XEP-0167: Jingle Audio via RTP

This document defines methods for negotiating Jingle audio sessions that use the Real-time Transport Protocol (RTP) for media exchange.

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.

Document Information

Series: XEP
Number: 0167
Publisher: XMPP Standards Foundation
Status: Proposed
Type: Standards Track
Version: 0.11
Last Updated: 2007-11-15
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0166
Supersedes: None
Superseded By: None
Short Name: TO BE ASSIGNED
Wiki Page: <http://wiki.jabber.org/index.php/Jingle Audio via RTP (XEP-0167)>

Author Information

Scott Ludwig

Email: scottlu@google.com
JabberID: scottlu@google.com

Peter Saint-Andre

JabberID: stpeter@jabber.org
URI: https://stpeter.im/

Sean Egan

Email: seanegan@google.com
JabberID: seanegan@google.com

Robert McQueen

Email: robert.mcqueen@collabora.co.uk
JabberID: robert.mcqueen@collabora.co.uk

Legal Notices

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which may be found at <http://www.xmpp.org/extensions/ipr-policy.shtml> or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201 USA).

Copyright

This XMPP Extension Protocol is copyright (c) 1999 - 2007 by the XMPP Standards Foundation (XSF).

Permissions

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. Jingle Conformance
4. Application Format
5. Negotiating a Jingle Audio Session
6. Scenarios
    6.1. Responder is Busy
    6.2. Jingle Audio via RTP/AVP, Negotiated with ICE-UDP
    6.3. Jingle Audio and Video via RTP/AVP, Negotiated with ICE-UDP
    6.4. Secure Jingle Audio via UDP/TLS/RTP/AVP, Negotiated with ICE-UDP
7. Mapping to Session Description Protocol
8. Informational Messages
    8.1. Format
    8.2. Examples
9. Error Handling
10. Determining Support
11. Implementation Notes
    11.1. Codecs
    11.2. DTMF
    11.3. When to Listen
12. Security Considerations
13. IANA Considerations
14. XMPP Registrar Considerations
    14.1. Protocol Namespaces
    14.2. Jingle Application Formats
15. XML Schemas
    15.1. Application Format
    15.2. Errors
    15.3. Informational Messages
Notes
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 audio chat. This document specifies an application format for negotiating Jingle audio sessions, where the media is exchanged over the Realtime Transport Protocol (RTP; see RFC 3550 [2]).

2. Requirements

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

  1. Enable negotiation of parameters necessary for audio chat over Realtime Transport Protocol (RTP).
  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., ringing, on hold, on mute).

3. Jingle Conformance

In accordance with Section 8 of XEP-0166, this document specifies the following information related to the Jingle Audio via RTP application type:

  1. The application format negotiation process is defined in the Negotiating a Jingle Audio Session section of this document.

  2. The semantics of the <description/> element are defined in the Application Format section of this document.

  3. A mapping of Jingle semantics to the Session Description Protocol is provided in the Mapping to Session Description Protocol section of this document.

  4. A Jingle audio session SHOULD use a lossy transport method such as Jingle Raw UDP Transport Method [4] or the "ice-udp" method specified in Jingle ICE Transport Method [5], but MAY use a reliable transport such as "ice-tcp" if a low-bandwidth codec is employed.

  5. Content is to be sent and received as follows:

4. Application Format

A Jingle audio session is described by a content type that contains one application format and one transport method. The application format consists of one or more encodings contained within a wrapper <description/> element qualified by the 'http://www.xmpp.org/extensions/xep-0167.html#ns' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). In the language of RFC 4566 each encoding is a payload-type; therefore, each <payload-type/> element specifies an encoding that can be used for the audio stream, as illustrated in the following example.

Example 1. Audio description format

    <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
      <payload-type id='96' name='speex' clockrate='16000'/>
      <payload-type id='97' name='speex' clockrate='8000'/>
      <payload-type id='18' name='G729'/>
      <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
      <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      <payload-type id='102' name='iLBC'/>
      <payload-type id='4' name='G723'/>
      <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 <content/> element as specified in XEP-0166.

The <content/> element SHOULD possess a 'profile' attribute that specifies the exact protocol in use as would be encapsulated in SDP (e.g., "RTP/AVP" or "UDP/TLS/RTP/AVP").

The encodings SHOULD be provided in order of preference by placing the most-preferred <payload-type/> element as the first child of the <description/> element (etc.).

