Hi, >My previous mail to Christer is about the same topic. > > >To be honest, your agree almost all of your reply. And I once have the same understanding of RFC3261. >But when I reviewed again during the interworking-testing(in new interworking-testing, we always face some new equipment and hear some new understanding of RFC3261 from them), I feel it seams need correction. That is why we are working with the o/a draft, which hopefully will clarify things for people. Regards, Christer Thanks, Gao =================================== Zip : 210012 Tel : 87211 Tel2 :(+86)-025-52877211 e_mail : gao.yang2@xxxxxxxxxx =================================== Paul Kyzivat <pkyzivat@xxxxxxxxx> 2010-04-15 22:59 收件人 gao.yang2@xxxxxxxxxx 抄送 Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>, "Somogyi, Gabor (NSN - HU/Budapest)" <gabor.somogyi@xxxxxxx>, OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>, "sipping@xxxxxxxx" <sipping@xxxxxxxx> 主题 Re: [Sipping] About offeranswer draft: inline gao.yang2@xxxxxxxxxx wrote: > > > sipping-bounces@xxxxxxxx 写于 2010-04-15 04:38:21: > > > Hi, > > > > >> In your chart SDP4 is a reliable answer. Therefore SDP5 might be > > >> interpreted as a new offer, hence UAC could send an answer in PRACK. > > >> Quite similarly to 3PCC cases, where 200 contains the offer and > ACK the > > >> answer. > > > > > >That has been investigated. Its not allowed. (Unfortunately I cannot > > >recall the chain of reasoning that derived its illegality - it wasn't > > >obvious but it was sound. It was worked out a *long* time ago.) > > > > The rule we have agreed to is very simple: at most one offer/answer > > exchange per SIP transaction. > > Yes, it is. And what I talked here is also under this basic rule. > > > > > Whether it's clearly specified somewhere needs to be checked, though. > > > > I know there are implementations that "update" the SDP answer from > > one reliable response to another (within the same transaction), for > > the same transaction, but that is certainly nothing we have > standardized. > > I think it should be mentioned here, what is the *lawful* answer? > It is the one in the first reliable response. > > As it is the *lawful* answer, I think the UAC should using it when it > get the answer. And this seems *should* be made normative. > While how UAC handle SDP(from UAS) before the real answer, it can be BCP > issue. I think you are arguing that it is "lawful" for the UAS to send differing values for the SDP successive unreliable responses and in the subsequent reliable response. And that it is then the responsibility of the UAC to make this work "right" and "deterministically" by honoring the first and ignoring the subsequent ones. Is that right? But that makes no sense. The UAS cannot know if the UAC will receive the first, or any of, the unreliable responses. So if it were to do this odd behavior it must be satisfied that *any* of then are the one that the UAC uses. Or else it must be assuming that the UAC *might* use one or more of the unreliable ones, and eventually *switch* to the one in the reliable response. But 3261 is clear that the UAC should use the first one it receives, and ignore the remainder, *including* the reliable one. There is no provision for *switching*. Hence, its a corollary that the only behavior that the UAC can follow that is valid and consistent in the face of loss of unreliable responses is for them all to contain the same SDP. So that is the *lawful* behavior - a UAS that violates this is unreasonable. Thanks, Paul -------------------------------------------------------- ZTE Information Security Notice: The information contained in this mail is solely property of the sender's organization. This mail communication is confidential. Recipients named above are obligated to maintain secrecy and are not permitted to disclose the contents of this communication to others. This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the originator of the message. Any views expressed in this message are those of the individual sender. This message has been scanned for viruses and Spam by ZTE Anti-Spam system. _______________________________________________ Sipping mailing list https://www.ietf.org/mailman/listinfo/sipping This list is for NEW development of the application of SIP Use sip-implementors@xxxxxxxxxxxxxxx for questions on current sip Use sip@xxxxxxxx for new developments of core SIP
