Network Working Group N. Freed
Internet-Draft Sun Microsystems
Obsoletes: 2048 (if approved) J. Klensin
Expires: August 24, 2003 February 23, 2003
Multipurpose Internet Mail Extensions (MIME) Part Four: Registration
Procedures
draft-freed-mime-p4-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on August 24, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document specifies various IANA registration procedures for the
following MIME facilities:
o media types,
o external body access types, and
o content-transfer-encodings.
Registration of charsets for use in MIME is covered elsewhere and is
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no longer addressed by this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions Used In This Document . . . . . . . . . . . . . 5
3. Media Type Registration . . . . . . . . . . . . . . . . . . 6
3.1 Registration Trees and Subtype Names . . . . . . . . . . . . 6
3.1.1 Standards Tree . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.2 Vendor Tree . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.3 Personal or Vanity Tree . . . . . . . . . . . . . . . . . . 7
3.1.4 Special x. Tree . . . . . . . . . . . . . . . . . . . . . . 7
3.1.5 Additional Registration Trees . . . . . . . . . . . . . . . 8
3.2 Registration Requirements . . . . . . . . . . . . . . . . . 8
3.2.1 Functionality Requirement . . . . . . . . . . . . . . . . . 8
3.2.2 Naming Requirements . . . . . . . . . . . . . . . . . . . . 8
3.2.3 Parameter Requirements . . . . . . . . . . . . . . . . . . . 9
3.2.4 Canonicalization and Format Requirements . . . . . . . . . . 9
3.2.5 Interchange Recommendations . . . . . . . . . . . . . . . . 10
3.2.6 Security Requirements . . . . . . . . . . . . . . . . . . . 10
3.2.7 Usage and Implementation Non-requirements . . . . . . . . . 12
3.2.8 Publication Requirements . . . . . . . . . . . . . . . . . . 12
3.2.9 Additional Information . . . . . . . . . . . . . . . . . . . 13
3.3 Registration Procedure . . . . . . . . . . . . . . . . . . . 13
3.3.1 Preliminary Community Review . . . . . . . . . . . . . . . . 13
3.3.2 IESG Approval . . . . . . . . . . . . . . . . . . . . . . . 14
3.3.3 IANA Registration . . . . . . . . . . . . . . . . . . . . . 14
3.3.4 Media Types Reviewer . . . . . . . . . . . . . . . . . . . . 14
3.4 Comments on Media Type Registrations . . . . . . . . . . . . 14
3.5 Location of Registered Media Type List . . . . . . . . . . . 15
3.6 IANA Procedures for Registering Media Types . . . . . . . . 15
3.7 Change Procedures . . . . . . . . . . . . . . . . . . . . . 15
3.8 Registration Template . . . . . . . . . . . . . . . . . . . 16
4. External Body Access Types . . . . . . . . . . . . . . . . . 18
4.1 Registration Requirements . . . . . . . . . . . . . . . . . 18
4.1.1 Naming Requirements . . . . . . . . . . . . . . . . . . . . 18
4.1.2 Mechanism Specification Requirements . . . . . . . . . . . . 18
4.1.3 Publication Requirements . . . . . . . . . . . . . . . . . . 18
4.1.4 Security Requirements . . . . . . . . . . . . . . . . . . . 18
4.2 Registration Procedure . . . . . . . . . . . . . . . . . . . 19
4.2.1 Present the Access Type to the Community . . . . . . . . . . 19
4.2.2 Access Type Reviewer . . . . . . . . . . . . . . . . . . . . 19
4.2.3 IANA Registration . . . . . . . . . . . . . . . . . . . . . 19
4.3 Location of Registered Access Type List . . . . . . . . . . 19
4.4 IANA Procedures for Registering Access Types . . . . . . . . 19
5. Transfer Encodings . . . . . . . . . . . . . . . . . . . . . 21
5.1 Transfer Encoding Requirements . . . . . . . . . . . . . . . 21
5.1.1 Naming Requirements . . . . . . . . . . . . . . . . . . . . 21
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5.1.2 Algorithm Specification Requirements . . . . . . . . . . . . 21
5.1.3 Input Domain Requirements . . . . . . . . . . . . . . . . . 22
5.1.4 Output Range Requirements . . . . . . . . . . . . . . . . . 22
5.1.5 Data Integrity and Generality Requirements . . . . . . . . . 22
5.1.6 New Functionality Requirements . . . . . . . . . . . . . . . 22
5.2 Transfer Encoding Definition Procedure . . . . . . . . . . . 22
5.3 IANA Procedures for Transfer Encoding Registration . . . . . 23
5.4 Location of Registered Transfer Encodings List . . . . . . . 23
Normative References . . . . . . . . . . . . . . . . . . . . 24
Informative References . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 25
A. Grandfathered Media Types . . . . . . . . . . . . . . . . . 26
B. Changes made since RFC 2048 . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . 28
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1. Introduction
Recent Internet protocols have been carefully designed to be easily
extensible in certain areas. In particular, MIME [1] is an
open-ended framework and can accommodate additional object types,
charsets, and access methods without any changes to the basic
protocol. A registration process is needed, however, to ensure that
the set of such values is developed in an orderly, well-specified,
and public manner.
