This document defines methods for negotiating Jingle audio sessions that use the Real-time Transport Protocol (RTP) for media exchange.
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.
Series: XEP
Number: 0167
Publisher: XMPP Standards Foundation
Status:
Experimental
Type:
Standards Track
Version: 0.10
Last Updated: 2007-11-13
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Superseded By: None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)>
Email:
scottlu@google.com
JabberID:
scottlu@google.com
JabberID:
stpeter@jabber.org
URI:
https://stpeter.im/
Email:
seanegan@google.com
JabberID:
seanegan@google.com
Email:
robert.mcqueen@collabora.co.uk
JabberID:
robert.mcqueen@collabora.co.uk
The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.
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.
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".
1. Introduction
2. Requirements
3. Jingle Conformance
4. Content Description Format
5. Negotiating a Jingle Audio Session
6. Mapping to Session Description Protocol
7. Informational Messages
7.1. Format
7.2. Examples
8. Error Handling
9. Determining Support
10. Implementation Notes
10.1. Codecs
10.2. DTMF
10.3. When to Listen
11. Security Considerations
12. IANA Considerations
13. XMPP Registrar Considerations
13.1. Protocol Namespaces
13.2. Jingle Content Description Formats
14. XML Schemas
14.1. Content Description Format
14.2. Errors
14.3. Informational Messages
Notes
Revision History
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 a format for negotiating Jingle audio sessions over the Realtime Transport Protocol (RTP; see RFC 3550 [2]).
The Jingle content description format defined herein is designed to meet the following requirements:
In accordance with Section 8 of XEP-0166, this document specifies the following information related to the Jingle Audio via RTP application type:
The content negotiation process is defined in the Negotiating a Jingle Audio Session section of this document.
The semantics of the <description/> element are defined in the Content Description Format section of this document.
A mapping of Jingle semantics to the Session Description Protocol is provided in the Mapping to Session Description Protocol section of this document.
A Jingle audio session SHOULD use a lossy transport method such as Jingle Raw UDP Transport Method [5] or the "ice-udp" method specified in Jingle ICE Transport Method [6], but MAY use a reliable transport such as "ice-tcp".
Content is to be sent and received as follows:
For lossy transports, outbound audio content shall be encoded into RTP packets and each packet shall be sent individually over the transport. Each inbound packet received over the transport is an RTP packet.
For reliable transports, outbound audio content shall be encoded into RTP packets and each packet data shall be sent in succession over the transport. Incoming data received over the transport shall be processed as a stream of RTP packets, where each RTP packet boundary marks the location of the next packet.
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 [7] (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 allowable attributes are as follows:
| 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 |
The encodings SHOULD be provided in order of preference.
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 <jingle/> element as specified in XEP-0166.
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 [8], the "cng", "mode", and "vbr" parameters may be specified in relation to usage of the Speex [9] 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) [10] maintains a registry of SDP parameters (see <http://www.iana.org/assignments/sdp-parameters>).
When the initiator sends a session-initiate stanza to the receiver, 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):
<iq from='romeo@montague.net/orchard'
to='juliet@capulet.com/balcony'
id='jingleaudio1'
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 receiver determines whether it can provisionally accept the session and proceed with the negotiation. The general Jingle error cases are specified in XEP-0166. In addition, the receiver must determine if it supports any of the payload types advertised by the initiator; if it does not, it MUST reject the session by sending a <unsupported-codecs/> error:
Example 3. Receiver Does Not Support Codecs
<iq type='error'
from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='jingleaudio1'>
<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 receiver provisionally accepts the session:
Example 4. Receiver Provisionally Accepts Session
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='jingleaudio1'
type='result'/>
The receiver 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 receiver sends MAY include any payload types (not a subset of the payload types sent by the initiator) but SHOULD retain the ID numbers and order specified by the initiator.
