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rfc:rfc1468

Network Working Group J. Murai Request for Comments: 1468 Keio University

                                                            M. Crispin
                                                     Panda Programming
                                                       E. van der Poel
                                                             June 1993
         Japanese Character Encoding for Internet Messages

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard.  Distribution of this memo is
 unlimited.

Introduction

 This document describes the encoding used in electronic mail [RFC822]
 and network news [RFC1036] messages 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.
 The name given to this encoding is "ISO-2022-JP", which is intended
 to be used in the "charset" parameter field of MIME headers (see
 [MIME1] and [MIME2]).

Description

 The text 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 was called JIS C 6226 until the name was changed

Murai, Crispin & van der Poel [Page 1] RFC 1468 Japanese Character Encoding for Internet Messages June 1993

 on March 1st, 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 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 text must end in ASCII.
 Other restrictions are given in the Formal Syntax below.

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.
 message             = headers 1*( CRLF *single-byte-char *segment
                       single-byte-seq *single-byte-char )
                                         ; see also [MIME1] "body-part"
                                         ; note: must end in ASCII
 headers             = <see [RFC822] "fields" and [MIME1] "body-part">
 segment             = single-byte-segment / double-byte-segment
 single-byte-segment = single-byte-seq 1*single-byte-char

Murai, Crispin & van der Poel [Page 2] RFC 1468 Japanese Character Encoding for Internet Messages June 1993

 double-byte-segment = double-byte-seq 1*( one-of-94 one-of-94 )
 single-byte-seq     = ESC "(" ( "B" / "J" )
 double-byte-seq     = ESC "$" ( "@" / "B" )
 CRLF                = CR LF
                                                  ; ( 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.)
 CR                  = <ASCII CR, carriage return>; (    15,      13.)
 LF                  = <ASCII LF, linefeed>       ; (    12,      10.)
 one-of-94           = <any one of 94 values>     ; (41-176, 33.-126.)
 7BIT                = <any 7-bit value>          ; ( 0-177,  0.-127.)
 single-byte-char    = <any 7BIT, 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
 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.
 ISO-2022-JP may also be used in MIME Part 2 headers.  The "B"
 encoding should be used with ISO-2022-JP text.

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

Murai, Crispin & van der Poel [Page 3] RFC 1468 Japanese Character Encoding for Internet Messages June 1993

 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 Kana set of JIS X 0201 is 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.
 For further information about Japanese character encodings such as PC
 codes, FTP locations of implementations, etc, see "Electronic
 Handling of Japanese Text" [JPN.INF].

References

 [ASCII] American National Standards Institute, "Coded character set
 -- 7-bit American national standard code for information
 interchange", ANSI X3.4-1986.
 [ISO646] International Organization for Standardization (ISO),
 "Information technology -- ISO 7-bit coded character set for
 information interchange", International Standard, Ref. No. ISO/IEC
 646:1991.
 [ISO2022] International Organization for Standardization (ISO),
 "Information processing -- ISO 7-bit and 8-bit coded character sets

Murai, Crispin & van der Poel [Page 4] RFC 1468 Japanese Character Encoding for Internet Messages June 1993

  1. - 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.
 [JPN.INF] Ken R. Lunde <lunde@adobe.com>, "Electronic Handling of
 Japanese Text", March 1992,
 msi.umn.edu(128.101.24.1):pub/lunde/japan[123].inf
 [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.
 [MIME1] Borenstein N., and N. Freed, "MIME (Multipurpose
 Internet Mail Extensions): Mechanisms for Specifying and
 Describing the Format of Internet Message Bodies", RFC 1341,
 Bellcore, Innosoft, June 1992.
 [MIME2] Moore, K., "Representation of Non-ASCII Text in Internet
 Message Headers", RFC 1342, University of Tennessee, June 1992.
 [RFC822] Crocker, D., "Standard for the Format of ARPA Internet
 Text Messages", STD 11, RFC 822, UDEL, August 1982.
 [RFC1036] Horton M., and R. Adams, "Standard for Interchange of USENET
 Messages", RFC 1036, AT&T Bell Laboratories, Center for Seismic
 Studies, December 1987.

Acknowledgements

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

Security Considerations

 Security issues are not discussed in this memo.

Murai, Crispin & van der Poel [Page 5] RFC 1468 Japanese Character Encoding for Internet Messages June 1993

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

Murai, Crispin & van der Poel [Page 6]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1468.txt · Last modified: 1993/06/02 22:23 (external edit)