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rfc:rfc1922

Network Working Group HF. Zhu Request for Comments: 1922 Tsinghua U Category: Informational DY. Hu

                                                            Tsinghua U
                                                              ZG. Wang
                                                                  CITS
                                                               TC. Kao
                                                                   III
                                                            WCH. Chang
                                                                   III
                                                            M. Crispin
                                                          U Washington
                                                            March 1996
          Chinese 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.

Abstract

 This memo describes methods of transporting Chinese characters in
 Internet services which transport text, such as electronic mail
 [RFC-822], network news [RFC-1036], telnet [RFC-854] and the World
 Wide Web [RFC-1866].

Introduction

 As the use of Internet covers more and more Chinese people in the
 world, the need has increased for the ability to send documents
 containing Chinese characters on the Internet.  The methods described
 in this document provide means of transporting existing Chinese
 character sets as well as leaving space for future extension.
 This document describes two encodings, ISO-2022-CN and
 ISO-2022-CN-EXT.  These are designed with interoperability in mind
 and are encouraged in this document for current Chinese interchange;
 they are 7-bit, support both simplified and traditional characters
 using both GB and CNS/Big5, and do not impose any unusual quoting
 requirements on ASCII characters.
 As important related issues, this document gives detailed
 descriptions of the two encodings CN-GB and CN-Big5, and a brief
 description of ISO/IEC 10646 [ISO-10646].  CN-GB and CN-Big5 are

Zhu, et al Informational [Page 1] RFC 1922 Chinese Character Encoding March 1996

 currently used as the internal codes for Chinese documents.
 ISO-10646 is the universal multi-octet character set defined by ISO;
 we feel that in the future it may become the preferred technology for
 Chinese documents and electronic mail when it is widely available.

Specification

1. 7-bit Chinese encodings: ISO-2022-CN and ISO-2022-CN-EXT

1.1. Description

 ISO-2022-CN is based on ISO 2022 [ISO-2022], similar to earlier work
 on ISO-2022-JP [RFC-1468] and ISO-2022-KR [RFC-1557] for the Japanese
 and Korean languages respectively.  It is 7-bit, and supports both
 simplified Chinese characters using GB 2312-80 [GB-2312] and
 traditional Chinese characters using the first two planes of CNS
 11643 [CNS-11643], as well as ASCII [ASCII] characters.
 ISO-2022-CN-EXT is a superset of ISO-2022-CN that additionally
 supports other GB character sets and planes of CNS 11643.
 Since ISO-2022-CN and ISO-2022-CN-EXT are 7-bit encodings, they do
 not require the 8-bit SMTP extensions.  ISO-2022-CN supports all the
 Chinese characters that appear in Big5 [BIG5].

1.2. ISO-2022-CN

 The starting code of ISO-2022-CN is ASCII.  ASCII and Chinese
 characters are distinguished by designations (ESC sequences) and
 shift functions.
 Designations define the Chinese character sets used in the text.
 There are three kinds of designations: SOdesignation, SS2designation
 and SS3designation.
 The SOdesignation is in the form ESC $ ) <F>, where <F> is the "final
 character" assigned to the character set by ISO (refer to the ISO
 registry [ISOREG] for more details).  The SS2designation is in the
 form ESC $ * <F>, and the SS3designation is in the form ESC $ + <F>.
 A designation overrides any previous designation for subsequent bytes
 in the text.
 There are four kinds of shifts: SI, SO, SS2 and SS3.  Shift functions
 specify how to interpret the subsequent bytes.
 The shift SI (one byte with hexadecimal value 0F) declares that
 subsequent bytes are interpreted in ASCII.

Zhu, et al Informational [Page 2] RFC 1922 Chinese Character Encoding March 1996

 The shift SO (one byte with hexadecimal value 0E) declares that
 subsequent bytes are interpreted in the character set defined by
 SOdesignation.
 The shift SS2 (two bytes with hexadecimal values 1B 4E) declares that
 the subsequent TWO bytes are interpreted in the character set defined
 by SS2designation, after which the previous interpretation (from SI
 or SO) is restored.
 The shift SS3 (two bytes with hexadecimal values 1B 4F) declares that
 the subsequent TWO bytes are interpreted in the character set defined
 by SS3designation, after which the previous interpretation (from SI
 or SO) is restored.
 The escape sequences, shift functions and character sets used in an
 ISO-2022-CN text are as follows:
  Character sets                                       Shift in with
 --------------------------------------------------------------------
   ASCII                                                     SI
   GB 2312, CNS 11643-plane-1                                SO
            CNS 11643-plane-2                                SS2
    ESC $ ) A         Indicates the bytes following SO are Chinese
                      characters as defined in GB 2312-80, until
                      another SOdesignation appears
    ESC $ ) G         Indicates the bytes following SO are as defined
                      in CNS 11643-plane-1, until another
                      SOdesignation appears
    ESC $ * H         Indicates the two bytes immediately following
                      SS2 is a Chinese character as defined in CNS
                      11643-plane-2, until another SS2designation
                      appears
 If there are any GB or CNS characters on a line, a designation for
 the corresponding character set must be used so that each line has
 its own character set information and the text can be displayed
 correctly when scroll back in a window.  Also, there must be a shift
 to ASCII (SI) before the end of the line (i.e., before the CRLF).  In
 other words, each line starts in ASCII, and ends in ASCII.
    Example: the hex sequence
       1b 24 29 41 0e 3d 3b 3b 3b 1b 24 29 47 47 28 5f 50 0f
    represents the Chinese word for "Interchange" (jiao huan) twice;

Zhu, et al Informational [Page 3] RFC 1922 Chinese Character Encoding March 1996

    the first time in simplified form using GB-2312 (the 3d 3b 3b 3b
    sequence above), and the second time in traditional form using
    CNS-11643 (the 47 28 5f 50 sequence above).  The sequence 1b 24 29
    41 is the SOdesignation for GB-2312, the 0e is SO to switch to
    Chinese from ASCII, the 1b 24 29 47 is the SOdesignation for
    CNS-11643 plane 1, and finally the 0f is the SI to return to ASCII
    at the end of the line.
 The name given to this character encoding is "ISO-2022-CN". This name
 is intended to be used as the "charset" parameter in MIME [MIME-1,
 MIME-2] messages.
    Content-Type: text/plain; charset=iso-2022-cn
 The ISO-2022-CN encoding is already in 7-bit form, so it is not
 necessary to use a Content-Transfer-Encoding header.
 Other restrictions are given in the "Formal Syntax of ISO-2022-CN"
 (Section 7.1 of this document).

