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; [email protected]
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: [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
_______________________________________________
Sip mailing list https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol Use
[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> for questions
on current
sip Use [EMAIL PROTECTED] <mailto:[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
_______________________________________________
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
_______________________________________________
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
