draft-ietf-imapext-i18n-14.txt   draft-ietf-imapext-i18n-15.txt 
Network Working Group Chris Newman Network Working Group Chris Newman
Internet-Draft Sun Microsystems Internet-Draft Sun Microsystems
Intended Status: Proposed Standard Arnt Gulbrandsen Intended Status: Proposed Standard Arnt Gulbrandsen
Oryx Mail Systems GmhH Oryx Mail Systems GmhH
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
December 8, 2007 February 1, 2008
Internet Message Access Protocol Internationalization Internet Message Access Protocol Internationalization
draft-ietf-imapext-i18n-14.txt draft-ietf-imapext-i18n-15.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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This Internet-Draft expires in February 2008. This Internet-Draft expires in August 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
Internet Message Access Protocol (IMAP) version 4rev1 has basic Internet Message Access Protocol (IMAP) version 4rev1 has basic
support for non-ASCII characters in mailbox names and search support for non-ASCII characters in mailbox names and search
substrings. It also supports non-ASCII message headers and content substrings. It also supports non-ASCII message headers and content
encoded as specified by Multipurpose Internet Mail Extensions encoded as specified by Multipurpose Internet Mail Extensions
(MIME). This specification defines a collection of IMAP extensions (MIME). This specification defines a collection of IMAP extensions
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which improve international support including comparator negotiation which improve international support including comparator negotiation
for search, sort and thread, language negotiation for international for search, sort and thread, language negotiation for international
error text, and translations for namespace prefixes. error text, and translations for namespace prefixes.
Table of Contents Table of Contents
1. Conventions Used in this Document . . . . . . . . . . . . . . 2 1. Conventions Used in this Document . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3 3. LANGUAGE Extension . . . . . . . . . . . . . . . . . . . . . 3
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3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 3.5 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
4. I18NLEVEL=1 and I18NLEVEL=2 Extensions . . . . . . . . . . . 7 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions . . . . . . . . . . . 7
4.1 Introduction and Overview . . . . . . . . . . . . . . . . . . 8 4.1 Introduction and Overview . . . . . . . . . . . . . . . . . . 8
4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 . . . 4.2 Requirements common to both I18NLEVEL=1 and I18NLEVEL=2 . . .
4.3 I18NLEVEL=1 Extension Requirements . . . . . . . . . . . . . 8 4.3 I18NLEVEL=1 Extension Requirements . . . . . . . . . . . . . 8
4.4 I18NLEVEL=2 Extension Requirements . . . . . . . . . . . . . 8 4.4 I18NLEVEL=2 Extension Requirements . . . . . . . . . . . . . 8
4.5 Compatibility Notes 4.5 Compatibility Notes
4.6 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9 4.6 Comparators and Charsets . . . . . . . . . . . . . . . . . . 9
4.7 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9 4.7 COMPARATOR Command . . . . . . . . . . . . . . . . . . . . . 9
4.8 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10 4.8 COMPARATOR Response . . . . . . . . . . . . . . . . . . . . . 10
4.9 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10 4.9 BADCOMPARATOR Response Code . . . . . . . . . . . . . . . . .
4.10 Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 10
5. Other IMAP Internationalization Issues . . . . . . . . . . . 11 5. Other IMAP Internationalization Issues . . . . . . . . . . . 11
5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11 5.1 UTF-8 Userids and Passwords . . . . . . . . . . . . . . . . . 11
5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11 5.2 UTF-8 Mailbox Names . . . . . . . . . . . . . . . . . . . . . 11
5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11 5.3 UTF-8 Domains, Addresses and Mail Headers . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Relevant Standards for i18n IMAP Implementations . . . . . . 13 9. Relevant Standards for i18n IMAP Implementations . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . 13 Normative References . . . . . . . . . . . . . . . . . . . . 13
Informative References . . . . . . . . . . . . . . . . . . . 14 Informative References . . . . . . . . . . . . . . . . . . . 14
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Intellectual Property and Copyright Statements . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . 16
Conventions Used in This Document Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The formal syntax use the Augmented Backus-Naur Form (ABNF) The formal syntax use the Augmented Backus-Naur Form (ABNF)
[RFC4234] notation including the core rules defined in Appendix A. [RFC4234] notation including the core rules defined in Appendix A.
The UTF8-related productions are defined in [RFC3629].
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The UTF8-related productions are defined in [RFC3629].
In examples, "C:" and "S:" indicate lines sent by the client and In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. If a single "C:" or "S:" label applies to server respectively. If a single "C:" or "S:" label applies to
multiple lines, then the line breaks between those lines are for multiple lines, then the line breaks between those lines are for
editorial clarity only and are not part of the actual protocol editorial clarity only and are not part of the actual protocol
exchange. exchange.
2. Introduction 2. Introduction
This specification defines two IMAP4rev1 [RFC3501] extensions to This specification defines two IMAP4rev1 [RFC3501] extensions to
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done with a separate mechanism such as the proposed METADATA done with a separate mechanism such as the proposed METADATA
extension (see [METADATA]). extension (see [METADATA]).
