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Versions: 00 01 02 03 04 05 RFC 4573

AVT                                                              R. Even
Internet-Draft                                                   Polycom
Expires: June 12, 2005                                 December 12, 2004

        MIME type registration for RTP Payload format for H.224

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
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   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2004).


   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 MIME 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.  Normative References . . . . . . . . . . . . . . . . . . . . .  8
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  9
       Intellectual Property and Copyright Statements . . . . . . . . 10

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1.  Introduction

   The ITU-T recommendation H.281 [ITU.281] specifies a protocol for far
   end camera control.  This protocol is carried in H.320 systems using
   H.224 [ITU.H224].  For H.323 systems, H.323 annex Q specifies how to
   carry H.281/H.224 frames using RTP packets.

   The document will register a H224 MIME type that can be used by
   systems that uses SDP[RFC2327].

   This MIME type will be used for supporting the simple far end camera
   control protocol on SDP based systems.  The MIME type will help
   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 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 protocol is based on ITU-T H.281 running over ITU-T H.224 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 is described in H.281 and H.323 annex Q

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4.  IANA Considerations

   This section describes the MIME types and names associated with this
   payload format.  The section registers the MIME types, as per

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 that will like to send 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

   Author/Change controller:

   Roni Even

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5.  SDP Parameters

   The MIME 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.

   H.281 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 will be dependent on the functionality of both side.

   The offerer will offer 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 camera can be remotely
   controlled and/or it intends to use H.224 capabilities negotiation,
   the offerer will offer a sendrecv channel.

   The answerer behavior will be as follows:

   If it receives an offer with sendonly it will answer with a recvonly
   if it supports far end camera control, otherwise it will ignore
   reject the offer.

   If it receives an offer with sendrecv and its camera can be remotely
   controlled it will answer with a sendrecv option.  If its camera
   cannot be remotely control it will reject 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.

7  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

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

Author's Address

   Roni Even
   94 Derech Em Hamoshavot
   Petach Tikva  49130

   EMail: roni.even@polycom.co.il

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