mirror of
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259 lines
8.9 KiB
XML
Executable File
259 lines
8.9 KiB
XML
Executable File
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM 'xep.ent'>
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>Jingle RTP Header Extensions Negotiation</title>
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<abstract>This specification defines an XMPP extension to negotiate
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the use of the use of RTP Header Extension as defined by RFC 5285
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with Jingle RTP sessions</abstract>
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&LEGALNOTICE;
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<number>0294</number>
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<status>Deferred</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<approver>Council</approver>
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<dependencies>
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<spec>XEP-0167</spec>
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<spec>RFC 5285</spec>
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</dependencies>
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<author>
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<firstname>Olivier</firstname>
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<surname>Crête</surname>
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<email>olivier.crete@collabora.co.uk</email>
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<jid>olivier.crete@collabora.co.uk</jid>
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</author>
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<discuss>jingle</discuss>
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<revision>
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<version>0.1</version>
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<date>2011-03-24</date>
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<initials>psa</initials>
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<remark><p>Initial published version.</p></remark>
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</revision>
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<revision>
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<version>0.0.1</version>
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<date>2011-01-10</date>
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<initials>oc</initials>
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<remark><p>First draft.</p></remark>
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</revision>
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</header>
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<section1 topic='Introduction' anchor='introduction'>
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<p>This documents specifies how to negotiate the use of the RTP
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Header Extensions as defined by &rfc5285; with Jingle RTP
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sessions.</p>
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</section1>
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<section1 topic='Requirements' anchor='requirements'>
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<p>The Jingle extension defined herein is designed to meet the following requirements:</p>
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<ol>
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<li>Enable negotiations of the RTP Header extensions as defined in
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<cite>RFC 5285</cite>.</li>
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<li>Map these parameters to Session Description Protocol (SDP; see
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&rfc4566;) to enable interoperability.</li>
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</ol>
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</section1>
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<section1 topic='New element' anchor='element'>
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<p>This specification defines a new element, <rtp-hdrext/>,
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that can be inserted in the <description/> element of a
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XEP-0167 RTP session.</p>
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<p>The attributes of the <rtp-hdrext/> element are:</p>
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<table caption='rtp-hdrext attributes'>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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<th>Inclusion</th>
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<th>Possible values</th>
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</tr>
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<tr>
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<td>id</td>
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<td>The ID of the extensions</td>
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<td>REQUIRED</td>
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<td>1-256, 4096-4351</td>
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</tr>
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<tr>
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<td>uri</td>
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<td>The URI that defines the extension</td>
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<td>REQUIRED</td>
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<td>Any valid URI</td>
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</tr>
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<tr>
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<td>senders</td>
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<td>Which party is allowed to send the negotiated RTP Header Extensions</td>
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<td>OPTIONAL (defaults to "both")</td>
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<td>"initiator", "responder", and "both"</td>
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</tr>
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</table>
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<p>Any type of RTP Header Extension that requires extra
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parameters in the a=b form can embed <parameter/> elements to
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describe it. Any other form of parameter can be stored in the CDATA
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inside the <rtp-hdrext/> element.</p>
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</section1>
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<section1 topic='Negotiation' anchor='negotiation'>
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<p>RTP header extensions are negotiated along the codecs. They
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follow the same Offer/Answer mechanism based on SDP
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Offer/Answer. The initiator signals which RTP header extensions it
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wants to send or receive in the the <session-initiate/> iq
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stanza. If the responder does not understand the type of header
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extensions, it MUST remove the element from the reply. If the
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responder does not wish to provide or receive some kind of RTP
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header extension, it MUST remove the relevant element from the
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reply. It MUST then send the remaining elements it wants to keep
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as-is without modifying them in the <session-accept/> iq
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stanza.</p>
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<p> It MUST NOT add any <rtp-hdrext/> element that was not
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offered by the initiator. The responder MAY downgrade the senders
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field from "both" to "initator" or "responder", but MUST NOT modify it
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if it is "initator" or "responder".</p>
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<p>Example negotiation where the initiator offers to use the
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timestamp offset header extension as defined in &rfc5450; and also
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the requests synchronisation metadata header extension (&rfc6051;)
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with either the 56-bit or the 64-bit format.</p>
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<example caption='Initiator sends description inside session-initiate'>
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<![CDATA[
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<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:toffset'
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id='1'/>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:ntp-64'