1.3. ISO-2022-CN-EXT

 ISO-2022-CN-EXT supports all characters in existing GB, Big5 and CNS
 11643 character sets.
 The escape sequences, shift functions and character sets used in an
 ISO-2022-CN-EXT text are as follows:
  Character sets                                       Shift in with
 --------------------------------------------------------------------
   ASCII                                                    SI
   GB 2312, GB 12345, CNS 11643-plane-1, ISO-IR-165         SO
   GB 7589, GB 13131, CNS 11643-plane-2                     SS2
   GB 7590, GB 13132 or other new GBs,CNS 11643-plane-3 or  SS3
    higher planes of CNS 11643
    Note: Currently, there are some GB sets that have not been
    registered in ISO. Here <X7589>, <X7590>, <X12345>, <X13131> and
    <X13132> represent the final character that will be assigned by
    ISO for those sets.  These GB sets shall only be used once these
    final characters are assigned.

Zhu, et al Informational [Page 4] RFC 1922 Chinese Character Encoding March 1996

    ESC $ ) A         Indicates the bytes following SO are Chinese
                      characters as defined in GB 2312-80, until
                      another SOdesignation appears
    ESC $ * <X7589>   Indicates the two bytes immediately following
                      SS2 is a Chinese character as defined in GB
                      7589-87 [GB-7589], until another SS2designation
                      appears
    ESC $ + <X7590>   Indicates the two bytes immediately following
                      SS3 is a Chinese character as defined in GB
                      7590-87 [GB-7590], until another SS3designation
                      appears
    ESC $ ) <X12345>  Indicates the bytes following SO are as defined
                      in GB 12345-90 [GB-12345], until another
                      SOdesignation appears
    ESC $ * <X13131>  Indicates the two bytes immediately following
                      SS2 is a Chinese character as defined in GB
                      13131-91 [GB-13131], until another
                      SS2designation appears
    ESC $ + <X13132>  Indicates the two bytes immediately following
                      SS3 is a Chinese character as defined in GB
                      13132-91 [GB-13131], until another
                      SS3designation appears
    ESC $ ) E         Indicates the bytes following SO are as defined
                      in ISO-IR-165 (for details, see section 2.1),
                      until another SOdesignation appears
    ESC $ ) G         Indicates the bytes following SO are as defined
                      in CNS 11643-plane-1, until another
                      SOdesignation appears
    ESC $ * H         Indicates the two bytes immediately following
                      SS2 is a Chinese character as defined in CNS
                      11643-plane-2, until another SS2designation
                      appears
    ESC $ + I         Indicates the immediate two bytes following SS3
                      is a Chinese character as defined in CNS
                      11643-plane-3, until another SS3designation
                      appears

Zhu, et al Informational [Page 5] RFC 1922 Chinese Character Encoding March 1996

    ESC $ + J         Indicates the immediate two bytes following SS3
                      is a Chinese character as defined in CNS
                      11643-plane-4, until another SS3designation
                      appears
    ESC $ + K         Indicates the immediate two bytes following SS3
                      is a Chinese character as defined in CNS
                      11643-plane-5, until another SS3designation
                      appears
    ESC $ + L         Indicates the immediate two bytes following SS3
                      is a Chinese character as defined in CNS
                      11643-plane-6, until another SS3designation
                      appears
    ESC $ + M         Indicates the immediate two bytes following SS3
                      is a Chinese character as defined in CNS
                      11643-plane-7, until another SS3designation
                      appears
 As in ISO-2022-CN, each line starts in ASCII, and ends in ASCII, and
 has its own designation information before any Chinese characters
 appear.
 The name given to this character encoding is "ISO-2022-CN-EXT". This
 name is intended to be used as the "charset" parameter in MIME
 messages.
    Content-Type: text/plain; charset=ISO-2022-CN-EXT
 The ISO-2022-CN-EXT encoding is also in 7-bit form, so it is not
 necessary to use a Content-Transfer-Encoding header.
 Other restrictions are given in the "Formal Syntax of
 ISO-2022-CN-EXT" (Section 7.2 of this document).

1.4. How to Support Big5 or other internal codesets with ISO-2022-CN

    and ISO-2022-CN-EXT
 Since there are many different Chinese internal coding systems
 [CJKINF], such as EUC GB, Big5, CCCII (an encoding for library
 systems mainly used in Taiwan), GBK (the new standard specification
 for Chinese internal code, also is the codepage for Microsoft
 simplified Chinese Windows 95) etc., ISO-2022-CN and ISO-2022-CN-EXT,
 which are 7-bit and will not lose information during communication
 among different codesets,  facilitate interchange between the various
 Chinese coding systems in the Internet.

Zhu, et al Informational [Page 6] RFC 1922 Chinese Character Encoding March 1996

 For instance, ISO-2022-CN and ISO-2022-CN-EXT can be used to support
 the popular Big5 codeset, because the first two planes of CNS-11643
 contain the same Chinese characters as Big5's "common part" except
 two duplicate characters.  By the "common part" we mean the part that
 is not specific to any Big5 vendor, consisting of 5401 more
 frequently used characters in Big5 range 0xA440-0xC67E, 7652 less
 frequently used characters in Big5 range 0xC940-0xF9D5, and 441 other
 symbols in Big5 range 0xA140-0xA3E0, as defined in Institute for
 Information Industry's (III) technical report C-26 (see also [Big5]).
 The appendix of this document presents a conversion table for
 converting Big5 into CNS-11643, including specific extensions of some
 popular vendors.  For other extensions, vendors and implementors of
 Big5 products are ENCOURAGED to create detailed conversion tables, in
 order to increase interoperability between different coding systems.
 Public domain software (binary or C source code) for conversion
 between Big5 and CNS-11643 is available on many Internet sites.  At
 the time of this writing, the following FTP sites and software are
 advertised:
 1) Beijing:
    ftp://ftp.net.tsinghua.edu.cn/pub/Chinese/convert/big5cns.zip
    (IP address: 166.111.1.6)
 2) Xi'an:
    ftp://ftp.xanet.edu.cn
    /pub/chinese-soft/unix/convert/BeTTY-1.534.tar.gz
    (IP address: 202.112.11.131)
 3) Taiwan:
    ftp://ftp.seed.net.tw/Pub/Chinese/DOS/code-convert/chcode.zip
    (IP address: 140.92.1.65)
 4) US:
    ftp://ftp.ifcss.org/pub/software/unix/convert/BeTTY-1.534.tar.gz
    (IP address: 128.123.1.55)
 5) Japan:
    ftp://etlport.etl.go.jp/pub/iso-2022-cn/convert/big5cns.zip
    (IP address: 192.31.197.99)

