Network Working Group J. Postel
Request for Comments: 1590 ISI
Updates: 1521 March 1994
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 
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.
RFC 1521  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
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-
firstname.lastname@example.org" 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 "email@example.com". 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 Media Type registrations will be posted in the anonymous FTP
directory "ftp.isi.edu:in-notes/media-types" and the Media Type will
be listed in the periodically issued "Assigned Numbers" RFC . The
Media Type description may be published as an Informational RFC by
sending it to "firstname.lastname@example.org" (please follow the instructions to
RFC authors ).
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.
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.
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.
6. Author's Address
USC/Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
 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.
 Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
USC/Information Sciences Institute, July 1992.
 Postel,J., "Instructions to RFC Authors", RFC 1543,
USC/Information Sciences Institute, October 1993.
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.
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:
(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: