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 Levin, et al. Expires: September 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 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. Levin, et al. Expires: September 2003 3 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" /> Levin, et al. Expires: September 2003 4 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> Levin, et al. Expires: September 2003 5 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> Levin, et al. Expires: September 2003 6 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 Levin, et al. Expires: September 2003 7 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. Levin, et al. Expires: September 2003 8 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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draft-levin-mmusic-xml-media-control-01
Internet-Draft
