I'm surprised to see that a fundamental concept "SIP Session" does not have
a clear definition documented anywhere. I was eagerly waiting for a IETF
Guru
to clarify this. I wish somebody writes a draft clarifying all the
undocumented
fundamental concepts in SIP. If i knew it all, i would have done it :-)
My 2 cents on it.
A Session is a Rendezvous Contract between 2 or more UA's for communnicating
with some modality. SIP dialog is a context over which such a Contract is
negotiated
decided, and upheld.
Normally the SDP Session Id should identify the Contract/Session. But not
necessarily
always. If its a multiparty the Conference ID would serve such a purpose.
I can get into a session with a non-INVITE dialog as well. Example:
SUBSCRIBE to
a specialized Event package. In this case some Identifier in the Event
package probably will
serve as the Session Id.
As you can see there can be more than 1 dialog related a Session.
But there is no documentation saying what exactly threads all the dialogs to
a Session except
the mentioning of a ID in the SDP RFC to identify the session being
described in a SDP.
My understanding is that a Session Identifier can take the form of
Conference ID or any
other depending on the method used to setup the rendezvoud/session.
Well, the above is my understanding of it, not based on any existing draft
or RFC, so i welcome
whatever corrections need be.
regards
Mahesh
----- Original Message -----
From: "Paul Kyzivat" <[EMAIL PROTECTED]>
To: "gaurav katiyar" <[EMAIL PROTECTED]>
Cc: <[email protected]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Tuesday, April 29, 2008 10:32 PM
Subject: Re: [Sip] [SIPForum-discussion] What's the difference between
session and dialog in SIP?
gaurav katiyar wrote:
Sip "Session Initiation Protocol". It talks about media session, i mean
how to initiate, modify and terminate a session and Dialog provides a
sort of context (like caller, callee, location, routing etc.) to modify
this session. So dialog is more related to route the sip message to
right node and body (SDP) handles media session if present. Dialogs may
have media sessions Or may not.
Take an example of B2BUA. It is a type of statefull proxy having two
dialog and one media session if doing media routing.
Maybe. IMO these concepts aren't sufficiently defined.
One view is that a session is whatever SDP describes. Thus its one
session regardless of how many media streams it contains. And in the
case of an SDP containing multicast media addresses, and possibly
advertised via SAP, there could be many participants in the same session.
But then in sip it takes a pair of SDPs to establish a call. Is that one
session, or two? And in your case above with the B2BUA, is it one
session, or two, or four?
Another view is that a session in the context of sip is whatever is
established as a result of an INVITE. Then I guess the pair of SDPs
together describe one session, regardless of how many media streams. But
in that case the B2BUA example would be two sessions.
Then consider a more complex case:
audio
/-------- C
/
A ========== B
audio \
video \-------- D
video
Here B is a B2BUA and media relay as in your example, but one stream is
relayed to C and the other to D.
In this case, how many sessions are there? A, C, and D each have one,
but are any of those the same? Or are there three altogether?
When I see "session" used, I just assume it means something vague, and
read on to see what is actually meant.
Paul
*/Donald Lee <[EMAIL PROTECTED]>/* wrote:
old good questions in sip, also add another "transaction".
On Fri, Apr 25, 2008 at 8:18 AM, å™å®—å�› <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
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
2008/4/24, Vijay K. Gurbani <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>:
> 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: [EMAIL PROTECTED]
<http://alcatel-lucent.com/>,bell-labs.com
<http://bell-labs.com/>,acm.org <http://acm.org/>}
> WWW: http://www.alcatel-lucent.com/bell-labs
>
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