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Network Working Group J. Postel Request for Comments: 1590 ISI Updates: 1521 March 1994 Category: Informational

                 Media Type Registration Procedure

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.


 Several protocols allow the use of data representing different
 "media" such as text, images, audio, and video, and within such media
 different encoding styles, such as (in video) jpeg, gif, ief, and
 tiff.  The Multimedia Internet Message Extensions (MIME) protocol [1]
 defined several initial types of multimedia data objects, and a
 procedure for registering additional types with the Internet Assigned
 Numbers Authority (IANA).  Several questions have been raised about
 the requirements and administrative procedure for registering MIME
 content-type and subtypes, and the use of these Media Types for other
 applications.  This document addresses these issues and specifies a
 procedure for the registration of new Media Types (content-
 type/subtypes).  It also generalizes the scope of use of these Media
 Types to make it appropriate to use the same registrations and
 specifications with other applications.

1. Introduction

 RFC 1521 [1] defines a procedure for the registration of new data
 types for use with the Multimedia Internet Message Extensions (MIME).
 This registration mechanism was designed to make the identifiers for
 a given data type available for use and to prevent naming conflicts.
 With the growth of new multi-media protocols and access mechanisms,
 this process has the promise of forming a unified general
 registration service for Internet Protocols.  These types, previously
 called "MIME Types", are now called "Media Types".
 The registration process for Media Types (content-type/subtypes) was
 initially defined in the context of the asynchronous mail
 environments.  In this mail environment, there is a need to limit the
 number of possible Media Types to increase the likelihood of
 interoperability when the capabilities of the remote mail system are
 not known.  As Media Types are used in new environments, where the

IANA [Page 1] RFC 1590 Media Type Registration Procedure March 1994

 proliferation of Media Types is not a hindrance to interoperability,
 the original procedure is excessively restrictive and needs to be
 This document addresses the specific questions raised and provides an
 administrative procedure for the registration of Media Types.  This
 procedure also address the registration requirements needed for the
 mapping of Object Identifiers (OIDs) for X.400 MHS use to Media

2. Media Type Registration Procedure

 The following procedure has been implemented by the IANA for review
 and approval of new Media Types.  This is not a formal standards
 process, but rather an administrative procedure intended to allow
 community comment and sanity checking without excessive time delay.

2.1 Present the Request for Registration to the Community

 Send a proposed Media Type (content-type/subtype) to the "ietf-" mailing list.  This mailing list has been
 established for the sole purpose of reviewing proposed Media Types.
 Proposed content-types are not formally registered and must use the
 "x-" notation for the subtype name.
 The intent of the public posting is to solicit comments and feedback
 on the choice of content-type/subtype name, the unambiguity of the
 references with respect to versions and external profiling
 information, the choice of which OIDs to use, and a review of the
 security considerations section.  It should be noted that the
 proposed Media Type does not need to make sense for every possible
 application.  If the Media Type is intended for a limited or specific
 use, this should be noted in the submission.

2.2 Submit the Content Type to the IANA for Registration

 After two weeks, submit the proposed Media Type to the IANA for
 registration.  The request and supporting documentation should be
 sent to "".  Provided a reasonable review period has
 elapsed, the IANA will register the Media Type, assign an OID under
 the IANA branch, and make the Media Type registration available to
 the community.

IANA [Page 2] RFC 1590 Media Type Registration Procedure March 1994

 The Media Type registrations will be posted in the anonymous FTP
 directory "" and the Media Type will
 be listed in the periodically issued "Assigned Numbers" RFC [2].  The
 Media Type description may be published as an Informational RFC by
 sending it to "" (please follow the instructions to
 RFC authors [3]).

3. Clarifications On Specific Issues

3.1 MIME Requirements for a Limited Number of Content-Types

 Issue:  In the asynchronous mail environment, where information on
 the capabilities of the remote mail agent is not available to the
 sender, maximum interoperability is attained by restricting the
 number of content-types used to those "common" content-types expected
 to be widely implemented.  This was asserted as a reason to limit the
 number of possible content-types and resulted in a registration
 process with a significant hurdle and delay for those registering
 Comment:  The need for "common" content-types formats does not
 require limiting the registration of new content-types.  This
 restriction may, in fact, hinder interoperability by causing separate
 registration authorities for specific applications which may register
 values in conflict with or otherwise incompatible with each other.
 If a limited set of content-types recommended for a particular
 application, that should be asserted by a separate applicability
 statement specific for the application and/or environment.

