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. 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