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

Table 1: Payload-Type Attributes

Attribute Description Datatype Inclusion
channels The number of channels; if omitted, it MUST be assumed to contain one channel positiveInteger (defaults to 1) RECOMMENDED
clockrate The sampling frequency in Hertz positiveInteger RECOMMENDED
id The payload identifier positiveInteger REQUIRED
maxptime Maximum packet time as specified in RFC 4566 positiveInteger OPTIONAL
name The appropriate subtype of the audio MIME type string RECOMMENDED for static payload types, REQUIRED for dynamic payload types
ptime Packet time as specified in RFC 4566 positiveInteger OPTIONAL

In Jingle Audio, the 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 [6] (these "static" types are reserved from payload ID 0 through payload ID 95), although other encodings are allowed (these "dynamic" types use payload IDs 96 to 127) in accordance with the dynamic assignment rules described in Section 3 of RFC 3551. The payload IDs are represented in the 'id' attribute.

Each <payload-type/> element MAY contain one or more child elements that specify particular parameters related to the payload. For example, as described in RTP Payload Format for the Speex Codec [7], the "cng", "mode", and "vbr" parameters may be specified in relation to usage of the Speex [8] codec. Where such parameters are encoded via the "fmtp" SDP attribute, they shall be represented in Jingle via the following format:

<parameter name='foo' value='bar'/>

Note: The parameter names are effectively guaranteed to be unique, since the Internet Assigned Numbers Authority (IANA) [9] maintains a registry of SDP parameters (see <http://www.iana.org/assignments/sdp-parameters>).

5. Negotiating a Jingle Audio Session

When the initiator sends a session-initiate stanza to the responder, the <description/> element includes all of the payload types that the initiator can receive for Jingle audio (each one encapsulated in a separate <payload-type/> element):

Example 2. Initiation

<iq from='romeo@montague.net/orchard' 
    id='jingleaudio1' 
    to='juliet@capulet.com/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'>
          action='session-initiate'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'/>
    </content>
  </jingle>
</iq>

Upon receiving the session-initiate stanza, the responder determines whether it can proceed with the negotiation. The general Jingle error cases are specified in XEP-0166 and illustrated in the Scenarios section of this document. In addition, the responder must determine if it supports any of the payload types advertised by the initiator; if it supports none of the offered payload types, it must reject the session by returning a <not-acceptable/> error with a Jingle-Audio-specific condition of <unsupported-codecs/>:

Example 3. Responder does not support any of the codecs

<iq from='juliet@capulet.com/balcony' 
    id='jingleaudio1'
    to='romeo@montague.net/orchard' 
    type='error'>
  <error type='cancel'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <unsupported-codecs xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-errors'/>
  </error>
</iq>

If there is no error, the responder acknowledges the session-initiation request.

Example 4. Responder acknowledges session-initiate

  <iq from='juliet@capulet.com/balcony' 
      id='jingleaudio1' 
      to='romeo@montague.net/orchard' 
      type='result'/>

The responder then should send a list of the payload types that it can receive via a Jingle "content-accept" (or "session-accept") action. The list that the responder sends MAY include any payload types (not a subset of the payload types sent by the initiator) but SHOULD retain the ID numbers specified by the initiator. The order of the <payload-type/> elements indicates the responder's preferences, with the most-preferred types first.

Example 5. Responder accepts content type

<iq from='juliet@capulet.com/balcony' 
    id='jingleaudio2' 
    to='romeo@montague.net/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'>
          action='content-accept'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <content name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='102' name='iLBC'/>
        <payload-type id='4' name='G723'/>
        <payload-type id='8' name='PCMA'/>
        <payload-type id='13' name='CN'/>
      </description> 
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'/>
    </content>
  </jingle>
</iq>

The initiator acknowledges the 'content-accept' with an empty IQ result:

Example 6. Initiator acknowledges modified application format

  <iq from='romeo@montegue.net/orchard' 
      id='jingleaudio2' 
      to='juliet@capulet.com/balcony' 
      type='result'/>

After successful transport negotiation (not shown here), the responder then accepts the session:

Example 7. Responder definitively accepts the session

<iq from='juliet@capulet.com/balcony' 
    id='accept1'
    to='romeo@montague.net/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-accept'
          initiator='romeo@montague.net/orchard'
          responder='juliet@capulet.com/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='102' name='iLBC'/>
        <payload-type id='4' name='G723'/>
        <payload-type id='8' name='PCMA'/>
        <payload-type id='13' name='CN'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'>
        <candidate component='2'
                   foundation='1'
                   generation='0' 
                   ip='192.0.2.3' 
                   network='1'
                   port='45664'
                   priority='1107821052'
                   protocol='udp'
                   pwd='asd88fgpdd777uzjYhagZg'
                   type='srflx'
                   ufrag='8hhy'/>
      </transport>
    </content>
  </jingle>
</iq>

And the initiator acknowledges session acceptance:

Example 8. Initiator acknowledges session acceptance

  <iq from='romeo@montague.net/orchard' 
      id='accept1' 
      to='juliet@capulet.com/balcony' 
      type='result'/>

Note: Because a "session-accept" action implicitly indicates acceptance of the application format (i.e., "content-accept"), it is not necessary to send a separate "content-accept" action. This flow is shown for completeness only.

