Subject: [SIP] Third-party call control with already initiated call

From: "Eber Mello" <[email-masked]>
Date: Wed, 26 Apr 2000 15:13:26 -0700

Hi,

The third-party call control draft (expires September 2000) describes a 
generic way of setting up parties using a "controller".
It also mentions in section 4 that "if a participant initiates 
the call, the controller must step in as a virtual UAC/UAS and 
act as a termination and re-initiation point". I have a couple of
questions regarding this mechanism:

1) A Re-Invite initiated by the controller to one of the UAs to 
put it on hold would use the same call-leg ids of the original
Invite transaction? Note that the original Invite was not
addressed to the controller but rather to a third UA. The controller 
happened to be on the signalling path and was only monitoring the 
messages between the UAs and decided to step in.

2)Could the controller be used to "intercept" Invite requests 
to third-party users and respond to them with 200 OK in order to, say, 
connect (in the RTP sense) the UAC to a non-SIP enabled entity (e.g.
a music source). In this case would the 200 OK use the same call-leg ids
of the original Invite?

Thanks,

Eber Mello

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 27 Apr 2000 01:57:14 -0400

Eber Mello wrote:
> Invite transaction? 

They would use the call-leg ids in place between the controller and the
given UA.

Note that the original Invite was not
> messages between the UAs and decided to step in.

Yup. You can think of it as a gateway, much like SIP to H.323 or SIP to
ISUP, but here its SIP to SIP.

> a music source). In this case would the 200 OK use the same call-leg ids

Of course. Here, the controller is just a UAS. It follows the rules for
UAS.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
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