MMUSIC G. Salgueiro
Internet-Draft Cisco Systems
Intended status: Standards Track May 20, 2011
Expires: November 21, 2011
IANA Registration of the 'image' Media Type
for the Session Description Protocol (SDP)
draft-salgueiro-mmusic-image-iana-registration-02
Abstract
This document describes the usage of the 'image' media type and
registers it with IANA as a top-level media type for the Session
Description Protocol (SDP). This media type is primarily used by SDP
to negotiate and establish T.38 media streams.
Status of this Memo
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Table of Contents
1. Conventions Used in This Document . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Conventions Used in This Document
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 [RFC2119].
2. Overview
In an earlier version of the SDP specification [RFC2327] packetized
media types, such as those shared by the Real-Time Transport Protocol
(RTP) [RFC3550], share the namespace with Multipurpose Internet Mail
Extensions (MIME) media types registry [RFC2048] (i.e. "MIME
types"). This is in contrast to the latest version of the SDP
specification [RFC4566] where an SDP-specific media type registry is
created and maintained by IANA. The top-level SDP media content
types registered by RFC 4566 [RFC4566] are "audio", "video", "text",
"application", and "message". A glaring omission on this list is the
'image' media type.
The 'image' media type is an existing top-level MIME type and is
widely used by SDP for setting up T.38 Real-Time Facsimile [T38]
media streams. This media type is extensively referenced by examples
in ITU-T T.38 [T38] and IETF standards like RFC 4145 [RFC4145]. The
following example shows the media description of a T.38 media stream
that is commonly found in a Session Initiation Protocol (SIP) INVITE
containing an SDP offer supporting both T.38 over UDPTL/UDP and TCP.
For the sake of brevity, the main portion of the session description
is omitted in this example, which only shows 'm' lines and their
attributes (including 'c' lines).
c=IN IP4 192.0.2.2
m=image 49170 udptl t38
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPFEC
m=image 49172 tcp t38
a=T38FaxRateManagement:localTCF
This document complies with the request of section 8.2.1 of RFC 4566
[RFC4566] that indicates:
"The same rules should apply for media names as for top-level
media content types, and where possible the same name should be
registered for SDP as for MIME. For media other than existing
top-level media content types, a Standards Track RFC MUST be
produced for a new top-level content type to be registered, and
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the registration MUST provide good justification why no existing
media name is appropriate."
The purpose of this document is to register with IANA the 'image'
media type as a top-level SDP media type. This ensures seamless
continuity with documentation that uses the 'image' MIME type and
also simplifies the usage of previously registered MIME sub-types
like 'image/t38' [RFC3362] that are used as SDP media descriptors for
T.38 [T38].
3. IANA Considerations
This document registers with IANA the 'image' media type in the
Session Description Protocol (SDP) Parameters registry. This
registration contains the REQUIRED information elements outlined in
the SDP registration procedure defined in Section 8.2.8 of RFC 4566
[RFC4566].
Contact Information:
Name: Gonzalo Salgueiro
Email: gsalguei@cisco.com
Telephone Number: (919) 392-3266
Name being registered (as it will appear in SDP): image
Long-form name in English: image
Type of name ('media', 'proto', 'fmt', 'bwtype', 'nettype', or
'addrtype'): media
Purpose of the registered name:
The currently registered list of SDP media types ('audio',
'video', 'text', 'application', and 'message') does not include
one suitable for real-time facsimile (fax) applications. The
'image' media type for the Session Description Protocol (SDP)
is primarily intended to be utilized as a parameter by SDP
[RFC4566] in SIP [RFC3261] to establish T.38 [T38] media
streams.
Specification for the registered name: RFC XXXX [This document]
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Packet Format: (As requested in Section 5.14 of RFC 4566
[RFC4566])
The current usage of the 'image' media type is for
establishment of T.38 media streams. Packet formats used for
each of the T.38 transport protocols (TCP, UDPTL/UDP, or RTP)
are clearly defined in the ITU-T T.38 recommendation [T38].
Therefore, this registration forgoes the description of the
packet format in the context of T.38, and instead delegates
that discussion to the T.38 fax relay standard.
Any future uses of the 'image' media type by the Session
Description Protocol SHOULD define the packet format in the
appropriate specification.
4. Security Considerations
The 'image' media type registered by this document to the SDP
parameters registry maintained by IANA [SDP-IANA] is primarily for
use by the offer/answer model of the Session Description Protocol
[RFC3264] for the negotiation and establishment of T.38 [T38] media
streams using the Session Initiation Protocol (SIP) [RFC3261]. This
additional SDP media type does not introduce any new security
considerations beyond those detailed in Section 7 of RFC 4566
[RFC4566]. The security vulnerabilities in T.38 [T38] and its
associated transport protocols (TCP [RFC0793], UDP [RFC0768], or RTP
[RFC3550]) are well documented in each of their respective
specifications.
5. Acknowledgements
Thanks goes to the chairs of the IETF Multiparty Multimedia Session
Control (MMUSIC) working group (Miguel A. Garcia and Flemming
Andreasen) for their guidance, encouragement, and the creation of the
media type registry. Special thanks to Miguel A. Garcia for his
thorough and insightful review of the early revisions of the draft.
This document has benefited from the discussion and review of the
MMUSIC working group, especially the detailed and thoughtful comments
and corrections of Keith Drage.
The author would also like to acknowledge the considerable efforts of
Kevin Fleming and the members of the FoIP TG in the SIP Forum that
contributed to the new revision of the ITU-T T.38 Recommendation that
prompted the need to register the 'image' media type for SDP.
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6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[SDP-IANA]
IANA, "Session Description Protocol (SDP) Parameters",
http://www.iana.org/assignments/sdp-parameters , 2011.
6.2. Informative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four: Registration
Procedures", BCP 13, RFC 2048, November 1996.
[RFC2327] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3362] Parsons, G., "Real-time Facsimile (T.38) - image/t38 MIME
Sub-type Registration", RFC 3362, August 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.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
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[T38] International Telecommunications Union, "Procedures for
real-time Group 3 facsimile communication over IP
Networks", ITU-T Recommendation T.38, 2010.
Author's Address
Gonzalo Salgueiro
Cisco Systems
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
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