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MMUSIC                                                      G. Salgueiro
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                            May 24, 2011
Expires: November 25, 2011

              IANA Registration of the 'image' Media Type
               for the Session Description Protocol (SDP)


   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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 25, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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",
   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
           m=image 49170 udptl t38
           m=image 49172 tcp t38

   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

   (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 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

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, Yasubumi Chimura, and Kevin Fleming.

   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.

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.

              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, 2010.

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Author's Address

   Gonzalo Salgueiro
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709

   Email: gsalguei@cisco.com

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