<?xml version='1.0' encoding='UTF-8'?> <!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>Draft</status> <type>Standards Track</type> <sig>Standards</sig> <approver>Council</approver> <dependencies> <spec>XEP-0167</spec> <spec>RFC 5285</spec> </dependencies> <schemaloc> <url>http://xmpp.org/schemas/jingle-apps-rtp-rtp-hdrext.xsd</url> </schemaloc> <author> <firstname>Olivier</firstname> <surname>CrĂȘte</surname> <email>olivier.crete@collabora.co.uk</email> <jid>olivier.crete@collabora.co.uk</jid> </author> <discuss>jingle</discuss> <revision> <version>1.0</version> <date>2015-08-11</date> <initials>XEP Editor (mam)</initials> <remark><p>Advanced to Draft per a vote of the XMPP Council.</p></remark> </revision> <revision> <version>0.2</version> <date>2015-03-25</date> <initials>ph</initials> <remark><p>Added XML Schema; Updated based on last call feedback.</p></remark> </revision> <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, <rtp-hdrext/>, that can be inserted in the <description/> element of a XEP-0167 RTP session.</p> <p>The attributes of the <rtp-hdrext/> 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 <parameter/> elements to describe it. Any other form of parameter can be stored as the 'key' attribute in a parameter element with an empty value.</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 <session-initiate/> 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 <session-accept/> iq stanza.</p> <p> It MUST NOT add any <rtp-hdrext/> 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 <rtp-hdrext/> 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 ®ISTRAR; 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'> <code><![CDATA[ <?xml version='1.0' encoding='UTF-8'?> <xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema' targetNamespace='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0' xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0' elementFormDefault='qualified'> <xs:annotation> <xs:documentation> The protocol documented by this schema is defined in XEP-0294: http://www.xmpp.org/extensions/xep-0294.html </xs:documentation> </xs:annotation> <xs:element name='rtp-hdrext'> <xs:complexType> <xs:sequence> <xs:element name='parameter' type='parameterElementType' minOccurs='0' maxOccurs='unbounded'/> </xs:sequence> <xs:attribute name='id' type='xs:unsignedInt' use='required'/> <xs:attribute name='uri' type='xs:string' use='required'/> <xs:attribute name='senders' use='optional' default='both'> <xs:simpleType> <xs:restriction base='xs:NCName'> <xs:enumeration value='both'/> <xs:enumeration value='initiator'/> <xs:enumeration value='none'/> <xs:enumeration value='responder'/> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> <xs:complexType name='parameterElementType'> <xs:simpleContent> <xs:extension base='empty'> <xs:attribute name='name' type='xs:string' use='required'/> <xs:attribute name='value' type='xs:string' use='optional'/> </xs:extension> </xs:simpleContent> </xs:complexType> </xs:schema> ]]></code> </section1> <section1 topic='Acknowledgements' anchor='ack'> <p>Thanks to Youness Alaoui for his feedback.</p> </section1> </xep>