3.2 Requirements for a Published Specification

 Issue:  Content-Type registration requires an RFC specifying the data
 format or a reference to a published specification of the data
 stream.  This requirement may be overly restrictive for the use of
 content-type registration for file attachments and distribution
 because a public specification may not be available for a number of
 widely used and exchanged objects.
 Comment:  MIME required the documentation of a specific content-type
 to allow the unambiguous identification of a defined type.  This
 intent is met by the identification of a particular software package
 and version when registering the content-type and is allowed for
 registration.  The appropriateness of using a Media Type with an
 unavailable specification should not be an issue in the registration.

IANA [Page 3] RFC 1590 Media Type Registration Procedure March 1994

3.3 Identification of Security Considerations

 Issue:  The registration process requires the identification of any
 known security problems with the content-type.
 Comment:  It is not required that the content-type be secure or that
 it be free from risks, but that the known risks be identified.
 Publication of a content-type does not require an exhaustive security
 review, and the security considerations section is subject to
 continuing evaluation.  Additional security considerations should be
 periodically published in an RFC by IANA.

3.4. Recommendations and Standards Status

 Issue:  The registration of a data type does not imply endorsement,
 approval, or recommendation by IANA or IETF or even certification
 that the specification is adequate.
 Comment: To become Internet Standards, protocol, data objects, or
 whatever must go through the IETF standards process.  This is too
 difficult and to lengthly a process for the convenient and practical
 need to register Media Types.  It is expected that applicability
 statements for particular applications will be published from time to
 time that recommend implementation of, and support for, data types
 that have proven particularly useful in those contexts.

4. Security Considerations

 This memo does not address specific security issues but outlines a
 security review process for Media Types.

5. Acknowledgements

 Most of the words in this RFC were written by other people --
 primarily John Klensin and Greg Vaudreuil -- and my contribution has
 been to slightly modify some sentences, delete some phrases, and to
 rearrange some paragraphs.  This means that i am responsible for all
 the bad ideas and mangled English, and they deserve the credit (and
 rightly) all the good ideas.

IANA [Page 4] RFC 1590 Media Type Registration Procedure March 1994

6. Author's Address

 Jon Postel
 USC/Information Sciences Institute
 4676 Admiralty Way
 Marina del Rey, CA  90292
 Phone: 310-822-1511
 Fax:   310-823-6714
 EMail: Postel@ISI.EDU

7. References

 [1] Borenstein N., and N. Freed, "MIME (Multipurpose Internet Mail
     Extensions) Part One:  Mechanisms for Specifying and Describing
     the Format of Internet Message Bodies", RFC 1521, Bellcore,
     Innosoft, September 1993.
 [2] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
     USC/Information Sciences Institute, July 1992.
 [3] Postel,J., "Instructions to RFC Authors", RFC 1543,
     USC/Information Sciences Institute, October 1993.

IANA [Page 5] RFC 1590 Media Type Registration Procedure March 1994

Appendix A – IANA Registration Procedures for Media Types

 MIME has been carefully designed to have extensible mechanisms, and
 it is expected that the set of content-type/subtype pairs and their
 associated parameters will grow significantly with time.  Several
 other MIME fields, notably character set names, access-type
 parameters for the message/external-body type, and possibly even
 Content-Transfer-Encoding values, are likely to have new values
 defined over time.
 In general, parameters in the content-type header field are used to
 convey supplemental information for various content types, and their
 use is defined when the content-type and subtype are defined.  New
 parameters should not be defined as a way to introduce new
 In order to ensure that the content-type and subtype (that is Media
 Type) values are developed in an orderly, well-specified, and public
 manner, MIME and other applications use the registration process for
 Media Types defined in this RFC which uses the Internet Assigned
 Numbers Authority (IANA) as a central registry for such values.
 In order to simplify and standardize this Media Type registration
 process, this appendix gives templates for the registration of new
 values with IANA.  Each of these is given in the form of an email
 message template, to be filled in by the registering party.
 Registration of New Content-type/subtype Values:
 Note that MIME is generally expected to be extended by subtypes.  If
 a new fundamental top-level type is needed, its specification must be
 published as an RFC or submitted in a form suitable to become an RFC,
 and be subject to the Internet standards process.

IANA [Page 6] RFC 1590 Media Type Registration Procedure March 1994

    Subject:  Registration of new Media Type content-type/subtype
    Media Type name:
    (If the above is not an existing top-level Media Type, please
    explain why an existing type cannot be used.)
    Media subtype name:
    Required parameters:
    Optional parameters:
    Encoding considerations:
    Security considerations:
    Published specification:
    (The published specification must be an Internet RFC or RFC-to-be
    if a new top-level type is being defined, and must be a publicly
    available specification in any case.)
    Person & email address to contact for further information:

IANA [Page 7]

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