This documents specifies how to negotiate the use of the RTP Header Extensions as defined by RFC 5285 [1] with Jingle RTP sessions.
The Jingle extension defined herein is designed to meet the following requirements:
This specification defines a new element, <rtp-hdrext/>, that can be inserted in the <description/> element of a XEP-0167 RTP session.
The attributes of the <rtp-hdrext/> element are:
| Attribute | Description | Inclusion | Possible values |
|---|---|---|---|
| id | The ID of the extensions | REQUIRED | 1-256, 4096-4351 |
| uri | The URI that defines the extension | REQUIRED | Any valid URI |
| senders | Which party is allowed to send the negotiated RTP Header Extensions | OPTIONAL (defaults to "both") | "initiator", "responder", and "both" |
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.
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.
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".
Example negotiation where the initiator offers to use the timestamp offset header extension as defined in RFC 5450 [3] and also the requests synchronisation metadata header extension (RFC 6051 [4]) with either the 56-bit or the 64-bit format.
<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 reply where the responder accepts the timestamp offset and the 56-bit synchronisation metadata header extensions.
<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>
Another reply to the same request where the responder accepts only the synchronisation data header extension with the 64-bit format.
<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>
The <rtp-hdrext/> element maps to the "a:extmap=" SDP line defined in RFC 5285. The ID is mapped to the 'id' attribute, the direction to the 'senders' attribute and the URI to the 'uri' attribute.
Example conversion of a incomplete sample fragment of a SDP taken from RFC 5285 section 6 into equivalent XMPP:
m=video a=sendrecv a=extmap:1 URI-toffset a=extmap:2/recvonly URI-gps-string a=extmap:3 URI-frametype
<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>
To advertise its support for Generic Header extensions in Jingle RTP Sessions, when replying to Service Discovery (XEP-0030) [5] information requests an entity MUST return the following features:
An example follows:
<iq from='romeo@montague.lit/orchard'
id='bh3vd715'
to='juliet@capulet.lit/balcony'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<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>
This document requires no interaction with the Internet Assigned Numbers Authority (IANA).
This specification defines the following XML namespaces:
The XMPP Registrar [6] includes the foregoing namespaces in its registry at <https://xmpp.org/registrar/namespaces.html>, as governed by XMPP Registrar Function (XEP-0053) [7].
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
<?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>
Thanks to Youness Alaoui for his feedback.
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This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
There exists a special venue for discussion related to the technology described in this document: the <jingle@xmpp.org> mailing list.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Given that this XMPP Extension Protocol normatively references IETF technologies, discussion on the <xsf-ietf@xmpp.org> list might also be appropriate.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. RFC 5285: A General Mechanism for RTP Header Extensions <http://tools.ietf.org/html/rfc5285>.
2. RFC 4566: SDP: Session Description Protocol <http://tools.ietf.org/html/rfc4566>.
3. RFC 5450: Transmission Time Offsets in RTP Streams <http://tools.ietf.org/html/rfc5450>.
4. RFC 6051: Rapid Synchronisation of RTP Flows <http://tools.ietf.org/html/rfc6051>.
5. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
6. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
7. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Advanced to Draft per a vote of the XMPP Council.
Added XML Schema; Updated based on last call feedback.
Initial published version.
First draft.
END