Zhu, et al Informational [Page 7] RFC 1922 Chinese Character Encoding March 1996

2. 8-bit Chinese encodings: CN-GB and CN-Big5

 The CN-GB and CN-Big5 MIME charsets are defined below.
    Note: the use of 8-bit character sets requires the use of either
    an 8-to-7 Content-Transfer-Encoding mechanism such as "BASE64" or
    "QUOTED-PRINTABLE" if the network is not 8-bit clean, or the 8-bit
    SMTP extensions [SMTPEXT] with the "8BIT"
    Content-Transfer-Encoding on 8-bit clean networks.  Otherwise, an
    8-bit message that passes through a 7-bit mailer is likely to have
    the 8th bit truncated, resulting in an unreadable message.
    Although "just send 8-bit data" has been common practice in the
    past, it is incorrect according to the Internet standards and
    causes interoperability problems.

2.1. CN-GB

 E-mail using CN-GB characters is sent in this way:
 GB 2312-80 characters are used with ASCII characters, not GB 1988-89
 [GB-1988].
 GB 2312-80 is also 7-bit, to avoid conflicting with ASCII.  If the
 character is from GB 2312-80, the MSB (bit-8) of each byte is set to
 1, and therefore becomes a 8-bit character.  Otherwise, the byte is
 interpreted as ASCII.  This constructs a character set named "GB
 Internal Code".
 This method is also adopted in the .gb files in the Internet.
 To use this character scheme with MIME, CN-GB is used as the value
 for the charset parameter:
    Content-Type: text/plain; charset=cn-gb; charset-edition=1980
    Note: The "charset-edition" is a new MIME parameter described in
    section 4.1 of the "Specification" part of this document.
 GB 12345-90 is the traditional form of GB 2312, the charset name
 given to this set is CN-GB-12345 with the charset-edition of 1990.
 There are also character sets that can only be used with other GB
 sets.  For example, GB 8565-88 [GB-8565] is used with GB 2312 and
 some other characters to form the ISO-IR-165 set (also known as GB
 2312 + GB 8565.2).  ISO-IR-165 contains all characters from GB
 2312-80 as revised by GB 6345.1-86 and GB 8565.2-88.  Its MIME
 charset name is CN-GB-ISOIR165 with the charset-edition of 1992.

Zhu, et al Informational [Page 8] RFC 1922 Chinese Character Encoding March 1996

 CN-GB-12345 and CN-GB-ISOIR165 support ASCII in a similar manner to
 CN-GB; the MSB of Chinese characters is set to 1 to distinguish from
 ASCII.
    Note: There are some supplementary character sets in GB, i.e.  GB
    7589-87, GB 7590-87, GB 13131-91 and GB 13132-91.  Normally, they
    won't be used independently without using GB-2312 or GB-12345, so
    they are not necessarily to be registered.  Characters in these
    standards could be supported with ISO-2022-CN and ISO-2022-CN-EXT.
    If, in the future, they need to be used with "charset" names, it
    is the responsibility of any interested third party (the
    standardization organization or anybody else) to write the
    necessary documents and register the charset with the IANA.  It is
    encouraged that the charset names take the form of CN-GB-<number>,
    such as CN-GB-12345, where <number> is the GB standard number.  A
    charset-edition should also be given.  All CN-GB-<number> sets
    should be coded in 8-bit in a similar fashion to CN-GB.
 To ensure interoperability, the CN-GB charset should be used whenever
 possible instead of a CN-GB-<number> charset.

2.2. CN-Big5

 Big5 is a two-byte character set of traditional Chinese characters,
 widely used in Taiwan and overseas.  E-mail of CN-Big5 is sent in
 this way:
 Big5 is used with ASCII.  The MSB of ASCII characters is always 0.
 The MSB of the first byte of a Big5 character is always 1; this
 distinguishes it from an ASCII character.  The second byte has 8
 significant bits.  Therefore, CN-Big5 is an 8-bit encoding with a
 15-bit codespace.
 To use this character scheme with MIME, CN-Big5 is used as the value
 for the charset parameter:
    Content-Type: text/plain; charset=cn-big5; charset-edition=1984
    Note: The "charset-edition" is a new MIME parameter described in
    section 4.1 of the "Specification" part of this document.

3. Universal Multilingual Character Set: ISO/IEC-10646/Unicode

 ISO/IEC 10646 defines a 32bit character space with the intent to
 encode all characters in the world. Currently, only the lowest 16bit
 plane of ISO 10646, the Basic Multilingual Plane (BMP), is defined.
 The BMP is code-by-code identical to Unicode [Unicode 1.1].  it
 contains a large repertoire of Chinese characters (it currently

Zhu, et al Informational [Page 9] RFC 1922 Chinese Character Encoding March 1996

 includes all the characters of GB 2312-80, GB 12345-90, GB 8565-89,
 CNS 11643's plane 1 and 2, and part of some other standards) and
 therefore can be used to transport Chinese characters in the Internet
 community.  This document does not give any details on how to do
 this, as this has been done elsewhere.  For details of using Unicode
 with MIME, refer to RFC 1641 [RFC-1641], RFC 1642 [RFC-1642].  For
 assigned names for 10646 set, refer to STD 2--"Assigned Numbers",
 which is RFC 1700 [RFC-1700] currently.  For more up-to-date assigned
 numbers, please check:
    ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets

4. Two New MIME parameters

 Here we define two new MIME parameters to be used with "charset"
 parameters.