This document defines registration procedures which use the Internet
Assigned Numbers Authority (IANA) as a central registry for such
values. Of particular interest is the registration procedure for
media types described in Section 3.3.
Historical Note
The media types registration process was initially defined for the
purpose of registering media types for use in the context of the
asynchronous Internet mail environment. 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 was excessively
restrictive and had to be generalized.
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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 in RFC 2119 [3].
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3. Media Type Registration
Registration of a new media type or types starts with the
construction of a registration proposal. Registration may occur in
several different registration trees, which have different
requirements as discussed below. In general, the new registration
proposal is circulated and reviewed in a fashion appropriate to the
tree involved. The media type is then registered if the proposal is
acceptable. The following sections describe the requirements and
procedures used for each of the different registration trees.
3.1 Registration Trees and Subtype Names
In order to increase the efficiency and flexibility of the
registration process, different structures of subtype names may be
registered to accomodate the different natural requirements for,
e.g., a subtype that will be recommended for wide support and
implementation by the Internet Community or a subtype that is used to
move files associated with proprietary software. The following
subsections define registration "trees", distinguished by the use of
faceted names (e.g., names of the form "tree.subtree...subtype").
Note that some media types defined prior to this document do not
conform to the naming conventions described below. See Appendix A
for a discussion of them.
3.1.1 Standards Tree
The standards tree is intended for types of general interest to the
Internet Community. Registrations in the standards tree MUST be
approved by the IESG and MUST correspond to a formal publication by a
recognized standards body. In the case of registrations for the IETF
itself, the registration MUST be published as an RFC.
Media types in the standards tree are normally denoted by names that
are not explicitly faceted, i.e., do not contain period (".", full
stop) characters.
The "owner" of a media type registration in the standards tree is
assumed to be the standards body itself. Modification or alteration
of the specification requires the same level of processing (e.g.,
standards track) required for the initial registration.
3.1.2 Vendor Tree
The vendor tree is used for media types associated with commercially
available products. "Vendor" or "producer" are construed as
equivalent and very broadly in this context.
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A registration may be placed in the vendor tree by anyone who has
need to interchange files associated with the particular product.
However, the registration formally belongs to the vendor or
organization producing the software or file format. Changes to the
specification will be made at their request, as discussed in
subsequent sections.
Registrations in the vendor tree will be distinguished by the leading
facet "vnd.". That may be followed, at the discretion of the
registration, by either a media subtype name from a well-known
producer (e.g., "vnd.mudpie") or by an IANA-approved designation of
the producer's name which is then followed by a media type or product
designation (e.g., vnd.bigcompany.funnypictures).
While public exposure and review of media types to be registered in
the vendor tree is not required, using the ietf-types list for review
is strongly encouraged to improve the quality of those
specifications. Registrations in the vendor tree may be submitted
directly to the IANA.
3.1.3 Personal or Vanity Tree
Registrations for media types created experimentally or as part of
products that are not distributed commercially may be registered in
the personal or vanity tree. The registrations are distinguished by
the leading facet "prs.".
The owner of "personal" registrations and associated specifications
is the person or entity making the registration, or one to whom
responsibility has been transferred as described below.
While public exposure and review of media types to be registered in
the personal tree is not required, using the ietf-types list for
review is strongly encouraged to improve the quality of those
specifications. Registrations in the personal tree may be submitted
directly to the IANA.
