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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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RFC 4713        Recommendations for Chinese Domain Names    October 2006

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