SIMPLE WG M. Isomaki
Internet-Draft E. Leppanen
Expires: December 22, 2004 Nokia
June 23, 2004
An Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) Usage for Manipulating Presence Document Contents
draft-ietf-simple-xcap-pidf-manipulation-usage-01
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Abstract
This document describes a usage of the Extensible Markup Language
(XML) Configuration Access Protocol (XCAP) for manipulating the
contents of Presence Information Data Format (PIDF) based presence
document. It is intended to be used in Session Initiation Protocol
(SIP) based presence systems, where the Event State Compositor can
use the XCAP-manipulated presence document as one of the inputs based
on which it builds the overall presence state for the presentity.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Relationship with Presence State Published Using SIP
PUBLISH . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Application Usage ID . . . . . . . . . . . . . . . . . . . . 5
5. Structure of Manipulated Presence Information . . . . . . . 5
6. Additional Constraints . . . . . . . . . . . . . . . . . . . 6
7. Naming Conventions . . . . . . . . . . . . . . . . . . . . . 6
8. Authorization Policies . . . . . . . . . . . . . . . . . . . 6
9. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Example Document . . . . . . . . . . . . . . . . . . . . . . 6
11. Security Considerations . . . . . . . . . . . . . . . . . . 7
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 8
12.1 XCAP Application Usage ID . . . . . . . . . . . . . . . 8
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
14. Document Change History . . . . . . . . . . . . . . . . . . 8
14.1 Changes since
draft-ietf-simple-xcap-pidf-manipulation-usage-00 . . . 8
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
15.1 Normative References . . . . . . . . . . . . . . . . . . . 8
15.2 Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . 11
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1. Introduction
The Session Initiation Protocol (SIP) for Instant Messaging and
Presence (SIMPLE) specifications allow a user, called a watcher, to
subscribe to another user, called a presentity, in order to learn
their presence information [8].
A SIP based mechanism, SIP PUBLISH method, has been defined for
publishing presence state [4]. However, SIP PUBLISH has a limited
scope and does not address all the requirements for setting presence
state. First, it only allows a single Presence User Agent (PUA) to
publish its view of the presence state, independently of and without
the possibility to learn about the states set by other PUAs. Since
each PUA is typically tied to a single physical device, this means
that it is hard to set device independent presence state using SIP
PUBLISH. Second, SIP PUBLISH creates a soft state which expires
after the negotiated lifetime unless it is refreshed. This makes it
unsuitable for setting state that should prevail even without active
refreshing. There are several use cases where setting of permanent
presence state that can be manipulated independent of any device is
needed. For instance presentity's e-mail (mailto: URI) and WWW
homepage (http: URI) address are this kind of information. Similarly
a user might want to set information, such as a note, that should
constitute his presence information in the absence of any active
publications, i.e. serve as a sort of default presence state.
SIMPLE based presence systems thus require a mechanism to complement
SIP PUBLISH in order to address these use cases.
XML Configuration Access Protocol (XCAP) [2] allows a client to read,
write and modify application configuration data, stored in XML format
on a server. The data has no expiration time, so it must be
explicitly inserted and deleted. The protocol allows multiple
clients to manipulate the data, provided that they are authorized to
do so. XCAP is already used in SIMPLE based presence systems for
manipulation of presence lists and presence authorization policies.
This makes XCAP an ideal choice for doing device independent presence
document manipulation.
This document defines an XML Configuration Access Protocol (XCAP)
application usage for manipulating the contents of presence document.
Presence Information Document Format (PIDF) [3] is used as the
presence document format, since event state compositor already has to
support it, as it is used in SIP PUBLISH.
Section 3 describes in more detail how the presence document
manipulated with XCAP is related to soft state publishing done with
SIP PUBLISH.
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XCAP requires application usages to standardize several pieces of
information, including a unique application usage ID (AUID), and an
XML schema for the manipulated data. These are specified starting
from the Section 4.
2. Conventions
In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
and 'OPTIONAL' are to be interpreted as described in RFC 2119 [1]
and indicate requirement levels for compliant implementations.
Comprehensive terminology of presence and event state publishing is
provided in Session Initiation Protocol (SIP) Extension for Event
State Publication [4].
3. Relationship with Presence State Published Using SIP PUBLISH
The framework for publishing presence state is introduced in SIMPLE
Presence Publication Requirements [11]. A central part of the
framework is the event state compositor element whose function is to
compose presence information received from several sources into a
single coherent presence document.