3.1.4 Special x. Tree
For convenience and symmetry with this registration scheme, subtype
names with "x." as the first facet may be used for the same purposes
for which names starting in "x-" are normally used. These types are
unregistered, experimental, and should be used only with the active
agreement of the parties exchanging them.
However, with the simplified registration procedures described above
for vendor and personal trees, it should rarely, if ever, be
necessary to use unregistered experimental types, and as such use of
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both "x-" and "x." forms is discouraged.
Types in this tree MUST NOT be registered.
3.1.5 Additional Registration Trees
From time to time and as required by the community, the IANA may,
with the advice and consent of the IESG, create new top-level
registration trees. It is explicitly assumed that these trees may be
created for external registration and management by well-known
permanent bodies, such as scientific societies for media types
specific to the sciences they cover. In general, the quality of
review of specifications for one of these additional registration
trees is expected to be equivalent to registrations in the standards
tree. Establishment of these new trees will be announced through RFC
publication approved by the IESG.
3.2 Registration Requirements
Media type registration proposals are all expected to conform to
various requirements laid out in the following sections. Note that
requirement specifics sometimes vary depending on the registration
tree, again as detailed in the following sections.
3.2.1 Functionality Requirement
Media types MUST function as an actual media format: Registration of
things that are better thought of as a transfer encoding, as a
charset, or as a collection of separate entities of another type, is
not allowed. For example, although applications exist to decode the
base64 transfer encoding [1], base64 cannot be registered as a media
type.
This requirement applies regardless of the registration tree
involved.
3.2.2 Naming Requirements
All registered media types MUST be assigned MIME type and subtype
names. The combination of these names then serves to uniquely
identify the media type and the format of the subtype name identifies
the registration tree.
Type and subtype names beginning with "X-" are reserved for
experimental use and MUST NOT be registered.
The choice of top-level type name MUST take the nature of media type
involved into account. For example, media normally used for
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representing still images should be a subtype of the image content
type, whereas media capable of representing audio information should
be under the audio content type. See RFC 2046 [2] for additional
information on the basic set of top-level types and their
characteristics.
New subtypes of top-level types MUST conform to the restrictions of
the top-level type, if any. For example, all subtypes of the
multipart content type MUST use the same encapsulation syntax.
In some cases a new media type may not "fit" under any currently
defined top-level content type. Such cases are expected to be quite
rare. However, if such a case arises a new top-level type can be
defined to accommodate it. Such a definition MUST be done via
standards-track RFC; no other mechanism can be used to define
additional top-level content types.
These requirements apply regardless of the registration tree
involved.
3.2.3 Parameter Requirements
Media types MAY elect to use one or more MIME content type
parameters, or some parameters may be automatically made available to
the media type by virtue of being a subtype of a content type that
defines a set of parameters applicable to any of its subtypes. In
either case, the names, values, and meanings of any parameters MUST
be fully specified when a media type is registered in the standards
tree, and SHOULD be specified as completely as possible when media
types are registered in the vendor or personal trees.
New parameters SHOULD NOT be defined as a way to introduce new
functionality in types registered in the standards tree, although new
parameters MAY be added to convey additional information that does
not otherwise change existing functionality. An example of this
would be a "revision" parameter to indicate a revision level of an
external specification such as JPEG. Similar behavior is encouraged
for media types registered in the vendor or personal trees but is not
required.
3.2.4 Canonicalization and Format Requirements
All registered media types MUST employ a single, canonical data
format, regardless of registration tree.
A precise and openly available specification of the format of each
media type MUST exist for all types registered in the standards tree
and MUST at a minimum be referenced by, if it isn't actually included
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in, the media type registration proposal itself.
The specifications of format and processing particulars may or may
not be publically available for media types registered in the vendor
tree, and such registration proposals are explicitly permitted to
include only a specification of which software and version produce or
process such media types. References to or inclusion of format
specifications in registration proposals is encouraged but not
required.
Format specifications are still required for registration in the
personal tree, but may be either published as RFCs or otherwise
deposited with the IANA. The deposited specifications will meet the
same criteria as those required to register a well-known TCP port
and, in particular, need not be made public.
