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Versions: 00 RFC 2130

The Report of the IAB Character Set Workshop
held 29 February - 1 March, 1996
INTERNET-DRAFT - version 3.3 15 October 1996
<draft-weider-iab-char-wrkshop-00.txt>
Expire in six months

Chris Weider,  Chair
Cecilia Preston, Preston & Lynch
Keld Simonsen, DKUUG
Harald Alvestrand, UNINETT
Ran Atkinson, Cisco Systems
Mark Crispin, University of Washington
Peter Svanberg, KTH

Acknowledgments

The authors would like to sincerely thank Information Science
Institute (ISI), and in particular Joyce Reynolds for graciously
hosting this event; Joe Kemp and Jeanine Yamazaki of ISI made sure the
facilities met our needs.  We also wish to thank the Internet Society,
which underwrote travel for participants who might not otherwise have
been able to attend.  Of course, we also wish to thank the many
experts who participated in the workshop and on the mailing list; a
complete list of these people can be found in Appendix D.  Bunyip
Information Systems was kind enough to provide mailing list facilities
for this work.

Table of Contents

Abstract
0:    Executive summary
1:    Introduction
2:    Character sets on the Internet -- the problem today
2.1:  Character set handling in existing protocols
3:    The model
3.1:  Components of the model
3.2:  Recommended defaults
3.3:  Guidelines for conversions between coded character sets
4:    Presentation issues
5:    Open issues
6:    Security considerations
7:    Conclusions
8:    Recommendations
8.1:  To the IAB
8.2:  For new Internet protocols
8.3:  For registration of new character sets

Appendix A: List of protocols affected by character set issues
Appendix B: Acronyms
Appendix C: Glossary
Appendix D: References
Appendix E: Recommended reading
Appendix F: Workshop attendee list
Appendix G: Author's addresses




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Abstract

This report details the conclusions of an IAB-sponsored invitational
workshop held 29 February  - 1 March, 1996, to discuss the use of
character sets on the Internet.  It motivates the need to have
character set handling in Internet protocols which transmit text,
provides a conceptual framework for specifying character sets,
recommends the use of MIME tagging for transmitted text, recommends a
default character set *without* stating that there is no need for
other character sets, and makes a series of recommendations to the
IAB, IANA, and the IESG for furthering the integration of the
character set framework into text transmission protocols.

0: Executive summary

The term 'Character Set' means many things to many people. Even the
MIME registry of character sets registers items that have great
differences in semantics and applicability. This workshop provides
guidance to the IAB and IETF about the use of character sets on the
Internet and provides a common framework for interoperability between
the many characters in use there.

The framework consists of four components: an architecture model, which
specifies components necessary for on-the-wire transmission of text;
recommendations for tagging transmitted (and stored) text; recommended
defaults for each level of the model; and a set of recommendations to
the IAB, IANA, and the IESG for furthering the integration of  this
framework into text transmission protocols.

The architectural model specifies 7 layers, of which only three are
required for on-the-wire transmission. The Coded Character Set is a
mapping from a set of abstract characters to a set of integers. The
Character Encoding Scheme is a mapping from a Coded Character Set (or
several) to a set of octets. The Transfer Encoding Syntax is a
transformation applied to data which has been encoded using a
Character Encoding Scheme to allow it to be transmitted. These layers
should be specified in a transmitted text stream by using the MIME
encoding mechanisms.

This report recommends the use of ISO 10646 as the default Coded
Character Set, and UTF-8 as the default Character Encoding Scheme in
the creation of new protocols or new version of old protocols which
transmit text. These defaults do not deprecate the use of other
character sets when and where they are needed; they are simply
intended to provide guidance and a specification for interoperability.

1:  Introduction

This is the report of an IAB-sponsored invitational workshop on the
use of Character Sets on the Internet, held 29 February - 1 March 1996
at Information Science Institute (ISI) in Marina del Rey, California.
In addition, this report covers the discussion on the mailing list up
to and slightly beyond the workshop itself.  The goals of this


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workshop were to provide guidance to the IAB and the IETF about the
use of character sets on the Internet, and if possible a common
framework for interoperability between the many character sets in use
there.  Both goals were achieved.

2:  Character sets on the Internet - the problem

The term 'character set' is typically applied to the contents of a
wide variety of text transmission and display protocols used on the
Internet.  Because the term is used to mean different things,
confusion has arisen.  For example, the MIME registry of character
sets [MIME] contains items that may differ greatly in their
applicability and semantics in various Internet protocols.

In addition, there is a vast profusion of different text encoding
schemes in use on the Internet.  This per se is not a problem; each
scheme has evolved to meet real needs.  However, information
applications such as mail, directories, and the World Wide Web have
each developed different techniques for dealing with the growing number
of schemes.  A robust information architecture for the Internet
requires as much interoperability between these techniques as possible.

2.1:  Related topics deemed out of scope for this workshop

Successful display of plain text transmitted over the Internet requires
a lot of information about the text itself, such as the underlying
character set, language, and so forth.  An additional set of formatting
information is needed if the receiving application wishes to use local
(cultural) conventions when it presents the data to the user.  This
formatting includes information, that provides the data necessary to
format certain  types of textual data (dates, times, numbers and
monetary notation) into a form which is familiar to the user.  The POSIX
[POSIX] notation of locale encompasses language, coded character set and
cultural conventions.

To avoid unfruitful discussion, and to make the best use of the time
available for the workshop, we declared the following  issues out of
scope for the purposes of this workshop:

-  glyphs
-  sorting
-  culture (e.g. do we present the American or British spelling?)
-  user interface issues
-  internal representation of textual data
-  included characters (why aren't certain characters available in
       any character set?)
-  locale (in the POSIX sense)
-  font registration
-  semantics
-  user input/output issues
-  Han unification issues



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There are some related issues which were included for discussion, most
importantly the 'locale' components necessary for transport and
identification of multilingual texts.

2.2:  Character Set handling in existing protocols

One of the group's overriding concerns was that the framework
developed for character set handling not break existing protocols.
With that in mind, the way character sets are being used in existing
protocols was examined.  See Appendix A for a list of those protocols
and some recommendations for change.

