[SIPForum-discussion] Difference between a session and a dialog in SIP

[Kai Zhang]

Hi
    My summary following:
     A *dialog* represents a peer-to-peer SIP relationship between two user
agents that persists for some time, as a call-leg.It is identified at each
UA with a *dialog* ID, which consists of a Call-ID, From tag and To tag. We
can call a *dialog* is established when three values are all
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     A *sip transaction* consists of a single request and any responses to
that request, which includes zero or more provisional responses and one or
more final responses.The branch parameter value in the VIA header is used to
identify the transaction created by that request.

     Session: In the SDP specification, a multimedia *session* is a set of
multimedia senders and receivers and the data streams flowing from senders
to receivers.  A sessionis defined by the SDP user name, *session* id,
network type, address type, and address elements in the origin field.
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A *session* can have multiple RTP sessions corresponding to the UDP ports
define in the m= line of the SDP.%nN
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1.Dialog and tranaction are the cocepts in the signalling part; But the *
session* is the concept in the media transport part. SIP uses the SDP to
notify the transport protocol(RTP) to create, add, remove and modify the
sessions.h
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2.Generally, SIP can invite the user to attend an existing *session*, which
occures in the conference call. In such case, the To tag as well as the
call-ID which uniquely identifies a particular invitation, could be
different to those of the existing *dialog*, so a new *dialog* is needed. `


/Kevin

27 Jan 2007 18:07:18 -0000, anuj srivastava <anuj18sh at rediffmail.com>:
>
> Hello,
> Is there a difference between a "session" and a "dialog" in SIP? If we
> have multiple calls in a session, would all of them have different dialog
> identifiers?
>
> thanks
> anuj
>
>
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