XEP-0180: Jingle Video via RTP

This document defines methods for negotiating Jingle video 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: 0180
Publisher: XMPP Standards Foundation
Status: Proposed
Type: Standards Track
Version: 0.9
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Superseded By: None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 Video via RTP (XEP-0180)>

Author Information

Legal Notices

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

Jingle [1] can be used to initiate and negotiate a wide range of peer-to-peer sessions. One session type of interest is video chat. This document specifies a format for describing Jingle video sessions, where the media exchange occurs using the Real-time Transport Protocol (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 video chat.
2. Map these parameters to the Session Description Protocol (SDP; see RFC 4566 [3]) to enable interoperability.
3. Define informational messages related to video chat.

3. Jingle Conformance

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

1. The application format negotiation process is defined in the Negotiating a Jingle Video 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 video session MUST 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].

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

   • Outbound video 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.

4. Application Format

A Jingle video 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-0180.html#ns' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). In the language of RFC 4566 these encodings are payload-types; therefore, each <payload-type/> child element specifies an encoding that can be used for the video stream. In Jingle Video, 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 [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.

Example 1. Video application format

    <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>
  

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

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

Table 1: Video Description Attributes

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 Theora Encoded Video [7], the "configuration", "configuration-uri", "delivery-method", and "sampling" parameters may be specified in relation to usage of the Theora [8] codec. Where such parameters are encoded via the "fmtp" SDP attribute, they shall be represented in Jingle via the following format, where the <parameter/> element is a child of the <payload-type/> element:

<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 Video Session

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 video (each one encapsulated in a separate <payload-type/> element):

Example 2. Initiation

<iq from='romeo@montague.net/orchard' 
    to='juliet@capulet.com/balcony' 
    id='jinglevideo1' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'>
          action='session-initiate'
          initiator='romeo@montague.net/orchard'
          sid='v1d30k1ll3dth3r4d10st4r'>
    <content content='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-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 and illustrated Jingle Audio via RTP [10]. In addition, the receiver 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-Video-specific condition of <unsupported-codecs/>:

Example 3. Receiver does not support any of the 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-0180.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='jinglevideo1' 
      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 specified by the initiator. The order of the <payload-type/> elements indicates the receiver's preferences, with the most-preferred types first.

Example 5. Receiver accepts content type

<iq from='juliet@capulet.com/balcony' 
    to='romeo@montague.net/orchard' 
    id='jinglevideo2' 
    type='set'>
  <jingle xmlns='http://www.xmpp.org/extensions/xep-0166.html#ns'>
          action='content-accept'
          initiator='romeo@montague.net/orchard'
          sid='v1d30k1ll3dth3r4d10st4r'>
    <content content='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' 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-udp'/>
    </content>
  </jingle>
</iq>
  

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

Example 6. Initiator acknowledges modified application type

  <iq from='romeo@montegue.net/orchard' 
      to='juliet@capulet.com/balcony' 
      id='jinglevideo2' 
      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='v1d30k1ll3dth3r4d10st4r'>
    <content creator='initiator' name='this-is-the-video-content' profile='RTP/AVP'>
      <description xmlns='http://www.xmpp.org/extensions/xep-0180.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' />
  

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. 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 video sessions, the <media> is "video", 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/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="28" name="nv"/>
  

That Jingle-formatted information would be mapped to SDP as follows:

Example 10. SDP mapping of static payload-type

m=video 9000 RTP/AVP 28
  

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 VC-1 payload such as that described in RFC 4425 [11]:

Example 11. Jingle format for dynamic payload-type

<payload-type id='98' name='vc1' height='288' width='352'/>
  

That Jingle-formatted information would be mapped to SDP as follows:

Example 12. SDP mapping of dynamic payload-type

m=video 49170 RTP/AVP 98
a=rtpmap:98 vc1/90000
a=fmtp:98 width=352;height=288;
  

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

Example 13. Jingle format for dynamic payload-type with parameters

<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>
  

That Jingle-formatted information would be mapped to SDP as follows:

Example 14. SDP mapping of dynamic payload-type with parameters

m=video 49170 RTP/AVP 98
a=rtpmap:96 theora/90000
a=fmtp:96 sampling=YCbCr-4:2:2; width=1280; height=720; 
delivery-method=inline; configuration=somebase16string;
  

7. Error Handling

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

Table 2: Other Error Conditions

8. Determining Support

If an entity supports Jingle video exchanges via RTP, it MUST advertise that fact by returning a feature of "http://www.xmpp.org/extensions/xep-0180.html#ns" in response to Service Discovery [12] information requests (see Protocol Namespaces regarding issuance of one or more permanent namespaces).

Example 15. 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 16. 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-0180.html#ns'/>
    ...
  </query>
</iq>
  

9. Informational Messages

Informational messages may be sent by either party within the context of Jingle to communicate the status of a Jingle video session, device, or principal. The informational message MUST be an IQ-set containing a <jingle/> element of type "session-info". No informational message payload elements have yet been defined, but they may be specified in a future version of this document.

10. Implementation Notes

11. 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 [13]. RTP Over DTLS [14] 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.

12. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [15].

13. XMPP Registrar Considerations

<application>
  <name>video-rtp</name>
  <desc>Jingle sessions that support video exchange via the Real-time Transport Protocol</desc>
  <transport>lossy</transport>
  <doc>XEP-0180</doc>
</application>
    

14. XML Schemas

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0180.html#ns'
    xmlns='http://www.xmpp.org/extensions/xep-0180.html#ns'
    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:sequence minOccurs='0' maxOccurs='unbounded'>
        <xs:element ref='parameter'/>
      </xs:sequence>
      <xs:attribute name='channels' type='xs:integer' use='optional' default='1'/>
      <xs:attribute name='height' type='xs:nonNegativeInteger' use='optional'/>
      <xs:attribute name='id' type='xs:unsignedByte' use='required'/>
      <xs:attribute name='layer' type='xs:nonNegativeInteger' use='optional'/>
      <xs:attribute name='name' type='xs:string' use='optional'/>
      <xs:attribute name='rate' type='xs:short' use='optional'/>
      <xs:attribute name='transparent' type='xs:boolean' use='optional'/>
      <xs:attribute name='width' type='xs:nonNegativeInteger' use='optional'/>
      <xs:attribute name='x' type='xs:integer' use='optional'/>
      <xs:attribute name='y' type='xs:integer' use='optional'/>
    </xs: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-0180.html#ns-errors'
    xmlns='http://www.xmpp.org/extensions/xep-0180.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>
    

Notes

Revision History

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