3.1 LANGUAGE Extension Requirements 3.1 LANGUAGE Extension Requirements
IMAP servers that support this extension MUST list the keyword IMAP servers that support this extension MUST list the keyword
LANGUAGE in their CAPABILITY response as well as in the greeting LANGUAGE in their CAPABILITY response as well as in the greeting
CAPABILITY data. CAPABILITY data.
A server that advertises this extension MUST use the language "i- A server that advertises this extension MUST use the language "i-
default" as described in [RFC2277] as its default language until
another supported language is negotiated by the client. A server
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default" as described in [RFC2277] as its default language until
another supported language is negotiated by the client. A server
MUST include "i-default" as one of its supported languages. MUST include "i-default" as one of its supported languages.
Clients and servers that support this extension MUST also support Clients and servers that support this extension MUST also support
the NAMESPACE extension [RFC2342]. the NAMESPACE extension [RFC2342].
The LANGUAGE command is valid in all states. Clients are urged to The LANGUAGE command is valid in all states. Clients are urged to
issue LANGUAGE before authentication, since some servers send issue LANGUAGE before authentication, since some servers send
valuable user information as part of authentication (e.g. "password valuable user information as part of authentication (e.g. "password
is correct, but expired"). is correct, but expired"). If a security layer (such as SASL or
TLS) is subsequently negotiated by the client, it MUST re-issue the
LANGUAGE command in order to make sure that no previous active
attack (if any) on LANGUAGE negotiation has effect on subsequent
error messages. (See Section 7 for a more detailed explanation of
the attack.)
3.2 LANGUAGE Command 3.2 LANGUAGE Command
Arguments: Optional language range arguments. Arguments: Optional language range arguments.
Response: A possible LANGUAGE response (see section 3.3). Response: A possible LANGUAGE response (see section 3.3).
A possible NAMESPACE response (see section 3.4). A possible NAMESPACE response (see section 3.4).
Result: OK - Command completed Result: OK - Command completed
NO - Could not complete command NO - Could not complete command
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effect immediately after the LANGUAGE response. effect immediately after the LANGUAGE response.
If the command fails, the server continues to return human-readable If the command fails, the server continues to return human-readable
responses in the language it was previously using. responses in the language it was previously using.
The special "default" language range argument indicates a request to The special "default" language range argument indicates a request to
use a language designated as preferred by the server administrator. use a language designated as preferred by the server administrator.
The preferred language MAY vary based on the currently active user. The preferred language MAY vary based on the currently active user.
If a language range does not match a known language tag exactly but If a language range does not match a known language tag exactly but
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does match a language by the rules of [RFC4647], the server MUST does match a language by the rules of [RFC4647], the server MUST
send an untagged LANGUAGE response indicating the language selected. send an untagged LANGUAGE response indicating the language selected.
If there aren't any arguments, the server SHOULD send an untagged If there aren't any arguments, the server SHOULD send an untagged
LANGUAGE response listing the languages it supports. If the server LANGUAGE response listing the languages it supports. If the server
is unable to enumerate the list of languages it supports it MAY is unable to enumerate the list of languages it supports it MAY
return a tagged NO response to the enumeration request. return a tagged NO response to the enumeration request.
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< The server defaults to using English i-default responses until < The server defaults to using English i-default responses until
the user explicitly changes the language. > the user explicitly changes the language. >
C: A001 LOGIN KAREN PASSWORD C: A001 LOGIN KAREN PASSWORD
S: A001 OK LOGIN completed S: A001 OK LOGIN completed
< Client requested MUL language, which no server supports. > < Client requested MUL language, which no server supports. >
C: A002 LANGUAGE MUL C: A002 LANGUAGE MUL
S: A002 NO Unsupported language MUL S: A002 NO Unsupported language MUL
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< Once the client changes the language, all responses will be in < Once the client changes the language, all responses will be in
that language starting after the LANGUAGE response. Note that that language starting after the LANGUAGE response. Note that
this includes the NAMESPACE response. Because RFCs are in US- this includes the NAMESPACE response. Because RFCs are in US-
ASCII, this document uses an ASCII transcription rather than ASCII, this document uses an ASCII transcription rather than
UTF-8 text, e.g. ue in the word "ausgefuehrt" > UTF-8 text, e.g. ue in the word "ausgefuehrt" >
C: C001 LANGUAGE DE C: C001 LANGUAGE DE
S: * LANGUAGE (DE) S: * LANGUAGE (DE)
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Mailboxen/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: C001 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< If a server does not support the requested primary language, < If a server does not support the requested primary language,
responses will continue to be returned in the current language responses will continue to be returned in the current language
the server is using. > the server is using. >
C: D001 LANGUAGE FR C: D001 LANGUAGE FR
S: D001 NO Diese Sprache ist nicht unterstuetzt S: D001 NO Diese Sprache ist nicht unterstuetzt
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C: D002 LANGUAGE DE-IT C: D002 LANGUAGE DE-IT
S: * LANGUAGE (DE-IT) S: * LANGUAGE (DE-IT)
S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/"))(("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Mailboxen/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: D002 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
C: D003 LANGUAGE "default" C: D003 LANGUAGE "default"
S: * LANGUAGE (DE) S: * LANGUAGE (DE)
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S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt S: D003 OK Sprachwechsel durch LANGUAGE-Befehl ausgefuehrt
< Server does not speak French, but does speak English. User < Server does not speak French, but does speak English. User
speaks Canadian French and Canadian English. > speaks Canadian French and Canadian English. >
C: E001 LANGUAGE FR-CA EN-CA C: E001 LANGUAGE FR-CA EN-CA
S: * LANGUAGE (EN) S: * LANGUAGE (EN)
S: E001 OK Now speaking English S: E001 OK Now speaking English
3.3 LANGUAGE Response 3.3 LANGUAGE Response
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string, containing the modified UTF-7 [RFC3501] encoded translation string, containing the modified UTF-7 [RFC3501] encoded translation
of the namespace prefix. It is the responsibility of the client to of the namespace prefix. It is the responsibility of the client to
convert between the namespace prefix and the translation of the convert between the namespace prefix and the translation of the
namespace prefix when presenting mailbox names to the user. namespace prefix when presenting mailbox names to the user.
