Doken, Serhad wrote:
-----Original Message-----
From: Paul Kyzivat [mailto:[email protected]]
Sent: Tuesday, March 24, 2009 7:43 AM
To: Doken, Serhad
Cc: Dale Worley; SIP IETF; Brett Tate
Subject: Re: [Sip] Is REFER within dialog part of INVITE or
subscription usage? (was RE: SIP INFO)
Doken, Serhad wrote:
I guess the question is: would it be valid to send a REFER within an
existing dialog that had no INVITE usage? If it were valid,
presumably
Yes, I think so.
it would have the same meaning as sending one outside a dialog,
except
that the resulting subscription would share the dialog. I expect
that
is
a usage it would be difficult to find in the wild.
Consider a third party control application that forces an endpoint to
register :
REFER sip:phone.doken.com SIP/2.0
Refer-To: <sip:[email protected];method=REGISTER>
that triggers a REG to the registrar as :
REGISTER sip:[email protected] SIP/2.0
You are suggesting that first this 3pcc application sends a SUBSCRIBE
to
this UA, establishing a dialog. Then it sends a REFER within the
dialog,
asking the UA REGISTER? That then would presumably result in a
subscription to the refer event package sharing the dialog with the
prior subscription. I guess this is *possible*, though I don't know
*why* it would be done. What would the initial SUBSCRIBE be to, and how
would it be established before the UA has registered?
3rd party contact center desktop monitoring application is used by the supervisor to
see agent's activities. Thru a CTI <->SIP translator, it SUBs to the agent's
presence. Once the customer service agent comes in the morning and turns his phone's
status to Online(Open), app notices this and forces it to Register. At the end of the
day when agent leaves, does the opposite and de-registers it. Thus, it is made sure
that they only get billed for the time that agent was registered(online) by the
service provider.
I find this less than compelling. How does the monitoring application
discover and address the UA to establish the subscription? If that was
possible, then the UA must have a globally routable URI that is known to
the application. And that could be used to send an out-of-dialog REFER.
Thanks,
Paul
Are you aware of such usage in the wild?
I have seen somewhat similar examples. If you are offering enough stimulus/TARP
money, wild frontiers will get closer.
It's mostly used for Xfer however as you alluded to, REFER is implicit or
ambiguous that it is open to be used as the Swiss knife if I wanted the other
side to do something for me. As long as the sender and receiver know/understand
what is meant or the context(especially if they are from the same vendor),
everything is fine, if not misinterpretations may happen.
(Its incidental to this discussion, but REGISTER presents unique
challenges because of the way addressing works for it. Contrary to your
example above, we would typically expect that the To: would contain the
full URI, while the R-URI would only be sip:doken.com. This would
You are right.
Thanks,
Serhad
require more special case processing.)
Thanks,
Paul
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