Example 5. Receiver Accepts Content Type
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='jingleaudio2'
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 Content Description
<iq from='romeo@montegue.net/orchard'
to='juliet@capulet.com/balcony'
id='jingleaudio2'
type='result'/>
After successful transport negotiation (not shown here), the receiver then accepts the session:
Example 7. Receiver Definitively Accepts the Session
<iq type='set' from='juliet@capulet.com/balcony' to='romeo@montague.net/orchard' id='accept1'>
<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'/>
<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'
to='juliet@capulet.com/balcony'
id='accept1'
type='result'/>
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 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 9. Jingle Format for Static Payload-Type
<payload-type id="13" name="CN"/>
Example 10. 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 11. Jingle Format for Dynamic Payload-Type
<payload-type id='96' name='speex' clockrate='16000'/>
Example 12. 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 <payload-type/> element of the child <parameter/> element, as in the following example.
Example 13. 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 14. 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
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).
Example 15. Receiver Sends Active Message
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='active1'
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 16. Receiver Sends Hold Message
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='hold1'
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 17. Receiver Sends Mute Message
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='mute1'
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 18. Receiver Sends Ringing Message
<iq from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='ringing1'
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>
The Jingle Audio-specific error conditions are as follows:
Table 3: Other Error Conditions
| Jingle Condition | XMPP Condition | Description |
|---|---|---|
| <unsupported-codecs/> | <not-acceptable/> | The recipient does not support any of the offered audio encodings. |
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 19. 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 20. 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>
Support for the Speex codec is RECOMMENDED.
If it is necessary to send Dual Tone Multi-Frequency (DTMF) tones, it is REQUIRED to use the XML format specified Jingle DTMF [13].
When the Jingle Audio content 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 description. For interoperability with telephony systems, each entity SHOULD both play any audio received and send a ringing tone at this time (i.e., before the receiver sends a 'session-accept' action).
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 [14]. RTP Over DTLS [15] 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.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [16].
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].
The XMPP Registrar shall include "audio-rtp" in its registry of Jingle content description formats. The registry submission is as follows:
<content>
<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>
</content>
<?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:choice>
<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>
<?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>
<?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>
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 3550: RTP: A Transport Protocol for Real-Time Applications <http://tools.ietf.org/html/rfc3550>.
4. RFC 4566: SDP: Session Description Protocol <http://tools.ietf.org/html/rfc4566>.
5. XEP-0177: Jingle Raw UDP Transport Method <http://www.xmpp.org/extensions/xep-0177.html>.
6. XEP-0176: Jingle ICE Transport Method <http://www.xmpp.org/extensions/xep-0176.html>.
7. RFC 3551: RTP Profile for Audio and Video Conferences with Minimal Control <http://tools.ietf.org/html/rfc3551>.
8. RTP Payload Format for the Speex Codec <http://tools.ietf.org/html/draft-ietf-avt-rtp-speex>. Work in progress.
9. See <http://www.speex.org/>.
10. 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/>.
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-0181: Jingle DTMF <http://www.xmpp.org/extensions/xep-0181.html>.
14. RFC 4347: Datagram Transport Layer Security <http://tools.ietf.org/html/rfc4347>.
15. Real-Time Transport Protocol (RTP) over Datagram Transport Layer Security (DTLS) <http://tools.ietf.org/html/draft-fischl-mmusic-sdp-dtls>. Work in progress.
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>.
Removed info message for busy since it is now a Jingle-specific error condition defined in XEP-0166; defined info message for active.
(psa)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)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)Modified spec to use provisional namespace before advancement to Draft (per XEP-0053).
(psa)Specified how to include SDP parameters and codec-specific parameters; clarified negotiation process; added Speex examples; removed queued info message.
(psa/se)Modified namespace to track XEP-0166.
(psa)Specified when to play received audio (early media); specified that DTMF must use in-band signalling (XEP-0181).
(se/psa)Defined info messages for hold and mute.
(psa)Defined info message for busy; added info message examples; recommended use of Speex; updated schema and XMPP Registrar considerations.
(psa)Initial version.
(psa)Described service discovery usage; defined initial informational messages.
(psa)Added SDP mapping, security considerations, IANA considerations, XMPP Registrar considerations, and XML schema.
(psa)First draft.
(psa/sl)END