6. Scenarios

The following sections show a number of Jingle audio scenarios, in relative order of complexity.

6.1 Responder is Busy

In this scenario, Romeo initiates a voice chat with Juliet but she is otherwise engaged.

The session flow is as follows:

Romeo                         Juliet
  |                             |
  |   session-initiate          |
  |---------------------------->|
  |   error                     |
  |   (recipient-unavailable)   |
  |<----------------------------|

The protocol flow is as follows.

Example 9. Initiator sends session-initiate

<iq from='romeo@montague.lit/orchard' to='juliet@capulet.lit/balcony' id='jingle1' type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'/>
    </content>
  </jingle>
</iq>

Example 10. Responder returns recipient-unavailable error

<iq from='juliet@capulet.lit/balcony'
    id='jingle1'
    to='romeo@montague.lit/orchard'
    type='error'>
  <error type='wait'>
    <recipient-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <busy xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns-errors'/>
  </error>
</iq>

6.2 Jingle Audio via RTP/AVP, Negotiated with ICE-UDP

In this scenario, Romeo initiates a voice chat with Juliet using a transport method of ICE-UDP. The parties also exchange informational messages.

The session flow is as follows:

Romeo                         Juliet
  |                             |
  |   session-initiate          |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   session-info (ringing)    |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   transport-info (X times)  |
  |   (with acks)               |
  |<--------------------------->|
  |   session-accept            |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   AUDIO (RTP)               |
  |<===========================>|
  |   session-terminate         |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |                             |

The protocol flow is as follows.

Example 11. Initiator sends session-initiate

<iq from='romeo@montague.lit/orchard' to='juliet@capulet.lit/balcony' id='jingle1' type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'/>
    </content>
  </jingle>
</iq>

Example 12. Responder sends provisional acceptance

<iq from='juliet@capulet.lit/balcony'
    id='accept1'
    to='romeo@montague.lit/orchard'
    type='result'/>

Example 13. Responder sends ringing message

<iq from='juliet@capulet.com/balcony'
    id='ringing1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <ringing xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 14. Initiator acknowledges ringing message

<iq from='romeo@montague.lit/orchard' 
    id='ringing1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

Example 15. Initiator sends a candidate

<iq from='romeo@montague.lit/orchard' 
    id='info1' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns' 
          action='transport-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'>
        <candidate component='1'
                   foundation='1'
                   generation='0' 
                   ip='10.0.1.1' 
                   network='0'
                   port='8998'
                   priority='2114978302'
                   protocol='udp'
                   pwd='asd88fgpdd777uzjYhagZg'
                   type='host'
                   ufrag='8hhy'/>
      </transport>
    </content>
  </jingle>
</iq>

Example 16. Initiator sends a second candidate

<iq from='romeo@montague.lit/orchard' 
    id='info2' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns' 
          action='transport-info' 
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'>
        <candidate component='1'
                   foundation='1'
                   generation='0' 
                   ip='192.0.2.3' 
                   network='1'
                   port='45664'
                   priority='1678246398'
                   protocol='udp'
                   pwd='asd88fgpdd777uzjYhagZg'
                   type='srflx'
                   ufrag='8hhy'/>
      </transport>
    </content>
  </jingle>
</iq>

Example 17. Initiator sends a third candidate

<iq from='romeo@montague.lit/orchard' 
    id='info3' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns' 
          action='transport-info' 
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'>
        <candidate component='1'
                   foundation='1'
                   generation='0' 
                   ip='208.245.212.67' 
                   network='2'
                   port='53267'
                   priority='1677984254'
                   protocol='udp'
                   pwd='asd88fgpdd777uzjYhagZg'
                   type='srflx'
                   ufrag='8hhy'/>
      </transport>
    </content>
  </jingle>
</iq>

For each candidate received, the other party acknowledges receipt or returns an error:

Example 18. Responder acknowledges receipt

<iq from='juliet@capulet.lit/balcony' 
    id='info1' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

<iq from='juliet@capulet.lit/balcony' 
    id='info2' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

<iq from='juliet@capulet.lit/balcony' 
    id='info3' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

At the same time (i.e., immediately after acknowledging the session-initation request, not waiting for the initiator to begin or finish sending candidates), the responder also begins sending candidates that may work for it. As above, the initiator acknowledges receipt of the candidates.

