Subject: [Sipping] Sidebars

From: "Rosen, Brian" <[email-masked]>
Date: Mon, 24 Feb 2003 11:26:09 -0500

In the latest conferencing framework draft, sidebars are
proposed as a separate conference URI with special properties.
In particular there is this text:
   A sidebar is represented by a separate conference URI. This URI is a
   type of "alias" for the main conference URI. Both route to the same
   focus. Like any other conference, the sidebar conference URI has a
   conference policy and a media policy associated with it. Like any
   other conference, one can join it by sending an INVITE to this URI,
   or ask others to join by referring them to it. However, it differs
   from a normal conference URI in several ways. First, users in the
   main conference do not need to establish a separate dialog to the
   sidebar conference. The focus recognizes the sidebar as a special
   URI, and knows to use the existing dialog to the main conference as a
   "virtual" connection to the sidebar URI.

   The second difference is the way in which conference and media
   policies are implemented. If the conference policy control protocol
   is used to add a user to a normal conference, the focus will
   typically send an INVITE to the participant to ask them to join. For
   a sidebar conference, it is done differently. If the conference
   policy control protocol is used to add a user to it, and that user is
   already part of the main conference, the focus will use the
   conference notification service to alert the existing participant
   that they have been asked to join the sidebar. The invited user can
   then make use of the CPCP to formally add themselves to the sidebar.

I'm interested in how a non-conference aware UA participates in a sidebar.
Clearly, an out-of-band mechanism can be used to manipulate the CPCP
to add such a UA to a sidebar, and similar means to control media
policy.  This is very encouraging.

I'm confused, however, on exactly how this special sidebar URI
will work with a non-conference aware UA.

Specifically:
The text says that an INVITE with the sidebar URI will not be sent
by the focus to request the user to join.  Is there any circumstance
in which the focus would use the sidebar URI?  I'm thinking of,
for example, what would normally be a re-invite to add a media
stream when another user, who is not a main conference participant
already, joins the sidebar.  Any use of the sidebar URI with a non
conference aware UA would confuse the heck out of it.

So far, I'm thinking that the only real use of this URI is for
a UA which is not a main conference participant to get added to
the sidebar, but not the main conference.  The wording in the framework
document could offer more clarity on the use of this URI.

Brian
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