4.1. "charset-edition"

 This parameter is used after the MIME "charset" parameter, using four
 digits (AD) to indicate what the year of edition is for the character
 set standard shown in "charset".  Its use is optional.
 Implementations should ignore this parameter unless the
 implementation has specific support for that particular character set
 edition.
 The reason for defining this parameter is that there are often
 differences in the defined characters between editions of a character
 set standard.  Sometimes, the difference can not be ignored,
 otherwise implementations would have problems when processing it.
 There are only two ways to indicate this difference, in the current
 MIME syntax.  One way is to indicate the edition in the charset name,
 such as CN-GB-1988-80 (the 1980's edition of GB 1988).  The other way
 is to define a new optional parameter such as "charset-edition".  The
 latter way is better because receiving applications that can only
 process an older edition can still recognize the character set and
 offer to display the text in the older edition.  This display may
 have a few mistakes, but it is better than refusing to display any
 text at all or defaulting to an inappropriate character set such as
 US-ASCII or ISO-8859-1.

4.2. "charset-extension"

 This parameter is also used after the MIME "charset" parameter.  It
 is case-insensitive and optional, and any value of this parameter
 should be registered in IANA.  Unregistered value should start with
 "x-" as with any MIME extension-token.  Implementations should ignore
 this parameter unless the implementation has specific support for

Zhu, et al Informational [Page 10] RFC 1922 Chinese Character Encoding March 1996

 that particular character set extension.
 A character set extension has displayed glyphs for code points that
 are not assigned in the character set, for example, vendor-specific
 extensions of standard character sets.  This parameter provides the
 option of using these extensions.  Although character set extensions
 may cause interoperability problems, we recognize the existence of
 such extensions.
 For example:
    Content-Type: text/plain; charset=CN-Big5; charset-edition=1984;
     charset-extension=ETen-2.00.03-DOS
 This may indicate Eten company's extension of Big5: ETen 2.00.03 for
 DOS, assuming that "ETen-2.00.03-DOS" is registered with the IANA..

4.3. Formal Syntax:

 The following changes and additions are made to the MIME syntax:
 charset-edition   := "charset-edition" "=" 4DIGIT
                       ; year of edition in four digits
 charset-extension := "charset-extension" "=" extension-token

5. Background Information

5.1. Writing systems and their encodings in Chinese-speaking nations and

   regions
 The mainland provinces of China use simplified Chinese character in
 daily life.  GB is the standard electronic character set.  It is the
 main means for communications between people who share simplified
 Chinese characters in the world.
 Taiwan uses traditional Chinese characters in daily life.  CNS-11643
 is the formal character set for information interchange in Taiwan;
 however, Big5, a widely-used character set of traditional Chinese
 characters, is the de-facto internal code standard in Taiwan.
 Hong Kong uses traditional Chinese characters in daily life, but uses
 both GB and Big5 in electronic form, because Hong Kong people often
 communicate with people in all of China's provinces.
 Singapore seldom uses Chinese characters, and uses the simplified
 form when Chinese characters are used.  In electronic form, Unicode
 is more popular, however GB is also used.

Zhu, et al Informational [Page 11] RFC 1922 Chinese Character Encoding March 1996

5.2. Miscellaneous information about Chinese character sets

 The GB 1988-89 character set is identical to ISO 646 [ISO-646] except
 for currency symbol and tilde. The currency symbol and the tilde are
 replaced by the Yuan sign and the overline.  This set is GB's variant
 of ISO 646.  This character set and CNS 5205 [CNS-5205] are not
 encouraged for use in the Internet, since ASCII combined with GB 2312
 or CNS 11643-plane 1 and plane 2 contains all the characters in them.
 The GB 2312-80 character set consists of simplified Chinese
 characters, digits, and the Latin, Greek and Russian alphabets, and
 some other symbols; in all, 7445 characters.  Each character is
 represented with two bytes.
 GB 13000-95 [GB-13000] is GB's variant of ISO 10646.  However, for
 interoperability in the Internet, assigned names for ISO 10646 are
 encouraged instead.
 Currently both sides of the Taiwan Straits are cooperating closely in
 promoting the use of ISO 10646's BMP and in continuing its
 development together with other organizations under ISO.

5.3. Miscellaneous implementation information

 For maximum interoperability, implementations SHOULD at least support
 sending and receiving ISO-2022-CN.  Supporting all registered
 character sets in ISO-2022-CN-EXT is greatly encouraged.
 To meet the current usage, support of CN-GB (the status quo for
 simplified Chinese e-mail ) or CN-Big5 (the status quo for
 traditional Chinese e-mail) may be necessary.  However, it is not
 reliable to send documents directly with these internal codes,
 therefore sending ISO-2022-CN message is always encouraged whenever
 possible.
 To the maximum extent possible, implementations should be capable of
 receiving messages in any of the encodings described in this
 document, even if they only transmit messages in one form.
 Preferably the implementation should display the characters with
 glyphs appropriate to the typographic tradition that is implied in
 the encoding of the received text.  Implementation may also translate
 these encodings to the encoding that its platform supports.
 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
 Chinese character takes up two columns, and the shift sequences do

Zhu, et al Informational [Page 12] RFC 1922 Chinese Character Encoding March 1996

 not take up any columns.  The implementor is reminded that Chinese
 characters take up two bytes and should not be split in the middle to
 break lines for displaying, etc.
 Freely available fonts of Chinese characters:
    Beijing:
       ftp://ftp.net.tsinghua.edu.cn/pub/Chinese/fonts/
    Xi'an:
       ftp://ftp.xanet.edu.cn/pub/chinese-soft/fonts/
    Taiwan:
       ftp://ftp.edu.tw/Chinese/ifcss/software/fonts/
       ftp://ftp.ntu.edu.tw/Chinese/ifcss/software/fonts/
    Hong Kong:
       ftp://ftp.cuhk.hk/pub/chinese/ifcss/software/fonts/
    Singapore:
       ftp://ftp.technet.sg:/pub/chinese/fonts/
    US:
       ftp://ftp.ifcss.org/pub/software/fonts/
       http://ccic.ifcss.org/www/pub/software/fonts/

