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rfc:rfc4713

Network Working Group X. Lee Request for Comments: 4713 W. Mao Category: Informational CNNIC

                                                               E. Chen
                                                                N. Hsu
                                                                 TWNIC
                                                            J. Klensin
                                                          October 2006

Registration and Administration Recommendations for Chinese Domain Names

Status of This Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2006).

IESG Note

 This RFC is not a candidate for any level of Internet Standard.  The
 IETF disclaims any knowledge of the fitness of this RFC for any
 purpose and in particular notes that the decision to publish is not
 based on IETF review for such things as security, congestion control,
 or inappropriate interaction with deployed protocols.  The RFC Editor
 has chosen to publish this document at its discretion.  Readers of
 this document should exercise caution in evaluating its value for
 implementation and deployment.  See RFC 3932 for more information.

Abstract

 Many Chinese characters in common use have variants, which makes most
 of the Chinese Domain Names (CDNs) have at least two different forms.
 The equivalence between Simplified Chinese (SC) and Traditional
 Chinese (TC) characters is very important for CDN registration.  This
 memo builds on the basic concepts, general guidelines, and framework
 of RFC 3743 to specify proposed registration and administration
 procedures for Chinese domain names.  The document provides the
 information needed for understanding and using the tables defined in
 the IANA table registrations for Simplified and Traditional Chinese.

Lee, et al. Informational [Page 1] RFC 4713 Recommendations for Chinese Domain Names October 2006

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................3
    2.1. Chinese Characters .........................................3
    2.2. Chinese Domain Name Label (CDNL) ...........................3
    2.3. Simplified Chinese Variant Table (SCVT) ....................4
    2.4. Traditional Chinese Variant Table (TCVT) ...................4
    2.5. Original Chinese Domain Name Label (OCDNL) .................4
 3. Procedure for Registration of Chinese Domain Name Labels ........4
    3.1. Terminology and Context ....................................4
    3.2. Procedure in Terms of the RFC 3743 Model ...................4
    3.3. RFC 3743 Optional Registry Processing ......................5
 4. Security Considerations .........................................5
 5. Acknowledgements ................................................6
 6. References ......................................................6
    6.1. Normative References .......................................6
    6.2. Informative References .....................................7

1. Introduction

 With the standardization of Internationalized Domain Names for
 Application (IDNA, described in [RFC3490], [RFC3491], and [RFC3492]),
 internationalized domain names (IDNs), i.e., those that contain non-
 ASCII characters, are included in the DNS, and users can access the
 Internet with their native languages, most of which are not English.
 However, many languages have special requirements, which are not
 addressed in the IDNA RFCs.  One way to deal with some of the
 remaining issues involves grouping characters that could be confused
 together as "variants".  The variant approach is discussed in RFC
 4290 [RFC4290] and specifically for documents written in Chinese,
 Japanese, or Korean (CJK documents), in the so-called "JET
 Guidelines" RFC 3743 [RFC3743].  Readers of this document are assumed
 to be familiar with the concepts and terminology of the latter.  The
 guidelines specified in this document provide a set of specific
 tables and methods required to apply the JET Guidelines to Chinese
 characters.  For example, changes were made in the forms of a large
 number of Chinese characters during the last century to simplify
 writing and reading.  These "Simplified" characters have been adopted
 in some Chinese-speaking communities, while others continue to use
 the "Traditional" forms.  On the global Internet, if IDNA were used
 alone, there would be considerable potential for confusion if the two
 forms were not considered together.  Consequently, effective use of
 Chinese Domain Names (CDNs) requires variant equivalence, as
 described in RFC 3743, to handle character differences between
 Simplified and Traditional Chinese forms.

Lee, et al. Informational [Page 2] RFC 4713 Recommendations for Chinese Domain Names October 2006

 Chinese variant equivalence itself is very complicated in principle
 (please read [C2C] for further information).  When it comes to the
 usage of Chinese domain names, the basic requirement is to match the
 user perception of Chinese characters between Simplified Chinese (SC)
 and Traditional Chinese (TC) forms.  When users register SC or TC
 domain names, they will wish to obtain the other forms (Traditional
 or Simplified, respectively) as well, and expect others to be able to
 access the website or other resources in both forms.
 This document specifies a solution for Chinese domain name
 registration and administration that has been adopted and deployed by
 CNNIC (the top-level domain registry for "CN") and TWNIC (the top-
 level domain registry for "TW") to manage Simplified Chinese and
 Traditional Chinese domain name equivalence.  In the terminology of
 RFC 3743, this solution is based on Internationalized Domain Labels
 (IDLs).