As the initiator and responder receive candidates, they probe the various candidate transports for connectivity. In performing these connectivity checks, the parties follow the procedure specified in Section 7 of draft-ietf-mmusic-ice.

If one of the candidate transports is found to work, the responder accepts the session.

Example 19. Responder sends session-accept

<iq from='juliet@capulet.lit/balcony' 
    id='accept1'
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='102' name='iLBC'/>
        <payload-type id='4' name='G723'/>
        <payload-type id='8' name='PCMA'/>
        <payload-type id='13' name='CN'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'>
        <candidate ip='208.245.212.67' port='9876' generation='0'/>
      </transport>
    </content>
  </jingle>
</iq>

If the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.

Example 20. Initiator acknowledges session-accept

<iq from='romeo@montague.lit/orchard' 
    id='accept1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the <payload-type/> children).

The parties may continue the session as long as desired.

Eventually, one of the parties terminates the session.

Example 21. Responder terminates the session

<iq from='juliet@capulet.lit/balcony'
    id='term1'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-terminate'
          initiator='romeo@montague.lit/orchard'
          reason='Sorry, gotta go!'
          sid='a73sjjvkla37jfea'/>
</iq>

The other party then acknowledges termination of the session:

Example 22. Initiator acknowledges termination

<iq from='romeo@montague.lit/orchard' 
    id='term1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

6.3 Jingle Audio and Video via RTP/AVP, Negotiated with ICE-UDP

In this scenario, Romeo initiates a combined audio and video chat with Juliet using a transport method of ICE-UDP. Juliet at first refuses the video portion, then later offers to add video, which Romeo accepts. The parties also exchange various informational messages

The session flow is as follows:

Romeo                         Juliet
  |                             |
  |   session-initiate          |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   session-info (ringing)    |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-remove            |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-accept            |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   transport-info (X times)  |
  |   (with acks)               |
  |<--------------------------->|
  |   session-accept            |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   AUDIO (RTP)               |
  |<===========================>|
  |   session-info (hold)       |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   session-info (active)     |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-add               |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-accept            |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   AUDIO + VIDEO (RTP)       |
  |<===========================>|
  |   session-terminate         |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |                             |

The protocol flow is as follows.

Example 23. Initiation

<iq from='romeo@montague.lit/orchard' 
    id='jingle1' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'/>
    </content>
    <content creator='initiator' name='this-is-the-video-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0180.html#ns'>
        <payload-type id='96' name='theora' clockrate='90000' height='720' width='1280'>
          <parameter name='delivery-method' value='inline'/>
          <parameter name='configuration' value='somebase16string'/>
          <parameter name='sampling' value='YCbCr-4:2:2'/>
        </payload-type>
        <payload-type id='28' name='nv' clockrate='90000'/>
        <payload-type id='25' name='CelB' clockrate='90000'/>
        <payload-type id='32' name='MPV' clockrate='90000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'/>
    </content>
  </jingle>
</iq>

Example 24. Responder acknowledges session-initiate request

<iq from='juliet@capulet.lit/balcony' 
    id='jingle1'
    to='romeo@montague.lit/orchard' 
    type='result'/>

Example 25. Responder sends ringing message

<iq from='juliet@capulet.com/balcony'
    id='ringing1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <ringing xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 26. Initiator acknowledges ringing message

<iq from='romeo@montague.lit/orchard' 
    id='ringing1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

However, Juliet doesn't want to do video because she is having a bad hair day, so she sends a "content-remove" request to Romeo.

Example 27. Responder requests content-remove

<iq from='juliet@capulet.lit/balcony' 
    id='remove1' 
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-remove'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-video-content' profile='RTP/AVP'/>
  </jingle>
</iq>

Romeo then acknowledges the content-remove request and, if it is acceptable, returns a content-accept:

Example 28. Initiator acknowledges content-remove

<iq from='romeo@montague.lit/orchard' 
    id='remove1' 
    to='juliet@capulet.lit/balcony' 
    type='result'/>

Example 29. Initiator accepts content definition

<iq from='romeo@montague.lit/orchard' 
    id='remove2' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-accept'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' name='this-is-the-audio-content' profile='RTP/AVP'/>
  </jingle>
</iq>

The other party then acknowledges the acceptance.

Example 30. Responder acknowledges content-accept

<iq from='juliet@capulet.lit/balcony' 
    id='remove2' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

As in the previous scenario, the parties exchange ICE candidates (see above for examples).

Once the parties find candidate transports that work, the responder accepts the session.

