GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2048

Network Working Group N. Freed Request for Comments: 2048 Innosoft BCP: 13 J. Klensin Obsoletes: 1521, 1522, 1590 MCI Category: Best Current Practice J. Postel

                                                                   ISI
                                                         November 1996
               Multipurpose Internet Mail Extensions
                         (MIME) Part Four:
                      Registration Procedures

Status of this Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.

Abstract

 STD 11, RFC 822, defines a message representation protocol specifying
 considerable detail about US-ASCII message headers, and leaves the
 message content, or message body, as flat US-ASCII text.  This set of
 documents, collectively called the Multipurpose Internet Mail
 Extensions, or MIME, redefines the format of messages to allow for
  (1)   textual message bodies in character sets other than
        US-ASCII,
  (2)   an extensible set of different formats for non-textual
        message bodies,
  (3)   multi-part message bodies, and
  (4)   textual header information in character sets other than
        US-ASCII.
 These documents are based on earlier work documented in RFC 934, STD
 11, and RFC 1049, but extends and revises them.  Because RFC 822 said
 so little about message bodies, these documents are largely
 orthogonal to (rather than a revision of) RFC 822.

Freed, et. al. Best Current Practice [Page 1] RFC 2048 MIME Registration Procedures November 1996

 This fourth document, RFC 2048, specifies various IANA registration
 procedures for the following MIME facilities:
  (1)   media types,
  (2)   external body access types,
  (3)   content-transfer-encodings.
 Registration of character sets for use in MIME is covered elsewhere
 and is no longer addressed by this document.
 These documents are revisions of RFCs 1521 and 1522, which themselves
 were revisions of RFCs 1341 and 1342.  An appendix in RFC 2049
 describes differences and changes from previous versions.

Table of Contents

 1. Introduction .........................................    3
 2. Media Type Registration ..............................    4
 2.1 Registration Trees and Subtype Names ................    4
 2.1.1 IETF Tree .........................................    4
 2.1.2 Vendor Tree .......................................    4
 2.1.3 Personal or Vanity Tree ...........................    5
 2.1.4 Special `x.' Tree .................................    5
 2.1.5 Additional Registration Trees .....................    6
 2.2 Registration Requirements ...........................    6
 2.2.1 Functionality Requirement .........................    6
 2.2.2 Naming Requirements ...............................    6
 2.2.3 Parameter Requirements ............................    7
 2.2.4 Canonicalization and Format Requirements ..........    7
 2.2.5 Interchange Recommendations .......................    8
 2.2.6 Security Requirements .............................    8
 2.2.7 Usage and Implementation Non-requirements .........    9
 2.2.8 Publication Requirements ..........................   10
 2.2.9 Additional Information ............................   10
 2.3 Registration Procedure ..............................   11
 2.3.1 Present the Media Type to the Community for  Review   11
 2.3.2 IESG Approval .....................................   12
 2.3.3 IANA Registration .................................   12
 2.4 Comments on Media Type Registrations ................   12
 2.5 Location of Registered Media Type List ..............   12
 2.6 IANA Procedures for Registering Media Types .........   12
 2.7 Change Control ......................................   13
 2.8 Registration Template ...............................   14
 3. External Body Access Types ...........................   14
 3.1 Registration Requirements ...........................   15
 3.1.1 Naming Requirements ...............................   15

Freed, et. al. Best Current Practice [Page 2] RFC 2048 MIME Registration Procedures November 1996

 3.1.2 Mechanism Specification Requirements ..............   15
 3.1.3 Publication Requirements ..........................   15
 3.1.4 Security Requirements .............................   15
 3.2 Registration Procedure ..............................   15
 3.2.1 Present the Access Type to the Community ..........   16
 3.2.2 Access Type Reviewer ..............................   16
 3.2.3 IANA Registration .................................   16
 3.3 Location of Registered Access Type List .............   16
 3.4 IANA Procedures for Registering Access Types ........   16
 4. Transfer Encodings ...................................   17
 4.1 Transfer Encoding Requirements ......................   17
 4.1.1 Naming Requirements ...............................   17
 4.1.2 Algorithm Specification Requirements ..............   18
 4.1.3 Input Domain Requirements .........................   18
 4.1.4 Output Range Requirements .........................   18
 4.1.5 Data Integrity and Generality Requirements ........   18
 4.1.6 New Functionality Requirements ....................   18
 4.2 Transfer Encoding Definition Procedure ..............   19
 4.3 IANA Procedures for Transfer Encoding Registration...   19
 4.4 Location of Registered Transfer Encodings List ......   19
 5. Authors' Addresses ...................................   20
 A. Grandfathered Media Types ............................   21

