Fundamentally I think one can have one offer-answer in a single transaction. Which does not seems to be in the below case. There are two offers in INVITE transaction ( One in 180 and another in 200 OK ). So to me it does not look like valid call-flow.
For early dialog cases to renegotiate media/change the offer UPDATE method should be used by UAS/UACs I do not know if this is specified in any specific RFC ( Offer-Answer RFC ) or SIP RFC. You may want to go through few earlier discussion on this subject https://lists.cs.columbia.edu/pipermail/sip-implementors/2005-July/00974 1.html Regards, Indresh K Singh -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of ext Bu, Wenfei (Leo) Sent: Thursday, April 05, 2007 1:13 PM To: [email protected] Subject: [Sip-implementors] Could the UAS change the SDP offer in 200 OK? All, Take a look at the following call flow: UAC UAS -------->F1 INVITE w/o SDP <--------F2 180 w/ SDP1, Required: 100rel -------->F3 PRACK w/ SDP2 <--------F4 200 for PRACK <--------F5 200 for INVITE w/ SDP3 -------->F6 ACK w/ SDP4 Is this a valid call flow? Could the UAS change its SDP offer in 200 OK for INVITE? If there's any RFC that clarifies this scenario, please let me know. Thanks, Leo _______________________________________________ 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