Example 31. Responder sends session-accept

<iq from='juliet@capulet.lit/balcony' 
    id='accept1'
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='102' name='iLBC'/>
        <payload-type id='4' name='G723'/>
        <payload-type id='8' name='PCMA'/>
        <payload-type id='13' name='CN'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'>
        <candidate ip='208.245.212.67' port='9876' generation='0'/>
      </transport>
    </content>
  </jingle>
</iq>

As above, if the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.

Example 32. Initiator acknowledges session-accept

<iq from='romeo@montague.lit/orchard' 
    id='accept1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the <payload-type/> children).

The parties chat for a while. Eventually Juliet wants to get her hair in order so she puts Romeo on hold.

Example 33. Responder sends hold message

<iq from='juliet@capulet.com/balcony'
    id='hold1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <hold xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 34. Initiator acknowledges hold message

<iq from='romeo@montague.lit/orchard' 
    id='hold1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

Juliet returns so she informs Romeo that she is actively engaged in the call again.

Example 35. Responder sends active message

<iq from='juliet@capulet.com/balcony'
    id='active1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <active xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 36. Initiator acknowledges active message

<iq from='romeo@montague.lit/orchard' 
    id='active1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

The parties now continue the audio chat.

Finally Juliet decides that she is presentable for a video chat so she sends a content-add request to Romeo.

Example 37. Responder sends a content-add

<iq from='juliet@capulet.lit/balcony' 
    id='add1' 
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-add'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' name='video-is-back' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0180.html#ns'>
        <payload-type id='96' name='theora' height='720' width='1280'>
          <parameter name='delivery-method' value='inline'/>
          <parameter name='configuration' value='somebase16string'/>
          <parameter name='sampling' value='YCbCr-4:2:2'/>
        </payload-type>
        <payload-type id='32' name='MPV' clockrate='90000'/>
        <payload-type id='33' name='MP2T' clockrate='90000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'>
    </content>
  </jingle>
</iq>

The entity receiving the content-add request then acknowledges the request and, if it is acceptable, returns a content-accept:

Example 38. Initiator acknowledges content-add

<iq from='romeo@montague.lit/orchard' 
    id='add1' 
    to='juliet@capulet.lit/balcony' 
    type='result'/>

Example 39. Initiator accepts content type definition

<iq from='romeo@montague.lit/orchard' 
    id='add2' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-accept'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' name='video-is-back' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0180.html#ns'>
        <payload-type id='96' name='theora' height='720' width='1280'>
          <parameter name='delivery-method' value='inline'/>
          <parameter name='configuration' value='somebase16string'/>
          <parameter name='sampling' value='YCbCr-4:2:2'/>
        </payload-type>
        <payload-type id='32' name='MPV' clockrate='90000'/>
        <payload-type id='33' name='MP2T' clockrate='90000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'/>
    </content>
  </jingle>
</iq>

The other party then acknowledges the acceptance.

Example 40. Responder acknowledges content-accept

<iq from='juliet@capulet.lit/balcony' 
    id='add2' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

The media session proceeds. Now they would exchange both audio and video, where the audio is exchanged the Speex codec at a clockrate of 8000 and the video is exchanged using the Theora codec with a height of 720 pixels, a width of 1280 pixels, and so on.

The parties may continue the session as long as desired.

Eventually, one of the parties terminates the session.

Example 41. Initiator sends session-terminate

<iq from='romeo@montague.lit/orchard'
    id='term1'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-terminate'
          initiator='romeo@montague.lit/orchard'
          reason='I&apos;m outta here!'
          sid='a73sjjvkla37jfea'/>
</iq>

Example 42. Responder acknowledges session-terminate

<iq from='juliet@capulet.lit/balcony' 
    id='term1'
    to='romeo@montague.lit/orchard' 
    type='result'/>

6.4 Secure Jingle Audio via UDP/TLS/RTP/AVP, Negotiated with ICE-UDP

In this scenario, Romeo initiates a voice chat with Juliet using a transport method of ICE-UDP and an unencrypted profile of "RTP/AVP", but Juliet wants to chat securely so she requests the use of a secure transport as specified in RTP Over DTLS [10] (via a profile of "UDP/TLS/RTP/AVP").

The session flow is as follows:

Romeo                         Juliet
  |                             |
  |   session-initiate          |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   session-info (ringing)    |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-modify            |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   content-accept            |
  |---------------------------->|
  |   ack                       |
  |<----------------------------|
  |   transport-info (X times)  |
  |   (with acks)               |
  |<--------------------------->|
  |   session-accept            |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |   AUDIO (RTP)               |
  |<===========================>|
  |   session-terminate         |
  |<----------------------------|
  |   ack                       |
  |---------------------------->|
  |                             |

The protocol flow is as follows.