The presence state manipulated with XCAP can be seen as one of the
information sources for the compositor to be combined with the soft
state information published using SIP PUBLISH. This is illustrated
in Figure 1. It is expected that in the normal case there can be
several PUAs publishing their separate views with SIP PUBLISH, but
only a single XCAP manipulated presence document. As shown in the
figure, there can be multiple XCAP clients (for instance in different
physical devices) manipulating the same document on the XCAP server,
but this still creates only one input to the event state compositor.
As individual inputs the presence states set by XCAP and SIP PUBLISH
are completely separated and it is not possible to directly
manipulate the state set by one mechanism with the other. How the
compositor treats XCAP based inputs with respect to SIP PUBLISH based
inputs is a matter of compositor policy, which is beyond the scope of
this specification. Since the SIP PUBLISH specification already
mandates the compositor to be able to construct the overall presence
state from multiple inputs which may contain non-orthogonal (or in
some ways even conflicting) information, this XCAP usage does not
impose any new requirements on the compositor functionality. One
reasonable compositor policy is that the XCAP manipulated presence
document is used as the default presence state in absence of any soft
state set by SIP PUBLISH, and the soft state augments or overrides
the default state.
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+---------------+ +------------+
| Event State | | Presence |<-- SIP SUBSCRIBE
| Compositor +---------+ Agent |--> SIP NOTIFY
| | | (PA) |
+-------+-------+ +------------+
^ ^ ^
| | |
| | | +---------------+
+--------+ | +-------| XCAP server |
| | +-------+-------+
| | ^ ^
| SIP Publish | | XCAP |
| | | |
+--+--+ +--+--+ +-------+ +-------+
| PUA | | PUA | | XCAP | | XCAP |
| | | | | client| | client|
+-----+ +-----+ +-------+ +-------+
Figure 1: Framework for Presence Publishing and Event State
Composition
The protocol interface between XCAP server and the event state
compositor is not specified here.
4. Application Usage ID
XCAP requires application usages to define a unique application usage
ID (AUID) in either the IETF tree or a vendor tree. This
specification defines the 'pidf-manipulation' AUID within the IETF
tree, via the IANA registration in the Section 12.
5. Structure of Manipulated Presence Information
The XML [7] format of the presence information (PIDF) is defined in
CPIM Presence Information Data Format [3]. The PIDF also defines a
mechanism for extending presence information.
The PIDF defines the presence information to consist of the root
element 'presence'. The 'presence' element can contain 'tuple'
elements which contain a mandatory 'status' element, a communication
mean specific presence attribute and other markups. Additionally,
the presence information can contain other presentity level
information outside tuples.
The namespace URI for PIDF is 'urn:ietf:params:xml:ns:pidf'.
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6. Additional Constraints
There are no constraints on the document beyond those described in
the XML schemas (PIDF and its extensions) and in the description of
CPIM PIDF [3].
7. Naming Conventions
There are no naming conventions beyond the possible conventions
defined in CPIM PIDF [3] that need to be defined for this application
usage.
8. Authorization Policies
This application usage does not modify the default XCAP authorization
policy, which allows only a user (owner) to read, write or modify
their own documents. A server can allow privileged users to modify
documents that they do not own, but the establishment and indication
of such policies is outside the scope of this document.
9. XML Schema
The XML schema definition for the presence information can be found
from CPIM PIDF [3]. PIDF based presence information can contain
extensions as e.g., RPID: Rich Presence Extensions to the Presence
Information Data Format (PIDF) which XML schema is defined in [9].
10. Example Document
The section provides an example of presence document provided by an
XCAP Client to an XCAP Server. The presence document illustrates the
situation where a (human) presentity has left for vacation, and
before that has set his presence information such that he is only
available via cellular phone and e-mail. In the absence of any
published soft state information, this would be the sole input to the
compositor forming the presence document. The example document
contain PIDF extensions specified in RPID: Rich Presence Extensions
to the Presence Information Data Format (PIDF) [9] and CIPID: Contact
Information in Presence Information Data Format [10].