1. Introduction

 Recent Internet protocols have been carefully designed to be easily
 extensible in certain areas.  In particular, MIME [RFC 2045] is an
 open-ended framework and can accommodate additional object types,
 character sets, 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.
 Historical Note: The registration process for media types was
 initially defined 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.

Freed, et. al. Best Current Practice [Page 3] RFC 2048 MIME Registration Procedures November 1996

2. 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.

2.1. 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...type").  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.

2.1.1. IETF Tree

 The IETF tree is intended for types of general interest to the
 Internet Community. Registration in the IETF tree requires approval
 by the IESG and publication of the media type registration as some
 form of RFC.
 Media types in the IETF 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 IETF tree is assumed
 to be the IETF itself.  Modification or alteration of the
 specification requires the same level of processing (e.g.  standards
 track) required for the initial registration.

2.1.2. 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.

Freed, et. al. Best Current Practice [Page 4] RFC 2048 MIME Registration Procedures November 1996

 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 type 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.

2.1.3. 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 personl tree may be submitted
 directly to the IANA.

2.1.4. Special `x.' Tree

 For convenience and symmetry with this registration scheme, media
 type 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.

Freed, et. al. Best Current Practice [Page 5] RFC 2048 MIME Registration Procedures November 1996

 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
 both "x-" and "x." forms is discouraged.

2.1.5. 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 that which IETF would give to
 registrations in its own tree. Establishment of these new trees will
 be announced through RFC publication approved by the IESG.

2.2. 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.

2.2.1. 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
 character set, or as a collection of separate entities of another
 type, is not allowed.  For example, although applications exist to
 decode the base64 transfer encoding [RFC 2045], base64 cannot be
 registered as a media type.
 This requirement applies regardless of the registration tree
 involved.

2.2.2. 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.
 The choice of top-level type name must take the nature of media type
 involved into account. For example, media normally used for
 representing still images should be a subtype of the image content
 type, whereas media capable of representing audio information belongs

Freed, et. al. Best Current Practice [Page 6] RFC 2048 MIME Registration Procedures November 1996

 under the audio content type. See RFC 2046 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.

2.2.3. 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 IETF tree,
 and should be specified as completely as possible when media types
 are registered in the vendor or personal trees.
 New parameters must not be defined as a way to introduce new
 functionality in types registered in the IETF 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.

2.2.4. 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 is required for all types registered in the IETF tree and
 must at a minimum be referenced by, if it isn't actually included in,
 the media type registration proposal itself.

Freed, et. al. Best Current Practice [Page 7] RFC 2048 MIME Registration Procedures November 1996

 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 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
 1602 on the use of patented technology in standards-track protocols
 must be respected when the specification of a media type is part of a
 standards-track protocol.

2.2.5. Interchange Recommendations

 Media types should, whenever possible, 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.

2.2.6. Security Requirements

 An analysis of security issues is required for for all types
 registered in the IETF Tree.  (This is in accordance with the basic
 requirements for all IETF protocols.) A similar analysis for media
 types registered in the vendor or personal trees is encouraged but
 not required.  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

Freed, et. al. Best Current Practice [Page 8] RFC 2048 MIME Registration Procedures November 1996

 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 subsequent sections.
 Some of the issues that should be looked at in a security analysis of
 a media type are:
  (1)   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 for
        an example of such directives and how to handle them.
  (2)   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.
  (3)   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.

2.2.7. 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

Freed, et. al. Best Current Practice [Page 9] RFC 2048 MIME Registration Procedures November 1996

 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.