Example 43. Initiator sends session-initiate

<iq from='romeo@montague.lit/orchard' 
    id='jingle1' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns-udp'/>
    </content>
  </jingle>
</iq>

Example 44. Responder acknowledges session-initiate

<iq from='juliet@capulet.lit/balcony'
    id='jingle1'
    to='romeo@montague.lit/orchard'
    type='result'/>

Example 45. Responder sends ringing message

<iq from='juliet@capulet.com/balcony'
    id='ringing1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <ringing xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 46. Initiator acknowledges ringing message

<iq from='romeo@montague.lit/orchard' 
    id='ringing1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

However, Juliet wants to make sure that the communications are encrypted, so she sends a "content-modify" request to Romeo.

Example 47. Responder requests content-modify

<iq from='juliet@capulet.lit/balcony' 
    id='mod1' 
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-modify'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' 
             name='this-is-the-audio-content' 
             profile='UDP/TLS/RTP/AVP'/>
  </jingle>
</iq>

Romeo then acknowledges the content-modify request and, if it is acceptable, returns a content-accept:

Example 48. Initiator acknowledges content-modify

<iq from='romeo@montague.lit/orchard' 
    id='mod1' 
    to='juliet@capulet.lit/balcony' 
    type='result'/>

Example 49. Initiator accepts content definition

<iq from='romeo@montague.lit/orchard' 
    id='mod2' 
    to='juliet@capulet.lit/balcony' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='content-accept'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='responder' name='this-is-the-audio-content' profile='UDP/TLS/RTP/AVP'/>
  </jingle>
</iq>

The other party then acknowledges the acceptance.

Example 50. Responder acknowledges content-accept

<iq from='juliet@capulet.lit/balcony' 
    id='mod2' 
    to='romeo@montague.lit/orchard' 
    type='result'/>

As in the previous scenario, the parties exchange ICE candidates (see above for examples).

If one of the candidate transports is found to work, the responder accepts the session.

Example 51. Responder sends session-accept

<iq from='juliet@capulet.lit/balcony' 
    id='accept1'
    to='romeo@montague.lit/orchard' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-accept'
          initiator='romeo@montague.lit/orchard'
          responder='juliet@capulet.lit/balcony'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='this-is-the-audio-content' profile='UDP/TLS/RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='102' name='iLBC'/>
        <payload-type id='4' name='G723'/>
        <payload-type id='8' name='PCMA'/>
        <payload-type id='13' name='CN'/>
      </description>
      <transport xmlns='http://www.xmpp.org/extensions/xep-0176.html#ns'>
        <candidate ip='208.245.212.67' port='9876' generation='0'/>
      </transport>
    </content>
  </jingle>
</iq>

If the payload types and transport candidate can be successfully used by both parties, then the initiator acknowledges the session-accept.

Example 52. Initiator acknowledges session-accept

<iq from='romeo@montague.lit/orchard' 
    id='accept1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

The parties now begin to exchange media. In this case they would exchange audio using the Speex codec at a clockrate of 8000 since that is the highest-priority codec for the responder (as determined by the XML order of the <payload-type/> children).

The parties may continue the session as long as desired.

Eventually, one of the parties terminates the session.

Example 53. Responder terminates the session

<iq from='juliet@capulet.lit/balcony'
    id='term1'
    to='romeo@montague.lit/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-terminate'
          initiator='romeo@montague.lit/orchard'
          reason='Sorry, gotta go!'
          sid='a73sjjvkla37jfea'/>
</iq>

The other party then acknowledges termination of the session:

Example 54. Initiator acknowledges termination

<iq from='romeo@montague.lit/orchard' 
    id='term1'
    to='juliet@capulet.lit/balcony' 
    type='result'/>

7. Mapping to Session Description Protocol

If the payload type is static (payload-type IDs 0 through 95 inclusive), it MUST be mapped to a media field defined in RFC 4566. The generic format for the media field is as follows:

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

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

For example, consider the following static payload-type:

Example 55. Jingle format for static payload-type

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

Example 56. SDP mapping of static payload-type

m=audio 9999 RTP/AVP 13

If the payload type is dynamic (payload-type IDs 96 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 96:

Example 57. Jingle format for dynamic payload-type

<payload-type id='96' name='speex' clockrate='16000'/>

Example 58. SDP mapping of dynamic payload-type

m=audio 9999 RTP/AVP 96
a=rtpmap:96 speex/16000

As noted, if additional parameters are to be specified, they shall be represented as attributes of the <parameter/> child of the <payload-type/> element, as in the following example.

Example 59. Jingle format for dynamic payload-type with parameters

<payload-type id='96' name='speex' clockrate='16000' ptime='40'>
  <parameter name='vbr' value='on'/>
  <parameter name='cng' value='on'/>
</payload-type>

Example 60. SDP mapping of dynamic payload-type with parameters

m=audio 9999 RTP/AVP 96
a=rtpmap:96 speex/16000
a=ptime:40
a=fmtp:96 vbr=on;cng=on

8. Informational Messages

8.1 Format

Informational messages may be sent by either party within the context of Jingle to communicate the status of a Jingle audio session, device, or principal. The informational message MUST be an IQ-set containing a <jingle/> element of type "session-info", where the informational message is a payload element qualified by the 'http://www.xmpp.org/extensions/xep-0167.html#ns-info' namespace; the following payload elements are defined: [11]

Table 2: Information Payload Elements

Element Meaning
<active/> The principal or device is again actively participating in the session after having been on hold or on mute.
<hold/> The principal is temporarily pausing the chat (i.e., putting the other party on hold).
<mute/> The principal is temporarily stopping audio output but continues to accept audio input.
<ringing/> The device is ringing but the principal has not yet interacted with it to answer (this maps to the SIP 180 response code).

Note: Because the informational message is sent in an IQ-set, the receiving party MUST return either an IQ-result or an IQ-error (normally only an IQ-result to acknowledge receipt; no error flows are defined or envisioned at this time).

8.2 Examples

Example 61. Responder sends active message

<iq from='juliet@capulet.com/balcony'
    id='active1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'>
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <active xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 62. Responder sends hold message

<iq from='juliet@capulet.com/balcony'
    id='hold1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <hold xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 63. Responder sends mute message

<iq from='juliet@capulet.com/balcony'
    id='mute1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <mute xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

Example 64. Responder sends ringing message

<iq from='juliet@capulet.com/balcony'
    id='ringing1'
    to='romeo@montague.net/orchard'
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'
          action='session-info'
          initiator='romeo@montague.net/orchard'
          sid='a73sjjvkla37jfea'>
    <ringing xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'/>
  </jingle>
</iq>

9. Error Handling

The Jingle-Audio-specific error conditions are as follows:

Table 3: Error Conditions

Jingle Audio Condition XMPP Condition Description
<unsupported-codecs/> <not-acceptable/> The recipient does not support any of the offered audio encodings.

10. Determining Support

If an entity supports Jingle audio exchanges via RTP, it MUST advertise that fact by returning a feature of "http://www.xmpp.org/extensions/xep-0167.html#ns" (see Protocol Namespaces regarding issuance of one or more permanent namespaces) in response to Service Discovery [12] information requests.

Example 65. 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 66. 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://www.xmpp.org/extensions/xep-0166.html#ns'/>
    <feature var='http://www.xmpp.org/extensions/xep-0167.html#ns'/>
    ...
  </query>
</iq>

Naturally, support may also be discovered by the dynamic, presence-based profile of service discovery defined in Entity Capabilities [13].

11. Implementation Notes

11.1 Codecs

Support for the Speex codec is RECOMMENDED.

11.2 DTMF

If it is necessary to send Dual Tone Multi-Frequency (DTMF) tones, it is REQUIRED to use the XML format specified Jingle DTMF [14].

11.3 When to Listen

When the Jingle Audio content type is accepted via a "content-accept" action, both initiator and responder SHOULD start listening for audio as defined by the negotiated transport method and audio application format. For interoperability with telephony systems, after the responder acknowledges the session-initiate request, the responder SHOULD send a "ringing" message and both parties SHOULD play any audio received.

12. Security Considerations

In order to secure the data stream, implementations SHOULD use encryption methods appropriate to the transport method and media being exchanged; for example, in the case of UDP, that would include Datagram Transport Layer Security (DTLS) as specified in RFC 4347 [15]. The work-in-progress draft-fishl-mmusic-sdp-dtls defines such methods for the Session Description Protocol; the relevant RTP profile (e.g., "UDP/TLS/RTP/AVP" for transporting the RTP stream over DTLS with UDP) shall be specified as the value of the <content/> element's 'profile' attribute.

13. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [16].

14. XMPP Registrar Considerations

14.1 Protocol Namespaces

Until this specification advances to a status of Draft, its associated namespaces shall be "http://www.xmpp.org/extensions/xep-0167.html#ns" and "http://www.xmpp.org/extensions/xep-0167.html#ns-info"; upon advancement of this specification, the XMPP Registrar [17] shall issue permanent namespaces in accordance with the process defined in Section 4 of XMPP Registrar Function [18].

