One document matched: draft-levin-mmusic-xml-media-control-01.txt
Differences from draft-levin-mmusic-xml-media-control-00.txt
MMUSIC WG O. Levin/RADVISION
Internet Draft S. Olson/Microsoft
draft-levin-mmusic-xml-media-control-01 R. Even/Polycom
P. Monfort/France Telecom
Expires: September 2003 March 2003
XML Schema for Media Control
draft-levin-mmusic-xml-media-control-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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........................................................6
EXAMPLES..............................................................6
THE SCHEMA APPLICATIONS...............................................7
CONVENTIONS USED IN THIS DOCUMENT.....................................7
SECURITY CONSIDERATIONS...............................................8
AUTHOR'S ADDRESSES....................................................8
REFERENCES............................................................8
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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
regardless encoding scheme specifics. (Previously, a subset of this
functionality was defined for H.261 [5] only).
The existing techniques address indication and recovery from
detected loss conditions.
This document introduces a way to perform operations on media
streams as a result of application logic.
Any requested operation SHALL be validated by the remote entity
against current media capacity and known network conditions before
being performed.
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 "Intra" frames. In order to save bandwidth,
other frames can carry only changes relative to previously sent
frames. Frames carrying relative information are known as "Inter"
frames.
Some CODECs (such as H.261 [2] and H.263 [3]), in addition to a
"full" picture, have a notion of picture slices: MB (Macro Block)
and GOB (Group Of Blocks).
Based on the application logic (such as a presentation of a new
video source), the application needs to have the ability to
explicitly ask from a remote encoder for a complete (in-time)
information about a "full" picture or a specific slice of the
picture.
Additionally, when 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 signal the decoding side
to freeze the picture, i.e. to stop presenting the changes until a
new stable image is encoded and transmitted.
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XML Schema for Media Control
In order to meet these requirements, the following video primitives
are defined:
- Video Picture Fast Update.
- Video GOB Fast Update (first_GOB, no_of_GOBs).
- Video MB Fast Update (first_GOB, first_MB, no_of_MBs).
These commands are to be sent to a remote encoder.
- Video Picture Freeze.
This command is to be sent to a remote decoder.
The Schema Definition
<?xml version="1.0" encoding="utf-8" ?>
<xsd:schema id="TightMediaControl"
targetNamespace="urn:ietf:params:xml:ns:media_control"
elementFormDefault="qualified" xmlns="
urn:ietf:params:xml:ns:media_control"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="media_control">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="vc_primitive" type="vc_primitive"
minOccurs="0" maxOccurs="unbounded" />
<xsd:element name="general_error" type="xs:string"
minOccurs="0" maxOccurs="unbounded" />
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- Video control primitive. Each primitive is directed either
to a remote encode or to a remote decoder. -->
<xsd:complexType name="vc_primitive">
<xsd:sequence>
<xsd:choice>
<xsd:element name="to_encoder" type="to_encoder" />
<xsd:element name="to_decoder" type="to_decoder" />
</xsd:choice>
<xsd:element name="stream_id" type="xsd:string"
minOccurs="0" maxOccurs="unbounded" />
</xsd:sequence>
<xsd:attribute name="type" type="primitive_type"
use="optional" default="cmd" />
<xsd:attribute name="stream" type="stream_type"
use="optional" default="all" />
</xsd:complexType>
<xsd:simpleType name="primitive_type">
<xsd:restriction base="xsd:string">
<xsd:enumeration value="cmd" />
<xsd:enumeration value="ind" />
<xsd:enumeration value="req" />
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XML Schema for Media Control
<xsd:enumeration value="rsp" />
</xsd:restriction>
</xsd:simpleType>
<xsd:simpleType name="stream_type">
<xsd:restriction base="xsd:string">
<xsd:enumeration value="mid" />
<xsd:enumeration value="all" />
</xsd:restriction>
</xsd:simpleType>
<!-- Decoder Commands:
Currently only Picture Freeze is defined.
-->
<xsd:complexType name="to_decoder">
<xsd:sequence>
<xsd:element name="picture_freeze" />
</xsd:sequence>
</xsd:complexType>
<!-- Encoder Commands:
Picture Fast Update
Group of Blocks Fast Update
Macro Block Fast Update
-->
<xsd:complexType name="to_encoder">
<xsd:choice>
<xsd:element name="picture_fast_update" />
<xsd:element name="gob_fast_update">
<xsd:complexType>
<xsd:attribute name="first_gob"
type="xsd:nonNegativeInteger" use="optional" default="0" />
<xsd:attribute name="no_of_gobs"
type="xsd:nonNegativeInteger" use="optional" default="1" />
</xsd:complexType>
</xsd:element>
<xsd:element name="mb_fast_update">
<xsd:complexType>
<xsd:attribute name="first_gob"
type="xsd:nonNegativeInteger" use="optional" default="0" />
<xsd:attribute name="first_mb"
type="xsd:nonNegativeInteger" use="optional" default="1" />
<xsd:attribute name="no_of_mbs"
type="xsd:nonNegativeInteger" use="optional" default="1" />
</xsd:complexType>
</xsd:element>
</xsd:choice>
</xsd:complexType>
</xsd:schema>
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XML Schema for Media Control
Error Handling
Currently, only a single general error primitive is defined. It MAY
be used for indicating different type of errors in a free text
format. The general error MAY report problems in the XML document
parsing, inadequate level of media control support, inability to
perform the requested action, etc.
The error primitive MUST NOT be used for indication of errors other
then related to the media control parsing and the resultant
execution.
The error primitive MUST NOT be sent back as a result of getting an
error primitive.
Examples
In the following example the "Freeze" and the full picture "Fast
Update" commands are issued towards the remote video decoder(s) and
remote video encoder(s) respectively for all video streams.
<?xml version="1.0" encoding="utf-8" ?>
<media_control>
<vc_primitive>
<to_decoder>
<picture_freeze>
</picture_freeze>
</to_decoder>
</vc_primitive>
<vc_primitive>
<to_encoder>
<picture_fast_update>
</picture_fast_update>
</to_encoder>
</vc_primitive>
</media_control>
If an error occurs during the parsing of the XML document, the
following XML document would be sent back to the originator of the
original Media Control document.
<?xml version="1.0" encoding="utf-8" ?>
<media_control>
<general_error>
Parsing error: The original XML segment is:...
</general_error>
</media_control>
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XML Schema for Media Control
The following example demonstrates the full format of the defined
schema. The "Freeze" command is issued towards the remote video
decoder(s) to be applied to streams with "mid" [9] values "1" and
"2". The GOB "Fast Update" command is issued towards the remote
video encoder to be applied to a video stream with "mid" value "3".
<?xml version="1.0" encoding="utf-8" ?>
<media_control>
<vc_primitive stream="mid">
<to_decoder >
<picture_freeze>
</picture_freeze>
</to_decoder>
<stream_id>1</stream_id>
<stream_id>2</stream_id>
</vc_primitive>
<vc_primitive stream="mid">
<to_encoder>
<mb_fast_update first_gob="2" first_mb="3" no_of_mbs="4">
</mb_fast_update>
</to_encoder>
<stream_id>3</stream_id>
</vc_primitive>
</media_control>
The Schema Applications
As the first step, the defined XML document will be conveyed using a
SIP INFO method [8] with the "Content-Type" set to
"application/xml". This approach benefits from the SIP built-in
reliability.
The authors plan registering the defined schema with IANA according
to the guidelines specified in [10] and issuing a separate SIPPING
usage document(s). The document(s) will describe procedures for
conveying an XML document defined according to the Schema by means
of SIP INFO and SIP NOTIFY.
The authors hope that the XML schema, documented in this document,
will provide a base for a standard Tight Media Control protocol
definition within the IETF. It is expected that in future SIP will
define standard means for running this protocol as a part of SIP
architecture.
Conventions used in this document
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XML Schema for Media Control
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [1].
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
Patrick Monfort
France Telecom, R&D DMI/SGV
38-40 Av du Leclerc
92794 Issy Les Moulineaux Phone: +33-1-45-29-43-95
France Email: patrick.monfort@rd.francetelecom.com
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, "The SIP INFO Method", RFC2976, Internet Engineering
Task Force, October 2000.
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XML Schema for Media Control
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: September 2003 9
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