[moving to sip-implementors...] re-INVITEs are also used to maintain session state, see draft-ietf-sip-session-timer-05.txt. regards, Bert -----Original Message----- From: Chen, Xin (Xin) [mailto:[EMAIL PROTECTED]] Sent: Thursday, August 16, 2001 3:11 PM To: 'Bert Culpepper'; Chen, Xin (Xin); [EMAIL PROTECTED] Subject: RE: [Sip] Question about SIP bis04 Thanks, I understand your explaination. But why Bis04 says that this is to synchronize the state of the session? Maybe some other reason as well. Xin Chen Lucent Technologies Tel: +44 1793 883137 Mobile: +44 7799 034668 -----Original Message----- From: Bert Culpepper [mailto:[EMAIL PROTECTED]] Sent: 16 August 2001 19:06 To: 'Chen, Xin (Xin)'; [EMAIL PROTECTED] Subject: RE: [Sip] Question about SIP bis04 Well, one use of a re-INVITE is to change the media characteristics of an existing session. So if a UAS never gets acknowledgement of its response (times out waiting for the ACK), it can (SHOULD) assume the transaction failed and continue with the media that existed prior to the re-INVITE. But, the other end has already changed presumably to match its re-INVITE and it may have even received the 200 from the UAS in which case it did change its media, leading to a "failed call" situation (UAC using new media and UAS using old media). The text you ask about describes a fall-back procedure for the UAS to "recover" the call. The UAC is not aware of the problem with the UAS receiving its ACK. regards, Bert -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Chen, Xin (Xin) Sent: Thursday, August 16, 2001 9:58 AM To: '[EMAIL PROTECTED]' Subject: [Sip] Question about SIP bis04 Could someone please explain to me: 15.4 If a UAS never receives an ACK for a 2xx response to a re-INVITE, it SHOULD generate a re-INVITE itself in order to synchronize the state of the session. What does this description mean? If UAS needs a ACK, why it has to generate a re-INVITE? Thanks and Regards Xin Chen Lucent Technologies Tel: +44 1793 883137 Mobile: +44 7799 034668 _______________________________________________ Sip mailing list http://www1.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
