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draft HARPOON Jan 93
HARPOON
Rules for downgrading messages from X.400/88 to X.400/84 when
MIME content-types are present in the messages
Tue Apr 13 15:50:23 MET DST 1993
Harald Tveit Alvestrand
SINTEF DELAB
Harald.T.Alvestrand@delab.sintef.no
Jim Romaguera
NetConsult AG
Romaguera@netconsult.ch
Kevin Jordan
Control Data Systems, Inc.
kej@mercury.udev.cdc.com
Status of this Memo
This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or
obsoleted by other documents at any time. It is not
appropriate to use Internet Drafts as reference material or
to cite them other than as a "working draft" or "work in
progress."
Please check the I-D abstract listing contained in each
Internet Draft directory to learn the current status of this
or any other Internet Draft.
If consensus is reached in the IETF MIME-MHS Interworking
Working Group, it will be submitted to the IESG asking that
Alvestrand et al Expires Sep 13 1993 [Page 1]
draft HARPOON Jan 93
it be recommended to the IAB as a Proposed Standard protocol
specification.
This RFC updates RFC 1328.
HARPOON stands for Holistic Approach to Reliable Provision of
Open Networking, and is used solely to catch the eye of
readers.
Please send comments to the MIME-MHS mailing list
<mime-mhs@surfnet.nl>
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1. Introduction
Interworking between X.400(88) and MIME is achieved by [MAPPING],
which modifies RFC-1327 [RFC 1327], which specifies the
interworking between X.400(88) and RFC-822 based mail.
Interworking between X.400(88) and X.400 (84) is achieved by RFC-
1328 [RFC 1328]. That document does not describe what to do in the
case where body parts arrive at the gateway that cannot be
adequately represented in the X.400(84) system.
This document describes how RFC-1328 must be modified in order to
provide adequate support for the scenarios:
SMTP(MIME) -> X.400(84)
X.400(84) -> SMTP(MIME)
It replaces chapter 6 of RFC-1328.
NOTE: A desireable side-effect of HARPOON is that a standardized
method for the identification and transmission of multimedia and
binary data (like spreadsheets) between X.400/84 UAs is achieved.
While this method is not compatible with current proprietary
approaches, we believe that it requires less invasive changes to
current UAs than other possible methods.
2. Basic approach
The approach is to imagine that the connection X.400(84) <->
SMTP(MIME) never happens. This, of course, is an illusion, but can
be a very useful illusion.
All mail will therefore go on one of the paths
X.400(84) -> X.400(88) -> SMTP(MIME)
SMTP(MIME) -> X.400(88) -> X.400(84)
when it goes between a MIME user and an X.400(84) user.
The approach at the interface between X.400(88) and X.400(84) is:
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o Convert what you can
o Encapsulate what you have to
o Never drop a message
Of course, for X.400/88 body parts that are already defined in
X.400/84, no downgrading should be done. In particular, multi-body
messages should remain multi-body messages, IA5 messages
(including IA5 messages encoded as Extended Body Parts) should
remain IA5 messages, and G3Fax messages should remain G3Fax
messages.
3. Conversion rules
3.1. EBP conversions to Basic
Some body parts are defined by X.400(88) as having both a Basic
form and an Extended form. These are listed in Annex B of X.420.
For all of these, the transformation from the Extended Body Part
to the Basic Body Part takes the form of putting the PARAMETERS
and the DATA members together in a SEQUENCE.
This transformation should be applied by the gateway in order to
allow (for example) X.400(88) systems that use the Extended form
of the IA5 body part to communicate with X.400(84) systems.
3.2. Encapsulation format
For any body part that cannot be used directly in X.400(84), the
following IA5Text body part is made:
- Content = IA5String
- First bytes of content: (the description is in USASCII, with
C escape sequences used to represent control characters):
MIME-version: <version>\r\n
Content-type: <the proper MIME content type>\r\n
Content-transfer-encoding: <quoted-printable or base64>\r\n
<Possibly other Content headings here, terminated by\r\n>
\r\n
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<Here follows the bytes of the content, as per [MAPPING], encoded
in the proper encoding>
All implementations MUST place the MIME-version: header first in
the body part. Headers that are placed by [RFC-1327] and [MAPPING]
into other parts of the message MUST NOT be placed in the MIME
body part.
This includes RFC-822 headings carried as heading-extensions,
which must be placed in a new IA5 body part starting with the
string "RFC-822-HEADERS", as specified in [RFC-1327], Appendix G.
Other heading-extensions are still handled as described in chapter
5 of RFC 1328: They are dropped.
Since all X.400(88) body parts can be represented in MIME by using
the x400-bp MIME content-type, this conversion will never fail.
In the reverse direction, any IA5 body part that starts with the
token "MIME-Version:" will be subjected to conversion according to
[MAPPING] before including the body part into an X.400(88)
message.
4. Implications
The implications are several:
- People with X.400(84) readers who have the ability to save
messages to file will now be able to save MIME multimedia
messages
- People who can use features like the "Mailcaps" file to
identify what to do about a bodypart can now grab MetaMail or
MHN and achieve at least some multimedia functionality
5. Security considerations
The security considerations in [MIME] and [MAPPING] (beware of
trojans that can hit you if your UA automagically starts programs
for you) are now relevant also for X.400(84) systems.
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6. Authors' address
Harald Tveit Alvestrand
SINTEF DELAB
N-7034 Trondheim
NORWAY
Harald.T.Alvestrand@delab.sintef.no
Kevin E. Jordan, ARH215
Control Data Systems, Inc.
4201 Lexington Avenue N
Arden Hills, MN 55126
USA
Kevin.E.Jordan@mercury.oss.arh.cpg.cdc.com
James A. Romaguera
NetConsult AG
Mettlendwaldweg 20a
3037 Herrenschwanden
Switzerland
Romaguera@netconsult.ch
7. References
[MIME]
N. Borenstein, N. Freed, MIME: Mechanisms for Specifying and
Describing the Format of Internet Message Bodies. RFC 1341
[RFC-1327]
S.E. Hardcastle-Kille, Mapping between X.400(1988) / ISO
10021 and RFC-822.
[RFC-1328]
S.E. Hardcastle-Kille, X.400 1988 to 1984 downgrading.
[MAPPING]
H.T. Alvestrand, R.S. Miles, M.T. Rose, S.J. Thompson,
Mapping between X.400 and RFC-822 Message Bodies Internet-
Draft, (June, 1992).
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Table of Contents
Status of this Memo ........................................ 1
1 Introduction .............................................. 3
2 Basic approach ............................................ 3
3 Conversion rules .......................................... 4
3.1 EBP conversions to Basic ................................ 4
3.2 Encapsulation format .................................... 4
4 Implications .............................................. 5
5 Security considerations ................................... 5
6 Authors' address .......................................... 6
7 References ................................................ 6
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