Some media types involve the use of patented technology. The
registration of media types involving patented technology is
specifically permitted. However, the restrictions set forth in RFC
2026 [5] on the use of patented technology in IETF standards-track
protocols must be respected when the specification of a media type is
part of a standards-track protocol. In addition, other standards
bodies making use of the standards tree may have their own rules
regarding intellectual property that must be observed in their
registrations.
3.2.5 Interchange Recommendations
Media types SHOULD interoperate across as many systems and
applications as possible. However, some media types will inevitably
have problems interoperating across different platforms. Problems
with different versions, byte ordering, and specifics of gateway
handling can and will arise.
Universal interoperability of media types is not required, but known
interoperability issues SHOULD be identified whenever possible.
Publication of a media type does not require an exhaustive review of
interoperability, and the interoperability considerations section is
subject to continuing evaluation.
These recommendations apply regardless of the registration tree
involved.
3.2.6 Security Requirements
An analysis of security issues MUST be done for all types registered
in the standards Tree. A similar analysis for media types registered
in the vendor or personal trees is encouraged but not required.
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However, regardless of what security analysis has or has not been
done, all descriptions of security issues MUST be as accurate as
possible regardless of registration tree. In particular, a statement
that there are "no security issues associated with this type" MUST
NOT be confused with "the security issues associates with this type
have not been assessed".
There is absolutely no requirement that media types registered in any
tree be secure or completely free from risks. Nevertheless, all
known security risks MUST be identified in the registration of a
media type, again regardless of registration tree.
The security considerations section of all registrations is subject
to continuing evaluation and modification, and in particular MAY be
extended by use of the "comments on media types" mechanism described
in a subsequent section of this document.
Some of the issues that should be looked at in a security analysis of
a media type are:
o Complex media types may include provisions for directives that
institute actions on a recipient's files or other resources. In
many cases provision is made for originators to specify arbitrary
actions in an unrestricted fashion which may then have devastating
effects. See the registration of the application/postscript media
type in RFC 2046 [2] for an example of such directives and how to
handle them.
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 which, 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 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 which in turn
requires an external confidentiality service, or which is designed
for use only within a secure environment.
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3.2.7 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
number of 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 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.
As such, universal support and implementation of a media type is NOT
a requirement for registration. If, however, a media type is
explicitly intended for limited use, this SHOULD be noted in its
registration.
3.2.8 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.
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, protocol,
data objects, or whatever must go through the IETF standards process.
This is too difficult and too lengthy a process for the convenient
registration of media types.
The stanards tree exists for media types that do require 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 that recommend implementation of, and support for,
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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.
3.2.9 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 and thus can be used to identify
entities as being of a given media type.
o File extension(s) commonly used on one or more platforms to
indicate that some file containing a given type of media.
o Macintosh File Type code(s) (4 octets) used to label files
containing a given type of media.
o Information about how fragment/anchor identifiers RFC 2396 [4] 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.
3.3 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.
The normal IETF processes should be followed for all registrations in
the standards tree, with the posting of an internet-draft being a
necessary first step.
Proposed registrations in the standards tree by other standards
bodies should be communicated to the IESG (at iesg@ietf.org).
Registrations in the vendor and personal tree may be submitted
directly to the IANA.
3.3.1 Preliminary Community Review
In all cases notice of a potential media type registration may be
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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.
The intent of the public posting 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, at any time.
3.3.2 IESG Approval
Media types registered in the standards tree MUST be approved by the
IESG prior to registration.
3.3.3 IANA Registration
Provided that the media type meets all of the relevant requirements
and has obtained whateveer approval is necessary, the author may
submit the registration request to the IANA. Registration requests
must be sent to iana@iana.org. Sending to ietf-types@iana.org does
not constitute submitting the registration to the IANA.
When the registration is part of an RFC publication request, 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.
3.3.4 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 which 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.
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.
3.4 Comments on Media Type Registrations
Comments on registered media types may be submitted by members of the
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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 itself.
3.5 Location of Registered Media Type List
Media type registrations are listed by the IANA at http://
www.iana.org/assignments/media-types/index.html.
3.6 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 review 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
subtype names MUST be unique, must conform to the MIME grammar for
such names, 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 exclude it.)
o Registrations in the standards tree MUST satisfy the additional
requirement that they originate from another standards body
recognized as such by the IETF.
