The whole issue of target refresh seems filled with potential race
conditions and ambiguities. The second REFER before the first is
complete presents no new issues compared to a second SUBSCRIBE before a
first is complete, and that is a much more likely case, especially with
differing event packages.
The semantics of target refresh have always troubled me. Presumably
there must be some period of time during which both the old and new
addresses are valid. But when does that period end? And what if you are
making the change because the old address stopped working already?
Paul
Christer Holmberg wrote:
Hi,
RFC 3261 says that overlapping non-Invite transactions are allowed and REFER
RFC is silent on it,
Yes, but I wonder whether there are more strict rules for target refresh requests.
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.
Yes, but if the first 202 contains a new remote target, I guess the intention
is that it should be used for future requests - including the second REFER.
Regards,
Christer
-----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
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