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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