2.2.1:  General comments

The problem areas here fall into three main categories: protocols,
identifiers, and data.

2.2.1.1:  Protocols

The protocol machinery SHOULD NOT be changed; allowing, for instance,
SMTP [SMTP] to use both MAIL FROM and POST FRA is dangerous to the
protocols' stability.  However, many protocols carry error messages
and other information that is intended for human consumption; it MIGHT
be an advantage to allow these to be localized into a specific
language and character set, rather than staying in English and
US-ASCII [ASCII].  If this is done, new extensions should follow the
framework outlined below.

2.2.1.2:  Identifiers.

There is a strong statement of direction from the IAB, RFC 1958
[RFC 1958],  which states:

     4.3 Public (i.e. widely visible) names should be in case
         independent ASCII.  Specifically, this refers to DNS names,
         and to protocol elements that are transmitted in text format.
         ...
     5.4 Designs should be fully international, with support for
         localization (adaptation to local character sets). In
         particular, there should be a uniform approach to character
         set tagging for information content.

In protocols that up to now have used US-ASCII only, UTF-8 [UTF-8]
forms a simple upgrade path; however, its use should be negotiated
either by negotiating a protocol version or by negotiating charset
usage, and a fallback to a US-ASCII compatible representation such as
UTF-7 [UTF-7] MUST be available.

The need for passing application data such as language on individual
identifiers varies between applications; protocols SHOULD attempt to
evaluate this need when designing mechanisms.  Applying the ASCII
requirement for identifiers that are only used in a local context



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(such as private mailbox folder names) is both unrealistic and
unreasonable; in such cases, methods for consistency in the handling
of character set should be considered.

2.2.1.3:  Data

Data that require character set handling includes text, databases,
and HTML [HTML] pages, for example.  In these the support for multiple
character sets and proper application information is absolutely
vital, and MUST be supported.

2.3:  Architectural requirements

To address the issues enumerated for this work, first an architectural
model was created which establishes the components that are required
to fully specify the transmission of textual data. Many of these
components are already familiar to the users of encoding protocols
such as MIME.  Not all of these are discussed in detail in this
report; we restrict ourselves primarily to those components which are
required to specify the 'on-the-wire' phase of text transmission.

Mandating a single, all-encompassing character set would not fit well
with the IETF philosophy of planning for architectural diversity.  So,
the best that can be done is to provide a common *framework* for
identifyin and using the multitude of character sets available on the
Internet.  It would be an advantage if the total number of Coded
Character Sets could be kept to a minimum.  This framework should meet
the following requirements:

-  it should not break existing protocols (because then the likelihood
     of deployment is very small),
-  it should allow the use of character sets currently used on the
     Internet, and
-  it should be relatively easy to build into new protocols.

3:  Architectural model

The basic architectural model which guided our discussions is shown in
below.  A distinction was made between those segments which were
necessary to successfully transmit character set data on-the-wire and
those needed to present that data to a user in a comprehensible manner.
The discussions were primarily restricted to those segments of the model
which specify the 'on-the-wire' transmission of textual data.

User interface issues: these are briefly discussed in Section 3.1.1.
     Layout
     Culture
     Locale
     Language
On-the-wire: see section 3.2 for detailed discussion.
     Transfer Syntax
     Character Encoding Scheme
     Coded Character Set


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3.1:  Segments defined

3.1:1:  User interface

3.1.1.1:  Layout

Layout includes the elements needed for displaying text to the user,
such as font selection, word-wrapping, etc.  It is similar to the
'presentation' layer in the 7-layer ISO telecommunications model
[ISO-7498].

3.1.1.2:  Culture

Culture includes information about cultural preferences, which affect
spelling, word choice, and so forth.

3.1.1.3:  Locale

The locale component includes the information necessary to make choices
about text manipulation which will present the text to the user in an
expected format.  This information may include the display of date, time
and monetary symbol preferences.  Notice that locale modifications are
typically applied to a text stream before it is presented to the user,
although they also are used to specify input formats.

3.1.1.4:  Language

This component specifies the language of the transmitted text.  At
times and in specific cases, language information may be required to
achieve a particular level of quality for the purpose of displaying a
text stream.  For example, UTF-8 encoded Han may require transmission
of a language tag to select the specific glyphs to be displayed at a
particular level of quality.

Note that information other than language may be used to achieve the
required level of quality in a display process.  In particular, a font
tag is sufficient to produce identical results.  However, the
association of a language with a specific block of text has usefulness
far beyond its use in display.  In particular, as the amount of
information available in multiple languages on the World Wide Web
grows, it becomes critical to specify which language is in use in
particular documents, to assist automatic indexing and retrieval of
relevant documents.

The term 'language tag' should be reserved for the short identifier of
RFC 1766 [RFC-1766] that only serves to identify the language.  While
there may be other text attributes intimately associated with the
language of the document, such as desired font or text direction,
these should be specified with other identifiers rather than
overloading the language tag.





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3.2:  On the wire

There are three segments of the model which are required for
completely specifying the content of a transmitted text stream (with
the occasional exception of the Language component, mentioned above).
These components are:

1)  Coded Character Set,
2)  Character Encoding Scheme, and
3)  Transfer Encoding Syntax.

Each of these abstract components must be explicitly specified by the
transmitter when the data is sent.  There may be instances of an
implicit specification due to the protocol/standard being used (i.e.
ANSI/NISO Z39.50).  Also, in MIME, the Coded Character Set and Character
Encoding Scheme are specified by the Charset parameter to the
Content-Type header field, and Transfer Encoding Syntax is specified by
the Content-Transfer-Encoding header field.

3.2.1:  Coded Character Set

A Coded Character Set (CCS) is a mapping from a set of abstract
characters to a set of integers.  Examples of coded character sets are
ISO 10646 [ISO-10646], US-ASCII [ASCII], and ISO-8859 series
[ISO-8859].

3.2.2:  Character Encoding Scheme

A Character Encoding Scheme (CES) is a mapping from a Coded Character
Set or several coded character sets to a set of octets. Examples of
Character  Encoding Schemes are ISO-2022 [ISO-2022] and UTF-8 [UTF-8].

