XEP-0180: Jingle Video Content Description Format

This document defines a content description format for Jingle video sessions.

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems should not deploy implementations of this protocol until it advances to a status of Draft.

Document Information

Series: XEP
Number: 0180
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.4
Last Updated: 2006-12-21
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0166
Supersedes: None
Superseded By: None
Wiki Page: <http://wiki.jabber.org/index.php/Jingle Video Content Description Format (XEP-0180)>

Author Information

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org

Milton Chen

Email: Milton.Chen@vseelab.com

Legal Notice

This XMPP Extension Protocol is copyright 1999 - 2007 by the XMPP Standards Foundation (XSF) and is in full conformance with the XSF's Intellectual Property Rights Policy <http://www.xmpp.org/extensions/ipr-policy.shtml>. This material may be distributed only subject to the terms and conditions set forth in the Creative Commons Attribution License (<http://creativecommons.org/licenses/by/2.5/>).

Discussion Venue

The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Conformance Terms

The following 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".

Table of Contents

1. Introduction
2. Requirements
3. Content Description Format
4. Mapping to Session Description Protocol
5. Service Discovery
6. Informational Messages
7. Implementation Notes
    7.1. Codecs
8. Security Considerations
9. IANA Considerations
10. XMPP Registrar Considerations
    10.1. Protocol Namespaces
    10.2. Jingle Content Description Formats
11. XML Schemas
    11.1. Content Description Format
    11.2. Informational Messages
Revision History

1. Introduction

Jingle [1] can be used to initiate and negotiate a wide range of peer-to-peer sessions. One session type of interest is video exchange. This document specifies a format for describing Jingle video sessions.

2. Requirements

The Jingle content description format defined herein is designed to meet the following requirements:

  1. Enable negotiation of parameters necessary for video exchange.
  2. Map these parameters to Session Description Protocol (SDP; see RFC 4566 [2]) to enable interoperability.
  3. Define informational messages related to video exchange chat.

3. Content Description Format

A Jingle video session is described by one or more encodings contained within a wrapper <description/> element. In the language of RFC 4566 these encodings are payload-types; therefore, each <payload-type/> child element specifies an encoding that can be used for the video stream. Such encodings are often used in the context of the Real-time Transfer Protocol (RTP; see RFC 3550 [3]) but may be used in other contexts as well. The most common encodings for the Audio/Video Profile (AVP) of RTP are listed in RFC 3551 [4] (these "static" types are reserved from payload ID 0 through payload ID 96), although other encodings are allowed (these "dynamic" types use payload IDs 97 to 127) in accordance with the dynamic assignment rules described in Section 3 of RFC 3551. The <payload-type/> element's 'id' attribute is REQUIRED and its 'name' attribute is RECOMMENDED. The encodings SHOULD be provided in order of preference.

Example 1. Video Description Format

    <description xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns/description/video'>
      <payload-type id='18' name='G729'/>
      <payload-type id='97' name='IPCMWB'/>
      <payload-type id='98' name='L16' transparent='true'/>
      <payload-type id='13' name='CN'/>

The <description/> element is intended to be a child of a <jingle/> element as specified in XEP-0166.

The defined attributes of the <payload-type/> element are as follows:

Table 1: Video Description Attributes

Attribute Description Datatype/Units
channels The number of channels (e.g., 2 for stereoscopic video) positiveInteger (defaults to 1)
height The vertical extent of the displayed video, in pixels positiveInteger
id A unique identifier for the payload type positiveInteger
layer The relationship of a layer to the "bottom" of the stack, where 0 = bottom (the first layer) nonNegativeInteger
name A name for the payload type string
transparent Whether or not a layer is transparent boolean
width The horizontal extent of the displayed video, in pixels positiveInteger
x The horizontal starting point of a tile, in pixels from the origin point positiveInteger
y The vertical starting point of a tile, in pixels from the origin point positiveInteger

4. Mapping to Session Description Protocol

To follow.

