Network Working Group                                          Jun Murai
Internet Draft                                              Mark Crispin
                                                       Erik van der Poel
                                                        25th August 1992


           Japanese Character Encoding for Internet Messages


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
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   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.

   This draft document will be submitted to the RFC editor as an
   informational document.  This document will expire before 2nd March
   1993.  Distribution of this memo is unlimited.  Please send comments
   to ietf-822@dimacs.rutgers.edu.


Introduction

   This document describes the encoding used in plain text electronic
   mail and network news in several Japanese networks. It was first
   specified by and used in JUNET [JUNET]. The encoding is now also
   widely used in Japanese IP communities.

   This document provides a name for the encoding which is intended to
   be used in the "charset" parameter field of MIME [MIME] messages.

   This document only describes the encoding of plain text. The encoding
   of other subtypes of text, such as rich text, is not discussed here.







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Informal Description

   The message body starts in ASCII, and switches to Japanese characters
   through an escape sequence. For example, the escape sequence ESC $ B
   (three bytes) indicates that the bytes following this escape sequence
   are Japanese characters, which are encoded in two bytes each.  To
   switch back to ASCII, the escape sequence ESC ( B is used.

   The following table gives the escape sequences and the character sets
   used in JUNET messages.

           ESC ( B         ASCII
           ESC ( J         JIS X 0201-1976 (left-hand part)
           ESC $ @         JIS X 0208-1978
           ESC $ B         JIS X 0208-1983

   The left-hand part of JIS X 0201-1976 is identical to ASCII except
   for backslash (\) and tilde (~). The backslash is replaced by the Yen
   sign, and the tilde is replaced by macron (overline). This set is
   Japan's national variant of ISO 646.

   The JIS X 0208 character sets consist of Kanji, Hiragana, Katakana
   and some other symbols and characters. Each character takes up two
   bytes.

   For further details about the JIS Japanese national character set
   standards, refer to the JIS standards themselves. For further
   information about the escape sequences, see ISO 2022 [ISO2022].

   If there are JIS X 0208 characters on a line, there must be a switch
   to ASCII or to the left-hand part of JIS X 0201 before the end of the
   line (i.e. before the CRLF). This means that the next line starts in
   the character set that was switched to before the end of the previous
   line. Other restrictions are given in the Formal Description below.


Formal Description

   This section provides a formal description of the JUNET encoding. In
   the event that this description is not consistent with the above
   informal description, this formal description shall take precedence.

   The notational conventions used here are identical to those used in
   RFC 822 [RFC822].

   The * (asterisk) convention is as follows:

           l*m something



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   meaning at least l and at most m somethings, with l and m taking
   default values of 0 and infinity, respectively.


   line                = *text *1( *segment single-byte-seq *text ) CRLF

   segment             = single-byte-segment / double-byte-segment

   single-byte-segment = single-byte-seq 1*text

   double-byte-segment = double-byte-seq 1*( one-of-94 one-of-94 )

   single-byte-seq     = ESC "(" ( "B" / "J" )

   double-byte-seq     = ESC "$" ( "@" / "B" )

                                                    ; ( Octal, Decimal.)

   ESC                 = <ISO 2022 ESC, escape>     ; (    33,      27.)

   one-of-94           = <any char in 94-char set>  ; (41-176, 33.-126.)

   CHAR                = <any ASCII character>      ; ( 0-177,  0.-127.)

   text                = <any CHAR, including bare
                          CR & bare LF, but NOT
                          including CRLF>


   Additional restrictions that are difficult to describe in the above
   are as follows.

   Adjacent segments should have different escape sequences. For
   example, the following is not recommended:

           ESC $ B .... ESC $ B ....


MIME Considerations

   The name given to the JUNET character encoding is "ISO-2022-JP". This
   name is intended to be used in MIME messages as follows:

           Content-Type: text/plain; charset=iso-2022-jp

   The JUNET encoding is already in 7-bit form, so it is not necessary
   to use a Content-Transfer-Encoding header. It should be noted that
   applying the Base64 or Quoted-Printable encoding will render the



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   message unreadable in current JUNET software.


Background Information

   The JUNET encoding was described in the JUNET User's Guide [JUNET]
   (JUNET Riyou No Tebiki Dai Ippan).

   The encoding is based on the particular usage of ISO 2022 [ISO2022]
   announced by 4/1. However, the escape sequence normally used for this
   announcement is not included in JUNET messages.


References

   [ISO2022] International Organization for Standardization (ISO),
   "Information processing -- ISO 7-bit and 8-bit coded character sets
   -- Code extension techniques", International Standard, 1986, Ref. No.
   ISO 2022-1986 (E)

   [JUNET] JUNET Riyou No Tebiki Sakusei Iin Kai (JUNET User's Guide
   Drafting Committee), "JUNET Riyou No Tebiki (Dai Ippan)" ("JUNET
   User's Guide (First Edition)"), February 1988

   [MIME] Nathaniel Borenstein and Ned Freed, "MIME (Multipurpose
   Internet Mail Extensions): Mechanisms for Specifying and Describing
   the Format of Internet Message Bodies", Proposed (Internet) standard,
   June 1992, rfc1341

   [RFC822] David H. Crocker, "Standard for the Format of ARPA Internet
   Text Messages", Internet standard, August 1982, rfc822


Security Considerations

   Security considerations are not discussed in this memo.


Acknowledgements

   Many people assisted in drafting this document. The authors wish to
   thank in particular Akira Kato, Masahiro Sekiguchi and Ken'ichi
   Handa.








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Authors' Addresses


   Jun Murai
   Keio University
   5322 Endo, Fujisawa
   Fujisawa 252 Japan

   Fax: +81 (466) 49-1101

   EMail: jun@wide.ad.jp


   Mark Crispin
   Panda Programming
   6158 Lariat Loop NE
   Bainbridge Island, WA 98110-2098
   USA

   Phone: +1 (206) 842-2385

   EMail: MRC@PANDA.COM


   Erik M. van der Poel
   A-105 Park Avenue
   4-4-10 Ohta, Kisarazu
   Chiba 292 Japan

   Phone: +81 (438) 22-5836
   Fax:   +81 (438) 22-5837

   EMail: erik@poel.juice.or.jp


















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