Re: [Sip] RFC 3515: Multiple REFER Requests in a Dialog - Need clarification

[Paul Kyzivat <pkyzivat at cisco.com>]

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-December/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
> >  
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>
>
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>
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_______________________________________________
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This list is for NEW development of the core SIP Protocol
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Use sipping at ietf.org for new developments on the application of sip