In this example a server supports the IMAP4 NAMESPACE command. It In this example a server supports the IMAP4 NAMESPACE command. It
uses no prefix to the user's Personal Namespace, a prefix of "Other uses no prefix to the user's Personal Namespace, a prefix of "Other
Users" to its Other Users' Namespace and a prefix of "Public Users" to its Other Users' Namespace and a prefix of "Public
Folders" to its only Shared Namespace. Since a client will often Folders" to its only Shared Namespace. Since a client will often
display these prefixes to the user, the server includes a display these prefixes to the user, the server includes a
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translation of them that can be presented to the user. translation of them that can be presented to the user.
C: A001 LANGUAGE DE-IT C: A001 LANGUAGE DE-IT
S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION" S: * NAMESPACE (("" "/")) (("Other Users/" "/" "TRANSLATION"
("Andere Ben&APw-tzer/"))) (("Public Folders/" "/" ("Andere Ben&APw-tzer/"))) (("Public Folders/" "/"
"TRANSLATION" ("Gemeinsame Mailboxen/"))) "TRANSLATION" ("Gemeinsame Postf&AM8-cher/")))
S: A001 OK LANGUAGE-Befehl ausgefuehrt S: A001 OK LANGUAGE-Befehl ausgefuehrt
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3.5 Formal Syntax 3.5 Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC4234] rules
from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the from IMAP4rev1 [RFC3501], IMAP4 Namespace [RFC2342], Tags for the
Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected Identifying Languages [RFC4646], UTF-8 [RFC3629] and Collected
Extensions to IMAP4 ABNF [RFC4466]. Extensions to IMAP4 ABNF [RFC4466].
command-any =/ language-cmd command-any =/ language-cmd
; LANGUAGE command is valid in all states ; LANGUAGE command is valid in all states
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resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR resp-text = ["[" resp-text-code "]" SP ] UTF8-TEXT-CHAR
*(UTF8-TEXT-CHAR / "[") *(UTF8-TEXT-CHAR / "[")
; After the server is changed to a language other than ; After the server is changed to a language other than
; i-default, this resp-text rule replaces the resp-text ; i-default, this resp-text rule replaces the resp-text
; rule from [RFC3501]. ; rule from [RFC3501].
UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4 UTF8-TEXT-CHAR = %x20-5A / %x5C-7E / UTF8-2 / UTF8-3 / UTF8-4
; UTF-8 excluding 7-bit control characters and "[" ; UTF-8 excluding 7-bit control characters and "["
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4. I18NLEVEL=1 and I18NLEVEL=2 Extensions 4. I18NLEVEL=1 and I18NLEVEL=2 Extensions
4.1 Introduction and Overview 4.1 Introduction and Overview
IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to IMAP4rev1 [RFC3501] includes the SEARCH command which can be used to
locate messages matching criteria including human-readable text. locate messages matching criteria including human-readable text.
The SORT extension [SORT] to IMAP allows the client to ask the The SORT extension [SORT] to IMAP allows the client to ask the
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server to determine the order of messages based on criteria server to determine the order of messages based on criteria
including human-readable text. These mechanisms require the ability including human-readable text. These mechanisms require the ability
to support non-English search and sort functions. to support non-English search and sort functions.
Section 4 defines two IMAP extensions for internationalizing IMAP Section 4 defines two IMAP extensions for internationalizing IMAP
SEARCH, SORT and THREAD [SORT] using the comparator framework SEARCH, SORT and THREAD [SORT] using the comparator framework
[RFC4790]. [RFC4790].
The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use The I18NLEVEL=1 extension updates SEARCH/SORT/THREAD to use
i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2 i;unicode-casemap comparator, as defined in [UCM]. See Sections 4.2
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"BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the "BODY", "CC", "FROM", "SUBJECT", "TEXT", "TO" and "HEADER". If the
server also advertises the "SORT" extension, then the active server also advertises the "SORT" extension, then the active
comparator applies to the following SORT keys: "CC", "FROM", comparator applies to the following SORT keys: "CC", "FROM",
"SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT, "SUBJECT" and "TO". If the server advertises THREAD=ORDEREDSUBJECT,
then the active comparator applies to the ORDEREDSUBJECT threading then the active comparator applies to the ORDEREDSUBJECT threading
algorithm. If the server advertises THREAD=REFERENCES, then the algorithm. If the server advertises THREAD=REFERENCES, then the
active comparator applies to the subject field comparisons done by active comparator applies to the subject field comparisons done by
REFERENCES threading algorithm. Future extensions may choose to REFERENCES threading algorithm. Future extensions may choose to
apply the active comparator to their SEARCH keys. apply the active comparator to their SEARCH keys.
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For SORT and THREAD, the pre-processing necessary to extract the For SORT and THREAD, the pre-processing necessary to extract the
base subject text from a Subject header occurs prior to the base subject text from a Subject header occurs prior to the
application of a comparator. application of a comparator.
A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
implement the i;unicode-casemap comparator, as defined in [UCM]. implement the i;unicode-casemap comparator, as defined in [UCM].
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A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST A server that advertises I18NLEVEL=1 or I18NLEVEL=2 extension MUST
support UTF-8 as a SEARCH charset. support UTF-8 as a SEARCH charset.
4.3 I18NLEVEL=1 Extension Requirements 4.3 I18NLEVEL=1 Extension Requirements
IMAP servers that satisfies all requirements specified in sections An IMAP server that satisfies all requirements specified in sections
4.2 and 4.6 (and doesn't support/advertise any other I18NLEVEL=<n> 4.2 and 4.6 (and doesn't support/advertise any other I18NLEVEL=<n>
extension, where n > 1) MUST list the keyword I18NLEVEL=1 in their extension, where n > 1) MUST list the keyword I18NLEVEL=1 in its
CAPABILITY data once IMAP enters authenticated state, and MAY list CAPABILITY data once IMAP enters the authenticated state, and MAY
that keyword in other states. list that keyword in other states.
4.4 I18NLEVEL=2 Extension Requirements 4.4 I18NLEVEL=2 Extension Requirements
IMAP servers that satisfies all requirements specified in sections IMAP server that satisfies all requirements specified in sections
4.2, 4.4, 4.6-4.9 (and doesn't support/advertise any other 4.2, 4.4, 4.6-4.10 (and doesn't support/advertise any other
I18NLEVEL=<n> extension, where n > 2) MUST list the keyword I18NLEVEL=<n> extension, where n > 2) MUST list the keyword
I18NLEVEL=2 in their CAPABILITY data once IMAP enters authenticated I18NLEVEL=2 in its CAPABILITY data once IMAP enters the
state, and MAY list that keyword in other states. authenticated state, and MAY list that keyword in other states.
A server that advertises this extension MUST implement the A server that advertises this extension MUST implement the
i;unicode-casemap comparator, as defined in [UCM]. It MAY implement i;unicode-casemap comparator, as defined in [UCM]. It MAY implement
other comparators from the IANA registry established by [RFC4790]. other comparators from the IANA registry established by [RFC4790].
See also section 4.5 of this document. See also section 4.5 of this document.
A server that advertises this extension SHOULD use i;unicode-casemap A server that advertises this extension SHOULD use i;unicode-casemap
as the default comparator. (Note that i;unicode-casemap is the as the default comparator. (Note that i;unicode-casemap is the
default comparator for I18NLEVEL=1, but not necessarily the default default comparator for I18NLEVEL=1, but not necessarily the default
for I18NLEVEL=2.) The selection of the default comparator MAY be for I18NLEVEL=2.) The selection of the default comparator MAY be
adjustable by the server administrator, and MAY be sensitive to the adjustable by the server administrator, and MAY be sensitive to the
current user. Once the IMAP connection enters authenticated state, current user. Once the IMAP connection enters authenticated state,
the default comparator MUST remain static for the remainder of that the default comparator MUST remain static for the remainder of that
connection. connection.
Note that since SEARCH uses the substring operation, IMAP servers Note that since SEARCH uses the substring operation, IMAP servers
can only implement collations that offer the substring operation can only implement collations that offer the substring operation
(see [RFC4790 section 4.2.2). Since SORT uses ordering operation (see [RFC4790 section 4.2.2). Since SORT uses ordering operation
(and by implication equality), IMAP servers which advertise the SORT (and by implication equality), IMAP servers which advertise the SORT
extension can only implement collations that offer all three extension can only implement collations that offer all three
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operations (see [RFC4790] sections 4.2.2-4). operations (see [RFC4790] sections 4.2.2-4).
If the active collation does not provide the operations needed by an If the active collation does not provide the operations needed by an
IMAP command, the server MUST respond with a tagged BAD. IMAP command, the server MUST respond with a tagged BAD.
4.5 Compatibility Notes 4.5 Compatibility Notes
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Several server implementations deployed prior to the publication of Several server implementations deployed prior to the publication of
this specification comply with I18NLEVEL=1 (see section 4.3), but do this specification comply with I18NLEVEL=1 (see section 4.3), but do
not advertise that. Other legacy servers use the i;ascii-casemap not advertise that. Other legacy servers use the i;ascii-casemap
(see [RFC4790]) comparator. (see [RFC4790]) comparator.
There is no good way for a client to know which comparator that a There is no good way for a client to know which comparator that a
legacy server uses. If the client has to assume the worst, it may legacy server uses. If the client has to assume the worst, it may
end up doing expensive local operations to obtain i;unicode-casemap end up doing expensive local operations to obtain i;unicode-casemap
comparisons even though the server implements it. comparisons even though the server implements it.
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(a) MIME encoding (for example see [RFC2047] for headers and (a) MIME encoding (for example see [RFC2047] for headers and
[RFC2045] for body parts) MUST be removed in the texts being [RFC2045] for body parts) MUST be removed in the texts being
collated. collated.
If MIME encoding removal fails for a message (e.g., a body part If MIME encoding removal fails for a message (e.g., a body part
of the message has an unsupported Content-Transfer-Encoding, of the message has an unsupported Content-Transfer-Encoding,
uses characters not allowed by the Content-Transfer-Encoding, uses characters not allowed by the Content-Transfer-Encoding,
etc.), the collation of this message is undefined by this etc.), the collation of this message is undefined by this
specification, and is handled in an implementation-dependent specification, and is handled in an implementation-dependent
Internet-draft February 2008
manner. manner.
(b) The decoded text from (a) MUST be converted to the charset (b) The decoded text from (a) MUST be converted to the charset
expected by the active comparator. expected by the active comparator.
(c) For the substring operation: (c) For the substring operation:
If step (b) failed (e.g., the text is in an unknown charset, If step (b) failed (e.g., the text is in an unknown charset,
contains a sequence which is not valid according in that contains a sequence which is not valid according in that
Internet-draft December 2007
charset, etc.), the original decoded text from (a) (i.e., charset, etc.), the original decoded text from (a) (i.e.,
before the charset conversion attempt) is collated using the before the charset conversion attempt) is collated using the
i;octet comparator (see [RFC4790]). i;octet comparator (see [RFC4790]).
If step (b) was successful, the converted text from (b) is If step (b) was successful, the converted text from (b) is
collated according to the active comparator. collated according to the active comparator.
For the ordering operation: For the ordering operation:
All strings that were successfully converted by step (b) are All strings that were successfully converted by step (b) are
separated from all strings that failed step (b). Strings in separated from all strings that failed step (b). Strings in
each group are collated independently. All strings that fail each group are collated independently. All strings successfully
step (b) are collated (after applying step (a)) using the converted by step (b) are then validated by the active
i;octet comparator (see [RFC4790]). All strings successfully comparator. Strings that pass validation are collated using the
converted by step (b) are collated using the active comparator. active comparator. All strings that either fail step (b) or fail
the active collation's validity operation are collated (after
applying step (a)) using the i;octet comparator (see [RFC4790]).
The resulting sorted list is produced by appending all collated The resulting sorted list is produced by appending all collated
"failed" strings after all strings collated using the active "failed" strings after all strings collated using the active
comparator. comparator.
<<Add an example>>
Example: The following example demonstrates ordering of 4
different strings using i;unicode-casemap [UCM] comparator.
Strings are represented using hexadecimal notation used by
ABNF [RFC4234].
(1) %xD0 %xC0 %xD0 %xBD %xD0 %xB4 %xD1 %x80 %xD0 %xB5
%xD0 %xB9 (labeled with charset=UTF-8)
(2) %xD1 %x81 %xD0 %x95 %xD0 %xA0 %xD0 %x93 %xD0 %x95
%xD0 %x99 (labeled with charset=UTF-8)
(3) %xD0 %x92 %xD0 %xB0 %xD1 %x81 %xD0 %xB8 %xD0 %xBB
%xD0 %xB8 %xFF %xB9 (labeled with charset=UTF-8)
(4) %xE1 %xCC %xC5 %xCB %xD3 %xC5 %xCA (labeled with
charset=KOI8-R)
Step (b) will convert string # 4 to the following
sequence of octets (in UTF-8):
Internet-draft February 2008
%xD0 %x90 %xD0 %xBB %xD0 %xB5 %xD0 %xBA %xD1 %x81 %xD0
%xB5 %xD0 %xB9
and will reject strings (1) and (3), as they contain
octets not allowed in charset=UTF-8.
After that, using the i;unicode-casemap collation,
string (4) will collate before string (2). Using the
i;octet collation on the original strings, string (3)
will collate before string (1). So the final ordering
is as follows: (4) (2) (3) (1).
If the substring operation (e.g., IMAP SEARCH) of the active If the substring operation (e.g., IMAP SEARCH) of the active
comparator returns the "undefined" result (see section 4.2.3 of comparator returns the "undefined" result (see section 4.2.3 of
[RFC4790]) for either the text specified in the SEARCH command or [RFC4790]) for either the text specified in the SEARCH command or
the message text, then the operation is repeated on the result of the message text, then the operation is repeated on the result of
step (a) using the i;octet comparator. step (a) using the i;octet comparator.
The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate The ordering operation (e.g., IMAP SORT and THREAD) SHOULD collate
the following together: strings encoded using unknown or invalid the following together: strings encoded using unknown or invalid
character encodings, strings in unrecognized charsets, and invalid character encodings, strings in unrecognized charsets, and invalid
skipping to change at page 12, line 4 skipping to change at page 12, line 43
Response: A possible COMPARATOR response (see Section 4.8). Response: A possible COMPARATOR response (see Section 4.8).
Result: OK - Command completed Result: OK - Command completed
NO - No matching comparator found NO - No matching comparator found
BAD - arguments invalid BAD - arguments invalid
The COMPARATOR command is valid in authenticated and selected The COMPARATOR command is valid in authenticated and selected
states. states.
The COMPARATOR command is used to determine or change the active The COMPARATOR command is used to determine or change the active
Internet-draft December 2007
comparator. When issued with no arguments, it results in a comparator. When issued with no arguments, it results in a
COMPARATOR response indicating the currently active comparator. COMPARATOR response indicating the currently active comparator.
When issued with one or more comparator argument, it changes the When issued with one or more comparator argument, it changes the
active comparator as directed. (If more than one installed active comparator as directed. (If more than one installed
comparator is matched by an argument, the first argument wins.) The comparator is matched by an argument, the first argument wins.) The
COMPARATOR response lists all matching comparators if more than one COMPARATOR response lists all matching comparators if more than one
matches the specified patterns. matches the specified patterns.
The argument "default" refers to the server's default comparator. The argument "default" refers to the server's default comparator.
Internet-draft February 2008
Otherwise each argument is an collation specification as defined in Otherwise each argument is an collation specification as defined in
the Internet Application Protocol Comparator Registry [RFC4790]. the Internet Application Protocol Comparator Registry [RFC4790].
< The client requests activating a Czech comparator if possible, < The client requests activating a Czech comparator if possible,
or else a generic international comparator which it considers or else a generic international comparator which it considers
suitable for Czech. The server picks the first supported suitable for Czech. The server picks the first supported
comparator. > comparator. >
C: A001 COMPARATOR "cz;*" i;basic C: A001 COMPARATOR "cz;*" i;basic
S: * COMPARATOR i;basic S: * COMPARATOR i;basic
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Contents: The active comparator. Contents: The active comparator.
An optional list of available matching comparators An optional list of available matching comparators
The COMPARATOR response occurs as a result of a COMPARATOR command. The COMPARATOR response occurs as a result of a COMPARATOR command.
The first argument in the comparator response is the name of the The first argument in the comparator response is the name of the
active comparator. The second argument is a list of comparators active comparator. The second argument is a list of comparators
which matched any of the arguments to the COMPARATOR command and is which matched any of the arguments to the COMPARATOR command and is
present only if more than one match is found. present only if more than one match is found.
4.9 Formal Syntax 4.9 BADCOMPARATOR response code
This response code SHOULD be returned as a result of server failing
an IMAP command (returning NO), when the server knows that none of
the specified comparators match the requested comparator(s).
4.10 Formal Syntax
The following syntax specification inherits ABNF [RFC4234] rules The following syntax specification inherits ABNF [RFC4234] rules
from IMAP4rev1 [RFC3501], and Internet Application Protocol from IMAP4rev1 [RFC3501], and Internet Application Protocol
Comparator Registry [RFC4790]. Comparator Registry [RFC4790].
command-auth =/ comparator-cmd command-auth =/ comparator-cmd
resp-text-code =/ "BADCOMPARATOR" / "BADMATCH" resp-text-code =/ "BADCOMPARATOR"
comparator-cmd = "COMPARATOR" *(SP comp-order-quoted) comparator-cmd = "COMPARATOR" *(SP comp-order-quoted)
response-payload =/ comparator-data response-payload =/ comparator-data
Internet-draft December 2007
comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "(" comparator-data = "COMPARATOR" SP comp-sel-quoted [SP "("
comp-id-quoted *(SP comp-id-quoted) ")"] comp-id-quoted *(SP comp-id-quoted) ")"]
Internet-draft February 2008
comp-id-quoted = astring comp-id-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-id rule from [RFC4790] ; follows the collation-id rule from [RFC4790]
comp-order-quoted = astring comp-order-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
; follows the collation-order rule from [RFC4790] ; follows the collation-order rule from [RFC4790]
comp-sel-quoted = astring comp-sel-quoted = astring
; Once any literal wrapper or quoting is removed, this ; Once any literal wrapper or quoting is removed, this
skipping to change at page 14, line 4 skipping to change at page 14, line 49
that. However, such userids cannot be used as part of email that. However, such userids cannot be used as part of email
addresses. addresses.
5.2 UTF-8 Mailbox Names 5.2 UTF-8 Mailbox Names
The modified UTF-7 mailbox naming convention described in section The modified UTF-7 mailbox naming convention described in section
5.1.3 of RFC 3501 is best viewed as an transition from the status 5.1.3 of RFC 3501 is best viewed as an transition from the status
quo in 1996 when modified UTF-7 was first specified. At that time, quo in 1996 when modified UTF-7 was first specified. At that time,
there was widespread unofficial use of local character sets such as there was widespread unofficial use of local character sets such as
ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant ISO-8859-1 and Shift-JIS for non-ASCII mailbox names, with resultant
Internet-draft December 2007
non-interoperability. non-interoperability.
The requirements in section 5.1 of RFC 3501 are very important if The requirements in section 5.1 of RFC 3501 are very important if
Internet-draft February 2008
we're ever going to be able to deploy UTF-8 mailbox names. Servers we're ever going to be able to deploy UTF-8 mailbox names. Servers
are encouraged to enforce them. are encouraged to enforce them.
5.3 UTF-8 Domains, Addresses and Mail Headers 5.3 UTF-8 Domains, Addresses and Mail Headers
There is now an IETF standard for Internationalizing Domain Names in There is now an IETF standard for Internationalizing Domain Names in
Applications [RFC3490]. While IMAP clients are free to support this Applications [RFC3490]. While IMAP clients are free to support this
standard, an argument can be made that it would be helpful to simple standard, an argument can be made that it would be helpful to simple
clients if the IMAP server could perform this conversion (the same clients if the IMAP server could perform this conversion (the same
argument would apply to MIME header encoding [RFC2047]). However, argument would apply to MIME header encoding [RFC2047]). However,
skipping to change at page 15, line 5 skipping to change at page 15, line 50
more difficult to interpret. This is not a new attack as the error more difficult to interpret. This is not a new attack as the error
messages themselves are subject to active attack. Clients MUST re- messages themselves are subject to active attack. Clients MUST re-
issue the LANGUAGE command once a security layer is active, so this issue the LANGUAGE command once a security layer is active, so this
does not impact subsequent protocol operations. does not impact subsequent protocol operations.
LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 extensions use the UTF-8 LANGUAGE, I18NLEVEL=1 and I18NLEVEL=2 extensions use the UTF-8
charset, thus the security considerations for UTF-8 [RFC3629] are charset, thus the security considerations for UTF-8 [RFC3629] are
relevent. However, neither uses UTF-8 for identifiers so the most relevent. However, neither uses UTF-8 for identifiers so the most
serious concerns do not apply. serious concerns do not apply.
Internet-draft December 2007
8. Acknowledgements 8. Acknowledgements
Internet-draft February 2008
The LANGUAGE extension is based on a previous Internet draft by Mike The LANGUAGE extension is based on a previous Internet draft by Mike
Gahrns, a substantial portion of the text in that section was Gahrns, a substantial portion of the text in that section was
written by him. Many people have participated in discussions about written by him. Many people have participated in discussions about
an IMAP Language extension in the various fora of the IETF and an IMAP Language extension in the various fora of the IETF and
Internet working groups, so any list of contributors is bound to be Internet working groups, so any list of contributors is bound to be
incomplete. However, the authors would like to thank Andrew McCown incomplete. However, the authors would like to thank Andrew McCown
for early work on the original proposal, John Myers for suggestions for early work on the original proposal, John Myers for suggestions
regarding the namespace issue, along with Jutta Degener, Mark regarding the namespace issue, along with Jutta Degener, Mark
Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo and Martin Crispin, Mark Pustilnik, Larry Osterman, Cyrus Daboo, Martin Duerst,
Duerst for their many suggestions that have been incorporated into Timo Sirainen, Ben Campbell and Magnus Nystrom for their many
this document. suggestions that have been incorporated into this document.
Initial discussion of the I18NLEVEL=2 extension involved input from Initial discussion of the I18NLEVEL=2 extension involved input from
Mark Crispin and other participants of the IMAP Extensions WG. Mark Crispin and other participants of the IMAP Extensions WG.
9. Relevant Standards for i18n IMAP Implementations 9. Relevant Standards for i18n IMAP Implementations
This is a non-normative list of standards to consider when This is a non-normative list of standards to consider when
implementing i18n aware IMAP software. implementing i18n aware IMAP software.
o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this o The LANGUAGE and I18NLEVEL=2 extensions to IMAP (this
skipping to change at page 16, line 4 skipping to change at page 16, line 51
(currently only relevant to IMAP clients). (currently only relevant to IMAP clients).
o The UTF-8 charset [RFC3629]. o The UTF-8 charset [RFC3629].
o The IETF policy on Character Sets and Languages [RFC2277]. o The IETF policy on Character Sets and Languages [RFC2277].
Normative References Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, "IETF Policy on Character Sets and [RFC2277] Alvestrand, "IETF Policy on Character Sets and
Internet-draft December 2007
Languages", BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
Internet-draft February 2008
[RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998. [RFC2342] Gahrns, Newman, "IMAP4 Namespace", RFC 2342, May 1998.
[RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
[RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646", [RFC3629] Yergeau, "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003. STD 63, RFC 3629, November 2003.
[RFC4234] Crocker, Overell, "Augmented BNF for Syntax [RFC4234] Crocker, Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, Brandenburg Specifications: ABNF", RFC 4234, Brandenburg
skipping to change at page 16, line 34 skipping to change at page 17, line 32
[RFC4466] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF", [RFC4466] Melnikov, Daboo, "Collected Extensions to IMAP4 ABNF",
RFC 4466, Isode Ltd., April 2006. RFC 4466, Isode Ltd., April 2006.
[RFC4646] Philips, Davis, "Tags for Identifying Languages", BCP 47, [RFC4646] Philips, Davis, "Tags for Identifying Languages", BCP 47,
RFC 4646, September 2006. RFC 4646, September 2006.
[RFC4647] Philips, Davis, "Matching of Language Tags", BCP 47, RFC [RFC4647] Philips, Davis, "Matching of Language Tags", BCP 47, RFC
4647, September 2006. 4647, September 2006.
[RFC4790] Newman, Duerst, Gulbrandsen, "Internet Application [RFC4790] Newman, Duerst, Gulbrandsen, "Internet Application
Protocol Comparator Registry", RFC 4790, February 2007 Protocol Comparator Registry", RFC 4790, February 2007.
[SORT] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS [SORT] Crispin, M. and K. Murchison, "INTERNET MESSAGE ACCESS
PROTOCOL - SORT AND THREAD EXTENSION", draft-ietf- PROTOCOL - SORT AND THREAD EXTENSION", draft-ietf-
imapext-sort-19 (work in progress), November 2006. imapext-sort-19 (work in progress), November 2006.
[UCM] Crispin, "i;unicode-casemap - Simple Unicode Collation [UCM] Crispin, "i;unicode-casemap - Simple Unicode Collation
Algorithm", RFC 5051, October 2007. Algorithm", RFC 5051, October 2007.
[RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions [RFC2045] Freed, Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies", RFC (MIME) Part One: Format of Internet Message Bodies", RFC
2045, November 1996. 2045, November 1996.
[RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part [RFC2047] Moore, "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", RFC Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996. 2047, November 1996.
Informative References Informative References
Internet-draft December 2007
[RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word [RFC2231] Freed, Moore, "MIME Parameter Value and Encoded Word
Extensions: Character Sets, Languages, and Extensions: Character Sets, Languages, and
Internet-draft February 2008
Continuations", RFC 2231, November 1997. Continuations", RFC 2231, November 1997.
[RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain [RFC3490] Faltstrom, Hoffman, Costello, "Internationalizing Domain
Names in Applications (IDNA)", RFC 3490, March 2003. Names in Applications (IDNA)", RFC 3490, March 2003.
[RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for [RFC3492] Costello, "Punycode: A Bootstring encoding of Unicode for
Internationalized Domain Names in Applications (IDNA)", Internationalized Domain Names in Applications (IDNA)",
RFC 3492, March 2003. RFC 3492, March 2003.
[METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap- [METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap-
annotatemore-11 (work in progress), November 2006. annotatemore-12 (work in progress), December 2007.
[IMAP-EAI] Resnick, Newman, "IMAP Support for UTF-8", draft-ietf- [IMAP-EAI] Resnick, Newman, "IMAP Support for UTF-8", draft-ietf-
eai-imap-utf8 (work in progress), May 2006. eai-imap-utf8 (work in progress), May 2006.
Authors' Addresses Authors' Addresses
Chris Newman Chris Newman
Sun Microsystems Sun Microsystems
3401 Centrelake Dr., Suite 410 3401 Centrelake Dr., Suite 410
Ontario, CA 91761 Ontario, CA 91761
skipping to change at page 18, line 5 skipping to change at page 19, line 5
Fax: +49 89 4502 9758 Fax: +49 89 4502 9758
Alexey Melnikov Alexey Melnikov
Isode Limited Isode Limited
5 Castle Business Village, 36 Station Road, 5 Castle Business Village, 36 Station Road,
Hampton, Middlesex, TW12 2BX, UK Hampton, Middlesex, TW12 2BX, UK
Email: Alexey.Melnikov@isode.com Email: Alexey.Melnikov@isode.com
Internet-draft December 2007 Internet-draft February 2008
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be found on the procedures with respect to rights in RFC documents can be found
skipping to change at page 18, line 33 skipping to change at page 19, line 33
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). This document is subject to Copyright (C) The IETF Trust (2008). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
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