XEP-0339: Source-Specific Media Attributes in Jingle

Abstract:This specification provides an XML mapping for translating the RFC 5766 Source-Specific Media Attributes from SDP to Jingle
Author:Philipp Hancke
Copyright:© 1999 – 2017 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Experimental
Type:Standards Track
Version:0.2
Last Updated:2015-11-09

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 are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.

Table of Contents


1. Introduction
2. Mapping to Session Description Protocol
    2.1. The ssrc attribute
    2.2. The ssrc-group attribute
3. Example
4. Determining Support
5. Security Considerations
6. IANA Considerations
7. XMPP Registrar Considerations
    7.1. Protocol Namespaces
    7.2. Protocol Versioning
8. XML Schema

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

RFC 5576 [1] provides a mechanism to describe attributes of individual media sources (identified by their synchronization source) within a media stream. A mapping to Jingle as an extension to Jingle RTP Sessions (XEP-0167) [2] is defined in this document.

2. Mapping to Session Description Protocol

2.1 The ssrc attribute

The SDP format defined in RFC 5576 is shown below.

a=ssrc:<ssrc-id> <attribute>
a=ssrc:<ssrc-id> <attribute>:<value>

This maps to Jingle as a <source/> element qualified by the 'urn:xmpp:jingle:apps:rtp:ssma:0' namespace. Since 'ssrc' is a media attribute in SDP, the <source/> element is included as child of the Jingle <description/> element.

<source ssrc='ssrc-id' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
    <parameter name='attribute'/>
    <parameter name='attribute' value='value'/>
</source>

Each ssrc-id maps to a <source/> element whose 'ssrc' attribute is set to the ssrc-id. The associated attributes map to <parameter/> children with 'name' and 'value' attributes. If there is no value in the SDP, the value parameter shall be omitted.

An example follows:

a=ssrc:1656081975 cname:Yv/wvbCdsDW2Prgd
a=ssrc:1656081975 msid:MLTJKIHilGn71fNQoszkQ4jlPTuS5vJyKVIv MLTJKIHilGn71fNQoszkQ4jlPTuS5vJyKVIva0

<source ssrc='1656081975' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
    <parameter name='cname' value='Yv/wvbCdsDW2Prgd'/>
    <parameter name='msid' value='MLTJKIHilGn71fNQoszkQ4jlPTuS5vJyKVIv MLTJKIHilGn71fNQoszkQ4jlPTuS5vJyKVIva0'/>
</source>

2.2 The ssrc-group attribute

The SDP format defined in RFC 5576 is shown below.

a=ssrc-group:<semantics> <ssrc-id> ...

This maps to Jingle as a <ssrc-group/> element qualified by the 'urn:xmpp:jingle:apps:rtp:ssma:0' namespace. Like the <source/> element, this is included as child of the Jingle <description/> element. The SDP 'semantics' parameter is mapped to the semantics attribute (for consistency with Jingle Grouping Framework (XEP-0338) [3]) and the list of ssrc-ids is mapped to <source/> elements whole 'ssrc' attribute is set to the ssrc-id.

<ssrc-group xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' semantics='semantics'>
   <source ssrc='ssrc-id'/>
   [...]
</ssrc-group>

3. Example

A minimal example follows:

m=video 1 RTP/SAVPF 100 116 117
a=rtpmap:100 VP8/90000
a=ssrc-group:FID 2301230316 386328120
a=ssrc:2301230316 cname:T5qvrIZj42v//eYQ
a=ssrc:386328120 cname:uEYgNtStZyTF74sM
a=ssrc-group:FID 3139499595 2613715171
a=ssrc:3139499595 cname:re8jhxkly9bxzuxr
a=ssrc:2613715171 cname:f83avsiw6n1m7vi

This is mapped to Jingle as follows:

<content creator='initiator' name='webcam'>
  <description xmlns='urn:xmpp:jingle:apps:rtp:1' media='video'>
    <payload-type id='100' name='VP8' clockrate='90000'/>
    <ssrc-group xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' semantics='FID'>
      <source ssrc='2301230316'/>
      <source ssrc='386328120'/>
    </ssrc-group>
    <ssrc-group xmlns='urn:xmpp:jingle:apps:rtp:ssma:0' semantics='FID'>
      <source ssrc='3139499595'/>
      <source ssrc='2613715171'/>
    </ssrc-group>
    <source ssrc='2301230316' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
      <parameter name='cname' value='T5qvrIZj42v//eYQ'/>
    </source>
    <source ssrc='386328120' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
      <parameter name='cname' value='uEYgNtStZyTF74sM'/>
    </source>
    <source ssrc='3139499595' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
      <parameter name='cname' value='re8jhxkly9bxzuxr'/>
    </source>
    <source ssrc='2613715171' xmlns='urn:xmpp:jingle:apps:rtp:ssma:0'>
      <parameter name='cname' value='f83avsiw6n1m7vi'/>
    </source>
  </description>
</content>

4. Determining Support

If an entity supports source specific media attributes as described in RFC 5576, it MUST advertise that fact in its responses to Service Discovery (XEP-0030) [4] information ("disco#info") requests by returning a feature of 'urn:ietf:rfc:5576':

Example 1. A disco#info query

<iq type='get'
    from='calvin@usrobots.lit/lab'
    to='herbie@usrobots.lit/home'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

Example 2. A disco#info response

<iq type='result'
    from='herbie@usrobots.lit/home'
    to='calvin@usrobots.lit/lab'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:jingle:1'/>
    <feature var='urn:ietf:rfc:5576'/>
  </query>
</iq>

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) [5]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

5. Security Considerations

This document introduces no additional security considerations above and beyond those defined in the documents on which it depends.

6. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

7. XMPP Registrar Considerations

7.1 Protocol Namespaces

This specification defines the following XML namespace:

The XMPP Registrar [7] includes the foregoing namespace to the registry located at <https://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) [8].

7.2 Protocol Versioning

If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.

8. XML Schema

TODO

Appendices

Appendix A: Document Information

Series: XEP
Number: 0339
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.2
Last Updated: 2015-11-09
Approving Body: XMPP Council
Dependencies: XEP-0166
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Philipp Hancke

Email: fippo@andyet.com
JabberID: fippo@goodadvice.pages.de

Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2017 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) 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.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

The following requirements 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".

Appendix G: Notes

1. RFC 5576: Source-Specific Media Attributes in the Session Description Protocol (SDP) <http://tools.ietf.org/html/rfc5576>.

2. XEP-0167: Jingle RTP Sessions <https://xmpp.org/extensions/xep-0167.html>.

3. XEP-0338: Jingle Grouping Framework <https://xmpp.org/extensions/xep-0338.html>.

4. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

5. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.html>.

6. 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/>.

7. 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 <https://xmpp.org/registrar/>.

8. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.2 (2015-11-09)

remove obsolete mslabel and label lines.

(ph)

Version 0.1 (2014-01-08)

Initial published version approved by the XMPP Council.

(psa)

Version 0.0.1 (2013-11-25)

First draft.

(ph)

END