6. X.400 Considerations

 X.400 has the ability of carrying different character sets in a
 message by using the body part "GeneralText" defined by
 ISO/IEC-10021-7 [ISO-10021].
 The X.400 ASN.1 definition of the GeneralText body part is:
  general-text-body-part EXTENDED-BODY-PART-TYPE
    PARAMETERS GeneralTextParameters IDENTIFIED BY id-ep-general-text
    DATA       GeneralTextData
    ::= id-et-general-text
  GeneralTextParameters ::= SET OF CharacterSetRegistration
  CharacterSetRegistration ::= INTEGER (1..32767)
  GeneralTextData ::= GeneralString
 Therefore, to use ISO-2022-CN, set the "CharacterSetRegistration"
 part as { 6 58 171 172 }, and add an ESC sequence of ESC ( B (three
 bytes, hexadecimal values: 1B 28 42) before the beginning of each

Zhu, et al Informational [Page 13] RFC 1922 Chinese Character Encoding March 1996

 line of ISO-2022-CN text.
 Similarly, to use ISO-2022-CN-EXT, set the registered numbers of all
 character sets in the "CharacterSetRegistration" part and add ESC ( B
 at the beginning of each line.  For the registered numbers, please
 refer to ISO registry.  In addition to the character sets supported
 by ISO-2022-CN, currently registered numbers are:
    ISO IR 165 (GB 2312+GB 8565.2):   165
    CNS 11643-plane 3:                183
    CNS 11643-plane 4:                184
    CNS 11643-plane 5:                185
    CNS 11643-plane 6:                186
    CNS 11643-plane 7:                187
 176 is the registered number for the BASESET of ISO/IEC 10646-1:1993
 UCS-2 with implementation level 3, Escape sequence of ESC % / E (four
 bytes, hexadecimal values 1B 25 2F 45) indicates starting of this
 codeset.
 For CN-GB and CN-Big5 character sets, there are no formal methods
 that could be used in X.400 yet.
 For detail about X.400 use of character sets, please refer to RFC
 1502 [RFC-1502].

Zhu, et al Informational [Page 14] RFC 1922 Chinese Character Encoding March 1996

7. Formal Syntax of ISO-2022-CN and ISO-2022-CN-EXT

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

7.1. Formal Syntax of ISO-2022-CN

 body  ::= * ( ascii_line / c_line )
 ascii_line  ::= *char CRLF
 c_line ::= *char 1*(1*designation 1*(*char 1*c_text *char)) CRLF
 designation  ::= SOdesignation / SS2designation
 SOdesignation  ::= ESC "$" ")" finalchar_for_SO
 SS2designation  ::= ESC "$" "*" finalchar_for_SS2
 finalchar_for_SO  ::= "A" / "G"
 finalchar_for_SS2  ::= "H"
 c_text  ::= 1* ( SO-SI-segment / SS2segment )
 SO-SI-segment ::= SO 1*c_char *designation *c_segment SI
 c_segment  ::= 1* ( c_char / SS2segment )
 SS2segment  ::= SS2 c_char
 c_char  ::= one_of_94  one_of_94
                                                 ; ( Octal, Decimal.)
 ESC             ::= <ISO-646 ESC, escape>       ; ( 33, 27.)
 SI              ::= <ASCII SI, shift in>        ; ( 17, 15.)
 SO              ::= <ASCII SO, shift out>       ; ( 16, 14.)
 SS2             ::= <ISO 2022 Single_shift two> ; ( 33 116, 27 78.)
 one_of_94       ::= <any char in 94_char set>   ; ( 41-176, 33-126. )
 char            ::= <any char in 96_char_set>   ; ( 40-177, 30-127. )

Zhu, et al Informational [Page 15] RFC 1922 Chinese Character Encoding March 1996

7.2. Formal Syntax of ISO-2022-CN-EXT

 body  ::= * ( ascii_line / c_line )
 ascii_line  ::= *char CRLF
 c_line ::= *char 1*(1*designation 1*(*char 1*c_text *char)) CRLF
 designation  ::= SOdesignation / SS2designation / SS3designation
 SOdesignation  ::= ESC "$" ")" finalchar_for_SO
 SS2designation  ::= ESC "$" "*" finalchar_for_SS2
 SS3designation  ::= ESC "$" "+" finalchar_for_SS3
 finalchar_for_SO  ::= "A" / <X12345> / "G" / "E"
 finalchar_for_SS2  ::= <X7589> / <X13131> / "H"
 finalchar_for_SS3  ::= <X7590> / <X13132> / "I" / "J" / "K" / "L"
                        / "M"
 c_text  ::= 1* ( SO-SI-segment / SS2segment / SS3segment )
 SO-SI-segment ::= SO 1*c_char *designation *c_segment SI
 c_segment  ::= 1* ( c_char / SS2segment / SS3segment )
 SS2segment  ::= SS2 c_char
 SS3segment  ::= SS3 c_char
 c_char  ::= one_of_94  one_of_94
                                                  ; ( Octal, Decimal.)
 ESC             ::= <ISO-646 ESC, escape>        ; ( 33, 27.)
 SI              ::= <ASCII SI, shift in>         ; ( 17, 15.)
 SO              ::= <ASCII SO, shift out>        ; ( 16, 14.)
 SS2             ::= <ISO 2022 Single_shift two>  ; ( 33 116, 27 78.)
 SS3             ::= <ISO 2022 Single_shift three>; ( 33 117, 27 79.)
 one_of_94       ::= <any char in 94_char set>    ; ( 41-176, 33-126.

