rfc1494.txt
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Network Working Group H. Alvestrand
Request for Comments: 1494 SINTEF DELAB
S. Thompson
Soft*Switch, Inc.
August 1993
Equivalences between 1988 X.400 and RFC-822 Message Bodies
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
Table of Contents
1. Introduction ............................................. 2
2. Equivalence Table Definition ............................. 2
3. Generic conversions ...................................... 3
3.1. Byte copy .............................................. 3
3.2. Text Conversion ........................................ 3
3.3. Image Conversion ....................................... 3
3.4. Tunneling .............................................. 3
4. Conversion Table for known X.400 and MIME Types ......... 4
4.1. MIME to X.400 Table .................................... 4
4.2. X.400 to MIME Table .................................... 4
5. Newly defined X.400 Body Parts ........................... 5
5.1. Use of OBJECT IDENTIFIERs and ASN.1 MACROS ............. 5
5.2. The Generic MIME Extended Body Part .................... 6
5.3. The PostScript body part ............................... 7
5.4. The JPEG body part ..................................... 7
5.5. The GIF body part ...................................... 8
6. Newly defined MIME content-types ......................... 8
6.1. The application/x400-bp content-type ................... 8
6.2. The image/g3fax content-type ........................... 9
6.2.1. G3Fax Parameters ..................................... 9
6.2.2. Content Encoding ..................................... 10
6.3. The Application/ODA content-type ....................... 11
7. Equivalence Definitions ................................... 11
7.1. IA5Text - text/plain .................................... 11
7.2. GeneralText - text/plain (ISO-8859) ..................... 12
7.3. BilaterallyDefined - application/octet-stream .......... 13
7.4. ODA - application/oda ................................... 14
7.5. g3-facsimile - image/g3fax .............................. 15
7.6. application/postscript - postscript-body-part .......... 16
7.7. application/jpeg - jpeg-body-part ....................... 16
Alvestrand & Thompson [Page 1]
RFC 1494 X.400/MIME Body Equivalences August 1993
7.8. image/gif - gif-body-part ............................... 16
8. OID Assignments ........................................... 17
9. IANA Registration form for new mappings ................... 17
10. Security Considerations .................................. 18
11. Authors' Addresses ....................................... 18
12. References ............................................... 19
1. Introduction
This document is a companion to [1], which defines the principles
behind interworking between MIME-based RFC-822 mail and X.400 mail.
This document describes the content of the "IANA MHS/MIME Equivalence
table" referenced in the companion document, and defines the initial
configuration of this table. Mappings for new MIME content-types
and/or X.400 body part types should be registered with the IANA to
minimize redundancy and promote interoperability.
In MIME, the term "content-type" is used to refer to an information
object contained in the body of a message. In contrast, X.400 uses
the term "body part type." In this document, the term "body part" is
used to refer to either.
Please send comments to the MIME-MHS mailing list:
<mime-mhs@surfnet.nl>.
2. Equivalence Table Definition
For each MIME content-type/X.400 body part pair, the Equivalence
Table will contain an entry with the following sections:
X.400 Body Part
This section identifies the X.400 Body Part governed by this
Table entry. It includes any OBJECT IDENTIFIERs or other
parameters necessary to uniquely identify the Body Part.
MIME Content-Type
This section identifies the MIME content-type governed by this
Table entry. The MIME content-type named here must be
registered with the IANA.
Conversion Type
This section identifies the type of conversion applied. See the
section on Generic Conversions for an explanation of the
possible values.
Alvestrand & Thompson [Page 2]
RFC 1494 X.400/MIME Body Equivalences August 1993
Comments (optional)
This section gives any additional commentary that might be
useful in understanding the mapping between the X.400 and MIME
representations.
The initial Equivalence Table entries in this document are described
using this convention. Any future submissions to the IANA should
follow this format.
3. Generic conversions
3.1. Byte copy
This is the trivial case, that is, no conversion at all. The byte
stream is simply copied between MIME and X.400.
This is the preferred conversion, since it is the simplest.
Implementors and vendors will be registering OBJECT IDENTIFIERs and
MIME content-types for their various objects. They are STRONGLY
ENCOURAGED to specify their content formats such that a gateway can
use Byte Copy to map between them.
Note that in some cases, it is necessary to define exactly which
ASN.1 construct to replace with the content of the MIME object.
3.2. Text Conversion
This type of conversion applies to text objects that cannot be mapped
using a simple Byte Copy. Conversion involves scanning and
reformatting the object. For example, the MIME and X.400 objects
might differ in their encoding of nonstandard characters, or line or
page breaks.
3.3. Image Conversion
This conversion type applies to raster images, like Group 3 Facsimile
or JPEG. Again, it differs from Byte Copy in that it involves
scanning reformatting the byte stream. It differs from Text
Conversion in that it is pixel- oriented, rather than character-
oriented.
3.4. Tunneling
This is not a conversion at all, but an encapsulation of the object.
This is the fallback conversion, used when no explicit mapping
applies.
Alvestrand & Thompson [Page 3]
RFC 1494 X.400/MIME Body Equivalences August 1993
4. Conversion Table for known X.400 and MIME Types
This section itemizes the equivalences for all currently known MIME
content-types and X.400 body parts.