3.7 Change Procedures
Once a content 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
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type of registration. The same procedure as 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 content type may pass responsibility for the content
type 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 which 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.
3.8 Registration Template
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To: ietf-types@iana.org
Subject: Registration of MIME media type XXX/YYY
MIME media type name:
MIME subtype name:
Required parameters:
Optional parameters:
Encoding considerations:
Security considerations:
Interoperability considerations:
Published specification:
Applications which 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)
Author/Change controller:
(Any other information that the author deems interesting may be
added below this line.)
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4. External Body Access Types
RFC 2046 [2] defines the message/external-body media type, whereby a
MIME entity can act as pointer to the actual body data in lieu of
including the data directly in the entity body. Each message/
external-body reference specifies an access type, which determines
the mechanism used to retrieve the actual body data. RFC 2046
defines an initial set of access types, but allows for the
registration of additional access types to accommodate new retrieval
mechanisms.
4.1 Registration Requirements
New access type specifications MUST conform to a number of
requirements as described below.
4.1.1 Naming Requirements
Each access type MUST have a unique name. This name appears in the
access-type parameter in the message/external-body content-type
header field, and MUST conform to MIME content type parameter syntax.
4.1.2 Mechanism Specification Requirements
All of the protocols, transports, and procedures used by a given
access type MUST be described, either in the specification of the
access type itself or in some other publicly available specification,
in sufficient detail for the access type to be implemented by any
competent implementor. Use of secret and/or proprietary methods in
access types are expressly prohibited. The restrictions imposed by
RFC 2026 [5] on the standardization of patented algorithms must be
respected as well.
4.1.3 Publication Requirements
All access types MUST be described by an RFC. The RFC may be
informational rather than standards-track, although standard-track
review and approval are encouraged for all access types.
4.1.4 Security Requirements
Any known security issues that arise from the use of the access type
MUST be completely and fully described. It is not required that the
access type be secure or that it be free from risks, but that the
known risks be identified. Publication of a new access type does not
require an exhaustive security review, and the security
considerations section is subject to continuing evaluation.
Additional security considerations SHOULD be addressed by publishing
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revised versions of the access type specification.
4.2 Registration Procedure
Registration of a new access type starts with the the publication of
the specification as an internet-draft.
4.2.1 Present the Access Type to the Community
Send a proposed access type specification to the
"ietf-types@iana.org" mailing list for a two week review period.
This mailing list has been established for the purpose of reviewing
proposed access and media types. Proposed access types are not
formally registered and must not be used.
The intent of the public posting is to solicit comments and feedback
on the access type specification and a review of any security
considerations.
4.2.2 Access Type Reviewer
When the two week period has passed, the access type reviewer, who is
appointed by the IETF Applications Area Director, either forwards the
request to iana@isi.edu, or rejects it because of significant
objections raised on the list.
Decisions made by the reviewer must be posted to the ietf-types
mailing list within 14 days. Decisions made by the reviewer may be
appealed to the IESG.
4.2.3 IANA Registration
Provided that the access type has either passed review or has been
successfully appealed to the IESG, the IANA will register the access
type and make the registration available to the community. The
specification of the access type must also be published as an RFC.
4.3 Location of Registered Access Type List
Access type registrations are listed by the IANA on the web page
http://www.iana.org/assignments/access-types
4.4 IANA Procedures for Registering Access Types
The identity of the access type reviewer is communicated to the IANA
by the IESG. The IANA then only acts in response to access type
definitions that either are approved by the access type reviewer and
forwarded by the reviewer to the IANA for registration, or in
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response to a communication from the IESG that an access type
definition appeal has overturned the access type reviewer's ruling.
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5. Transfer Encodings
Transfer encodings are tranformations applied to MIME media types
after conversion to the media type's canonical form. Transfer
encodings are used for several purposes:
o Many transports, especially message transports, can only handle
data consisting of relatively short lines of text. There can also
be severe restrictions on what characters can be used in these
lines of text -- some transports are restricted to a small subset
of US-ASCII and others cannot handle certain character sequences.
