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Versions: 00 01 02 RFC 1468

Network Working Group                                          Jun Murai
Internet Draft                                              Mark Crispin
                                                       Erik van der Poel
                                                       1st December 1992


        Japanese Character Encoding for Internet Message Bodies


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 1st June
   1993.  Distribution of this memo is unlimited.  Please send comments
   to ietf-822@dimacs.rutgers.edu.


Introduction

   This document describes the encoding used in electronic mail [RFC822]
   and network news [RFC1036] message bodies 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 names the encoding "ISO-2022-JP", which is intended to
   be used in the "charset" parameter field of MIME [MIME] messages. The
   use of ISO-2022-JP in RFC 1342 [RFC1342] headers is expected to be
   the subject of a separate document.

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





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Description

   The message body starts in ASCII [ASCII], and switches to Japanese
   characters through an escape sequence. For example, the escape
   sequence ESC $ B (three bytes, hexadecimal values: 1B 24 42)
   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 ISO-2022-JP messages. The ISOREG number is the registration
   number in ISO's registry [ISOREG].

       Esc Seq    Character Set                  ISOREG

       ESC ( B    ASCII                             6
       ESC ( J    JIS X 0201-1976 ("Roman" set)    14
       ESC $ @    JIS X 0208-1978                  42
       ESC $ B    JIS X 0208-1983                  87

   Note that JIS X 0208-1983 was called JIS C 6226-1983 until the name
   was changed in March 1987. Likewise, JIS C 6220 was renamed JIS X
   0201.

   The "Roman" character set of JIS X 0201 [JISX0201] 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 [ISO646].

   The JIS X 0208 [JISX0208] 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 [JISX0201] and [JISX0208].  For further
   information about the escape sequences, see [ISO2022] and [ISOREG].

   If there are JIS X 0208 characters on a line, there must be a switch
   to ASCII or to the "Roman" set 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.

   Also, the message body must end with CRLF, and there must be a switch
   to ASCII before the last CRLF (if there are any non-ASCII characters
   in the message body).

   Other restrictions are given in the Formal Syntax below.



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Formal Syntax

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

   The * (asterisk) convention is as follows:

           l*m something

   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.)

   SI                  = <ISO 2022 SI, shift-in>    ; (    17,      15.)

   SO                  = <ISO 2022 SO, shift-out>   ; (    16,      14.)

   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, and not including ESC, SI, SO>


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




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   The ISO-2022-JP 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 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 announced
   by 4/1 (see [ISO2022] for details). However, the escape sequence
   normally used for this announcement is not included in ISO-2022-JP
   messages.

   The so-called half-width (hankaku) Katakana, that is, the Kana set of
   JIS X 0201, are not used in ISO-2022-JP messages.

   In the past, some systems erroneously used the escape sequence ESC (
   H in JUNET messages. This escape sequence is officially registered
   for a Swedish character set [ISOREG], and should not be used in ISO-
   2022-JP messages.

   Some systems do not distinguish between ESC ( B and ESC ( J or
   between ESC $ @ and ESC $ B for display. However, when relaying a
   message to another system, the escape sequences must not be altered
   in any way.

   The human user (not implementor) should try to keep lines within 80
   display columns, or, preferably, within 75 (or so) columns, to allow
   insertion of ">" at the beginning of each line in excerpts. Each JIS
   X 0208 character takes up two columns, and the escape sequences do
   not take up any columns. The implementor is reminded that JIS X 0208
   characters take up two bytes and should not be split in the middle to
   break lines for displaying, etc.

   The JIS X 0208 standard was revised in 1990, to add two characters at
   the end of the table. Although ISO 2022 specifies special additional
   escape sequences to indicate the use of revised character sets, it is
   suggested here not to make use of this special escape sequence in
   ISO-2022-JP text, even if the two characters added to JIS X 0208 in
   1990 are used.








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References

   [ASCII] American National Standards Institute, "Coded character set
   -- 7-bit American national standard code for information
   interchange", ANSI X3.4-1968

   [ISO646] International Organization for Standardization (ISO),
   "Information processing -- ISO 7-bit coded character set for
   information interchange", International Standard, Ref. No. ISO 646-
   1983 (E)

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

   [ISOREG] International Organization for Standardization (ISO),
   "International Register of Coded Character Sets To Be Used With
   Escape Sequences"

   [JISX0201] Japanese Standards Association, "Code for Information
   Interchange", JIS X 0201-1976

   [JISX0208] Japanese Standards Association, "Code of the Japanese
   graphic character set for information interchange", JIS X 0208-1978,
   -1983 and -1990

   [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

   [RFC1036] M. Horton and R. Adams, "Standard for Interchange of USENET
   Messages", December 1987, rfc1036

   [RFC1342] Keith Moore, "Representation of Non-ASCII Text in Internet
   Message Headers", Proposed (Internet) standard, June 1992, rfc1342


Security Considerations




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   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.


Authors' Addresses


   Jun Murai
   Keio University
   5322 Endo, Fujisawa
   Kanagawa 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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