type in [RFC2046] for an example of such directives and how they
should be described in a media type registration.
o All registrations MUST state whether or not they employ such
"active content", and if they do, they MUST state what steps have
been taken to protect users of the media type from harm.
o Complex media types may include provisions for directives that
institute actions that, while not directly harmful to the
recipient, may result in disclosure of information that either
facilitates a subsequent attack or else violates a recipient’s
privacy in some way. Again, the registration of the
application/postscript media type illustrates how such directives
can be handled.
o A media type that employs compression may provide an opportunity
for sending a small amount of data that, when received and
evaluated, expands enormously to consume all of the recipient’s
resources. All media types SHOULD state whether or not they
employ compression, and if they do they should discuss what steps
need to be taken to avoid such attacks.
o A media type might be targeted for applications that require some
sort of security assurance but not provide the necessary security
mechanisms themselves. For example, a media type could be defined
for storage of confidential medical information that in turn
requires an external confidentiality service, or which is designed
for use only within a secure environment.
4.7. Requirements specific to XML media types
There are a number of additional requirements specific to the
registration of XML media types. These requirements are specified in
[RFC3023].
4.8. Encoding Requirements
Some transports impose restrictions on the type of data they can
carry. For example, Internet mail traditionally was limited to 7bit
US-ASCII text. Encoding schemes are often used to work around such
transport limitations.
It is therefore useful to note what sort of data a media type can
consist of as part of its registration. An "encoding considerations"
field is provided for this purpose. Possible values of this field
are:
7bit: The content of the media type consists solely of CRLF-delimited
7bit US-ASCII text.
8bit: The content of the media type consists solely of CRLF-delimited
8bit text.
binary: The content consists of unrestricted sequence of octets.
framed: The content consists of a series of frames or packets without
internal framing or alignment indicators. Additional out-of-band
information is needed to interpret the data properly, including
but not necessarily limited to, knowledge of the boundaries
between successive frames and knowledge of the transport
mechanism. Note that media types of this sort cannot simply be
stored in a file or transported as a simple stream of octets;
therefore, such media types are unsuitable for use in many
traditional protocols. A commonly used transport with framed
encoding is the Real-time Transport Protocol, RTP. Additional
rules for framed encodings defined for transport using RTP are
given in [RFC3555].
Additional restrictions on 7bit and 8bit text are given in [RFC2046].
4.9. Usage and Implementation Non-requirements
In the asynchronous mail environment, where information on the
capabilities of the remote mail agent is frequently not available to
the sender, maximum interoperability is attained by restricting the
media types used to those "common" formats expected to be widely
implemented. This was asserted in the past as a reason to limit the
number of possible media types, and it resulted in a registration
process with a significant hurdle and delay for those registering
media types.
However, the need for "common" media types does not require limiting
the registration of new media types. If a limited set of media types
is recommended for a particular application, that should be asserted
by a separate applicability statement specific for the application
and/or environment.
Therefore, universal support and implementation of a media type is
NOT a requirement for registration. However, if a media type is
explicitly intended for limited use, this MUST be noted in its
registration. The "Restrictions on Usage" field is provided for this
purpose.
4.10. Publication Requirements
Proposals for media types registered in the standards tree by the
IETF itself MUST be published as RFCs. RFC publication of vendor and
personal media type proposals is encouraged but not required. In all
cases the IANA will retain copies of all media type proposals and
"publish" them as part of the media types registration tree itself.
As stated previously, standards tree registrations for media types
defined in documents produced by other standards bodies MUST be
described by a formal standards specification produced by that body.
Such specifications MUST contain an appropriate media type
registration template taken from Section 10. Additionally, the
copyright on the registration template MUST allow the IANA to copy it
into the IANA registry.
Other than IETF registrations in the standards tree, the registration
of a data type does not imply endorsement, approval, or
recommendation by the IANA or the IETF or even certification that the
specification is adequate. To become Internet Standards, a protocol
or data object must go through the IETF standards process. This is
too difficult and too lengthy a process for the convenient
registration of media types.
The standards tree exists for media types that do require a
substantive review and approval process in a recognized standards
body. The vendor and personal trees exist for those media types that
do not require such a process. It is expected that applicability
statements for particular applications will be published from time to
time in the IETF, recommending implementation of, and support for,
media types that have proven particularly useful in those contexts.
As discussed above, registration of a top-level type requires
standards-track processing in the IETF and, hence, RFC publication.
4.11. Additional Information
Various sorts of optional information SHOULD be included in the
specification of a media type if it is available:
o Magic number(s) (length, octet values). Magic numbers are byte
sequences that are always present at a given place in the file and
thus can be used to identify entities as being of a given media
type.
o File name extension(s) commonly used on one or more platforms to
indicate that some file contains a given media type.
o Mac OS File Type code(s) (4 octets) used to label files containing
a given media type.
o Information about how fragment/anchor identifiers [RFC3986] are
constructed for use in conjunction with this media type.
