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Internet Engineering Task Force (IETF)                      G. SalgueiroRequest for Comments: 6466                                 Cisco SystemsCategory: Standards Track                                  December 2011ISSN: 2070-1721IANA Registration of the 'image' Media Typefor the Session Description Protocol (SDP)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   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6466.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Salgueiro                    Standards Track                    [Page 1]

RFC 6466             'image' Media Type Registration       December 2011Table of Contents1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document . . . . . . . . . . . . . . .33.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . . .45.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .46.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .56.1.  Normative References  . . . . . . . . . . . . . . . . . . .56.2.  Informative References  . . . . . . . . . . . . . . . . . .51.  Overview   In an earlier version of the SDP specification [RFC2327] of   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   [RFC4288] [RFC4289] (i.e., "MIME media 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   byRFC 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 media 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 Track   documents likeRFC 4145 [RFC4145].  The following example shows the   media description of a T.38 media stream as commonly found in a   Session Initiation Protocol (SIP) [RFC3261] INVITE; it contains an   SDP offer for T.38 over both UDP Transport Layer (UDPTL) and TCP.   For the sake of brevity, only the SDP body of the SIP INVITE request   is displayed in this example.Salgueiro                    Standards Track                    [Page 2]

RFC 6466             'image' Media Type Registration       December 2011       v=0       o=alice 53655765 2353687637 IN IP4 pc33.example.com       s=SDP image example       c=IN IP4 192.0.2.2       t=0 0       m=image 49170 udptl t38       a=T38FaxVersion:0       a=T38MaxBitRate:14400       a=T38FaxRateManagement:transferredTCF       a=T38FaxMaxBuffer:262       a=T38FaxMaxDatagram:90       a=T38FaxUdpEC:t38UDPRedundancy       a=sendrecv       m=image 49172 tcp t38       a=T38FaxRateManagement:localTCF   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 media type   and the previously registered MIME media sub-types like 'image/t38'   [RFC3362] that are used as SDP media descriptors for T.38 [T38].   This document complies with the request ofSection 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      the registration MUST provide good justification why no existing      media name is appropriate.2.  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 inRFC 2119 [RFC2119].3.  IANA Considerations   IANA has registered an 'image' token in the media sub-registry of the   Session Description Protocols (SDP) Parameters registry.  This   registration contains the required information elements outlined in   the SDP registration procedure defined inSection 8.2.8 of RFC 4566   [RFC4566].Salgueiro                    Standards Track                    [Page 3]

RFC 6466             'image' Media Type Registration       December 2011   (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 'image' media type for the Session Description Protocol           is used to describe a media stream whose content consists of           one or more separate images that require appropriate hardware           to display.  The media subtype further describes the specific           format of the image.  Currently, the 'image' media type for           SDP is used ubiquitously by the SIP control protocol to           establish T.38 media streams.   (6)  Specification for the registered name:RFC 64664.  Security Considerations   The 'image' media type registered by this document in the SDP   parameters registry maintained by 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   SIP [RFC3261].  This additional SDP media type does not introduce any   security considerations beyond those detailed in Section 7 ofRFC4566 [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.  The   ability to exchange images other than T.38 can expose the recipient   to potentially malicious executable code.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 theSalgueiro                    Standards Track                    [Page 4]

RFC 6466             'image' Media Type Registration       December 2011   media type registry.  Special thanks to Miguel A. Garcia for his   thorough and insightful review of the many draft revisions of this   document.   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, Kevin P. Fleming,   Bert Greevenbosch, and Gonzalo Camarillo.   The author would also like to acknowledge the considerable efforts of   Kevin P. Fleming and the members of the Fax-over-IP (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.  References6.1.  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 2006.6.2.  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.   [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.Salgueiro                    Standards Track                    [Page 5]

RFC 6466             'image' Media Type Registration       December 2011   [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.   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and              Registration Procedures",BCP 13,RFC 4288, December 2005.   [RFC4289]  Freed, N. and J. Klensin, "Multipurpose Internet Mail              Extensions (MIME) Part Four: Registration Procedures",BCP 13,RFC 4289, December 2005.   [T38]      International Telecommunication Union, "Procedures for              real-time Group 3 facsimile communication over IP              Networks", ITU-T Recommendation T.38 (Pre-Published),              September 2010,              <http://www.itu.int/rec/T-REC-T.38-201009-P/en>.Author's Address   Gonzalo Salgueiro   Cisco Systems   7200-12 Kit Creek Road   Research Triangle Park, NC  27709   US   EMail: gsalguei@cisco.comSalgueiro                    Standards Track                    [Page 6]