AVT R. Even
Internet-Draft Polycom
Expires: June 12, 2005 December 12, 2004
MIME type registration for RTP Payload format for H.224
draft-ietf-avt-mime-h224-00.txt
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Copyright (C) The Internet Society (2004).
Abstract
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
H.281.
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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
RFC2048[RFC2048]
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.
[ITU.H224]
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.
[ITU.H323]
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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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.
Author's Address
Roni Even
Polycom
94 Derech Em Hamoshavot
Petach Tikva 49130
Israel
EMail: roni.even@polycom.co.il
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