5. Service Discovery

If an entity supports the Jingle video content description format, it MUST advertise that fact by returning a feature of "http://www.xmpp.org/extensions/xep-0166.html#ns/description/video" in response to Service Discovery [5] information requests.

Example 2. Service Discovery Information Request

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

Example 3. Service Discovery Information Response

<iq from='juliet@capulet.com/balcony' 
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='http://www.xmpp.org/extensions/xep-0166.html#ns'/>
    <feature var='http://www.xmpp.org/extensions/xep-0166.html#ns/description/video'/>

6. Informational Messages

Informational messages may be sent by either party within the context of Jingle to communicate the status of a Jingle video session, device, or principal. The informational message MUST be an IQ-set containing a <jingle/> element of type "content-info", where the informational message is a payload element qualified by the 'http://www.xmpp.org/extensions/xep-0166.html#ns/info/video' namespace. No payload elements have yet been defined, but will be specified in a future version of this document.

7. Implementation Notes

7.1 Codecs

Support for the Theora codec [6] is RECOMMENDED.

8. Security Considerations

The description of a format for video sessions introduces no known security vulnerabilities.

9. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].

10. XMPP Registrar Considerations

10.1 Protocol Namespaces

Until this specification advances to a status of Draft, its associated namespaces shall be "http://www.xmpp.org/extensions/xep-0180.html#ns" and "http://www.xmpp.org/extensions/xep-0180.html#ns-info"; upon advancement of this specification, the XMPP Registrar [8] shall issue permanent namespaces in accordance with the process defined in Section 4 of XMPP Registrar Function [9].

10.2 Jingle Content Description Formats

The XMPP Registrar shall include "video" in its registry of Jingle content description formats. The registry submission is as follows:

  <desc>Jingle sessions that support video exchanges</desc>

11. XML Schemas

11.1 Content Description Format

<?xml version='1.0' encoding='UTF-8'?>


  <xs:element name='description'>
        <xs:element ref='payload-type' minOccurs='0' maxOccurs='unbounded'/>

  <xs:element name='payload-type'>
        <xs:extension base='empty'>
          <xs:attribute name='channels' type='xs:integer' use='optional' default='1'/>
          <xs:attribute name='height' type='xs:nonNegativeInteger' use='optional'/>
          <xs:attribute name='id' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='layer' type='xs:nonNegativeInteger' use='optional'/>
          <xs:attribute name='name' type='xs:string' use='optional'/>
          <xs:attribute name='rate' type='xs:short' use='optional'/>
          <xs:attribute name='transparent' type='xs:boolean' use='optional'/>
          <xs:attribute name='width' type='xs:nonNegativeInteger' use='optional'/>
          <xs:attribute name='x' type='xs:integer' use='optional'/>
          <xs:attribute name='y' type='xs:integer' use='optional'/>

  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>


11.2 Informational Messages

To follow.


1. XEP-0166: Jingle <http://www.xmpp.org/extensions/xep-0166.html>.

2. RFC 4566: SDP: Session Description Protocol <http://tools.ietf.org/html/rfc4566>.

3. RFC 3550: RTP: A Transport Protocol for Real-Time Applications <http://tools.ietf.org/html/rfc3550>.

4. RFC 3551: RTP Profile for Audio and Video Conferences with Minimal Control <http://tools.ietf.org/html/rfc3551>.

5. XEP-0030: Service Discovery <http://www.xmpp.org/extensions/xep-0030.html>.

6. See <http://www.theora.org/>.

7. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

8. 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://www.xmpp.org/registrar/>.

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

Revision History

Version 0.4 (2006-12-21)

Modified spec to use provisional namespace before advancement to Draft (per XEP-0053).


Version 0.3 (2006-08-23)

Modified namespace to track XEP-0166.


Version 0.2 (2006-07-12)

Updated to use content type instead of media type.


Version 0.1 (2006-03-23)

Initial version.


Version 0.0.1 (2006-03-20)

First draft.