RFC 3261 says that overlapping non-Invite transactions are allowed and REFER RFC is silent on it, but imo, the UAC should be discouraged from doing so. Overlapping transactions are application dependent and there is no one rule which applies to all usage. Having said that, I am not sure if call flow below is a problem. Since UAS will not update the remote target until it has sent a final response and UAC should not assume that the remote target is updated until it has received that final response. So even if second Refer contains an updated remote target, it will update the previous one.
Sanjay >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On >Behalf Of Christer Holmberg >Sent: Sunday, July 27, 2008 2:09 PM >To: Paul Kyzivat (pkyzivat); Robert Sparks >Cc: [email protected] >Subject: [Sip] New REFER request before 202 received for >previous [was RFC3515: Multiple REFER Requests in a Dialog >-Need clarification] > > >Hi, > >I have received a question related to this, so I assume there >ARE use-cases where multiple REFERs are sent within a single >dialog (sorry, I don't have any detailed information about the >use-case available). > >The question is: since REFER is a target refresh request, is >it allowed to send a new REFER request (within the same >dialog) before you have received the 202 response to the >previous REFER? > >Call-flow: > >UAC UAS > > --------- REFER (1) --------> > > --------- REFER (2) --------> > > <-------- 202 (1) ----------- > > <-------- 202 (2) ----------- > > >I don't know whether there is a problem from a transfer >perspective, but as far as I understand it is now allowed to >issue a new target refresh request one there is one pending. > >Regards, > >Christer > > > > > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On >Behalf Of Paul Kyzivat >Sent: 25. heinäkuuta 2008 17:32 >To: Robert Sparks >Cc: [email protected] >Subject: Re: [Sip] RFC 3515: Multiple REFER Requests in a >Dialog -Need clarification > >What Robert said. > >Perhaps it is possible that the operation requested by the >first refer fails, and is notified, but does not *immediately* >terminate the subscription. (Not that I can think of a reason >why.) Then the requester might try another refer and get a >second subscription before the first goes away. > >In the usual way of things, you should probably try to avoid >creating such a situation, unless you have some as yet unknown >good reason. But if you are on the receiving side you should >do the right thing if it happens to you. > > Paul > >Robert Sparks wrote: >> You are not likely to run into this for transfer. >> >> I'm not aware of any applications that will exercise this use case >> today, but I expect someone eventually will come up with >something (it >> might look like referring a UA to multiple MSRP connections or some >> other conference-like mesh, or somebody may eventually try to use >> REFER to ask the UA to look at several things over HTTP at once). >> >> The id= parameter on the Event header in the notify is there >to allow >> you to tell the subscriptions apart (so you can manage those usages >> independently). The element accepting the REFERs is required to send >> it in the NOTIFYs of the second and subsequent >subscriptions. Again, >> I haven't seen attempts to use this capability in applications yet - >> it would not surprise me if there's something there that >turns out to >> be really hard (like figuring out which of those subscriptions goes >> with which REFER). >> >> RjS >> >> On Jul 25, 2008, at 1:06 AM, Vavilapalli Srikanth-A19563 wrote: >> >>> Hi >>> >>> I have seen some discussion happened on this topic in the following >>> mail trail, but still not clear with one thing: >>> >https://lists.cs.columbia.edu/pipermail/sip-implementors/2003-Decembe >>> r/005829.html >>> >>> >>> Is there any use case where we receive second REFER message that >>> creates a subscription while there exists an already an 'active' >>> REFER subscription in the same dialog? RFC 3515 has given a >use case >>> by saying that "If more than one REFER is issued in the same dialog >>> (a second attempt at transferring a call for example)". But in the >>> above scenario, I assume that the first attempt to call >transfer has >>> failed (i.e. first REFER subscription terminated). >>> >>> Please clarify me. >>> >>> Regards >>> Srikanth >>> >>> _______________________________________________ >>> Sip mailing list https://www.ietf.org/mailman/listinfo/sip >>> This list is for NEW development of the core SIP Protocol Use >>> [EMAIL PROTECTED] >>> <mailto:[EMAIL PROTECTED]> for questions on current >>> sip Use [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> for new >>> developments on the application of sip >> >> >> >---------------------------------------------------------------------- >> -- >> >> _______________________________________________ >> Sip mailing list https://www.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 mailing list https://www.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 mailing list https://www.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 mailing list https://www.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