14.2 Jingle Application Formats

The XMPP Registrar shall include "audio-rtp" in its registry of Jingle application formats. The registry submission is as follows:

<application>
  <name>audio-rtp</name>
  <desc>Jingle sessions that support audio exchange via the Real-time Transport Protocol</desc>
  <transport>lossy</transport>
  <doc>XEP-0167</doc>
</application>

15. XML Schemas

15.1 Application Format

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0167.html#ns'
    xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns'
    elementFormDefault='qualified'>

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

  <xs:element name='payload-type'>
    <xs:complexType>
      <xs:sequence minOccurs='0' maxOccurs='unbounded'>
        <xs:element ref='parameter'/>
      </xs:sequence>
      <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='maxptime' type='xs:short' use='optional'/>
      <xs:attribute name='name' type='xs:string' use='optional'/>
      <xs:attribute name='ptime' type='xs:short' use='optional'/>
    </xs:complexType>
  </xs:element>

  <xs:element name='parameter'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='name' type='xs:string' use='required'/>
          <xs:attribute name='value' type='xs:string' use='required'/>
        </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>

15.2 Errors

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0167.html#ns-errors'
    xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-errors'
    elementFormDefault='qualified'>

  <xs:element name='unsupported-codecs' type='empty'/>

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

</xs:schema>

15.3 Informational Messages

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0167.html#ns-info'
    xmlns='http://www.xmpp.org/extensions/xep-0167.html#ns-info'
    elementFormDefault='qualified'>

  <xs:element name='active' type='empty'/>
  <xs:element name='hold' type='empty'/>
  <xs:element name='mute' 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

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

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

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

4. XEP-0177: Jingle Raw UDP Transport Method <http://www.xmpp.org/extensions/xep-0177.html>.

5. XEP-0176: Jingle ICE Transport Method <http://www.xmpp.org/extensions/xep-0176.html>.

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

7. RTP Payload Format for the Speex Codec <http://tools.ietf.org/html/draft-ietf-avt-rtp-speex>. Work in progress.

8. See <http://www.speex.org/>.

9. 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/>.

10. Real-Time Transport Protocol (RTP) over Datagram Transport Layer Security (DTLS) <http://tools.ietf.org/html/draft-fischl-mmusic-sdp-dtls>. Work in progress.

11. A <trying/> element (equivalent to the SIP 100 Trying response code) is not necessary, since each session-level action is acknowledged via XMPP IQ semantics.

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

13. XEP-0115: Entity Capabilities <http://www.xmpp.org/extensions/xep-0115.html>.

14. XEP-0181: Jingle DTMF <http://www.xmpp.org/extensions/xep-0181.html>.

15. RFC 4347: Datagram Transport Layer Security <http://tools.ietf.org/html/rfc4347>.

16. 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/>.

17. 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/>.

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

Revision History

Version 0.11 (2007-11-15)

Editorial review and consistency check; moved voice chat scenarios from XEP-0166 to this specification.

(psa)

Version 0.10 (2007-11-13)

Removed info message for busy since it is now a Jingle-specific error condition defined in XEP-0166; defined info message for active.

(psa)

Version 0.9 (2007-04-17)

Specified Jingle conformance, including the preference for lossy transports over reliable transports and the process of sending and receiving audio content over each transport type.

(psa)

Version 0.8 (2007-03-23)

Renamed to mention RTP as the associated transport; corrected negotiation flow to be consistent with SIP/SDP (each party specifies a list of the payload types it can receive); added profile attribute to content element in order to specify RTP profile in use.

(psa/ram)

Version 0.7 (2006-12-21)

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

(psa)

Version 0.6 (2006-10-31)

Specified how to include SDP parameters and codec-specific parameters; clarified negotiation process; added Speex examples; removed queued info message.

(psa/se)

Version 0.5 (2006-08-23)

Modified namespace to track XEP-0166.

(psa)

Version 0.4 (2006-07-12)

Specified when to play received audio (early media); specified that DTMF must use in-band signalling (XEP-0181).

(se/psa)

Version 0.3 (2006-03-20)

Defined info messages for hold and mute.

(psa)

Version 0.2 (2006-02-13)

Defined info message for busy; added info message examples; recommended use of Speex; updated schema and XMPP Registrar considerations.

(psa)

Version 0.1 (2005-12-15)

Initial version.

(psa)

Version 0.0.3 (2005-12-05)

Described service discovery usage; defined initial informational messages.

(psa)

Version 0.0.2 (2005-10-27)

Added SDP mapping, security considerations, IANA considerations, XMPP Registrar considerations, and XML schema.

(psa)

Version 0.0.1 (2005-10-21)

First draft.

(psa/sl)

END