XEP-0294: Jingle RTP Header Extensions Negotiation

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
Author:Olivier Crête
Copyright:© 1999 - 2014 XMPP Standards Foundation. SEE LEGAL NOTICES.
Type:Standards Track
Last Updated:2011-03-24

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the XSF standards process. The Last Call ends on 2015-01-20. Please send your feedback to the standards@xmpp.org discussion list.

Table of Contents

1. Introduction
2. Requirements
3. New element
4. Negotiation
5. Mapping to Session Description Protocol
6. Determining support
7. IANA Considerations
8. XMPP Registrar Considerations
    8.1. Protocol Namespaces
    8.2. Namespace Versioning
9. XML Schemas
10. Acknowledgements

    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

This documents specifies how to negotiate the use of the RTP Header Extensions as defined by RFC 5285 [1] with Jingle RTP sessions.

2. Requirements

The Jingle extension defined herein is designed to meet the following requirements:

  1. Enable negotiations of the RTP Header extensions as defined in RFC 5285.
  2. Map these parameters to Session Description Protocol (SDP; see RFC 4566 [2]) to enable interoperability.

3. New element

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:

Table 1: rtp-hdrext attributes

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 in the CDATA inside the <rtp-hdrext/> element.

4. Negotiation

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.

Example 1. Initiator sends description inside session-initiate

<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <payload-type id='96' name='THEORA' clockrate='90000'/>

Example reply where the responder accepts the timestamp offset and the 56-bit synchronisation metadata header extensions.

Example 2. Reponder sends description inside session-accept

<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <payload-type id='96' name='THEORA' clockrate='90000'/>

Another reply to the same request where the responder accepts only the synchronisation data header extension with the 64-bit format.

Example 3. Responder sends description inside session-accept with only the synchronisation data accepted

<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <payload-type id='96' name='THEORA' clockrate='90000'/>

5. Mapping to Session Description Protocol

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:

Example 4. SDP fragment

a=extmap:1 URI-toffset
a=extmap:2/recvonly URI-gps-string
a=extmap:3 URI-frametype

Example 5. The same description in XMPP format

<description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'
  <rtp-hdrext xmlns='urn:xmpp:jingle:apps:rtp:rtp-hdrext:0'

6. Determining support

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:

  1. 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

An example follows:

Example 6. Service discovery information request

    <iq from='romeo@montague.lit/orchard'
      <query xmlns='http://jabber.org/protocol/disco#info'/>

Example 7. Service discovery information response

    <iq from='juliet@capulet.lit/balcony'
      <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'/>

7. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA).

8. XMPP Registrar Considerations

8.1 Protocol Namespaces

This specification defines the following XML namespaces:

The XMPP Registrar [6] includes the foregoing namespaces in its registry at <http://xmpp.org/registrar/namespaces.html>, as governed by XMPP Registrar Function (XEP-0053) [7].

8.2 Namespace Versioning

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.

9. XML Schemas

TODO: Write actual schema

10. Acknowledgements

Thanks to Youness Alaoui for his feedback.


Appendix A: Document Information

Series: XEP
Number: 0294
Publisher: XMPP Standards Foundation
Status: Proposed
Type: Standards Track
Version: 0.1
Last Updated: 2011-03-24
Approving Body: XMPP Council
Dependencies: XEP-0167, RFC 5285
Supersedes: None
Superseded By: None
Short Name:
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Olivier Crête

Email: olivier.crete@collabora.co.uk
JabberID: olivier.crete@collabora.co.uk

Appendix C: Legal Notices


This XMPP Extension Protocol is copyright © 1999 - 2014 by the XMPP Standards Foundation (XSF).


Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

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 <http://xmpp.org/about-xmpp/xsf/xsf-ipr-policy/> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

Appendix D: Relation to XMPP

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.

Appendix E: Discussion Venue

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>.

Appendix F: Requirements Conformance

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".

Appendix G: Notes

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 <http://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 <http://xmpp.org/registrar/>.

7. XEP-0053: XMPP Registrar Function <http://xmpp.org/extensions/xep-0053.html>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.1 (2011-03-24)

Initial published version.


Version 0.0.1 (2011-01-10)

First draft.