[XCON] Control Values and the Data Model

[Adam Roach <adam at nostrum.com>]

In a recent discussion that the XCON operations document editors were
having, an interesting issue arose. It's not clear to me that we have
given a lot of thought to this issue, so I'd like to see what opinions
the working group has on the topic:

The current view of the data model as described in the framework is that
we have a common conference portion (based primarily on the schema given
in draft-ietf-sipping-conference-package-12); and we have a template
portion (such as those described in draft-boulton-xcon-media-template-02).

Eliding a lot of information, this leads us to a breakdown of
information roughly along the lines of:

<!-- COMMON PORTION -->

<conference-info>
  <users>
    <user entity="sip:bob at example.com">
      <roles>
        <entry>participant</entry>
      </roles>
      <endpoint entity="sip:bob at 123.45.67.8">
        <media id="1">
          <type>audio</audio>
        </media>
        <media id="2">
          <type>video</audio>
        </media>
      </endpoint>
    </user>
  </users>

<!-- TEMPLATE PORTION -->

  <template name="basic-audio-video">
    <role name="participant">
      <stream type="audio" name="AudioIn" dir="in">
        <control type="boolean" name="mute" enable="true">
          <label>Mute-Audio</label>
        </control>
      </stream>
      <stream type="video" name="VideoIn" dir="in">
        <control type="boolean" name="pause-video" enable="true">
          <label>Pause-Video</label>
        </control>
      </stream>
      <stream type="audio" name="AudioOut" dir="out">
        <control type="integer" name="gain" enable="true">
          <label>Volume</label>
        </control>
      </stream>
      <stream type="video" name="VideoOut" dir="out" />
    </role>
  </template>
</conference-info>



Now, here's the interesting issue: where, if anywhere, does this
document represent what the specific value for Bob's gain for his
AudioOut channel is?

With the current structure:

    * It can't go in the Template portion, since the template has
      entries for each role, not for each user. In other words, it has
      precisely one "Participant" section, even though there can be
      multiple participants.

    * It can't go in the Common portion, since that part of the document
      is defined to not change regardless of the template in use.
      Because of this, I don't think we can start putting control values
      specific to the template up there.

I can think of two ways to handle this, although there may be more:

   1. Add yet another section to the document, associated with the
      template part, that basically forms the cross product of each user
      and their relevant controls. In other words, add a section like:

      <conference-info>
      ...
        </template>
        <control-values>
          <endpoint entity="sip:alice at 123.45.67.7">
            <control stream="AudioOut" name="gain" value="92" />
            <control stream="AudioIn" name="mute" value="false" />
            <control stream="VideoOut" name="pause" value="false" />
          </endpoint>
          <endpoint entity="sip:bob at 123.45.67.8">
            <control stream="AudioOut" name="gain" value="92" />
            <control stream="AudioIn" name="mute" value="false" />
            <control stream="VideoOut" name="pause" value="false" />
          </endpoint>
          <endpoint entity="sip:charlie at 123.45.67.9">
            <control stream="AudioOut" name="gain" value="92" />
            <control stream="AudioIn" name="mute" value="false" />
            <control stream="VideoOut" name="pause" value="false" />
          </endpoint>
          <endpoint entity="sip:dinah at 123.45.67.10">
            <control stream="AudioOut" name="gain" value="92" />
            <control stream="AudioIn" name="mute" value="false" />
            <control stream="VideoOut" name="pause" value="false" />
          </endpoint>
        </control-values>
      </conference-info>

   2. Don't include the literal control values in the document. Instead,
      clients can use the list of user devices and the roles associated
      with them to ascertain which controls are valid for which
      user/endpoint/media-stream combination. Then, the control values
      could be explicitly queried and set by the operations protocol. As
      an example, the XML document representing the conference state
      would never include the value of my "gain" control -- but you
      could learn what it was by issuing a command that basically said
      "query user=sip:adam at estacado.net, device=sip:adam at 123.45.67.8,
      stream=AudioOut, control=gain".


Thoughts?

/a

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