O. Levin
Internet Draft RADVISION
Document: draft-levin-mmusic-xml-media-control-02 S. Olson
Microsoft
R. Even
Polycom
Expires: September 2003 April 2003
XML Schema for Media Control
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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Abstract
This document defines an XML Schema for Media Control in a tightly
controlled environment. The current version includes commands for
managing of video streams only. Implementation of this schema for
interactive video applications in SIP environments significantly
improves user experience.
Levin, et al. Expires: September 2003 1
XML Schema for Media Control
Table of Contents
STATUS OF THIS MEMO......................................................1
ABSTRACT...............................................................1
INTRODUCTION...........................................................3
BACKGROUND............................................................3
THE VIDEO CONTROL COMMANDS..............................................3
THE SCHEMA DEFINITION....................................................4
ERROR HANDLING..........................................................5
EXAMPLES...............................................................6
THE SCHEMA APPLICATIONS..................................................7
CONVENTIONS USED IN THIS DOCUMENT..........................................7
IANA CONSIDERATIONS......................................................7
APPLICATION/MEDIA_CONTROL+XML MIME TYPE.........................................8
URN FOR XML SCHEMA.......................................................9
SECURITY CONSIDERATIONS.................................................10
AUTHOR'S ADDRESSES......................................................10
REFERENCES............................................................10
Levin, et al. Expires: March 2003 2
XML Schema for Media Control
Introduction
This document defines an XML Schema for Media Control in a tightly
controlled environment. The current version includes commands for
managing of video streams only. Implementation of this schema for
interactive video applications in SIP [7] environments significantly
improves user experience. Both end users and conferencing servers
SHOULD implement this approach.
Background
SIP typically uses RTP [6] for transferring of real time media.
RTP is augmented by a control protocol (RTCP) to allow monitoring of
the data delivery in a manner scalable to large multicast networks.
An RTCP feedback mechanism [4] has been introduced in order to
improve basic RTCP feedback time in case of loss conditions across
different coding schemes. (Previously, a subset of this
functionality was defined for H.261 [5] only).
The above mentioned techniques address signaling of loss conditions
and the recommended recovery steps. Currently, there is no standard
way to express required operations on media streams as a result of
application logic rather then a result of loss conditions.
Of course, each command SHALL be validated by the remote entity
against current media capacity and network conditions before being
executed.
The Video Control Commands
Output of a video CODEC is a frame. The frame can carry complete (in
time) information about a picture or about a picture segment. These
frames are known as ôIntraö frames. In order to save bandwidth,
other frames can carry only changes relative to previously sent
frames. Frames carrying relative information are known as ôInterö
frames.
Some CODECs (such as H.261 [2] and H.263 [3]), in addition to a
ôfullö picture, have a notion of picture slices: MB (Macro Block)
and GOB (Group Of Blocks).
Based on application logic (such as a presentation of a new video
source), the application needs to have an ability to explicitly
request from a remote encoder the complete (in-time) information
about a ôfullö picture or a specific slice of the picture.
Additionally, in case the encoder is aware of upcoming changes in
the transmitted stream (that would result in synchronization lost by
the decoder), the encoder needs to be able to request the decoding
side to freeze the picture, i.e. to stop presenting the changes,
until a new stable image is encoded and transmitted.
In order to achieve these requirements, the following video
primitives are defined below:
Video Picture Fast Update Request
Video GOB Fast Update Request (first_GOB, no_of_GOBs)
Video MB Fast Update Request (first_GOB, first_MB, no_of_MBs)
These commands are to be sent to a remote encoder.
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XML Schema for Media Control
Video Picture Freeze Request
This command is to be sent to a remote decoder.
The Schema Definition
See RFCXXXX.
Levin, et al. Expires: March 2003 9 XML Schema for Media Control END Security Considerations This document doesnÆt introduce new security requirements beyond covered in [7]. Author's Addresses Orit Levin RADVISION 266 Harristown Road Phone: +1-201-689-6330 Glen Rock, NJ USA Email: orit@radvision.com Sean Olson Microsoft Corporation One Microsoft Way Phone: +1-425-707-2846 Redmond, WA USA Email: seanol@microsoft.com Roni Even Polycom 94 Derech Em Hamoshavot Phone: +972-3-9251200 Petach Tikva, Israel Email: roni.even@polycom.co.il References 1 RFC 2119 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 2 ITU-T Recommendation H.261 (1993), Video codec for audiovisual services at p . 64 kbit/s. 3 ITU-T Recommendation H.263 (1998), Video coding for low bit rate communication. 4 J. Ott et al., ôExtended RTP Profile for RTCP-based Feedback (RTP/AVPF)ö, draft-ietf-avt-rtcp-feedback-03.txt, June 2002, IETF Draft. Work in progress. 5 T. Turletti and C. Huitema, "RTP Payload Format for H.261 Video Streams, RFC 2032, October 1996. 6 H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP - A Transport Protocol for Real-time Applications", Internet Draft, draft-ietf-avt-rtp-new-11.txt, Work in Progress, November 2001. 7 J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation protocol," RFC 3261, Internet Engineering Task Force, June 2002. 8 S. Donovan, ôThe SIP INFO Methodö, RFC2976, Internet Engineering Task Force, October 2000. 9 Camarillo/Holler/Eriksson/Schulzrinne, "Grouping of m lines in SDP", draft-ietf-mmusic-fid-06.txt, Feb 2002, IETF Draft. Proposed Standard. 10 M. Mealling, "The IETF XML Registry", draft-mealling-iana-xmlns- registry-04.txt, June 2002, IETF draft. Work in progress. Levin, et al. Expires: March 2003 10