xeps/xep-0294.xml

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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Jingle RTP Header Extensions Negotiation</title>
  <abstract>This specification defines an XMPP extension to negotiate
  the use of the use of RTP Header Extension as defined by RFC 5285
  with Jingle RTP sessions</abstract>
  &LEGALNOTICE;
  <number>0294</number>
  <status>Deferred</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XEP-0167</spec>
    <spec>RFC 5285</spec>
  </dependencies>
  <author>
    <firstname>Olivier</firstname>
    <surname>Crête</surname>
    <email>olivier.crete@collabora.co.uk</email>
    <jid>olivier.crete@collabora.co.uk</jid>
  </author>
  <discuss>jingle</discuss>
  <revision>
    <version>0.1</version>
    <date>2011-03-24</date>
    <initials>psa</initials>
    <remark><p>Initial published version.</p></remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2011-01-10</date>
    <initials>oc</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>

<section1 topic='Introduction' anchor='introduction'>
  <p>This documents specifies how to negotiate the use of the RTP
  Header Extensions as defined by &rfc5285; with Jingle RTP
  sessions.</p>
</section1>

<section1 topic='Requirements' anchor='requirements'>
  <p>The Jingle extension defined herein is designed to meet the following requirements:</p>
  <ol>
    <li>Enable negotiations of the RTP Header extensions as defined in
    <cite>RFC 5285</cite>.</li>
    <li>Map these parameters to Session Description Protocol (SDP; see
    &rfc4566;) to enable interoperability.</li>
  </ol>
</section1> 

<section1 topic='New element' anchor='element'>
  <p>This specification defines a new element, &lt;rtp-hdrext/&gt;,
  that can be inserted in the &lt;description/&gt; element of a
  XEP-0167 RTP session.</p>

<p>The attributes of the &lt;rtp-hdrext/&gt; element are:</p>
<table caption='rtp-hdrext attributes'>
  <tr>
    <th>Attribute</th>
    <th>Description</th>
    <th>Inclusion</th>
    <th>Possible values</th>
  </tr>
  <tr>
    <td>id</td>
    <td>The ID of the extensions</td>
    <td>REQUIRED</td>
    <td>1-256, 4096-4351</td>
  </tr>
  <tr>
    <td>uri</td>
    <td>The URI that defines the extension</td>
    <td>REQUIRED</td>
    <td>Any valid URI</td>
  </tr>
  <tr>
    <td>senders</td>
    <td>Which party is allowed to send the negotiated RTP Header Extensions</td>
    <td>OPTIONAL (defaults to "both")</td>
    <td>"initiator", "responder", and "both"</td>
  </tr>
</table>

<p>Any type of RTP Header Extension that requires extra
parameters in the a=b form can embed &lt;parameter/&gt; elements to
describe it. Any other form of parameter can be stored in the CDATA
inside the &lt;rtp-hdrext/&gt; element.</p>

</section1> 

<section1 topic='Negotiation' anchor='negotiation'>
  <p>RTP header extensions are negotiated along the codecs. They
  follow the same Offer/Answer mechanism based on SDP
  Offer/Answer. The initiator signals which RTP header extensions it
  wants to send or receive in the the &lt;session-initiate/&gt; iq
  stanza. If the responder does not understand the type of header
  extensions, it MUST remove the element from the reply. If the
  responder does not wish to provide or receive some kind of RTP
  header extension, it MUST remove the relevant element from the
  reply. It MUST then send the remaining elements it wants to keep
  as-is without modifying them in the &lt;session-accept/&gt; iq
  stanza.</p>

  <p> It MUST NOT add any &lt;rtp-hdrext/&gt; element that was not
  offered by the initiator. The responder MAY downgrade the senders
  field from "both" to "initator" or "responder", but MUST NOT modify it
  if it is "initator" or "responder".</p>

  <p>Example negotiation where the initiator offers to use the
  timestamp offset header extension as defined in &rfc5450; and also
  the requests synchronisation metadata header extension (&rfc6051;)
  with either the 56-bit or the 64-bit format.</p>