Transfer encodings are used to transform binary data into textual
form that can survive such transports. Examples of this sort of
transfer encoding include the base64 and quoted-printable transfer
encodings defined in RFC 2045 [1].
o Image, audio, video, and even application entities are sometimes
quite large. Compression algorithms are often quite effective in
reducing the size of large entities. Transfer encodings can be
used to apply general-purpose non-lossy compression algorithms to
MIME entities.
o Transport encodings can be defined as a means of representing
existing encoding formats in a MIME context.
IMPORTANT: The standardization of a large numbers of different
transfer encodings is seen as a significant barrier to widespread
interoperability and is expressely discouraged. Nevertheless, the
following procedure has been defined to provide a means of defining
additional transfer encodings, should standardization actually be
justified.
5.1 Transfer Encoding Requirements
Transfer encoding specifications MUST conform to a number of
requirements as described below.
5.1.1 Naming Requirements
Each transfer encoding MUST have a unique name. This name appears in
the Content-Transfer-Encoding header field and MUST conform to the
syntax of that field.
5.1.2 Algorithm Specification Requirements
All of the algorithms used in a transfer encoding (e.g., conversion
to printable form, compression) MUST be described in their entirety
in the transfer encoding specification. Use of secret and/or
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proprietary algorithms in standardized transfer encodings are
expressly prohibited. The restrictions imposed by RFC 2026 [5] on
the standardization of patented algorithms MUST be respected as well.
5.1.3 Input Domain Requirements
All transfer encodings MUST be applicable to an arbitrary sequence of
octets of any length. Dependence on particular input forms is not
allowed.
It should be noted that the 7bit and 8bit encodings do not conform to
this requirement. Aside from the undesireability of having
specialized encodings, the intent here is to forbid the addition of
additional encodings along the lines of 7bit and 8bit.
5.1.4 Output Range Requirements
There is no requirement that a particular tranfer encoding produce a
particular form of encoded output. However, the output format for
each transfer encoding MUST be fully and completely documented. In
particular, each specification MUST clearly state whether the output
format always lies within the confines of 7bit data, 8bit data, or is
simply pure binary data.
5.1.5 Data Integrity and Generality Requirements
All transfer encodings MUST be fully invertible on any platform; it
MUST be possible for anyone to recover the original data by
performing the corresponding decoding operation. Note that this
requirement effectively excludes all forms of lossy compression as
well as all forms of encryption from use as a transfer encoding.
5.1.6 New Functionality Requirements
All transfer encodings MUST provide some sort of new functionality.
Some degree of functionality overlap with previously defined transfer
encodings is acceptable, but any new transfer encoding MUST also
offer something no other transfer encoding provides.
5.2 Transfer Encoding Definition Procedure
Definition of a new transfer encoding starts with the the publication
of the specification as an internet-draft. The draft MUST define the
transfer encoding precisely and completely, and MUST also provide
substantial justification for defining and standardizing a new
transfer encoding. This specification MUST then be presented to the
IESG for consideration. The IESG can
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o reject the specification outright as being inappropriate for
standardization,
o approve the formation of an IETF working group to work on the
specification in accordance with IETF procedures, or,
o accept the specification as-is and put it directly on the
standards track.
Transfer encoding specifications on the standards track follow normal
IETF rules for standards track documents. A transfer encoding is
considered to be defined and available for use once it is on the
standards track.
5.3 IANA Procedures for Transfer Encoding Registration
There is no need for a special procedure for registering Transfer
Encodings with the IANA. All legitimate transfer encoding
registrations MUST appear as a standards-track RFC, so it is the
IESG's responsibility to notify the IANA when a new transfer encoding
has been approved.
5.4 Location of Registered Transfer Encodings List
The list of transfer encoding registrations can be found at: http://
www.iana.org/assignments/transfer-encodings
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Normative References
[1] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[2] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
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Informative References
[5] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[6] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", BCP
13, RFC 2048, November 1996.
Authors' Addresses
Ned Freed
Sun Microsystems
1050 Lakes Drive
West Covina, CA 91790
USA
Phone: +1 626 850 4350
EMail: ned.freed@mrochek.com
John C Klensin
1770 Massachusetts Ave, #322
Cambridge, MA 02140
EMail: klensin@jck.com
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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.
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Appendix B. Changes made since RFC 2048
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.
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Intellectual Property Statement
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The IETF invites any interested party to bring to its attention any
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Freed & Klensin Expires August 24, 2003 [Page 29]