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:es="urn:ietf:params:xml:ns:pidf:status:rpid-status"
xmlns:et="urn:ietf:params:xml:ns:pidf:rpid-tuple"
xmlns:ci="urn:ietf:params:xml:ns:pidf:cipid"
entity="pres:someone@example.com">
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<tuple id="18x765">
<status>
<basic>open</basic>
<es:activities>
<es:activity>Vacation</es:activity>
</es:activities>
</status>
<et:class>auth-A</et:class>
<et:contact-type>presentity</et:contact-type>
<ci:homepage>http://www.example.com/~someone</ci:homepage>
<timestamp>2004-02-06T16:49:29Z</timestamp>
<note>I'm available only by e-mail and GSM phone.</note>
</tuple>
<tuple id="8eg92m">
<status>
<basic>open</basic>
<es:idle/>
</status>
<et:class>auth-1</et:class>
<et:contact-type>service</et:contact-type>
<note>cellphone</note>
<contact priority="0.5">tel:+358506767</contact>
</tuple>
<tuple id="8eg92n">
<status>
<basic>open</basic>
<es:idle/>
</status>
<et:class>auth-1</et:class>
<et:contact-type>service</et:contact-type>
<note>I'm reading mail a couple of times a week</note>
<contact priority="1.0">mailto:someone@example.com</contact>
</tuple>
</presence>
11. Security Considerations
A presence document may contain information that is highly sensitive.
Its delivery to watchers needs to happen strictly according to the
relevant authorization policies. It is also important that only
authorized clients are able to manipulate the presence information.
The XCAP base specification mandates that all XCAP servers MUST
implement HTTP Authentication: Basic and Digest Access Authentication
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[5]. Furthermore, XCAP servers MUST implement HTTP over TLS [6]. It
is recommended that administrators of XCAP servers use an HTTPS URI
as the XCAP root services URI, so that the digest client
authentication occurs over TLS. By using these means, XCAP client
and server can ensure the confidentiality and integrity of the XCAP
presence document manipulation operations, and that only authorized
clients are allowed to perform them.
12. IANA Considerations
There is an IANA consideration associated with this specification.
12.1 XCAP Application Usage ID
This section registers a new XCAP Application Usage ID (AUID)
according to the IANA procedures defined in [2].
Name of the AUID: pidf-manipulation
Description: Pidf-manipulation application usage defines how XCAP is
used to manipulate the contents of PIDF based presence documents.
13. Acknowledgements
The authors would like to thank Jonathan Rosenberg, Aki Niemi, Mikko
Lonnfors, Oliver Biot, Alex Audu, Krisztian Kiss, Jose Costa-Requena
and George Foti for their comments.
14. Document Change History
14.1 Changes since draft-ietf-simple-xcap-pidf-manipulation-usage-00
The following changes were made since the last version:
o Editorial changes and corrections based on review comments.
o References updated.
o SIP SUBSCRIBE/NOTIFY arrows in the figure 1 corrected.
o Change history added.
15. References
15.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
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Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)",
draft-ietf-simple-xcap-02 (work in progress), February 2004.
[3] Sugano, H., "CPIM presence information data format",
draft-ietf-impp-cpim-pidf-08, May 2003.
[4] Niemi, A., "An Event State Publication Extension for Session
Initiation Protocol (SIP)", draft-ietf-sip-publish-04.txt, May
2004.
[5] Franks, J., "HTTP Authentication: Basic and Digest Access
Authentication", RFC 2617, June 1999.
[6] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
15.2 Informative References
[7] Bray, T., "Extensible Markup Language (XML) 1.0 (Second
edition)", W3C REC REC-xml-20001006, October 2000.
[8] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions
for Presence", draft-ietf-simple-presence-10.txt (work in
progress), January 2003.
[9] Schulzrinne, H., "RPID: Rich Presence Extensions to the
Presence Information Data Format (PIDF)",
draft-ietf-simple-rpid-03.txt (work in progress), March 2004.
[10] Schulzrinne, H., "CIPID: Contact Information in Presence
Information Data Format", draft-ietf-simple-cipid-01.txt (work
in progress), March 2004.
[11] Campbell, B., "SIMPLE Presence Publication Requirements",
draft-ietf-simple-publish-reqs-00 (work in progress), February
2003.
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Authors' Addresses
Markus Isomaki
Nokia
Itamerenkatu 11-13
00180 Helsinki
Finland
Phone:
EMail: markus.isomaki@nokia.com
Eva Leppanen
Nokia
P.O BOX 785
Tampere
Finland
Phone:
EMail: eva-maria.leppanen@nokia.com
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