Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008
RFC 5895
Independent Submission P. Resnick
Request for Comments: 5895 Qualcomm Incorporated
Category: Informational P. Hoffman
ISSN: 2070-1721 VPN Consortium
September 2010
Mapping Characters for
Internationalized Domain Names in Applications (IDNA) 2008
Abstract
In the original version of the Internationalized Domain Names in
Applications (IDNA) protocol, any Unicode code points taken from user
input were mapped into a set of Unicode code points that "made
sense", and then encoded and passed to the domain name system (DNS).
The IDNA2008 protocol (described in RFCs 5890, 5891, 5892, and 5893)
presumes that the input to the protocol comes from a set of
"permitted" code points, which it then encodes and passes to the DNS,
but does not specify what to do with the result of user input. This
document describes the actions that can be taken by an implementation
between receiving user input and passing permitted code points to the
new IDNA protocol.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5895.
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RFC 5895 IDNA Mapping September 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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to this document.
1. Introduction
This document describes the operations that can be applied to user
input in order to get it into a form that is acceptable by the
Internationalized Domain Names in Applications (IDNA) protocol
[IDNA2008protocol]. It includes a general implementation procedure
for mapping.
It should be noted that this document does not specify the behavior
of a protocol that appears "on the wire". It describes an operation
that is to be applied to user input in order to prepare that user
input for use in an "on the network" protocol. As unusual as this
may be for a document concerning Internet protocols, it is necessary
to describe this operation for implementors who may have designed
around the original IDNA protocol (herein referred to as IDNA2003),
which conflates this user-input operation into the protocol.
It is very important to note that there are many potential valid
mappings of characters from user input. The mapping described in
this document is the basis for other mappings, and is not likely to
be useful without modification. Any useful mapping will have
features designed to reduce the surprise for users and is likely to
be slightly (or sometimes radically) different depending on the
locale of the user, the type of input being used (such as typing,
copy-and-paste, voice, and so on), the type of application used, etc.
Although most common mappings will probably produce similar results
for the same input, there will be subtle differences between
applications.
1.1. The Dividing Line between User Interface and Protocol
The user interface to applications is much more complicated than most
network implementers think. When we say "the user enters an
internationalized domain name in the application", we are talking
about a very complex process that encompasses everything from the
user formulating the name and deciding which symbols to use to
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express that name, to the user entering the symbols into the computer
using some input method (be it a keyboard, a stylus, or even a voice
recognition program), to the computer interpreting that input (be it
keyboard scan codes, a graphical representation, or digitized sounds)
into some representation of those symbols, through finally
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