2.2.8. Publication Requirements

 Proposals for media types registered in the IETF tree must be
 published as RFCs. RFC publication of vendor and personal media type
 proposals is encouraged but not required. In all cases IANA will
 retain copies of all media type proposals and "publish" them as part
 of the media types registration tree itself.
 Other than in the IETF tree, the registration of a data type does not
 imply endorsement, approval, or recommendation by IANA or IETF or
 even certification that the specification is adequate.  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 IETF tree exists for media types that do require require a
 substantive review and approval process with the vendor and personal
 trees exist for those that do not. It is expected that applicability
 statements for particular applications will be published from time to
 time that recommend 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 and, hence, RFC publication.

2.2.9. Additional Information

 Various sorts of optional information may be included in the
 specification of a media type if it is available:
  (1)   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

Freed, et. al. Best Current Practice [Page 10] RFC 2048 MIME Registration Procedures November 1996

        type.
  (2)   File extension(s) commonly used on one or more
        platforms to indicate that some file containing a given
        type of media.
  (3)   Macintosh File Type code(s) (4 octets) used to label
        files containing a given type of media.
 Such information is often quite useful to implementors and if
 available should be provided.

2.3. 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.
 For registration in the IETF tree, the normal IETF processes should
 be followed, treating posting of an internet-draft and announcement
 on the ietf-types list (as described in the next subsection) as a
 first step.  For registrations in the vendor or personal tree, the
 initial review step described below may be omitted and the type
 registered directly by submitting the template and an explanation
 directly to IANA (at iana@iana.org).  However, authors of vendor or
 personal media type specifications are encouraged to seek community
 review and comment whenever that is feasible.

2.3.1. Present the Media Type to the Community for Review

 Send a proposed media type registration 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 media and
 access types. Proposed media types are not formally registered and
 must not be used; the "x-" prefix specified in RFC 2045 can be used
 until registration is complete.
 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 withdraw the
 registration completely, at any time.

Freed, et. al. Best Current Practice [Page 11] RFC 2048 MIME Registration Procedures November 1996

2.3.2. IESG Approval

 Media types registered in the IETF tree must be submitted to the IESG
 for approval.

2.3.3. IANA Registration

 Provided that the media type meets the requirements for media types
 and has obtained approval that is necessary, the author may submit
 the registration request to the IANA, which will register the media
 type and make the media type registration available to the community.

2.4. Comments on Media Type Registrations

 Comments on registered media types may be submitted by members of the
 community to IANA.  These comments will be 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 IANA approves of this the comment will be made accessible in
 conjunction with the type registration itself.

2.5. Location of Registered Media Type List

 Media type registrations will be posted in the anonymous FTP
 directory "ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/"
 and all registered media types will be listed in the periodically
 issued "Assigned Numbers" RFC [currently STD 2, RFC 1700].  The media
 type description and other supporting material may also be published
 as an Informational RFC by sending it to "rfc-editor@isi.edu" (please
 follow the instructions to RFC authors [RFC-1543]).

2.6. IANA Procedures for Registering Media Types

 The IANA will only register media types in the IETF 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:
  (1)   Media types must function as an actual media format.
        In particular, character sets and transfer encodings
        may not be registered as media types.
  (2)   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.

Freed, et. al. Best Current Practice [Page 12] RFC 2048 MIME Registration Procedures November 1996

  (3)   Types registered in the personal tree must either
        provide a format specification or a pointer to one.
  (4)   Any security considerations given must not be obviously
        bogus. (It is neither possible nor necessary for the
        IANA to conduct a comprehensive security review of
        media type registrations.  Nevertheless, IANA has the
        authority to identify obviously incompetent material
        and exclude it.)

2.7. Change Control

 Once a media type has been published by IANA, the author may request
 a change to its definition. The descriptions of the different
 registration trees above designate the "owners" of each type of
 registration. The change request follows the same procedure as the
 registration request:
  (1)   Publish the revised template on the ietf-types list.
  (2)   Leave at least two weeks for comments.
  (3)   Publish using IANA after formal review if required.
 Changes should be requested only when there are serious omission 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 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 IANA.

