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Re: [Sip] New REFER request before 202 received for previous [was RFC3515: Multiple REFER Requests in a Dialog -Need clarification]



Sanjay Sinha (sanjsinh) wrote:
Pl. see inline .. 
-----Original Message-----
From: Paul Kyzivat (pkyzivat) Sent: Monday, July 28, 2008 10:00 AM 
To: Christer Holmberg
Cc: Sanjay Sinha (sanjsinh); Robert Sparks; sip at ietf.org
Subject: Re: [Sip] New REFER request before 202 received for previous [was RFC3515: Multiple REFER Requests in a Dialog -Need clarification]
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? 

I think having such a mechanism will add to the confusion and for the reasons you mentioned above, will be difficult to implement. I think a better approach will be to forbid sending overlapping target refresh request until the previous one is complete, as per the rules in RFC 5057.
That doesn't solve the problem. Even if you add that restriction, there are issues with: 
- non-target-refresh requests that might be sent
- *previously sent* requests that don't get replies and need to be retransmitted - retransmission of responses to earlier requests when a retransmission of the request is received. 

So these issues either need to be clarified, or will remain ambiguous.

	Paul


Sanjay



	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: sip-bounces at ietf.org [mailto:sip-bounces at ietf.org] On
Behalf Of 
Christer Holmberg
Sent: Sunday, July 27, 2008 2:09 PM
To: Paul Kyzivat (pkyzivat); Robert Sparks
Cc: sip at ietf.org
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: sip-bounces at ietf.org [mailto:sip-bounces at ietf.org] On
Behalf Of 
Paul Kyzivat
Sent: 25. heinäkuuta 2008 17:32
To: Robert Sparks
Cc: sip at ietf.org
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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_______________________________________________
Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol Use sip-implementors at cs.columbia.edu for questions on current sip Use sipping at ietf.org 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 sip-implementors at cs.columbia.edu for questions on current sip
Use sipping at ietf.org for new developments on the application of sip