Zhu, et al Informational [Page 16] RFC 1922 Chinese Character Encoding March 1996

 )
 char            ::= <any char in 96_char_set>    ; ( 40-177, 30-127.
 )

8. Registration of New "charset"s and New MIME parameter

8.1. This document defines the following MIME "charset" names for

    Chinese text:
    ISO-2022-CN, ISO-2022-CN-EXT
    CN-GB, CN-Big5
    CN-GB-12345
    CN-GB-ISOIR165

8.2. This document defines two new MIME parameters:

    charset-edition
    charset-extension

Acknowledgments

 This document is the result of cooperation in APNG-CC, the Chinese
 Character sub-working group of the I18N/L10N (Internationalization
 and Localization) working group of APNG (Asia-Pacific Networking
 Group), coordinator Zhu Haifeng <zhf@net.tsinghua.edu.cn>.  The
 membership of APNG-CC consists of individuals from both sides of the
 Taiwan Strait, HongKong, and from Singapore and other countries.  We
 wish to thank all members of APNG-CC.
 Prof. Yao Shiquan (Deputy chair of CITS--China Information Technology
 Standardization Technical Committee), Ms. Lin Ning (Secretary-General
 of CITS), Mr. Guo Chengzhong of the Office of the Joint Conference of
 China Economic Information,  and Prof. Zhao Jingrong, Prof. Wu
 Jianping, Prof. Li Xing, and Mr. You Yue (Tsinghua University) and
 other experts from CERNET Expert Committee, Prof. Meng Qingyu (China
 Computer Software & Technology Services Corporation), Prof. Cao
 Jinwen and Mr. Yu Jun (IBM Beijing) gave a lot of support and help in
 many aspects.
 Special thanks for the supports towards APNG-CC from Prof. Yang
 Tianxing (Chair of CITS).
 Prof. Ding ZyKaan from Academia Sinica of Taiwan, and Mr. C. J.
 Cherng and Mr. C. K. Fan of III (Institute for Information Industry),
 Mr. Chang JingShin from Tsinghua University in Hsinchu of Taiwan, Ms.
 C. C. Hsu from IBM Taiwan and  Ms. Tong-Lee Anita Lin from Microsoft

Zhu, et al Informational [Page 17] RFC 1922 Chinese Character Encoding March 1996

 Taiwan gave a lot of support and contributions in APNG-CC's work.  In
 particular, Ms. C. C. Hsu put much effort towards completing the
 Appendix of this document.
 We also wish to thank the following people who contributed in many
 ways towards this document.
    Zhang Zhoucai              Martin J. Duerst
    Zhang Ling                 Kenichi Handa
    Zhu Bin                    Lu Chin
    Sun Yufang                 Nelson Chin
    Chen Shuyi                 Mao Yonggang
    Masataka Ohta              Ken Lunde
    Lua Kim Teng               Victor Cheng
    Stephen G. Simpson         Yuan Jiang
    Liu Huifang                Harald T. Alvestrand
    Qian Hualin                Jiang Lin
    Lu Ming                    Emily Hsu
    Wu Jian                    Zhu Shuang
    Zheng Long                 Zhang Hailin
    Yonggang Zhang             Feng Hui
    Yao Jian

Security Considerations

 Security issues are not discussed in this memo.

Authors' Addresses

 Zhu Haifeng  (HF. Zhu)
 216 Central Main Building
 Tsinghua University
 Beijing, 100084
 China
 Tel: +86-10-2561144 ext. 3492
 Fax: +86-10-2564173
 EMail: zhf@net.tsinghua.edu.cn, zhf@net.edu.cn

Zhu, et al Informational [Page 18] RFC 1922 Chinese Character Encoding March 1996

 Hu Daoyuan  (DY. Hu)
 Tsinghua Networking Center
 Tsinghua University
 Beijing, 100084
 China
 Tel: +86-10-2594016
 Fax: +86-10-2564173
 EMail: hdy@tsinghua.edu.cn
 Wang Zhiguan  (ZG. Wang)
 Beijing 1101 MailBox
 SubCommitte 2 (SC2)
 China Information Technology Standardization Technical Committee
 (CITS)
 Beijing, 100007
 China
 Tel: +86-10-4012392
 Fax: +86-10-4010601
 Kao Tien-cheu (TC. Kao)
 I.T. Promotion Division
 Institute for Information Industry (III)
 Taipei
 Taiwan
 Tel: +886-2-5631688
 Fax: +886-2-563-4209
 EMail: tckao@iiidns.iii.org.tw
 Chang Wen-chung  (WCH. Chang)
 Institute for Information Industry (III)
 Taipei
 Taiwan
 Tel: +886-2-7327771
 Fax: +886-2-7370188
 EMail: chung@iiidns.iii.org.tw

Zhu, et al Informational [Page 19] RFC 1922 Chinese Character Encoding March 1996

 Mark R. Crispin
 Networks and Distributed Computing
 University of Washington
 4545 15th Avenue NE
 Seattle, WA  98105-4527
 USA
 Tel: +1 (206) 543-5762
 Fax: +1 (206) 685-4045
 EMail: MRC@CAC.Washington.EDU

Zhu, et al Informational [Page 20] RFC 1922 Chinese Character Encoding March 1996

Appendix – Conversion Table for ISO-2022-CN (EXT) and Big5

 This is a conversion table for the Chinese characters in Big5's
 common part and ISO-2022-CN/-EXT, including all the vendor-specific
 characters from Eten, Microsoft and IBM.  For conversion source and
 binary programs for Big5, III provides good on-line services (ftp
 site listed in section 1.4), and [CJKINF] is also a good reference.

A.1. Big5 (ETen, IBM, and Microsoft version) symbol set correspondence

    to CNS 11643 Plane 1:
    0xA140-0xA1F5 <-> 0x2121-0x2256
           0xA1F6 <-> 0x2258
           0xA1F7 <-> 0x2257
    0xA1F8-0xA2AE <-> 0x2259-0x234E
    0xA2AF-0xA3BF <-> 0x2421-0x2570
    0xA3C0-0xA3E0 <-> 0x4221-0x4241 (ETen and Microsoft
                                     defined as reserved area)

A.2. Big5 (ETen, IBM, and Microsoft version) Level 1 correspondence to

    CNS 11643-1992 Plane 1:
    0xA440-0xACFD <-> 0x4421-0x5322
           0xACFE <-> 0x5753
    0xAD40-0xAFCF <-> 0x5323-0x5752
    0xAFD0-0xBBC7 <-> 0x5754-0x6B4F
    0xBBC8-0xBE51 <-> 0x6B51-0x6F5B
           0xBE52 <-> 0x6B50
    0xBE53-0xC1AA <-> 0x6F5C-0x7534
    0xC1AB-0xC2CA <-> 0x7536-0x7736
           0xC2CB <-> 0x7535
    0xC2CC-0xC360 <-> 0x7737-0x782C
    0xC361-0xC3B8 <-> 0x782E-0x7863
           0xC3B9 <-> 0x7865
           0xC3BA <-> 0x7864
    0xC3BB-0xC455 <-> 0x7866-0x7961
           0xC456 <-> 0x782D
    0xC457-0xC67E <-> 0x7962-0x7D4B

