Network Working Group HF. Zhu

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

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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.

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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;

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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.

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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

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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.

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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)

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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.

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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

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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

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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.

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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

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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

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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].

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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. )

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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.

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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 <[email protected]>. 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: [email protected], [email protected]

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: [email protected]

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: [email protected]

Chang Wen-chung (WCH. Chang)
Institute for Information Industry (III)
Taipei
Taiwan

Tel: +886-2-7327771
Fax: +886-2-7370188
EMail: [email protected]

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: [email protected]

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

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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]