XML Schema for Media Control
RFC 5168

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Network Working Group                                           O. Levin
Request for Comments: 5168                         Microsoft Corporation
Category: Informational                                          R. Even
                                                                 Polycom
                                                            P. Hagendorf
                                                               RADVISION
                                                              March 2008

                      XML Schema for Media Control

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Abstract

   This document defines an Extensible Markup Language (XML) Schema for
   video fast update in a tightly controlled environment, developed by
   Microsoft, Polycom, Radvision and used by multiple vendors.  This
   document describes a method that has been deployed in Session
   Initiation Protocol (SIP) based systems over the last three years and
   is being used across real-time interactive applications from
   different vendors in an interoperable manner.  New implementations
   are discouraged from using the method described except for backward
   compatibility purposes.  New implementations are required to use the
   new Full Intra Request command in the RTP Control Protocol (RTCP)
   channel.

Levin, et al.                Informational                      [Page 1]
RFC 5168                     Media Control                    March 2008

Table of Contents

   1. Introduction ....................................................2
   2. Conventions .....................................................2
   3. Background ......................................................3
   4. The Video Control Commands ......................................3
   5. The Schema Definition ...........................................4
   6. Error Handling ..................................................5
   7. Examples ........................................................5
      7.1. The Fast Update Command for the Full Picture ...............5
      7.2. Reporting an Error .........................................5
   8. Transport .......................................................6
   9. IANA Considerations .............................................6
      9.1. Application/media_control+xml Media Type Registration ......6
   10. Security Considerations ........................................7
   11. References .....................................................8
      11.1. Normative References ......................................8
      11.2. Informative References ....................................8

1.  Introduction

   This document defines an Extensible Markup Language (XML) Schema for
   video fast update request in a tightly controlled environment,
   developed by Microsoft, Polycom, Radvision and used by multiple
   vendors.  Implementation of this schema for interactive video
   applications in Session Initiation Protocol (SIP) [5] environments
   was designed in order to improve user experience.  This mechanism is
   being used by both end user video conferencing terminals and
   conferencing servers in shipping products.  This document describes
   the current method, but new implementations are discouraged from
   using this method, except for backward compatibility with legacy
   systems.  Shipping products and new products SHOULD use the Full
   Intra Request, described in [7].

   Sending video fast update using the SIP signaling path, as described
   in this document, is inferior to using the RTP Control Protocol
   (RTCP) feedback method [7], since the command flows through all the
   proxies in the signaling path adding delay to the messages and
   causing unnecessary overload to the proxies.  RTCP messages flow
   end-to-end and not through the signaling proxies.  The RTCP feedback
   document [7] also adds other required control functions, such as the
   flow control command, which is missing from this document.

2.  Conventions

   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 [2].

Levin, et al.                Informational                      [Page 2]
RFC 5168                     Media Control                    March 2008

3.  Background

   SIP typically uses the Real-time Transport Protocol (RTP) [6] for the
   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.
   The RTCP feedback mechanism [8] has been introduced in order to
   improve basic RTCP feedback time in case of loss conditions across
   different coding schemes.  This technique addresses signaling of loss