A.3. Big5 (ETen, IBM, and Microsoft version) Level 2 correspondence to

    CNS 11643-1992 Plane 2:
    0xC940-0xC949 <-> 0x2121-0x212A
           0xC94A <-> 0x4442       # duplicate of Level 1's 0xA461
    0xC94B-0xC96B <-> 0x212B-0x214B
    0xC96C-0xC9BD <-> 0x214D-0x217C
           0xC9BE <-> 0x214C
    0xC9BF-0xC9EC <-> 0x217D-0x224C

Zhu, et al Informational [Page 21] RFC 1922 Chinese Character Encoding March 1996

    0xC9ED-0xCAF6 <-> 0x224E-0x2438
           0xCAF7 <-> 0x224D
    0xCAF8-0xD779 <-> 0x2439-0x387D
           0xD77A <-> 0x3F6A
    0xD77B-0xDBA6 <-> 0x387E-0x3F69
    0xDBA7-0xDDFB <-> 0x3F6B-0x4423
           0xDDFC <-> 0x4176         # duplicate of 0xDCD1
    0xDDFD-0xE8A2 <-> 0x4424-0x554A
    0xE8A3-0xE975 <-> 0x554C-0x5721
    0xE976-0xEB5A <-> 0x5723-0x5A27
    0xEB5B-0xEBF0 <-> 0x5A29-0x5B3E
           0xEBF1 <-> 0x554B
    0xEBF2-0xECDD <-> 0x5B3F-0x5C69
           0xECDE <-> 0x5722
    0xECDF-0xEDA9 <-> 0x5C6A-0x5D73
    0xEDAA-0xEEEA <-> 0x5D75-0x6038
           0xEEEB <-> 0x642F
    0xEEEC-0xF055 <-> 0x6039-0x6242
           0xF056 <-> 0x5D74
    0xF057-0xF0CA <-> 0x6243-0x6336
           0xF0CB <-> 0x5A28
    0xF0CC-0xF162 <-> 0x6337-0x642E
    0xF163-0xF16A <-> 0x6430-0x6437
           0xF16B <-> 0x6761
    0xF16C-0xF267 <-> 0x6438-0x6572
           0xF268 <-> 0x6934
    0xF269-0xF2C2 <-> 0x6573-0x664C
    0xF2C3-0xF374 <-> 0x664E-0x6760
    0xF375-0xF465 <-> 0x6762-0x6933
    0xF466-0xF4B4 <-> 0x6935-0x6961
           0xF4B5 <-> 0x664D
    0xF4B6-0xF4FC <-> 0x6962-0x6A4A
    0xF4FD-0xF662 <-> 0x6A4C-0x6C51
           0xF663 <-> 0x6A4B
    0xF664-0xF976 <-> 0x6C52-0x7165
    0xF977-0xF9C3 <-> 0x7167-0x7233
           0xF9C4 <-> 0x7166
           0xF9C5 <-> 0x7234
           0xF9C6 <-> 0x7240
    0xF9C7-0xF9D1 <-> 0x7235-0x723F
    0xF9D2-0xF9D5 <-> 0x7241-0x7244

A.4. Big5 (ETen and IBM Version) specific numeric symbols

    correspondence to CNS 11643 Plane 1: (Microsoft version defined
    this area as UDC - User Defined Character)

Zhu, et al Informational [Page 22] RFC 1922 Chinese Character Encoding March 1996

    0xC6A1-0xC6BE <-> 0x2621 - 0x263E

A.5. Big5 (ETen and IBM Version) specific KangXi radicals

    correspondence to CNS 11643 Plane 1: (Microsoft version defined as
    UDC - User Definable Character)
           0xC6BF <-> 0x2723
           0xC6C0 <-> 0x2724
           0xC6C1 <-> 0x2726
           0xC6C2 <-> 0x2728
           0xC6C3 <-> 0x272D
           0xC6C4 <-> 0x272E
           0xC6C5 <-> 0x272F
           0xC6C6 <-> 0x2734
           0xC6C7 <-> 0x2737
           0xC6C8 <-> 0x273A
           0xC6C9 <-> 0x273C
           0xC6CA <-> 0x2742
           0xC6CB <-> 0x2747
           0xC6CC <-> 0x274E
           0xC6CD <-> 0x2753
           0xC6CE <-> 0x2754
           0xC6CF <-> 0x2755
           0xC6D0 <-> 0x2759
           0xC6D1 <-> 0x275A
           0xC6D2 <-> 0x2761
           0xC6D3 <-> 0x2766
           0xC6D4 <-> 0x2829
           0xC6D5 <-> 0x282A
           0xC6D6 <-> 0x2863
           0xC6D7 <-> 0x286C

A.6. Big5 (ETen and Microsoft version) specific Ideographs

    correspondence to CNS 11643 Plane 3: (IBM version defined as UDC)
           0xF9D6 <-> 0x4337
           0xF9D7 <-> 0x4F50
           0xF9D8 <-> 0x444E
           0xF9D9 <-> 0x504A
           0xF9DA <-> 0x2C5D
           0xF9DB <-> 0x3D7E
           0xF9DC <-> 0x4B5C

A.7. Big5 (ETen version only) specific symbols correspondence to CNS

    11643 Plane 4:
           0xC879 <-> 0x2123

Zhu, et al Informational [Page 23] RFC 1922 Chinese Character Encoding March 1996

           0xC87B <-> 0x2124
           0xC87D <-> 0x212A
           0xC8A2 <-> 0x2152

A.8. Other Big5 specific symbols which cannot mapping to CNS 11643:

    0xC6D8-0xC878 <-> none  (ETen and IBM Version)
           0xC87A <-> none  (ETen version only)
           0xC87C <-> none  (ETen version only)
    0xC87E-0xC8A1 <-> none  (ETen version only)
    0xC8A3-0xC8CC <-> none  (ETen version only)
    0xC8CD-0xC8D3 <-> none  (ETen and IBM version)
    0xF9DD-0xF9FE <-> none  (ETen and Microsoft version)
    Note: However, most of them can be mapped to GB-2312 too.  For
    example, Big5(ETen and IBM version) Hiragana, Katakana, and
    Cyrillic symbols correspondence to GB-2312:
    0xC6E7-0xC77A <-> 0x2421-0x2473  # Japanese Hiragana
    0xC77B-0xC7F2 <-> 0x2521-0x2576  # Japanese Katakana
    0xC7F3-0xC854 <-> 0xA7A1-0xA7C1  # Cyrillic uppercase
    0xC855-0xC875 <-> 0xA7D1-0xA7F1  # Cyrillic lowercase
 Please notice that there are also many symbols that could be
 supported by GB-2312, for detail, please refer to the ftp sites in
 section 1.4 of the "Specification" part of this document.

