Subject: [Sip] Dialog state

From: "Papapanagiotou, Serafim" <[email-masked]>
Date: Thu, 15 Nov 2007 18:37:04 +0200

Hello,
 
I have a question concerning new requests within a Dialog (according to
RFC 3261).
In 12.1.1 is described the role for UAS in order to build the "state of
the Dialog" and 12.1.2 the role of UAC to build the "state of the
Dialog".
Up to here it is ok. The two Dialog states have been created !
The problem now is that in 12.2.1 is described how to send new requests
within a Dialog and the role of the UAC once again.
Hence as it is written " The URI in the To field of the request MUST be
set to the remote URI from the dialog state. ...etc"
Which of the two dialog states are chosen? (the one that was created as
a UAS ?) Of course this is the answer but you can see this only from
tracers and message flows.
Somehow the 12.2 is mixing the roles of UAs. So we have UAC/UAS for the
transaction and these roles can be interchanged according to who is
originating the Request during the Dialog life.
In terms of Dialog though the role of UAC seems to be always the same
(the one who sent the initial INVITE/ created the Dialog) and the UAS
(the one who received the initial INVITE)
Is it somewhere that I do not see that this is explicitly written or did
I misunderstand something? Especially for the way of choosing which of
the two Dialog states to select ?   

Thanx,
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---

From: [email-masked]
Date: Thu, 15 Nov 2007 14:48:59 -0500

From: "Papapanagiotou, Serafim" <[email-masked]>

Yes, the UA at each end of the connection must of necessity maintain
its own dialog state.  Any time the dialog is quiescent (all
outstanding messages are processed), the two states will be the same.
But of course, in the middle of a transaction, the two states may not
be the same.

   Which of the two dialog states are chosen?

The dialog state maintained by the UA which is composing the message.
(It has no access to the dialog state of the other UA.)

That is correct -- the roles of UAC and UAS are only defined with
respect to a single transaction, that is, a request and its response.

Dale