If you send an in dialog request (REFER in our case), then you cannot decouple its semantics with the existing dialog usage. So saying that even if i send a REFER within an existing dialog, and still decouple it from the existing dialog usage will not be possible. If there were such a requirement, then REFER should have been sent as a standalone dialog creating request outside the INVITE usage.
The recipient of the in dialog REFER will treat it like it should any in dialog request. It has no way to decide if this request potentially had nothing to do with the existing dialog usage. i agree with you when you say that an indialog refer receiving a 481 would mean that the INVITE dialog has been torn down. However, a refer dialog usage can also terminate, if the UAC sends a 481 in response to the NOTIFY sent by the UAS (Suppose the transaction did not match). This scenario may happen irrespective of whether the REFER was within the invite usage or created its own distinct dialog. If this happens when REFER was sent within an Invite dialog, then the UAC will be mistaken to clean up its INVITE dialog state. I did not understand one part in the paradox above when you said... "A REFER within an established dialog having no invite usage to be considered as an out of dialog REFER" Do you mean to imply a REFER in some other Subscribe event package dialog for example? aayush. On 3/25/09, Dale Worley <[email protected]> wrote: > On Mon, 2009-03-23 at 21:32 -0400, Paul Kyzivat wrote: >> > I would argue that the REFER is part of the INVITE usage, because REFER >> > in that context is intimately related to the INVITE usage -- it is >> > intended to transfer the INVITE usage/dialog transferred to a different >> > destination. >> >> Well, I guess there is that implied association. (Part of the "do what >> *I* had in mind" approach that REFER has.) Since this was never spelled >> out, it could also be simply "while this isn't part of an INVITE usage, >> if there happens to be an INVITE usage, please refer that one." >> >> I guess the question is: would it be valid to send a REFER within an >> existing dialog that had no INVITE usage? If it were valid, presumably >> it would have the same meaning as sending one outside a dialog, except >> that the resulting subscription would share the dialog. I expect that is >> a usage it would be difficult to find in the wild. > > That's a nice pathological case. But within the context of the current > 5 possible meanings of REFER, it seems to be most parallel to the > out-of-dialog REFER. > >> Ah, but now I want to reconsider. Remember that REFER can take a method >> name. So, rather than referring an INVITE, I could be referring MESSAGE, >> OPTIONS, BYE, or maybe (????) SUBSCRIBE. In some of those cases, the >> association to the INVITE usage is probably meaningless. (Of course its >> meaningful for BYE.) > > A fascinating possibility! But I'm not sure that we've ever defined how > a REFER within a simple INVITE dialog, specifying a non-INVITE method > should act. So there's no analog to follow. > >> > And it seems quite safe that if the REFER receives a 481 response, the >> > INVITE usage must not be functional any more, since the far end of that >> > usage has denied that it can act on the REFER. >> >> IIRC, 5057 decided that each dialog usage must get its own 481 before it >> goes away. I don't think there are any cases where a single 481 response >> can make multiple usages go away. >> >> So the important question is whether the REFER is part of the INVITE >> usage and so its 481 takes down the INVITE usage or not. That gets >> especially interesting if the dialog already had both an INVITE usage >> and a SUBSCRIBE usage. Does it make sense that the refer take down the >> INVITE usage and leave up the SUBSCRIBE usage? > > I think we're a victim of sloppy terminology here. If I send a REFER, > and the far end responds 481, then clearly the far end knows of no > INVITE usage, or otherwise it would not have responded 481. So I should > delete my belief that there is an INVITE usage. Whether we consider the > REFER in question to be "part of" the INVITE usage or not doesn't change > anything -- the 481 is evidence that the far end has no knowledge of the > usage. > > However, we do have this fine paradox: If we assume that a REFER within > an established dialog that has no INVITE usage is to be treated as an > out-of-dialog REFER, then *no* REFER will receive a 481 response! > Indeed, if I send a REFER thinking that there is an active INVITE usage, > but the far end believes the INVITE usage has ended, will cause the far > end to do something (initiate an independent dialog) that is > considerably different from what I expected (transfer the current INVITE > usage). > > Dale > > > _______________________________________________ > 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