Zhu, et al Informational [Page 24] RFC 1922 Chinese Character Encoding March 1996

References

 [ASCII] American National Standards Institute, "Coded character set:
 7-bit American National Standard Code for Information Interchange",
 ANSI X3.4-1986.
 [BIG5] Institute for Information Industry, "Chinese Coded Character
 Set in Computer ", March, 1984
 [CJKINF] Ken Lunde, On-line documentation of Chinese/Japanese/Korean
 Information Processing, 1995, available at:
 ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf
 [CNS-5205] "Information processing: 7-Bit Coded Character Set For
 Information Interchange", CNS-5205.
 [CNS-11643] "Chinese Standard Interchange Code", CNS-11643 version
 1992; "Standard Interchange Code for Generally-Used Chinese
 Characters", CNS 11643 version 1986.
 [GB-1988] "7-bit Coding Character Set for Information Interchange",
 GB 1988-89.
 [GB-2312] "Coding of Chinese Ideogram Set for Information Interchange
 Basic Set", GB 2312-80.
 [GB-7589] "Code of Chinese Ideograms Set for Information Interchange,
 the 2nd Supplementary Set", UDC 681.3.048, GB 7589-87.
 [GB-7590] "Code of Chinese Ideogram Set for Information Interchange,
 the 4th Supplementary Set", UDC 681.3.048, GB 7590-87.
 [GB-8565] "Information Processing Coded Character Sets for Text
 Communication", UDC 681.3, GB 8565-88.
 [GB-12345] "Code of Chinese Ideogram Set for Information Interchange
 Supplementary Set", GB/T 12345-90.
 [GB-13000]  "Information Technology: Universal Multiple-Octet Coded
 Character Set(UCS) Part 1: Architecture and Basic Multilingual
 Plane", GB13000.1
 [GB-13131] "Code of Chinese Ideogram Set for Information Interchange,
 the 3rd Supplementary Set", GB 13131-91.
 [GB-13132] "Code of Chinese Ideogram Set for Information Interchange,
 the 5th Supplementary Set", GB 13132-91.

Zhu, et al Informational [Page 25] RFC 1922 Chinese Character Encoding March 1996

 [ISO-646] International Organization for Standardization (ISO),
 "Information Technology: ISO 7-bit Coded Character Set for
 Information Interchange", International Standard, Ref. No. ISO/IEC
 646:1991.
 [ISO-2022] 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).
 [ISO-10021] Information Technology: Text communication:
 Message-Oriented Text Interchange Systems (MOTIS), ISO 10021, October
 1988.
 [ISO-10646] ISO/IEC 10646-1:1993(E) Information Technology: Universal
 Multiple-octet Coded Character Set (UCS) Part 1: Architecture and
 Basic Multilingual Plane"
 [ISOREG] International Organization for Standardization (ISO),
 "International Register of Coded Character Sets To Be Used With
 Escape Sequences".
 [MIME-1] Borenstein, N., and Freed, N., "MIME (Multipurpose Internet
 Mail Extensions) Part One: Mechanisms for Specifying and Describing
 the Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft,
 September 1993.
 [MIME-2] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
 Part Two: Message Header Extensions for Non-ASCII Text", RFC 1522,
 University of Tennessee, September 1993.
 [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text
 Messages", STD 11, RFC 822, University of Delaware, August 1982.
 [RFC-854] Postel, J., Reynolds J., Telnet Protocol Specification, RFC
 854, ISI, May 1983.
 [RFC-1036] Horton, M., and Adams, R., "Standard for Interchange of
 USENET Messages", RFC 1036, AT&T Bell Laboratories, Center for
 Seismic Studies, December 1987.
 [RFC-1468] Murai J., Crispin, M., and van der Poel, E., Japanese
 Character Encoding for Internet Messages, June 1993.
 [RFC-1557] Choi U., Chon K., and Park H., Korean Character Encoding
 for Internet Messages, December 1993.

Zhu, et al Informational [Page 26] RFC 1922 Chinese Character Encoding March 1996

 [RFC-1641] Goldsmith D., and Davis M., "Using Unicode with MIME", RFC
 1641, Taligent Inc., July 1994
 [RFC-1642] Goldsmith D., and Davis M.," UTF-7, A Mail-Safe
 Transformation Format of Unicode", July 1994
 [RFC-1700] Reynolds J., and Postel J., "Assigned Numbers",RFC 1700,
 STD 2, ISI, October 1994
 [SMTP] Postel, J. B. "Simple Mail Transfer Protocol", STD 10, RFC
 821, USC/Information Sciences Institute, August 1982.
 [SMTPEXT] Klensin J., Freed N., Rose M., Stefferud E., and Crocker
 D., "SMTP Service Extensions", RFC 1651, July 1994.
 [Unicode 1.1] "The Unicode Standard, Version 1.1", Addison-Wesley,
 Reading, MA (to be published; the contents of this standard is
 currently available by combining [Unicode92], [Unicode93], and
 [Unicode4]).
 [Unicode92] The Unicode Consortium, "The Unicode Standard: Worldwide
 Character Encoding: Version 1.0", Volume 1, Addison-Wesley, Reading,
 MA, 1992 (ISBN 0-201-56788-1).
 [Unicode93] The Unicode Consortium, "The Unicode Standard: Worldwide
 Character Encoding: Version 1.0", Volume 2, Addison-Wesley, Reading,
 MA, 1992 (ISBN 0-201-60845-6).
 [Unicode4] The Unicode Consortium, "The Unicode Standard: Version 1.1
 (Prepublication Edition)", Unicode Technical Report #4 (avaliable
 from the Unicode Consortium).

Zhu, et al Informational [Page 27]

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