3.2.3:  Transfer Encoding Syntax

It is frequently necessary to transform encoded text into a format
which is transmissible by specific protocols.  The Transfer Encoding
Syntax (TES) is a transformation applied to character data
encoded using a CCS and possibly a CES to allow it to be transmitted.
Examples of Transfer Encoding Syntaxes are Base64 Encoding [Base64],
gzip encoding, and so forth.

3.3:  Determining which values of CCS, CES, and TES are used

To completely specify which CCS, CES, and TES are used in a specific
text transmission, there needs to be a consistent set of labels for
specifying which CCS, CES, and TES are used.  Once the appropriate
mechanisms have been selected, there are six techniques for attaching
these labels to the data.

The labels themselves are named and registered, either with IANA
[IANA] or with some other registry.  Ideally, their definitions are
retrievable from some registration authority.



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Labels may be determined in one of the following ways:

-  Determined by guessing, where the receiver of the text has to
   guess the values of the CCS, CES, and TES. For example: "I got
   this from Sweden so it's probably  ISO-8859-1."  This is
   obviously not a very foolproof way to decode text.
-  Determined by the standard, where the protocol used to transmit
   the data has made documented choices of CCS, CES, and TES in the
   standard. Thus, the encodings used are known through the
   access protocol, for example HTTP [HTTP] uses (but is not
   limited to) ISO-8859-1, SMTP uses US-ASCII.
-  Attached to the transfer envelope, where the descriptive labels are
   attached to the wrapper placed around the text for transport.
   MIME headers are a good example of this technique.
-  Included in the data stream, where the data stream itself has
   been encoded in such a way as to signal the character set used.
   For example, ISO-2022 encodes the data with escape sequences to
   provide information on the character subset currently being used.
-  Agreed by prior bilateral agreement, where some out-of-band
   negotiation has allowed the text transmitter and receiver to
   determine the CCS, CES, and  TES for the transmitted text.
-  Agreed to by negotiation during some phase, typically initialization
   of the protocol.

3.3.1:  Recommendations for value specification mechanisms

While each of these techniques (with the  exception of guessing) is
useful in particular situations, interoperability requires a more
consistent set of techniques.  Thus, we recommend that MIME registered
values be used for all tagging of character sets and languages UNLESS
there is an existing mechanism for determining the required
information using one of the other techniques (except guessing).  This
recommendation will require a fair bit of work on the part of protocol
designers, implementors, the IETF, the IESG, and the IAB.

However, it is important to point out that the MIME concept of
'charset' in some cases cuts across several layers of components in
our model.  While this can be accepted in existing registrations, we
also recommend that the MIME registration procedure for character sets
be modified to show how a proposed character set deals with the CCS
and the CES.

There are a number of other recommendations, but these will be covered
in the next sections.

3.4:  Recommended Defaults

For a number of reasons, one cannot define a mandatory set of defaults
for all Internet protocols.  There is a mass of current practice,
future protocols are likely to have different purposes, which may
determine their handling of text, and protocols may need specific
variation support.  For example, in mail, text is a predominant data
type and coded character sets then become a major issue for the
protocol.  Also, since e-mail is ubiquitous and users expect to be

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able to send it to everyone, the mail protocols need to be quite adept
at handling different character set encodings.  On the other hand, if
strings are seldom used in a given protocol, there is no need to weigh
the protocol down with a sophisticated apparatus for handling multiple
character sets, assuming that the predicated character set can handle
all the protocol's needs. This observation also applies to the
specification techniques for character set parameters.  If only one
character set encoding is needed, it can be made explicit in the
protocol specification.  Protocols with a  greater need for character
set support will need a more elaborate specification technique.

3.4.1:  Clarity of specification

We recommend that each protocol clearly specify what it is using for
each of the layers of the transmission model.  Users (or clients)
should never have to guess what the parameter is for a given layer.

3.4.2:  Default Coded Character Set:

The default Coded Character Set is the repertoire of ISO-10646.

3.4.3:   Default Character Encoding Scheme

For text-oriented protocols, new protocols should use UTF-8, and
protocols that have a backwards compatibility requirement should use
the default of the existing protocol, e.g. US-ASCII for mail, and
ISO-8859-1 for HTTP.  The recommended specification scheme is the MIME
"charset" specification, using the IANA "charset" specifications.  The
MIME specifications will need to be clarified to meet this model in
the future.

For other protocols, the default should be UTF-8 as this initially
allows US-ASCII to be entered as-is, and enables the full repertoire
of ISO 10646.

Some protocols, such as those descended from SGML [SGML], have other
natural notations for characters outside their "natural" repertoire;
for instance, HTML [HTML] allows the use of &#nnnn to refer to any ISO
10646 character.  Note that this, like all other encodings that depend
on "escape characters", redefines at least one character from the base
character set for use as an indicator of "foreign" characters.  Use of
this approach must be weighed very carefully.

3.4.4:   Default Transport Encoding Scheme

There is no recommended default for this level.  For plain text
oriented protocols, the bytestream transport format should be 8-bit
clean, possibly with normalization of end-of-line indicators.  Some
special cases could be made for protocols that are not 8-bit clean,
such as encoding it for transport over 7-bit connections.  For binary
the same recommendation holds as above.  The specification technique
should either be defined in the  protocol, if only one way is
permitted, or by use of MIME content-transfer-encoding (CTE)
techniques, using IANA registered values.

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3.4.5:  Default Language

There is no recommended default for the language level.  For human
readable text, there should always be a way to specify the natural
language. The specification technique should be a MIME identifier with
IANA  registered values for languages.  If headers are used, the
header should be 'Content-Language'

3.4.6:  Default Locale

The default should be the POSIX locale.  The specification technique
should use the Cultural register of CEN ENV 12005 [CEN] for the values.
If headers are used, the header should be 'Content-Locale'.

3.4.7:  Default Culture

There is no recommended default for the Culture level.  The
specification  technique should be a MIME or MIME-like identifier
(e.g. Content-Culture) and should use the Cultural register of CEN ENV
12005 for its values.

3.4.8:  Default Presentation

There is no recommended default for the Presentation level.  The
specification technique should be a MIME or MIME-like identifier (e.g.
Content-Layout) and use the glyph register of ISO 10036 and other
registers for its values.

3.4.9:  Multiplexing

In some cases, text transmission may require the use of a number of
different values for a given parameter; for example, English
annotation of Japanese text might well require shifting the
Content-Language parameter.  The way to switch the value of parameters
within a single body of text depends on the application.  For
instance, the HTML I18N [I18N]work defines a <SPAN LANG=xx> construct
for the purpose of switching between different languages.  When only one
value is needed, this value should be as general as possible, and
specified in the protocol standard with reference to the IANA or other
registry value.  All levels should be specified explicitly.

3.4.10:  Storage

Because stored text may very well be stored without any of the
additional information necessary for decoding, stored text SHOULD be
tagged in a MIME compliant fashion.  This alleviates the problem of
being unable to interpret text which has been stored for a long time,
or text whose provenance is not available.

3.5:  Guidelines for conversions between coded character sets

This section covers various algorithms to convert a source text S,
encoded in the coded character set CCS(S), to a target text T, encoded
in the coded character set CCS(T).

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Rep(X) is the character repertoire of coded character set X, i.e. the
set of characters which can be represented with X.

3.5.1:  Exact conversion

When Rep(CCS(S)) and Rep(CCS(T)) are equal or Rep(CCS(S)) is a subset
of Rep(CCS(T)), exact conversion is possible; i.e. T is equal to S.
The octets just need to be remapped.  The algorithm for performing
this remapping is simple, if the IANA-registered definition tables for
CCS(S) and CCS(T) are available.

3.5.2:  Approximate conversion

In all other cases, any conversion creates a text T which differs from
S.  There are different principles for how this inevitable difference
should be handled.  A choice between them should be made, depending on
the purpose and requirements of the conversion.  Where possible, the
client application should be given mechanisms to determine what has
been done to the text.

3.5.2.1:  Length-modifying conversion for human display

When the length of the target text T is allowed to differ from the
length of the source text S, one should use a conversion method in
which each source character is converted to one or several target
character(s), using a best resemblance criteria in the choice of that
target character(s).

Examples:
   LATIN CAPITAL LETTER [*] ->  AE
   COPYRIGHT SIGN       [*] -> (c)

3.5.2.2:  Length-preserving conversion for human display

Where the text T must be presented and the length of T cannot differ
from the length of S, one should use a conversion method where each
source character is converted to one target character, using some kind
of best  resemblance criteria in the choice of target character.

Examples:
  LATIN CAPITAL LETTER  [*] -> A
  COPYRIGHT SIGN        [*] -> C

3.5.2.3:  Conversion without data loss

Where the conversion of the text S into T must be completely
reversible, apply a Character Encoding Syntax or other reversible
transformation method.  This case is most frequently met in data
storage requirements.

Examples:
  LATIN CAPITAL LETTER [*] -> &AE
  COPYRIGHT SIGN       [*] -> &(C


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An alternate method, which can be used if the size of Rep(CCS(T)) >=
Rep(CCS(S)), then for each character in Rep(CCS(S)) which is not
present in Rep(CCS(T)), define a mapping into a character in
Rep(CCS(T)) which is not present in Rep(CCS(S)).

Examples:
  LATIN CAPITAL LETTER  [*] -> CYRILLIC CAPITAL LETTER [*]
  COPYRIGHT SIGN  [*] -> PARTIAL DIFFERENTIAL SIGN [*]

Note that conversion without data loss requires redefining some member
of T to indicate "the introduction of character data outside T".  This
effectively adds another level of CES on top of CES(T).

4: Presentation issues

There are a number of considerations to make in selecting the base
character set.  One such consideration is the protocol's convenience
to users with limited equipment (for example only ISO 8859-1 or a
keyboard without the ability to enter all the characters in ISO
10646).  Alternative representation should be considered for these
users, both for input and output.  Possible options for the
representation of characters that can not be displayed include
transliteration (a la CEN/TC304 or ISO TC46/SC2 ), RFC 1345 [RFC-1345]
representative icons, or the WG2 short name (u+xxxx).

5: Open issues

In addition to the issues declared out of scope and enumerated in
section 2.1, the following issues are still open and will need to be
addressed in other forums.  These issues: language tags, public
identifiers such as URL names, and bi-directionality are briefly
discussed below as they repeatedly encroached the discussion.

5.1 Language tags

Although the workshop decided not to explicitly address the so-called
"CJK issue", a few members felt it was necessary to have some
mechanism to address the problem of correct Han character display in
the ISO-10646 issue, and that saying that it was a "font issue" would
not suffice.

The "CJK issue" refers to the extended discussion about "Han
unification", the use of a single ISO-10646 codepoint to represent
multiple national variants of a Chinese (Han) character.  ISO-10646
can map uniquely to any single CJK national character set, but in the
absence of additional  information an application can not display an
ISO-10646 text using the proper national variants for that text.

It was agreed that language tags would be sufficient to disambiguate
unified characters. There was not, in our opinion, a significant
technical difference between the use of different coded character sets
with overlapping codepoints, and a single coded character set with
language tags.  Either way, the application has sufficient information
to display the text properly.

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It was observed that in contemporary usage of MIME charsets, the
language is implied as well as the coded character set and the
character encoding syntax.  We agreed that this is excessive
overloading of MIME charsets.

To specify the language used in a particular block of text, we
recommend that the MIME tag "Content-Language" be used.  There are a
number of questions about this approach that need to be worked out,
however:

-  Is Content-Language: actually suitable?
-  Is there an overload between this function and the other
     intended functions of Content-Language: as described in RFC
     1766?
-  What, precisely, does "Content-Language: zh-tw, ja, ko, zh-cn"
     mean in this context? We believe it means that, in drawing a
     Han character, the Taiwanese variant (presumably traditional
     Han) is preferred, followed by the Japanese, Korean, and
     mainland Chinese (presumably simplified Han) variants. It does
     *NOT* mean "mixed text containing Taiwanese, Japanese, Korean,
     and mainland Chinese text with all the national variants in
     each of these".

Mixed CJK text, that simultaneously displays different variants
occupying the same codepoint, requires language tags embedded in the
data.  Ohta and Handa propose in RFC 1554 [RFC-1554] a MIME charset
using ISO-2022 shifts between multiple coded character sets; in effect
this is an encoding that uses coded character sets for displaying the
appropriate glyphs.

There is some speculation that states that mixed CJK text is
relatively infrequent, and that therefore it is acceptable to require
that such text be represented using a rich text format that can
support language tags.  In other words, that a simplifying assumption
can be made for TEXT/PLAIN in  email using ISO-10646 that will not
require multiple display representations for the same codepoint.  A
mechanism such as RFC 1554 could address this need if it was
important; although arguably RFC 1554 should really be identified as
TEXT/ISO-2022.

Note again that we recommend that support for language tagging SHOULD
be built into new protocols, as this will become a critical component
of the automated indexing and retrieval in information applications of
the future.

5.2:   Public identifiers

There is a considerable demand from the user community for the ability
to use non-ASCII characters in URL names, IMAP mailbox names, file
names, and other public identifiers. This is still an open problem.





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Internet-Draft       Character Set Workshop Report     November 1996

5.3:   Bi-directionality

It was realized that a consistent framework for bi-directional text
was needed but there was no attempt to work on it in this workshop.

6:  Security considerations

There are no security considerations associated with character sets.

7:  Conclusions

This paper provides a conceptual framework and a set of
recommendations which, if adopted, should provide a solid foundation
for interoperability on the Internet. There are, however, a number of
open issues which will need to be addressed to provide ever better use
of text on the Internet.

8:  Recommendations

8.1:  To the IAB

There were a number of recommendations to the IAB about making the
standards process more aware of the need for character set
interoperability, and about the framework itself.

A: The IAB should trigger the examination of all RFCs to determine the
way  they handle character sets, and obsolete or annotate the RFCs
where necessary.

B: The IESG should trigger the recommendation of procedures to the RFC
editor  to encourage RFCs to specify character set handling if they
specify the  transmission of text.

C: The IAB should trigger the production of a perspectives document on
the  character set work that has gone on in the past and relate it to
the current framework.

D: Full ISO 10646 has a sufficiently broad repertoire, and scope for
further extension, that it is sufficient for use in Internet Protocols
(without excluding the use of existing alternatives).  There is no
need for specific development of character set standards for the
Internet.

E: The IAB should encourage the IRTF to create a research group to
explore the open issues of character sets on the Internet. This group
should set its sights much higher than this workshop did.

F: The IANA (perhaps with the help of an IETF or IRTF group) should
develop  procedures for the registration of new character sets for use
in the Internet.

G: Register UTF-8 as a Character Encoding Scheme for MIME.



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Internet-Draft       Character Set Workshop Report     November 1996

H: The current use of the "x-*" format for distinguishing experimental
tags should be continued for private use among consenting parties. All
other namespaces should be allocated by IANA.

I: Application protocol RFCs SHOULD include a section on
"multilingual Considerations".

J: Application Protocol RFCs SHOULD indicate how to transfer 'on the
wire' all characters in the character sets they use. They SHOULD also
specify how to transfer other information that applications may need
to know about the data.

K: The IESG should trigger a set of extensions to RFC 1522 to allow
language  tagging of the free text parts of message headers.

8.2:  For new Internet protocols

New protocols do not suffer from the need to be compatible with old
7-bit pipes.  New protocol specifications SHOULD use ISO 10646 as the
base charset unless there is an overriding need to use a different
base character set.

New protocols SHOULD use values from the IANA registries when
referring to parameter values.  The way these values are carried in
the protocols is protocol dependent; if the protocol uses RFC-822-like
headers, the header names already in use SHOULD be used.

For protocols with only a single choice for each component, the
protocol  should use the most general specification and should be
specified with reference to the registered value in the protocol
standard.

Protocols SHOULD tag text streams with the language of the text.

8.3:  For the registration of new character sets

Ned Freed will be releasing a new MIME registration document in
conjunction with this paper.

8.3.1:   A definition table for a coded character set

A definition table for a coded character set A must for each character
C that is in the repertoire of A give:

a) If C is present in ISO 10646, the code value (in hexadecimal form)
     for that character.

b) If C is not present in ISO 10646, but may be constructed using ISO
     10646 combining characters, the series of code values (in
     hexadecimal form) used to construct that character.

c) if C is not present in ISO 10646, a textual description of the
     character,  and a reference to its origin.


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Internet-Draft       Character Set Workshop Report     November 1996

8.3.2:   A definition of a character encoding scheme

A definition of a character encoding scheme consists of:

-  A description of an algorithm which transforms every possible
     sequence of octets to either a sequence of pairs <CCS, code
     value> or to the  error state "illegal octet sequence"
-  Specifications, either by reference to CCS's registered by IANA or
   in text, of each CCS upon which this CES is based.














































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Internet-Draft       Character Set Workshop Report     November 1996

Appendix A:

A-1:  IETF Protocols

The following list describes how various existing protocols handle
multiple character set information.

Email

   SMTP
     See 8.2. ESMTP makes it easy to negotiate the use of alternate
     language and encoding if it is needed.
   Headers
     RFC 1522 forms an adequate framework for supporting text; UTF-8
     alone is not a possible solution, because the mail pathways are
     assumed to be 7-bit 'forever'. However, RFC 1522 should be extended
     to allow language tagging of the free text parts of message
     headers.
   Bodies
     Selection of charset parameters for Email text bodies is
     reasonably well covered by the charset= parameter on Text/* MIME
     types.  Language is defined by the Content-language header of RFC
     1766.  Other information will have to be added using body part
     headers; due to the way MIME differentiates between body part
     headers and message headers, these will all have to have names
     starting with Content- .

NetNews

   NNTP
     See 8.2. No strong tradition for negotiation of encoding in NNTP
     exists.
   NetNews Messages
     These should be able to leverage off the mechanisms defined for
     Email.  One difference is that nearly all NNTP channels are 8-bit
     clean; some NNTP newsgroups have a tradition of using 8-bit
     charsets in both headers and bodies. Defining character set
     default on a per newsgroup basis might be a suitable approach.

RTCP
     The identifiers carried as information about parties are already
     defined to be in UTF-8.

FTP
   Protocol
     See 8.2. The common use of welcome banners in the login response
     means that there might be strong reason here to allow client and
     server to negotiate a language different from the default for
     greetings and error messages. This should be a simple protocol
     extension.
   Filenames
     Many fileservers now how have the capability of using non-ASCII
     characters in filenames, while the "dir" and "get" commands of


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Draft RFC          Character Set Workshop Report          November 1996

FTP
     are defined in terms of US-ASCII only. One possible solution
     would be to define a "UTF-8" mode for the transfer of filenames
     and directory information; this would need to be a negotiated
     facility, with fallback to US-ASCII if not negotiated. The
     important point here is consistency between all implementations;
     a single charset is better here than the ability to handle
     multiple charsets.

World Wide Web
   HTTP
     See 8.2. The single-shot stype of HTTP makes negotiation more
     complex than it would otherwise be.
   HTML
     Internationalization of HTML [I18N] seems fairly well covered in
     the current "I18N" document. It needs review to see if it needs
     more specific details in order to carry application information
     apart from the language.

URLs
     URLs are "input identifiers", and powerful arguments should be
     made if they are ever to be anything but US-ASCII.

IMAP
     IMAP's information objects are MIME Email objects, and therefore
     are able to use that standard's methods. However, IMAP folder
     names are local identifiers; there is strong reason to allow
     non-ASCII characters in these. A UTF-8 negotiation might be the
     most appropriate thing, however, UTF-8 is awkward to use.
     Unfortunately, UTF-7 isn't suitable because it conflicts with
     popular hierarchy delimiters. The most recent IMAP draft
     specification describes a modified UTF-7 which avoids this
     problem.

DNS
     DNS names are the prime example of identifiers that need to stay
     in US-ASCII for global interoperability. However, some DNS
     information, in particular TXT records, may represent information
     (such as names) that is outside the ASCII range. A single
     solution is the best; problems resulting from UTF-8 should be
     investigated.

WHOIS++
     WHOIS++ version 1 is defined to use ISO 8859-1. The next version
     will use UTF-8. The currently designed changes will also allow the
     specification of individual attributes on attribute names; these
     will make the passing of application information about the values
     (such as language) easier. No immediate action seems necessary.

WHOIS
     This has been a stable protocol for so many years now that it
     seems unwise to suggest that it be modified. Furthermore,
compatible extensions exist in RWHOIS and WHOIS++; modification


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Draft RFC          Character Set Workshop Report          November 1996

     should rather be made to these protocols than to the WHOIS
     protocol itself.

Telnet
     This is a prime example of protocol where character set support
     is necessary and nonexistent. The current draft on character set
     negotiation in Telnet seems adequate to the task; the question of
     passing other application data that might be useful is still
     open.

A-2: Non-IETF protocols

For these protocols, the IETF does not have any power to change them.
However, the guidelines developed by the workshop may still be useful
as input to the further development of the protocols.

Gopher: Gopher, Gopher+

Prospero (Archie)

NFS:  Filesystem

CORBA, Finger, GEDI, IRC, ISO 10160/1, Kerberos, LPR, RSTAT, RWhois,
SGML, TFTP, X11, X.500, Z39.50































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Draft RFC               Character Set Workshop Report    November 1996

Appendix B: Acronyms

ASCII       American National Standard Code for Information Character
              Sets
CCS         Coded Character Sets
CEN ENV     European Committee for Standardisation (CEN) European
              pre-standard (ENV)
CES         Character Encoding Scheme
CJK         Chinese Japanese Korean
CORBA       Common Object Request Broker Architecture
CTE         Content Transfer Encoding
DNS         Domain Name Service
ESMTP       Extended SMTP
FTP         File Transfer Protocol
HTML        Hypertext Transfer Protocol
I18N        Internationalization (or 18 characters between the first
              (I) and last (n)character)
IAB         Internet Activities Board
IANA        Internet Assigned Numbers Authority
IESG        Internet Engineering Steering Group
IETF        Internet Engineering Task Force
IMAP        Internet Message Access Protocol
IRC         Internet Relay Chat
IRTF        Internet Research Task Force
ISI         Information Sciences Institute
ISO         International Standards Organization
MIME        Multipurpose Internet Mail Extensions
NFS         Networked File Server
NNTP        Net News Transfer Protocol
POSIX       Portable Operating System Interface
RFC         Request for Comments (Internet standards documents)
RPC         Remote Procedure Call
RSTAT       Remote Statistics
RTCP        Real-Time Transport Control Protocol
Rwhois      Referral Whois
SGML        Standard Generalized Mark-up Language
SMTP        Simple Mail Transfer Protocol
TES         Transfer Encoding Syntax
TFTP        Trivial File Transfer Protocol
URL         Uniform Resource Locator
UTF         Universal Text/Translation Format














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Draft RFC          Character Set Workshop Report          November 1996

Appendix C:  Glossary

Bi-directionality -  A property of some languages in which written
     text alternates direction from line to line (e.g. right-to-left
     one line, left-to-right the next)

Character - A single graphic symbol represented by sequence of one or
     more bytes.

Character Encoding Scheme - The mapping from a coded character set to
     an encoding which may be more suitable for specific purpose. For
     example, UTF-8 is a character encoding scheme for ISO 10646.

Character Set - An enumerated group of symbols (e.g., letters, numbers
     or glyphs)

Coded Character Set - The mapping from a set of integers to a
     character from a character set.

Culture - Preferences in the display of text based on cultural norms,
     such as spelling and word choice.

Language - The words and combinations of words the constitute a system
     of expression and communication among people with a shared
     history or set of traditions.

Layout - Information needed to display text to the user, similar to
     the presentation layer in the ISO telecommunications model.

Locale - The attributes of communication, such as language, character
     set and cultural conventions.

On-the-wire -  The data that actually gets put into packets for
     transmission to other computers.

Transfer Encoding Syntax -  The mapping from a coded character set
     which has been encoded in a Character Encoding Scheme to an
     encoding which may be more suitable for transmission using
     specific protocols. For example, Base64 is a transfer encoding
     syntax.















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Draft RFC          Character Set Workshop Report          November 1996

Appendix D:  References

[*]  Non-ASCII character

[ASCII]  ANSI X3.4:1986  "Coded  Character Sets - 7 Bit American
     National Standard Code for Information Interchange (7-bit ASCII)"

[Base64] N. Borenstein, N. Freed, "MIME (Multipurpose Internet Mail
     Extensions) Part One: Mechanisms for Specifying and Describing
     the Format of Internet Message Bodies", RFC 1521, September 1993.

[CEN]  see http://tobbi.iti.is/TC304/welcome.html for current status.

[HTML] T. Berners-Lee, D. Connolly, "Hypertext Markup Language - 2.0",
     RFC 1866, November 1995.

[HTTP] T. Berners-Lee, R. Fielding, H. Nielsen, "Hypertext Transfer
     Protocol -- HTTP/1.0", RFC 1945, May 1996

[I18N]  Yergeau, F., et.al.,  "Internationalization of the Hypertext
     Markup Language"  Internet draft August 1996.

[IANA]  Reynolds, J., and J. Postel,  "Assigned Numbers", RFC 1700,
     ISI, October 1994.

[ISO-2022]  ISO/IEC 2022:1994,  "Information technology -- Character
     Code Structure and Extension Techniques",  JTC1/SC2.

[ISO-7498]  ISO/IEC 7498-1:1994,  "Information technology - Open Systems
     Interconnection - Basic Reference Model:  The Basic Model".

[ISO-8859]  Information Processing -- 8-bit Single-Byte Coded Graphic
     Character Sets -- Part 1: Latin Alphabet no. 1,
     ISO 8859-1:1987(E). Part 2: Latin Alphabet no. 2, ISO 8859-2
     1987(E). Part 3: Latin Alphabet no. 3, ISO 8859-3:1988(E).
     Part 4: Latin Alphabet no. 4, ISO 8859-4, 1988(E). Part 5:
     Latin/Cyrillic Alphabet ISO 8859-5, 1988(E). Part 6:
     Latin/Arabic Alphabet, ISO 8859-6, 1987(E). Part 7: Latin/Greek
     Alphabet, ISO 8859-7, 1987(E). Part 8: Latin/Hebrew Alphabet, ISO
     8859-8-1988(E).Part 9: Latin Alphabet no. 5, ISO 8859-9, 1990(E).
     Part 10: Latin Alphabet no. 6, ISO 8859-10:1992(E).

[ISO-10646]  ISO/IEC 10646-1:1993(E ),  "Information technology --
     Universal Multiple-Octet Coded Character Set (UCS) -- Part 1:
     Architecture and Basic Multilingual Plane".  JTC1/SC2, 1993

[MIME]  Borenstein, N., and N. Freed, "MIME (Multipurpose Internet
     Mail Extensions) Part One: Mechanisms for Specifying and
     Describing the Format of Internet Message Bodies", RFC 1521,
     Bellcore, Innosoft, September 1993.

[POSIX]  Institute of Electrical and Electronics Engineers.  "IEEE
     standard interpretations for IEEE standard portable operating


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Draft RFC          Character Set Workshop Report          November 1996

     systems interface for computer environments". IEEE Std 1003.1
     -1988/Int, 1992 edition.  Sponsor, Technical Committee on Operating
     Systems of the IEEE Computer Society.  New York, NY: Institute of
     Electrical and Electronic Engineers, 1992.

RFC 1340  See [IANA]

[RFC 1345]  Simonsen, K., "Character Mnemonics & Character Sets".
     Rationel Alim Planlaegning, June 1992.

[RFC-1554]  Ohta, M., and K. Handa,  "ISO-2022-JP-2: Multilingual
     Extension of ISO-2022-JP",  Tokyo Institute of Technology, ETL,
     December 1993.

RFC 1642  See [UTF-7]

[RFC 1766]  Alvestrad, H., "Tags for the Identification of Languages",
     UNNETT, March 1995.

[RFC 1958]  Carpenter, B. (ed.) "Architectural Principles of the
     Internet", IAB, June 1996.

[SGML] ISO 8879:1986 "Information Processing - Text and Office Systems
     - Standard Generalized Markup Language (SGML)"

[SMTP] J. Postel, "Simple Mail Transfer Protocol", RFC 821, STD 10,
     August, 1982

[Unicode]  "The Unicode standard, version 2.0.  Unicode Consortium.
     Reading, Mass.: Addison-Wesley Developers Press, 1996

[UTF-7]  Goldsmith, D., and M. Davis, "UTF-7: A Mail Safe
     Transformation Format of Unicode", RFC 1642, Taligent, Inc., July
     1994.

[UTF-8]  International Standards Organization, Joint Technical
     Committee 1 (ISO/JTC1), "Amendment 2:1993, UCS Transformation
     Format 8 (UTF-8)", in ISO/IEC 10646-1:1993 Information technology
     - Universal Multiple-Octet Coded Character Set (UCS) -- Part 1:
     Architecture and Basic Multilingual Plane.  JTC1/SC2, 1993.















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Draft RFC          Character Set Workshop Report          November 1996

Appendix E:  Recommended reading

Alvestrand, H.  "Tags for the Identification of Languages."  RFC 1766.
     UNINETT, March 1995.

Alvestrand, H.  "X.400 Use of Extended Character Sets" RFC 1502. SINTEF
     DELAB, August 1993.

Borenstein, N.  "Implications of MIME for Internet Mail Gateways."
     RFC 1344.  Bellcore, June 1992.

Borenstein, N. and N. Freed.  "MIME (Multipurpose Internet Mail
     Extensions) Part One: Mechanisms for Specifying and Describing the
     Format of Internet Message Bodies."  RFC 1521.  Bellcore and
     Innasoft, September 1993.

Chernov, A. "Registration of a Cyrillic Character Set." RFC 1489. RELCOM
     Development Team, July 1993.

Choi, U. and K. Chan.  "Korean Character Encoding for Internet
     Messages."  RFC 1557.  KAIST, December 1993.

Freed, N. and N. Borenstein.  "Multipurpose Internet Mail Extensions
     (MIME) Part Two:  Media Types."  draft-ietf-822ext-mime-reg-02.txt.
     July 1993.

Goldsmith, D., and M. Davis.  "Transformation Format for Unicode."
     RFC 1642.  Taligent, Inc., July 1994.

Goldsmith, D., and M. Davis.  "Using Unicode with MIME."  RFC 1641.
     Taligent, Inc., July 1994.

Jerman-Blazic, B. "Character handling in computer communication" in
     "user needs in information technology standards", Computer Weekly
     Professional service, eds. C.D. Evans, B.L. Meed & R.S. Walker,
     P.C. Butterworth Heineman, 1993, Oxford, Boston, p. 102-129.

Jerman-Blazic, B. "Tool supporting the internationalization of the
     generic network services", Computer Networks and ISDN Systems,
     No. 27 (1994), p. 429-435.

Jerman-Blazic, B., A. Gogala and D. Gabrijelcic, "Transparent language
     processing: A solution for internationalization of Internet
     services", The LISA Forum Newsletter, 5 (1996) p. 12-21

Lee, F., "HZ - A Data Format for Exchanging Files of Arbitrarily Mixed
     Chinese and ASCII Characters."  RFC 1843.  Stanford University,
     August 1995.

McCarthy, J.  "Arbitrary Character Sets."  RFC 373.  Stanford
     University, July 1972.




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Draft RFC          Character Set Workshop Report          November 1996

Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part Two:
     Message Header Extensions for Non-ASCII Text."  RFC 1522.
     University of Tennessee, September 1993.

Murai, J., M. Crispin and E. von der Poel. "Japanese Character Encoding
     for Internet Messages." RFC 1468. Keio University & Panda
     Programming, June 1993.

Nussbacher, H.  "Handling of Bi-directional Texts in MIME."  Israeli
     Inter-University, December 1993.

Nussbacher, H. and Y. Bourvine.  "Hebrew Character Encoding for Internet
     Messages."  RFC 1555.  Israeli Inter-University and Hebrew
     University, December 1993.

Ohta, M.  "Character Sets ISO-10646 and ISO-10646-J-1."  RFC 1815.
     Tokyo Institute of Technology, July 1995.

Postel, J. and J. Reynolds.  "File Transfer Protocol (FTP)."  RFC 959.
     ISI, October 1985.

Postel, J. and J. Reynolds.  "Telnet Protocol Specification."  RFC 854.
     ISI, May 1983.

Reynolds, J., and J. Postel,  "Assigned Numbers", RFC 1700,
     ISI, October 1994. p.100-117.

Rose, M. "The Internet Message", Prentice Hall, 1992

Simonsen, K. "Character Mnemonics & Character Sets." RFC 1345.  Rationel
     Almen Planlaegning, June 1992.

Unicode Consortium.  "The Unicode standard, version 2.0.  Reading,
     Mass.: Addison-Wesley Developers Press, 1996

Wei, U., et.al.  "ASCII Printable Characters-Based Chinese Character
     Encoding for Internet Messages."  RFC 1842.  AsiInfo Services,
     Inc., et.al.  August 1995.

Zhu, H., et.al.  "Chinese Character Encoding for Internet Messages."
     RFC 1922.  Tsinghua University, et.al., March 1996














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Draft RFC          Character Set Workshop Report          November 1996

Appendix F: Workshop attendee list

These people were participants on the workshop mailing list.
An * indicates that the person attended the workshop in person.

  Glenn Adams <glenn@spyglass.com>
* Joan Aliprand <joan@unicode.org>
* Harald Alvestrand <Harald.T.Alvestrand@uninett.no>
* Ran Atkinson <ran@cisco.com>
* Bert Bos <bert@w3.org>
* Brian Carpenter <brian@dxcoms.cern.ch>
* Mark Crispin <mrc@panda.com>
  Makx Dekkers <dekkers@pica.nl>
  Robert Elz <kre@munnari.oz.au>
  Patrik Faltstrom <paf@paf.se>
* Zhu Haifeng <zhf@net.tsinghua.edu.cn>
  Keniichi Handa<handa@etl.go.jp>
  Olle Jarnefors <ojarnef@admin.kth.se>
  Borka Jerman-Blazic <borka@e5.ijs.si>
  John Klensin <klensin@mail1.reston.mci.net>
* Larry Masinter <masinter@parc.xerox.com>
* Rick McGowan <Rick_McGowan@next.com>
* Keith Moore <moore+charsets@cs.utk.edu>
* Lisa Moore <lisam@vnet.ibm.com>
  Ruth Moulton <ruth@muswell.demon.co.uk>
* Cecilia Preston <cecilia@well.com>
* Joyce Reynolds <jkrey@isi.edu>
* Keld Simonsen <keld@dkuug.dk>
* Gary Smith <Gary_Smith@oclc.org>
* Peter Svanberg <psv@nada.kth.se>
* Chris Weider <cweider@microsoft.com >
























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Draft RFC          Character Set Workshop Report          November 1996

Appendix G: Author's addresses

Chris Weider
cweider@microsoft.com
Microsoft Corp.
1 Microsoft Way
Redmond, WA 98052
USA

Cecilia Preston
cecilia@well.com
Preston & Lynch
PO Box 8310
Emeryville, CA 94662
USA

Keld Simonsen
Keld@dkuug.dk
DKUUG
Freubjergvey 3
DK-2100 Kxbenhavn X
Danmark

Harald T. Alvestrand
Harald.T.Alvestrand@uninett.no
UNINETT
P.O.Box 6883 Elgeseter
N-7002 TRONDHEIM
NORWAY

Randall Atkinson
rja@cisco.com
cisco Systems
170 West Tasman Drive
San Jose, CA 95134-1706
USA

Mark Crispin
mrc@cac.washington.edu
Networks & Distributed Computing
University of Washington
4545 15th Avenue NE
Seattle, WA  98105-4527












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