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Versions: 00 01 02 03 04 05 06 07 RFC 4289

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   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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   pertain to the implementation or use of the technology described in
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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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