane, Rm. 9F-546, Lisle, Illinois 60532 (USA)
Email: vkg@{alcatel-lucent.com,bell-labs.com,acm.org}
WWW:   http://www.alcatel-lucent.com/bell-labs
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From: "孙宗君" <[email-masked]>
Date: Fri, 25 Apr 2008 08:18:19 +0800

Hi, Vijay

Thanks very much for your timely answers.

From this specification,  session is a combination of signaling plane
and media plane messages and processes that enable two or more
participants to communicate. I think session is a larger scope than
dialog. In another word, one session can contain more than one dialog.
Is what I understand right?

Zongjun