Hi Yong Xin, Here are some quotes from RFC3262. It does say the UAC MUST create a dialog if not yet for 1xx reliable response. Also it said "PRACK is like any other non-INVITE request within a dialog". Therefore, I think the remote-target-uri should be updated to the contact address in 1xx (rel).
Jerry " 4 UAC Behavior The provisional response MUST establish a dialog if one is not yet created. Assuming the response is to be transmitted reliably, the UAC MUST create a new request with method PRACK. This request is sent within the dialog associated with the provisional response (indeed, the provisional response may have created the dialog). PRACK requests MAY contain bodies, which are interpreted according to their type and disposition. Note that the PRACK is like any other non-INVITE request within a dialog. In particular, a UAC SHOULD NOT retransmit the PRACK request when it receives a retransmission of the provisional response being acknowledged, although doing so does not create a protocol error. " > -----Original Message----- > From: Yong Xin [mailto:[EMAIL PROTECTED] > Sent: Wednesday, March 28, 2007 4:17 PM > To: 'Jerry Yin'; [email protected] > Cc: [EMAIL PROTECTED] > Subject: RE: [Sip-implementors] SIP Contact header > > > Thanks for the comments, please see my response in-line marked by [Yong]: > > -----Original Message----- > From: Jerry Yin [mailto:[EMAIL PROTECTED] > Sent: Wednesday, March 28, 2007 1:02 PM > To: [EMAIL PROTECTED]; [email protected] > Subject: RE: [Sip-implementors] SIP Contact header > > Please see the in-line comments. > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] Behalf Of Yong Xin > > Sent: Wednesday, March 28, 2007 1:34 PM > > To: [email protected] > > Subject: [Sip-implementors] SIP Contact header > > > > > > Hi, > > > > As per RFC 3261, the UAS MUST add a Contact header field to the 2xx > > response to the INVITE. The Contact header field contains an address > > where the UAS would like to be contacted for subsequent requests in > > the dialog (which includes the ACK for a 2xx response in the case of > > an INVITE). > > > > My questions are: > > > > 1) Would the ACK for a non-2xx response be using this contact > > address? (I assume not. My understanding is that UAC must > > send ACK for a non-2xx response using the same destination > > address as the INVITE) > > > > No. The none-2xx response does not create a dialog, therefore, > the ACK will > be sent to the same url as Invite request. > > > 2) How about PRACK or UPDATE request which is sent from UAC > > to UAS before the dialog is established (i.e.: 200 ok to > > INVITE is not sent by UAS yet)? (I assume same as the ACK > > for non-200 response). > > > > When you send PRACK, it means you have received a reliable 1xx response, > which will create an early dialog. As someone said, early dialog is a > dialog. Therefore, the PRACK will be sent to the "contact" address in 1xx > response. Since you shouldn't send "UPDATE" before the PRACK, > therefore the > UPDATE is also sent to the contact address in the early dialog. That's my > understanding. > > [Yong]: You're right, this is an early dialog. However, I incline to agree > with what Indresh has said that the remote-target-uri has not been updated > at this moment, so the PRACK should be still sent to the same > address where > the original INVITE was sent. I could not find a statement in the RFC 3261 > spec that says the remote-target-uri can be updated after receiving 1xx > response. Do you agree? > > As to the UPDATE without PRACK, I assume it should be sent to the same > address as request url, since there's no (early) dialog is created. > > > Your comments are appreciated. > > > > Thanks, > > Yong > > > > _______________________________________________ > > Sip-implementors mailing list > > [email protected] > > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > > > > _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
