XEP-0167: Jingle Audio Content Description Format

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

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the JSF standards process.

XEP Information

Status: Proposed
Type: Standards Track
Number: 0167
Version: 0.5
Last Updated: 2006-08-23
Publishing Organization: Jabber Software Foundation
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0166
Supersedes: None
Superseded By: None
Short Name: jingle-audio
Wiki Page: <http://wiki.jabber.org/index.php/Jingle Audio Content Description Format (XEP-0167)>

Author Information

Legal Notice

This XMPP Extension Protocol is copyright 1999 - 2006 by the Jabber Software Foundation (JSF) and is in full conformance with the JSF'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-JIG discussion list: <http://mail.jabber.org/mailman/listinfo/standards-jig>.

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 Jabber Software 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

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

2. Requirements

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

1. Enable negotiation of parameters necessary for audio chat over Realtime Transport Protocol (RTP; see RFC 3550 [2]).
2. Map these parameters to Session Description Protocol (SDP; see RFC 4566 [3]) to enable interoperability.
3. Define informational messages related to audio chat (e.g., busy and ringing).

3. Content Description Format

A Jingle audio 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/> element specifies an encoding that can be used for the audio stream. In Jingle Audio, these encodings are used in the context of RTP. 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 'id' attribute is REQUIRED. The 'name' attribute is RECOMMENDED for static payload types, and REQUIRED for dynamic payload types. The 'clockrate' attribute is RECOMMENDED and should specify the sampling frequency in hertz. The 'channels' attribute is RECOMMENDED and should specify the number of channels; if omitted, it MUST be assumed to contain one channel.

The encodings SHOULD be provided in order of preference.

Example 1. Audio Description Format

    <description xmlns='http://jabber.org/protocol/jingle/description/audio'>
      <payload-type id='18' name='G729'/>
      <payload-type id="97" name="IPCMWB"/>
      <payload-type id='98' name='L16' clockrate='16000' channels='2'/>
      <payload-type id="96" name="ISAC" clockrate="8000"/>
      <payload-type id="102" name="iLBC"/>
      <payload-type id="4" name="G723"/>
      <payload-type id="100" name="EG711U"/>
      <payload-type id="101" name="EG711A"/>
      <payload-type id="0" name="PCMU" clockrate="16000"/>
      <payload-type id="8" name="PCMA"/>
      <payload-type id="13" name="CN"/>
    </description>
  

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

When the session is provisionally accepted, as indicated by the target entity sending an empty IQ result in response to an 'initiate' message, both receiving and sending entities SHOULD start listening for audio as defined by the negotiated transport method. For interoperability with telephony systems, each entity SHOULD play any audio received at this time, before the target sends an 'accept' message.

4. Mapping to Session Description Protocol

If the payload type is static (payload-type IDs 0 through 96 inclusive), it MUST be mapped to a media field defined in RFC 4566: Session Description Protocol (SDP). The generic format for the media field is as follows:

m=<media> <port> <transport> <fmt list>
  

In the context of Jingle audio sessions, the <content> is "audio", the <port> is the preferred port for such communications (which may be determined dynamically), the <transport> is whatever transport method is negotiated via the Jingle negotiation (e.g., "RTP/AVT"), and the <fmt list> is the payload-type ID.

For example, consider the following static payload-type:

Example 2. Jingle Format for Static Payload-Type

<payload-type id="13" name="CN"/>
  

Example 3. SDP Mapping of Static Payload-Type

m=audio 9999 RTP/AVP 13
  

If the payload type is dynamic (payload-type IDs 97 through 127 inclusive), it SHOULD be mapped to an SDP media field plus an SDP attribute field named "rtpmap".

For example, consider a payload of 16-bit linear-encoded stereo audio sampled at 16KHz associated with dynamic payload-type 98:

Example 4. Jingle Format for Dynamic Payload-Type

<payload-type id='98' name='L16' clockrate='16000' channels='2'/>
  

Example 5. SDP Mapping of Dynamic Payload-Type

m=audio 9999 RTP/AVP 98
a=rtpmap:98 L16/16000/2
  

5. Service Discovery

If an entity supports the Jingle audio content description format, it MUST advertise that fact by returning a feature of "http://jabber.org/protocol/jingle/description/audio" in response to Service Discovery [5] information requests.

Example 6. Service Discovery Information Request

<iq from='romeo@montague.net/orchard'
    id='disco1'
    to='juliet@capulet.com/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 7. Service Discovery Information Response

<iq from='juliet@capulet.com/balcony'
    id='disco1'
    to='romeo@montague.net/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://jabber.org/protocol/jingle'/>
    <feature var='http://jabber.org/protocol/jingle/description/audio'/>
    ...
  </query>
</iq>
  

6. Informational Messages

<iq from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='busy1'
    type='set'>
  <jingle xmlns='http://jabber.org/protocol/jingle'
          action='content-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <busy xmlns='http://jabber.org/protocol/jingle/info/audio'/>
  </jingle>
</iq>
    

<iq from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='hold1'
    type='set'>
  <jingle xmlns='http://jabber.org/protocol/jingle'
          action='content-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <hold xmlns='http://jabber.org/protocol/jingle/info/audio'/>
  </jingle>
</iq>
    

<iq from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='mute1'
    type='set'>
  <jingle xmlns='http://jabber.org/protocol/jingle'
          action='content-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <mute xmlns='http://jabber.org/protocol/jingle/info/audio'/>
  </jingle>
</iq>
    

<iq from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='queued1'
    type='set'>
  <jingle xmlns='http://jabber.org/protocol/jingle'
          action='content-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <queued xmlns='http://jabber.org/protocol/jingle/info/audio'/>
  </jingle>
</iq>
    

<iq from='juliet@capulet.com/balcony'
    to='romeo@montague.net/orchard'
    id='ringing1'
    type='set'>
  <jingle xmlns='http://jabber.org/protocol/jingle'
          action='content-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <ringing xmlns='http://jabber.org/protocol/jingle/info/audio'/>
  </jingle>
</iq>
    

7. Implementation Notes

8. Security Considerations

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

9. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [9].

10. XMPP Registrar Considerations

<content>
  <name>audio</name>
  <desc>Jingle sessions that support audio exchanges</desc>
  <doc>XEP-0167</doc>
</content>
    

11. XML Schemas

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/jingle/description/audio'
    xmlns='http://jabber.org/protocol/jingle/description/audio'
    elementFormDefault='qualified'>

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

  <xs:element name='payload-type'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='channels' type='xs:byte' use='optional' default='1'/>
          <xs:attribute name='clockrate' type='xs:short' use='optional'/>
          <xs:attribute name='id' type='xs:unsignedByte' use='required'/>
          <xs:attribute name='name' type='xs:string' use='optional'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

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

</xs:schema>
    

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/jingle/info/audio'
    xmlns='http://jabber.org/protocol/jingle/info/audio'
    elementFormDefault='qualified'>

  <xs:element name='busy' type='empty'/>
  <xs:element name='hold' type='empty'/>
  <xs:element name='mute' type='empty'/>
  <xs:element name='queued' type='empty'/>
  <xs:element name='ringing' type='empty'/>

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

</xs:schema>
    

Notes

Revision History

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