"A "session" can contain multiple dialogs. A session is created by a
dialog creating request (INVITE/SUBSCRIBE/REFER) and can contain
multiple dialogs.
For example, an INVITE can fork to multiple UAs. If more than one UAS
responds with 1xx/2xx (w/to-tag) multiple dialogs are created. All those
dialogs belong to the session. "

I am confused ... A session is is nothing but exchange of media data
between participants if I understand 3261 correctly ,
So an offer/answer exchange is needed to to create such a session , in
this example , there will actually be multiple sessions exchanging
different kinds of media data (say one audio session and one video
session) , so each session is still associated with only one dialog ?


-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Bob
Penfield
Sent: Friday, August 11, 2006 5:59 PM
To: Benny Prijono; Young Tao
Cc: [email protected]
Subject: Re: [Sip-implementors] Session, Dialog in RFC



>
>> Is a session containing serveral dialogs
>
> No, that's not possible! An INVITE session can only have one
> underlying dialog. But, a dialog may have several sessions (for
> example, one INVITE session, and multiple event subscription
> "sessions").
>

"session" is not the correct term here. What you are referring to is a
"dialog usage".

A "session" can contain multiple dialogs. A session is created by a
dialog creating request (INVITE/SUBSCRIBE/REFER) and can contain
multiple dialogs.
For example, an INVITE can fork to multiple UAs. If more than one UAS
responds with 1xx/2xx (w/to-tag) multiple dialogs are created. All those
dialogs belong to the session.

Most UAs do not support multiple confirmed dialogs that happen when the
INVITE reaches multiple UASs and they send a 2xx before the forking
proxy can CANCEL them. The UA will typically keep the dialog for the
first 2xx it receives, and terminate the dialog for any subsequent 2xx
(send ACK, and then BYE).

cheers,
(-:bob

Robert F. Penfield
Chief Software Architect
Acme Packet, Inc.
71 Third Avenue
Burlington, MA 01803
[EMAIL PROTECTED]

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