4.1. MIME to X.400 Table
MIME content-type X.400 Body Part Section
----------------- ------------------ -------
text/plain
charset=us-ascii ia5-text 7.1
charset=iso-8859-x EBP - GeneralText 7.2
text/richtext no mapping defined 5.2
application/oda EBP - ODA 7.4
application/octet-stream bilaterally-defined 7.3
application/postscript EBP - mime-postscript-body 5.4, 7.6
image/g3fax g3-facsimile 6.2, 7.5
image/jpeg EBP - mime-jpeg-body 5.5, 7.7
image/gif EBP - mime-gif-body 5.6, 7.8
audio/basic no mapping defined 5.2
video/mpeg no mapping defined 5.2
Abbreviation: EBP - Extended Body Part
4.2. X.400 to MIME Table
Basic Body Parts
X.400 Basic Body Part MIME content-type Section
--------------------- -------------------- -------
ia5-text text/plain;charset=us-ascii 7.1
voice No Mapping Defined 6.1
g3-facsimile image/g3fax 6.2, 7.5
g4-class1 no mapping defined 6.1
teletex no mapping defined 6.1
videotex no mapping defined 6.1
encrypted no mapping defined 6.1
bilaterally-defined application/octet-stream 7.3
nationally-defined no mapping defined 6.1
externally-defined See Extended Body Parts 6.1
X.400 Extended Body Part MIME content-type Section
------------------------- -------------------- -------
GeneralText text/plain;charset=iso-8859-x 7.2
ODA application/oda 7.4
mime-postscript-body application/postscript 5.3, 7.6
mime-jpeg-body image/jpeg 5.4, 7.7
mime-gif-body image/gif 5.5, 7.8
Alvestrand & Thompson [Page 4]
RFC 1494 X.400/MIME Body Equivalences August 1993
5. Newly defined X.400 Body Parts
This section defines new X.400 Body Parts for the purposes of
interworking with MIME.
All new X.400 Body Parts defined here will be Extended Body Parts, as
defined in CCITT Recommendation X.420 [2].
5.1. Use of OBJECT IDENTIFIERs and ASN.1 MACROS
X.420 dictates that Extended Body Parts shall:
(1) use OBJECT IDENTIFIERs (OIDs) to uniquely identify
the contents, and
(2) be defined by using the ASN.1 Macro:
EXTENDED-BODY-PART-TYPE MACRO::=
BEGIN
TYPE NOTATION ::= Parameters Data
VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER)
Parameters ::= "PARAMETERS" type "IDENTIFIED"
"BY" value(OBJECT IDENTIFIER)
| empty;
Data ::= "DATA" type
END
To meet these requirements, this document uses the OID
mime-mhs-bodies
defined in [1], as the root OID for X.400 Extended Body Parts defined
for MIME interworking.
Each Extended Body Part contains Data and optional Parameters, each
being named by an OID. To this end, two OID subtrees are defined
under mime-mhs-bodies, one for Data, and the other for Parameters:
mime-mhs-bp-data OBJECT IDENTIFIER ::=
{ mime-mhs-bodies 1 }
mime-mhs-bp-parameter OBJECT IDENTIFIER ::=
{ mime-mhs-bodies 2 }
All definitions of X.400 body parts submitted to the IANA for
registration must use the Extended Body Part Type macro for the
definition. See the next section for an example.
Alvestrand & Thompson [Page 5]
RFC 1494 X.400/MIME Body Equivalences August 1993
Lastly, the IANA will use the mime-mhs-bp-data and mime-mhs-bp-
parameter OIDs as root OIDs for any new MIME content-type/subtypes
that aren't otherwise registered in the Equivalence Table.
5.2. The Generic MIME Extended Body Part
The following X.400 Body Part is defined to carry any MIME content-
type for which there is no explicit IANA registered mapping.
mime-body-part EXTENDED-BODY-PART-TYPE
PARAMETERS MimeParameters
IDENTIFIED BY mime-generic-parameters
DATA OCTET STRING
::= mime-generic-data
MimeParameters ::=
SEQUENCE {
content-type IA5String,
content-parameters SEQUENCE OF
SEQUENCE {
parameter IA5String,
parameter-value IA5String
}
-- from RFC-1327, sec. 5.1.12
other-header-fields RFC822FieldList
}
mime-generic-parameters OBJECT IDENTIFIER ::=
{ mime-mhs-bp-parameter 1 }
mime-generic-data OBJECT IDENTIFIER ::=
{ mime-mhs-bp-data 1 }
To convert the MIME content-type into the X.400 mime- body-part:
(1) Copy the "type/subtype" string from the MIME
Content-Type: header field into
MimeParameters.content-type
(2) For each "parameter=value" string in the MIME
Content-Type header field, create a
MimeParameters.content-parameters structure, and copy
the "parameter" string into MimeParameters.content-
parameters.parameter field and the "value" string
into the paired MimeParameters.content-
parameters.parameter-value field.
(3) Convert the MIME body part into its canonical form.
Alvestrand & Thompson [Page 6]
RFC 1494 X.400/MIME Body Equivalences August 1993
(See appendix H of RFC 1341 [3] for a discussion
of canonical in this context.) Said another way,
reverse the transfer encoding to recover the original
byte stream.
(4) Copy the canonical byte stream into the mime-body-
part.data octet string.
(5) Remove the Content-type and the Content-transfer-
encoding header fields from the MIME body part's
RFC822 header.
(6) Any header fields starting with "Content-" in the
MIME body part is placed in the optional other-
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