[SIPForum-discussion] Need clarity over Dialog and session in sip.

Pranab Bohra pranab.bohra at gmail.com
Wed Jun 16 18:08:34 UTC 2010


Adding to what Ayyanar already explained, a session can have more than one
media streams.
SDP (rfc 2327) is used by an endpoint to convey its media capabilities to
the far end.
The offer/answer model (rfc 3264) explains how 2 endpoints would exchange
their capabilities and establish a session on mutually agreed settings.
SIP acts as the transport for the above mentioned offer/answer exchange for
the purpose of session establishment.

The session-id along with username, address-type, network-type and address
within the o= line uniquely identify a session.

As indicated in rfc 3261, a session is associated with a single dialog, and
hence logically should cease to exist once the dialog terminates.


On Tue, Jun 15, 2010 at 9:10 AM, <ayyanar.kalimuthu at wipro.com> wrote:

>  Read section 15 Terminating a Session from RFC 3261. The below passage is
> from section 15 which explains what a session and dialog is.
> When a session is initiated with an INVITE, each 1xx or 2xx response from a
> distinct UAS creates a dialog, and if that response completes the
> offer/answer exchange, it also creates a session. As a result, each session
> is "associated" with a single dialog - the one which resulted in its
> creation.
>  It is true that dialog is established and terminated by INVITE  and BYE
> respectively, im not sure about the session.
> A session can be identified by session version in the SDP.
> Regards,
> Ayyanar
>  ------------------------------
> *From:* discussion-bounces at sipforum.org [mailto:
> discussion-bounces at sipforum.org] *On Behalf Of *Santosh Kumar
> *Sent:* Monday, June 14, 2010 9:36 PM
> *To:* discussion at sipforum.org
> *Subject:* [SIPForum-discussion] Need clarity over Dialog and session in
> sip.
>   Hi all,
>   Can anyone kindly clarify what's session and dialog?
>   Did try refering rfc, but that defination was'nt able to digest.
>   Have read,
>    session is something to do with media, while dialog is to do with
> signaling.
>   Is it true both session and dialog gets established by INVITE and
> terminate with BYE?
>   , in that case what makes unique between each?
>  ,Also have read dialog is identified by callid , tag.
>    then how is session is identified?
>  Need your help or links for understanding,
>  Thanks
> Santosh
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