X.400 Use of Extended Character Sets (RFC1502)
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2019-Feb-13
Internet Society Requests For Comment (RFCs)
This RFC defines a suggested method of using "GeneralText" in order to harmonize as much as possible the usage of this body part. [STANDARDS-TRACK]
Network Working Group H. Alvestrand Request for Comments: 1502 SINTEF DELAB August 1993
X.400 Use of Extended Character Sets
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Since 1988, X.400 has had the capacity for carrying a large number of different character sets in a message by using the body part "GeneralText" defined by ISO/IEC 10021-7.
Since 1992, the Internet also has the means of passing around messages containing multiple character sets, by using the mechanism defined in RFC-MIME.
This RFC defines a suggested method of using "GeneralText" in order to harmonize as much as possible the usage of this body part.
2. General principles
The target of this memo is to define a way of using existing standards to achieve:
(1) in the short term, a standard for sending E-mail in the European languages (Latin letters with European accents, Greek and Cyrillic)
(2) in the medium term, extending this to cover the Hebrew and Arabic character sets
(3) in the long term, opening up true international E-mail by allowing the full character set specified in ISO-10646 to be used.
Alvestrand [Page 1]
RFC 1502 X.400 Use of Extended Character Sets August 1993
The author believes that this document gives a specification that can easily accomodate the use of any character set in the ISO registry, and, by giving guidance rules for choosing character sets, will help interworking.
2.2. Families of character sets
2.2.1. ISO 6937/T.61
ISO 6937 is a code technique used and recommended in T.51 and T.101 (Teletex and Videotex service) and in X.500, providing a repertoire of 333 characters from the Latin script by use of non- spacing diacritical marks. It corresponds closely to CCITT recommendation T.61.
The problem with that technique is that the character stream comes in two modes, i.e., some characters are coded with one byte and some with two (composite characters). This makes information processing systems such as an E-mail UA or GW more complex.
It is also not extensible to other languages like Korean or Chinese, or even Greek, without invoking the character set switching techniques of ISO 2022.
2.2.2. ISO 8859
ISO 8859 defines a set of character sets, each suitable for use in some group of languages. Each character in ISO 8859 is coded in a single byte.
There are currently 11 parts of ISO 8859, plus a "supplementary" set, registered as ISO IR 154. Most languages using single-byte characters can be written in one or another of the ISO 8859 sets. There are sets covering Greek, Hebrew and Arabic, but there is still controversy over the problem of the rendering direction for Hebrew and Arabic.
All the ISO 8859 sets include US-ASCII as a subset. All use 8 bits. ...