In the case of a registration in the standards tree, this additional
information MAY be provided in the formal specification of the media
type. It is suggested that this be done by incorporating the IANA
media type registration form into the specification itself.
5. Registration Procedure
The media type registration procedure is not a formal standards
process, but rather an administrative procedure intended to allow
community comment and sanity checking without excessive time delay.
The normal IETF processes should be followed for all IETF
registrations in the standards tree. The posting of an Internet
Draft is a necessary first step, followed by posting to the
ietf-types@iana.org list as discussed below.
Registrations in the vendor and personal tree should be submitted
directly to the IANA, ideally after first posting to the
ietf-types@iana.org list for review.
Proposed registrations in the standards tree by other standards
bodies should be communicated to the IESG (at iesg@ietf.org) and to
the ietf-types list (at ietf-types@iana.org). Prior posting as an
Internet Draft is not required for these registrations, but may be
helpful to the IESG and is encouraged.
5.1. Preliminary Community Review
Notice of a potential media type registration in the standards tree
MUST be sent to the "ietf-types@iana.org" mailing list for review.
This mailing list has been established for the purpose of reviewing
proposed media and access types. Registrations in other trees MAY be
sent to the list for review as well.
The intent of the public posting to this list is to solicit comments
and feedback on the choice of type/subtype name, the unambiguity of
the references with respect to versions and external profiling
information, and a review of any interoperability or security
considerations. The submitter may submit a revised registration or
abandon the registration completely and at any time.
5.2. IESG Approval
Media types registered in the standards tree MUST be approved by the
IESG prior to registration.
5.3. IANA Registration
Provided that the media type meets all of the relevant requirements
and has obtained whatever approval is necessary, the author may
submit the registration request to the IANA. Registration requests
can be sent to iana@iana.org. A web form for registration requests
is also available:
http://www.iana.org/cgi-bin/mediatypes.pl
Sending to ietf-types@iana.org does not constitute submitting the
registration to the IANA.
When the registration is either part of an RFC publication request or
a registration in the standards tree submitted to the IESG, close
coordination between the IANA and the IESG means IESG approval in
effect submits the registration to the IANA. There is no need for an
additional registration request in such cases.
5.4. Media Types Reviewer
Registrations submitted to the IANA will be passed on to the media
types reviewer. The media types reviewer, who is appointed by the
IETF Applications Area Director(s), will review the registration to
make sure it meets the requirements set forth in this document.
Registrations that do not meet these requirements will be returned to
the submitter for revision.
Decisions made by the media types reviewer may be appealed to the
IESG using the procedure specified in [RFC2026] section 6.5.4.
Once a media type registration has passed review, the IANA will
register the media type and make the media type registration
available to the community.
6. Comments on Media Type Registrations
Comments on registered media types may be submitted by members of the
community to the IANA. These comments will be reviewed by the media
types reviewer and then passed on to the "owner" of the media type if
possible. Submitters of comments may request that their comment be
attached to the media type registration itself, and if the IANA
approves of this, the comment will be made accessible in conjunction
with the type registration.
7. Location of Registered Media Type List
Media type registrations are listed by the IANA at:
http://www.iana.org/assignments/media-types/
8. IANA Procedures for Registering Media Types
The IANA will only register media types in the standards tree in
response to a communication from the IESG stating that a given
registration has been approved. Vendor and personal types will be
registered by the IANA automatically and without any formal approval
process as long as the following minimal conditions are met:
o Media types MUST function as an actual media format. In
particular, charsets and transfer encodings MUST NOT be registered
as media types.
o All media types MUST have properly formed type and subtype names.
All type names MUST be defined by a standards-track RFC. All
type/subtype name pairs MUST be unique and MUST contain the proper
tree prefix.
o Types registered in the personal tree MUST either provide a format
specification or a pointer to one.
o All media types MUST have a reasonable security considerations
section. (It is neither possible nor necessary for the IANA to
conduct a comprehensive security review of media type
registrations. Nevertheless, the IANA has the authority to
identify obviously incompetent material and return it to the
submitter for revision.)
Registrations in the standards tree MUST satisfy the additional
requirement that they originate from the IETF itself or from another
standards body recognized as such by the IETF.
9. Change Procedures
Once a media type has been published by the IANA, the owner may
request a change to its definition. The descriptions of the
different registration trees above designate the "owners" of each
type of registration. The same procedure that would be appropriate
for the original registration request is used to process a change
request.
Changes should be requested only when there are serious omissions or
errors in the published specification. When review is required, a
change request may be denied if it renders entities that were valid
under the previous definition invalid under the new definition.
