MMUSIC G. Salgueiro
Internet-Draft Cisco Systems
Intended status: Standards Track May 25, 2011
Expires: November 26, 2011
IANA Registration of the 'image' Media Type
for the Session Description Protocol (SDP)
draft-salgueiro-mmusic-image-iana-registration-05
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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This Internet-Draft will expire on November 26, 2011.
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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 . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
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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 used with 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] which requested that an SDP-specific media
type registry be 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
from this list is the "image" media type.
The 'image' media type is an existing top-level MIME type and is
widely used in SDP implementations 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 as commonly found in a Session
Initiation Protocol (SIP) INVITE; it contains an SDP offer for T.38
over both UDPTL 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].
(1) Contact Information:
Name: Gonzalo Salgueiro
Email: gsalguei@cisco.com
Telephone Number: (919) 392-3266
(2) Name being registered (as it will appear in SDP): image
(3) Long-form name in English: image
(4) Type of name ('media', 'proto', 'fmt', 'bwtype', 'nettype', or
'addrtype'): media
(5) 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.
(6) Specification for the registered name: RFC XXXX [This document]
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4. Security Considerations
The 'image' media type registered by this document in 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 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], and RTP
[RFC3550]) are well documented in each of their respective
specifications.
5. Acknowledgements
Thanks go 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, Yasubumi Chimura, and Kevin P.
Fleming.
The author would also like to acknowledge the considerable efforts of
Kevin P. 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.
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.
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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.
[T38] International Telecommunications Union, "Procedures for
real-time Group 3 facsimile communication over IP
Networks", ITU-T Recommendation T.38, October 2010.
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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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