2. Terminology

 This document adopts the terminologies that are defined in RFC 3743.
 It is not possible to understand this document without first
 understanding the concepts and terminology or RFC 3743, including
 terminology introduced in its examples.  Additional terminology is
 defined later in this document.

2.1. Chinese Characters

 This document suggests permitting only a subset of Chinese characters
 in Chinese Domain Names (CDNs) and hence in the DNS.  When this
 document discusses Chinese characters, it only refers to the subset
 of the characters in the first column of the current IANA
 registration tables for Chinese as discussed in Section 2.3 and
 Section 2.4.  These are defined, in detail, in [LVT-SC] and [LVT-TC].
 Of course, characters excluded from these tables are still valid
 Chinese characters.  However, this document strongly suggests that
 registries do not permit any registration of Chinese characters that
 are not listed in the tables.  The tables themselves will be updated
 in the future if necessary.

2.2. Chinese Domain Name Label (CDNL)

 If an IDN label includes at least one Chinese character, it is called
 a Chinese Domain Name (CDN) Label.  CDN labels may contain characters
 from the traditional letter-digit-hyphen (LDH) set as well as Chinese
 characters.

Lee, et al. Informational [Page 3] RFC 4713 Recommendations for Chinese Domain Names October 2006

2.3. Simplified Chinese Variant Table (SCVT)

 Based on RFC 3743 [RFC3743], a language table for Simplified Chinese
 has been defined [LVT-SC].  It can be used for the registration of
 Simplified Chinese domain names.  The key feature of this table is
 that the preferred variant is the SC character, which is used by
 Chinese mainland users or defined in Chinese-related standards.

2.4. Traditional Chinese Variant Table (TCVT)

 Similarly, a language table has been defined for Traditional Chinese
 [LVT-TC].  It is also based on the rules of RFC 3743.  It can be used
 for registration of Traditional Chinese domain names.  The preferred
 variant is the TC character, which is used by Taiwan users or defined
 in related standards.

2.5. Original Chinese Domain Name Label (OCDNL)

 The Chinese Domain Name Label that users submit for registration.

3. Procedure for Registration of Chinese Domain Name Labels

3.1. Terminology and Context

 This document adopts the same procedure for Chinese Domain Name Label
 (CDNL) registration as the one defined for more general IDN labels in
 section 3.2.3 of RFC 3743 [RFC3743].  The terminology and notation
 used below, and the steps that are mentioned, derive from that
 document.  In particular, "CV" is the character variant associated
 with an input character ("IN") and a language table.  The language
 tables used here are those for Chinese as spoken and written in the
 Chinese mainland (ZH-CN) and on Taiwan (ZH-TW).  "PV" is the selected
 Preferred Variant.

3.2. Procedure in Terms of the RFC 3743 Model

 The first column of the Simplified Chinese Variant Table (SCVT) is
 the same as the first column of the corresponding Traditional Chinese
 Variant Table (TCVT) and so are the third columns of both tables.
 Consequently, the CV(IN, ZH-CN) will be same as the CV(IN, ZH-TW)
 after Step 3; the PV(IN, ZH-CN) is in SC form, and the PV(IN, ZH-TW)
 is in TC form.  As a result, there will not be more than three
 records (i.e., for the original label (OCDNL), the Simplified Chinese
 (SC) form, and the Traditional Chinese (TC) form) to be added into
 the zone file after applying this procedure.  In other words, the
 procedure does not generate labels that contain a mixture of
 Simplified and Traditional Chinese as variants.

Lee, et al. Informational [Page 4] RFC 4713 Recommendations for Chinese Domain Names October 2006

 The set of languages associated with the input (IN) is both ZH-CN and
 ZH-TW by default. The procedure for CDNL registration uses the
 optional registry-defined rules provided in RFC 3743 for optional
 processing, with the understanding that the rules may vary for
 different registries supporting CDNs.  The motivation for such rules
 is described below.
 The preferred variant(s) is/are TC in TCVT, and SC in SCVT.  There
 may be more than one preferred variant for a given valid character.

3.3. RFC 3743 Optional Registry Processing

 In actuality, while IDNA, and hence RFC 3743, process characters one
 at a time, the actual relationship between the valid code point and
 the preferred variant is contextual: whether one character can be
 substituted for another depends on the characters with which it is
 associated in a label or, more generally, in a phrase.  In
 particular, some of the preferred variants make no sense in
 combination with other characters; therefore, those combinations
 should not be added into the Zone file (described as "ZV" or zone
 variants in RFC 3743).  If desired, it should be possible to define
 and implement rules to reduce the preferred variant labels to only
 plausible ones.  This could be done, for example, with some
 artificial intelligence tools, or with feedback from the registrant,
 or with selection based on frequency of occurrence in other texts.
 To illustrate one possibility, the OCDNL could be required to be TC-
 only or SC-only, and if there is more than one preferred variant, the
 OCDNL will be used as the PV, instead of the PV produced by the
 algorithm.
 To reemphasize, the tables in [LVT-SC] and [LVT-TC] follow the table
 format and terminologies defined in [RFC3743].  If one intends to
 implement Chinese domain name registrations based on these two tables
 or ones similar to them, a complete understanding of RFC 3743 is
 needed for the proper use of those tables.