Freed, et. al. Best Current Practice [Page 13] RFC 2048 MIME Registration Procedures November 1996

2.8. Registration Template

   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.)

3. External Body Access Types

 RFC 2046 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

Freed, et. al. Best Current Practice [Page 14] RFC 2048 MIME Registration Procedures November 1996

 registration of additional access types to accommodate new retrieval
 mechanisms.

3.1. Registration Requirements

 New access type specifications must conform to a number of
 requirements as described below.

3.1.1. 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.

3.1.2. 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 1602 on the standardization of patented algorithms must be
 respected as well.

3.1.3. 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.

3.1.4. 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
 revised versions of the access type specification.

3.2. Registration Procedure

 Registration of a new access type starts with the construction of a
 draft of an RFC.

Freed, et. al. Best Current Practice [Page 15] RFC 2048 MIME Registration Procedures November 1996

3.2.1. 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.

3.2.2. 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.

3.2.3. 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.
 Informational RFCs are published by sending them to "rfc-
 editor@isi.edu" (please follow the instructions to RFC authors [RFC-
 1543]).

3.3. Location of Registered Access Type List

 Access type registrations will be posted in the anonymous FTP
 directory "ftp://ftp.isi.edu/in-notes/iana/assignments/access-types/"
 and all registered access types will be listed in the periodically
 issued "Assigned Numbers" RFC [currently RFC-1700].

3.4. 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
 response to a communication from the IESG that an access type
 definition appeal has overturned the access type reviewer's ruling.

Freed, et. al. Best Current Practice [Page 16] RFC 2048 MIME Registration Procedures November 1996

4. 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:
  (1)   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.
  (2)   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.
  (3)   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.

4.1. Transfer Encoding Requirements

 Transfer encoding specifications must conform to a number of
 requirements as described below.

4.1.1. 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.

Freed, et. al. Best Current Practice [Page 17] RFC 2048 MIME Registration Procedures November 1996

4.1.2. 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
 proprietary algorithms in standardized transfer encodings are
 expressly prohibited. The restrictions imposed by RFC 1602 on the
 standardization of patented algorithms must be respected as well.

4.1.3. 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.

4.1.4. 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.

4.1.5. 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.

4.1.6. 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.

Freed, et. al. Best Current Practice [Page 18] RFC 2048 MIME Registration Procedures November 1996

4.2. Transfer Encoding Definition Procedure

 Definition of a new transfer encoding starts with the construction of
 a draft of a standards-track RFC.  The RFC 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
  (1)   reject the specification outright as being
        inappropriate for standardization,
  (2)   approve the formation of an IETF working group to work
        on the specification in accordance with IETF
        procedures, or,
  (3)   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.

4.3. 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.

4.4. Location of Registered Transfer Encodings List

 Transfer encoding registrations will be posted in the anonymous FTP
 directory "ftp://ftp.isi.edu/in-notes/iana/assignments/transfer-
 encodings/" and all registered transfer encodings will be listed in
 the periodically issued "Assigned Numbers" RFC [currently RFC-1700].

Freed, et. al. Best Current Practice [Page 19] RFC 2048 MIME Registration Procedures November 1996

5. Authors' Addresses

 For more information, the authors of this document are best
 contacted via Internet mail:
 Ned Freed
 Innosoft International, Inc.
 1050 East Garvey Avenue South
 West Covina, CA 91790
 USA
 Phone: +1 818 919 3600
 Fax:   +1 818 919 3614
 EMail: ned@innosoft.com
 John Klensin
 MCI
 2100 Reston Parkway
 Reston, VA 22091
 Phone: +1 703 715-7361
 Fax:   +1 703 715-7436
 EMail: klensin@mci.net
 Jon Postel
 USC/Information Sciences Institute
 4676 Admiralty Way
 Marina del Rey, CA  90292
 USA
 Phone: +1 310 822 1511
 Fax:   +1 310 823 6714
 EMail: Postel@ISI.EDU

Freed, et. al. Best Current Practice [Page 20] RFC 2048 MIME Registration Procedures November 1996

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.

Freed, et. al. Best Current Practice [Page 21]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2048.txt · Last modified: 1997/02/24 19:58 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki