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   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.
















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                       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.

















































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