4. Security Considerations

 This document is subject to the same security considerations as RFC
 3743, which defines the table formats and operations.  As with that
 base document, part of its intent is to reduce the security problems
 that might be caused by confusion among characters with similar
 appearances or meanings.  While it will not introduce any additional
 security issues, additional registration restrictions such as those
 outlined in Section 3 may further reduce potential problems.

Lee, et al. Informational [Page 5] RFC 4713 Recommendations for Chinese Domain Names October 2006

5. Acknowledgements

 Thanks to these people for their suggestions and for their efforts to
 bring this tough work to conclusion and to promote the results: WANG
 YanFeng, Ai-Chin LU, Shian-Shyong TSENG, QIAN HuaLin, and Li-Ming
 TSENG.
 The authors especially thank Joe ZHANG and XiaoMing WANG for their
 outstanding contributions on SCVT in [LVT-SC].  Also, thanks to Kenny
 HUANG, Zheng-Wei LIN, Shi-Xiong TSENG, Lie-Neng WU, Cheng-Wu PAN,
 Lin-Mei WEI, and Qi-Qing HSU for their efforts and contributions on
 editing the TCVT in [LVT-TC].  These experts provided basic materials
 or gave very crucial suggestions and principles to accomplish these
 two variant tables.
 The authors also gratefully acknowledge the contributions of those
 who commented and made suggestions on this document, including James
 SENG, and other JET members.

6. References

6.1. Normative References

 [LVT-SC]   QIAN, H. and X. LEE, ".CN Chinese Character Table", IANA
            IDN Languages Tables, March 2005.
 [LVT-TC]   LU, A., ".TW Traditional Chinese Character Table", IANA
            IDN Languages Tables, March 2005.
 [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
            "Internationalizing Domain Names in Applications (IDNA)",
            RFC 3490, March 2003.
 [RFC3491]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
            Profile for Internationalized Domain Names (IDN)", RFC
            3491, March 2003.
 [RFC3492]  Costello, A., "Punycode: A Bootstring encoding of Unicode
            for Internationalized Domain Names in Applications
            (IDNA)", RFC 3492, March 2003.
 [RFC3743]  Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint
            Engineering Team (JET) Guidelines for Internationalized
            Domain Names (IDN) Registration and Administration for
            Chinese, Japanese, and Korean", RFC 3743, April 2004.

Lee, et al. Informational [Page 6] RFC 4713 Recommendations for Chinese Domain Names October 2006

6.2. Informative References

 [C2C]      Halpern, J. and J. Kerman, "Pitfalls and Complexities of
            Chinese to Chinese Conversion", International Unicode
            Conference (14th) in Boston, March 1999.
 [RFC4290]  Klensin, J., "Suggested Practices for Registration of
            Internationalized Domain Names (IDN)", RFC 4290, December
            2005.

Lee, et al. Informational [Page 7] RFC 4713 Recommendations for Chinese Domain Names October 2006

Authors' Addresses

 LEE Xiaodong
 CNNIC, No.4 South 4th Street, Zhongguancun
 Beijing  100080
 Phone: +86 10 58813020
 EMail: lee@cnnic.cn
 URI:   http://www.cnnic.cn
 MAO Wei
 CNNIC, No.4 South 4th Street, Zhongguancun
 Beijing  100080
 Phone: +86 10 58813055
 EMail: mao@cnnic.cn
 URI:   http://www.cnnic.cn
 Erin CHEN
 TWNIC, 4F-2, No. 9, Sec. 2, Roosevelt Rd.
 Taipei  100
 Phone: +886 2 23411313
 EMail: erin@twnic.net.tw
 URI:   http://www.twnic.net.tw
 Nai-Wen HSU
 TWNIC, 4F-2, No. 9, Sec. 2, Roosevelt Rd.
 Taipei  100
 Phone: +886 2 23411313
 EMail: snw@twnic.net.tw
 URI:   http://www.twnic.net.tw
 John C KLENSIN
 1770 Massachusetts Ave, #322
 Cambridge, MA  02140
 USA
 Phone: +1 617 491 5735
 EMail: john+ietf@jck.com

Lee, et al. Informational [Page 8] RFC 4713 Recommendations for Chinese Domain Names October 2006

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Lee, et al. Informational [Page 9]

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