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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 <baolovebao at gmail.com>/* wrote:

    old good questions in sip, also add another "transaction".


    On Fri, Apr 25, 2008 at 8:18 AM, 孙宗� <szj087 at gmail.com
    <mailto:szj087 at gmail.com>> 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 <vkg at alcatel-lucent.com
        <mailto:vkg at alcatel-lucent.com>>:
         > 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 at {alcatel-lucent.com
        <http://alcatel-lucent.com/>,bell-labs.com
        <http://bell-labs.com/>,acm.org <http://acm.org/>}
         >  WWW:   http://www.alcatel-lucent.com/bell-labs
         >
        _______________________________________________
        Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
        This list is for NEW development of the core SIP Protocol
        Use sip-implementors at cs.columbia.edu
        <mailto:sip-implementors at cs.columbia.edu> for questions on
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-- BR 
    Donald _______________________________________________
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Gaurav Katiyar
Induslogic india pvt. ltd
B-34/1 sector 59 NOIDA
Phone:9818381368

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_______________________________________________
Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use sip-implementors at cs.columbia.edu for questions on current sip
Use sipping at ietf.org for new developments on the application of sip

_______________________________________________
Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use sip-implementors at cs.columbia.edu for questions on current sip
Use sipping at ietf.org for new developments on the application of sip