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Versions: 00 01 02 03 04 05 RFC 4573

AVT                                                              R. Even
Internet-Draft                                                   Polycom
Expires: December 17, 2005                                 June 15, 2005

        MIME type registration for RTP Payload format for H.224

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   In conversional video applications far end camera control protocol is
   used by participants to control the remote camera.  The protocol that
   is commonly used is ITU H.281 over H.224.  The document registers the
   H224 media type.  It defines the syntax and the semantics of the SDP
   parameters needed to support far end camera control protocol using

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Far-end camera control protocol  . . . . . . . . . . . . . . .  5
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
     4.1   Registration of MIME media type application/h224 . . . . .  6
   5.  SDP Parameters . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1   Usage with the SDP Offer Answer Model  . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1   Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2   Informative References . . . . . . . . . . . . . . . . . .  9
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
       Intellectual Property and Copyright Statements . . . . . . . . 11

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1.  Introduction

   The document registers the H224 media type that may be used by
   systems that uses SDP[RFC2327].

   This media type is used for supporting the simple far end camera
   control protocol on SDP based systems.  The media type helps
   signaling gateways between H.323 [ITU.H323]and SDP based systems to
   use far end camera control, end to end, without having any protocol
   translation in the middle.

   The document defines H224 media type since the RTP packets in H.323
   annex Q[ITU.H323] carry H.224 frames.  The far end camera control
   protocol (FECC) is internal to H.224 frame and is identified by the
   client ID field of the H.224 packet.

   The document will define the SDP[RFC2327]parameters needed to support
   the above far end camera control protocol in systems that use SDP

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119[RFC2119] and
   indicate requirement levels for compliant RTP implementations.

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3.  Far-end camera control protocol

   This simple protocol is based on ITU-T H.281 frames inside ITU-T
   H.224 packets in an RTP/UDP channel.  H.323 annex Q specifies how to
   build the RTP packets from the H.224 packets.

   Using far end camera control protocol in point to point calls and
   multipoint calls for packet switch networks is described in H.323
   annex Q

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4.  IANA Considerations

   This section describes the media types and names associated with this
   payload format.  The section registers the media types, as per
   RFC2048[RFC2048] and

4.1  Registration of MIME media type application/h224

   MIME media type name: application

   MIME subtype name: H224

   Required parameters: None

   Optional parameters:  None

   Encoding considerations:

   This type is only defined for transfer via RTP [RFC3550]

   Security considerations: See Section 6

   Interoperability considerations: Terminals sending simple far end
   camera control command should use this MIME type, receivers who can
   not support the protocol will reject the channel.

   Published specification: RFC yyy

   Applications which use this media type:

   Video conferencing applications.

   Additional information: none

   Person and email address to contact for further information :

   Roni Even: roni.even@polycom.co.il

   Intended usage: COMMON


   Roni Even

   Change controller:

   IETF Audio/Video Transport working group delegated from the IESG.

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5.  SDP Parameters

   The media media type application/h224 string is mapped to fields in
   the Session Description Protocol (SDP)  as follows:

   o The media name in the "m=" line of SDP MUST be application.  The
   transport SHOULD be RTP and the payload type is dynamic.

   o The encoding name in the "a=rtpmap" line of SDP MUST be h224 (the
   MIME subtype).

   o The clock rate in the "a=rtpmap" line MUST be 0.

   The recommended maximum bandwidth for this protocol is 6.4 kbit/sec.

5.1  Usage with the SDP Offer Answer Model

   When offering FECC using SDP in an Offer/Answer model[RFC3264]  the
   following considerations are necessary.

   Far end camera control communication are uni-directional.  H.224 is
   bi-directional and can be used to learn the capabilities of the
   remote video end point e.g how many cameras it has.  The offer answer
   exchange is dependent on the functionality of both side.

   The offerer offers a sendonly channel if its camera can not be
   remotely controlled and if the offerer does not intend to use H.224
   to learn the capabilities of the remote video endpoints.

   In all other cases, when the offerer's camera can be remotely
   controlled and/or it intends to use H.224 capabilities negotiation,
   the offerer offers a sendrecv channel.

   The answerer behavior is as follows:

   If it receives an offer with sendonly it answers with a recvonly if
   it supports far end camera control, otherwise it ignores / reject the

   If it receives an offer with sendrecv and its camera can be remotely
   controlled it answers with a sendrecv option.  If its camera cannot
   be remotely control it rejects the offer but may later try to
   remotely control the offerer's camera using this procedure.

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6.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550].  This implies that confidentiality of the
   media streams is achieved by encryption.

   A potential denial-of-service threat exists.  The attacker can inject
   pathological datagrams into the stream which may cause the receiver
   to move the camera randomly.  The usage of authentication of at least
   the RTP packet is RECOMMENDED

   As with any IP-based protocol, in some circumstances a receiver may
   be overloaded simply by the receipt of too many packets, either
   desired or undesired.  Network-layer authentication may be used to
   discard packets from undesired sources, but the processing cost of
   the authentication itself may be too high.

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7.  References

7.1  Normative References

   [ITU.281]  International Telecommunications Union, "A far end camera
              control protocol for videoconferences using H.224", ITU-
              T Recommendation H.281, November 1994.

              International Telecommunications Union, "A real time
              control protocol for simplex applications using the H.221
              LSD/HSD/HLP channels.", ITU-T Recommendation H.224,
              February 2000.

              International Telecommunications Union, "Visual telephone
              systems and equipment for local area networks which
              provide a non-guaranteed quality of service", ITU-
              T Recommendation H.323, July 2003.

   [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2327]  Handley, M. and V. Jacobson, "SDP: Session Description
              Protocol", RFC 2327, April 1998.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

7.2  Informative References

              Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", draft-freed-media-type-reg-04
              (work in progress), April 2005.

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Author's Address

   Roni Even
   94 Derech Em Hamoshavot
   Petach Tikva  49130

   Email: roni.even@polycom.co.il

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