  <example caption='Initiator sends description inside session-initiate'>
    <![CDATA[
<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:toffset'
	      id='1'/>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:ntp-64'
	      id='4907'/>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:ntp-56'
	      id='4907'/>
  <payload-type id='96' name='THEORA' clockrate='90000'/>
</description>
  ]]></example>
  
  <p>Example reply where the responder accepts the timestamp offset
  and the 56-bit synchronisation metadata header extensions.</p>

 <example caption='Reponder sends description inside session-accept'><![CDATA[
<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:toffset'
	      id='1'/>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:ntp-56'
	      id='2'/>
  <payload-type id='96' name='THEORA' clockrate='90000'/>
</description>
]]></example>

 <p>Another reply to the same request where the responder accepts only the synchronisation data header extension with the 64-bit format.</p>
 
<example caption='Responder sends description inside session-accept with only the synchronisation data accepted'><![CDATA[
<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      uri='urn:ietf:params:rtp-hdrext:ntp-64'
	      id='2'/>
  <payload-type id='96' name='THEORA' clockrate='90000'/>
</description>
]]></example>
</section1>

<section1 topic='Mapping to Session Description Protocol' anchor='sdp-mapping'>
  <p>The &lt;rtp-hdrext/&gt; element maps to the "a:extmap=" SDP line
  defined in <cite>RFC 5285</cite>. The ID is mapped to the 'id' attribute, the
  direction to the 'senders' attribute and the URI to the 'uri'
  attribute.</p>

  <p>Example conversion of a incomplete sample fragment of a SDP taken from <cite>RFC 5285</cite> section 6 into equivalent XMPP:</p>
<example caption='SDP fragment'><![CDATA[
m=video
a=sendrecv
a=extmap:1 URI-toffset
a=extmap:2/recvonly URI-gps-string
a=extmap:3 URI-frametype
]]></example>
<example caption='The same description in XMPP format'><![CDATA[
<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      id='1'
	      uri='URI-toffset'/>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      id='2'
	      uri='URI-gps-string'
	      senders='initiator'/>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
	      id='3'
	      uri='URI-frametype'/>
</description>
]]></example>
</section1>

<section1 topic='Determining support' anchor='determining-support'>
  <p>To advertise its support for Generic Header extensions in Jingle
  RTP Sessions, when replying to &xep0030; information requests an
  entity MUST return the following features:</p>

  <ol>
     <li>URNs for any version of this protocol that the entity
     supports -- e.g., "urn:xmpp:jingle:apps:rtp:rtp-hdrext:0" for the
     current version</li>
  </ol>

  <p>An example follows:</p>

  <example caption="Service discovery information request"><![CDATA[
    <iq from='romeo@montague.lit/orchard'
	id='bh3vd715'
	to='juliet@capulet.lit/balcony'
	type='get'>
      <query xmlns='http://jabber.org/protocol/disco#info'/>
    </iq>
  ]]></example>

  <example caption="Service discovery information response"><![CDATA[
    <iq from='juliet@capulet.lit/balcony'
	id='bh3vd715'
	to='romeo@montague.lit/orchard'
	type='result'>
      <query xmlns='http://jabber.org/protocol/disco#info'>
	<feature var='urn:xmpp:jingle:1'/>
	<feature var='urn:xmpp:jingle:apps:rtp:1'/>
	<feature var='urn:xmpp:jingle:apps:rtp:video'/>
	<feature var='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'/>
      </query>
    </iq>
  ]]></example>
</section1>

<section1 topic='IANA Considerations' anchor='iana-considerations'>
  <p>This document requires no interaction with the Internet Assigned
  Numbers Authority (IANA).</p>
</section1>

<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
    <p>This specification defines the following XML namespaces:</p>
    <ul>
      <li>urn:xmpp:jingle:apps:rtp:rtp-hdrext:0</li>
    </ul>
    <p>The &REGISTRAR; includes the foregoing namespaces in its
    registry at &NAMESPACES;, as governed by &xep0053;.</p>
  </section2>
  <section2 topic='Namespace Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
</section1>
<section1 topic='XML Schemas'>
<p>TODO: Write actual schema</p>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
  <p>Thanks to Youness Alaoui for his feedback.</p>
</section1>

</xep>