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id='4907'/>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:ntp-56'
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id='4907'/>
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<payload-type id='96' name='THEORA' clockrate='90000'/>
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</description>
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]]></example>
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<p>Example reply where the responder accepts the timestamp offset
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and the 56-bit synchronisation metadata header extensions.</p>
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<example caption='Reponder sends description inside session-accept'><![CDATA[
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<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:toffset'
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id='1'/>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:ntp-56'
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id='2'/>
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<payload-type id='96' name='THEORA' clockrate='90000'/>
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</description>
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]]></example>
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<p>Another reply to the same request where the responder accepts only the synchronisation data header extension with the 64-bit format.</p>
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<example caption='Responder sends description inside session-accept with only the synchronisation data accepted'><![CDATA[
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<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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uri='urn:ietf:params:rtp-hdrext:ntp-64'
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id='2'/>
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<payload-type id='96' name='THEORA' clockrate='90000'/>
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</description>
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]]></example>
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</section1>
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<section1 topic='Mapping to Session Description Protocol' anchor='sdp-mapping'>
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<p>The <rtp-hdrext/> element maps to the "a:extmap=" SDP line
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defined in <cite>RFC 5285</cite>. The ID is mapped to the 'id' attribute, the
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direction to the 'senders' attribute and the URI to the 'uri'
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attribute.</p>
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<p>Example conversion of a incomplete sample fragment of a SDP taken from <cite>RFC 5285</cite> section 6 into equivalent XMPP:</p>
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<example caption='SDP fragment'><![CDATA[
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m=video
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a=sendrecv
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a=extmap:1 URI-toffset
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a=extmap:2/recvonly URI-gps-string
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a=extmap:3 URI-frametype
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]]></example>
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<example caption='The same description in XMPP format'><![CDATA[
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<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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id='1'
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uri='URI-toffset'/>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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id='2'
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uri='URI-gps-string'
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senders='initiator'/>
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<rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
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id='3'
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uri='URI-frametype'/>
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</description>
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]]></example>
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</section1>
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<section1 topic='Determining support' anchor='determining-support'>
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<p>To advertise its support for Generic Header extensions in Jingle
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RTP Sessions, when replying to &xep0030; information requests an
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entity MUST return the following features:</p>
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<ol>
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<li>URNs for any version of this protocol that the entity
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supports -- e.g., "urn:xmpp:jingle:apps:rtp:rtp-hdrext:0" for the
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current version</li>
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</ol>
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<p>An example follows:</p>
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<example caption="Service discovery information request"><![CDATA[
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<iq from='romeo@montague.lit/orchard'
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id='bh3vd715'
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to='juliet@capulet.lit/balcony'
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type='get'>
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<query xmlns='http://jabber.org/protocol/disco#info'/>
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</iq>
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]]></example>
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<example caption="Service discovery information response"><![CDATA[
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<iq from='juliet@capulet.lit/balcony'
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id='bh3vd715'
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to='romeo@montague.lit/orchard'
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type='result'>
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<query xmlns='http://jabber.org/protocol/disco#info'>
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<feature var='urn:xmpp:jingle:1'/>
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<feature var='urn:xmpp:jingle:apps:rtp:1'/>
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<feature var='urn:xmpp:jingle:apps:rtp:video'/>
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<feature var='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'/>
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</query>
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</iq>
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]]></example>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana-considerations'>
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<p>This document requires no interaction with the Internet Assigned
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Numbers Authority (IANA).</p>
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</section1>
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<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
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<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
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<p>This specification defines the following XML namespaces:</p>
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<ul>
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<li>urn:xmpp:jingle:apps:rtp:rtp-hdrext:0</li>
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</ul>
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<p>The ®ISTRAR; includes the foregoing namespaces in its
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registry at &NAMESPACES;, as governed by &xep0053;.</p>
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</section2>
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<section2 topic='Namespace Versioning' anchor='registrar-versioning'>
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&NSVER;
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</section2>
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</section1>
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<section1 topic='XML Schemas'>
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<p>TODO: Write actual schema</p>
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</section1>
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<section1 topic='Acknowledgements' anchor='ack'>
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<p>Thanks to Youness Alaoui for his feedback.</p>
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</section1>
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</xep>
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