The owner of a media type may pass responsibility to another person
or agency by informing the IANA and the ietf-types list; this can be
done without discussion or review.
The IESG may reassign responsibility for a media type. The most
common case of this will be to enable changes to be made to types
where the author of the registration has died, moved out of contact
or is otherwise unable to make changes that are important to the
community.
Media type registrations may not be deleted; media types that are no
longer believed appropriate for use can be declared OBSOLETE by a
change to their "intended use" field; such media types will be
clearly marked in the lists published by the IANA.
10. Registration Template
To: ietf-types@iana.org
Subject: Registration of media type XXX/YYY
Type name:
Subtype name:
Required parameters:
Optional parameters:
Encoding considerations:
Security considerations:
Interoperability considerations:
Published specification:
Applications that use this media type:
Additional information:
Magic number(s):
File extension(s):
Macintosh file type code(s):
Person & email address to contact for further information:
Intended usage:
(One of COMMON, LIMITED USE or OBSOLETE.)
Restrictions on usage:
(Any restrictions on where the media type can be used go here.)
Author:
Change controller:
(Any other information that the author deems interesting may be added
below this line.)
Some discussion of Macintosh file type codes and their purpose can be
found in [MacOSFileTypes]. Additionally, please refrain from writing
"none" or anything similar when no file extension or Macintosh file
type is specified, lest "none" be confused with an actual code value.
11. Security Considerations
Security requirements for media type registrations are discussed in
Section 4.6.
12. IANA Considerations
The purpose of this document is to define IANA registries for media
types.
13. Acknowledgements
The current authors would like to acknowledge their debt to the late
Dr. Jon Postel, whose general model of IANA registration procedures
and specific contributions shaped the predecessors of this document
[RFC2048]. We hope that the current version is one with which he
would have agreed but, as it is impossible to verify that agreement,
we have regretfully removed his name as a co-author.
14. References
14.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types", RFC
2046, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration
of RTP Payload Formats", RFC 3555, July 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.
[RFC4234] Crocker, D. Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 4234, October
2005.
14.2. Informative References
[MacOSFileTypes] Apple Computer, Inc., "Mac OS: File Type and Creator
Codes, and File Formats", Apple Knowledge Base
Article 55381, June 1993,
<http://www.info.apple.com/kbnum/n55381>.
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four:
Registration Procedures", BCP 13, RFC 2048, November
1996.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
Encoded Word Extensions: Character Sets, Languages,
and Continuations", RFC 2231, November 1997.
Appendix A. Grandfathered Media Types
A number of media types, registered prior to 1996, would, if
registered under the guidelines in this document, be placed into
either the vendor or personal trees. Reregistration of those types
to reflect the appropriate trees is encouraged but not required.
Ownership and change control principles outlined in this document
apply to those types as if they had been registered in the trees
described above.
Appendix B. Changes Since RFC 2048
o Media type specification and registration procedures have been
moved out of the MIME document set to this separate specification.
o The various URLs and addresses in this document have been changed
so they all refer to iana.org rather than isi.edu. Additionally,
many of the URLs have been changed to use HTTP; formerly they used
FTP.
o Much of the document has been clarified in the light of
operational experience with these procedures.
o The unfaceted IETF tree is now called the standards tree, and the
registration rules for this tree have been relaxed to allow use by
other standards bodies.
o The text describing the media type registration procedure has
clarified.
o The rules and requirements for constructing security
considerations sections have been extended and clarified.
o RFC 3023 is now referenced as the source of additional information
concerning the registration of XML media types.
o Several of the references in this document have been updated to
refer to current versions of the relevant specifications.
o A note has been added discouraging the assignment of multiple
names to a single media type.
o Security considerations and IANA considerations sections have been
added.
o Concerns regarding copyrights on media type registration templates
produced by other standards bodies have been dealt with by
requiring that the IANA be allowed to copy the registration
template into the registry.
o The basic registration requirements for the various top-level
types have been moved from RFC 2046 to this document.
o A syntax is now specified for media type, subtype, and parameter
names.
o Imposed a maximum length of 127 on all media type and subtype
names.
o A note has been added to caution against excessive use of
"+suffix" constructs in subtype names.
o The encoding considerations field has been extended to allow the
value "framed".
o A reference describing Macintosh Type codes has been added.
o Ietf-types list review of registrations in the standards tree is
now required rather than just recommended.
Authors’ Addresses
Ned Freed
Sun Microsystems
3401 Centrelake Drive, Suite 410
Ontario, CA 92761-1205
USA
Phone: +1 909 457 4293
EMail: ned.freed@mrochek.com
John C. Klensin
1770 Massachusetts Ave, #322
Cambridge, MA 02140
EMail: klensin+ietf@jck.com
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