SIMPLE WG M. Isomaki
Internet-Draft Nokia Research Center
Expires: November 1, 2004 E. Leppanen
Nokia
May 3, 2004
An Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) Usage for Manipulating Presence Document Contents
draft-ietf-simple-xcap-pidf-manipulation-usage-00
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Copyright (C) The Internet Society (2004). All Rights Reserved.
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 mainly 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 Unique ID . . . . . . . . . . . . . . . . . . . 5
5. Structure of Published Presence Information . . . . . . . . 5
6. Computed Data . . . . . . . . . . . . . . . . . . . . . . . 6
7. Additional Constraints . . . . . . . . . . . . . . . . . . . 6
8. Naming Conventions . . . . . . . . . . . . . . . . . . . . . 6
9. Authorization Policies . . . . . . . . . . . . . . . . . . . 6
10. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 6
11. Example Document . . . . . . . . . . . . . . . . . . . . . . 6
12. Security Considerations . . . . . . . . . . . . . . . . . . 7
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . 8
13.1 XCAP Application Usage ID . . . . . . . . . . . . . . . 8
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
15.1 Normative References . . . . . . . . . . . . . . . . . . . 8
15.2 Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . 10
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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 [7], in order to learn
their presence information [8].
A SIP based mechanism, SIP PUBLISH method, has been defined for
publishing presence state [12]. 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 note, that should
constitute his presence 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 an application unique 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 [12].
3. Relationship with presence state published using SIP PUBLISH
The framework for publishing presence state is introduced in [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
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 exact protocol interface between XCAP server and the event state
compositor is not specified here. The obvious requirement is that
such interface exists, and that the presentity indeed has an XCAP
server supporting the usage defined in this specification provisioned
for him.
4. Application Unique 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 13.
5. Structure of Published Presence Information
The XML [6] format of the presence information (PIDF) is defined in
[3] and its extensions. The PIDF defines the presence information to
consist of the root element 'presence' including 'tuples' 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 defined in [3].
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6. Computed Data
There are no computed data on the document beyond those described in
the schema.
7. Additional Constraints
There are no constraints on the document beyond those described in
the XML schemas and [3].
8. Naming Conventions
There are no naming conventions beyond the possible conventions
defined in [3] that need to be defined for this application usage.
9. 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 don't own, but the establishment and indication
of such policies is outside the scope of this document.
10. XML Schema
The XML schema definition for the presence information can be found
from [3] and its extensions.
11. Example Document
The following example document illustrates the situation where the
(human) presentity has left for vacation, and before that has set his
presence state 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
[9] and [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">
<tuple id="18x765">
<status>
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<basic>open</basic>
<es:activity>Vacation</es:activity>
</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>
12. Security Considerations
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.
XCAP base specification mandates that all XCAP servers MUST implement
HTTP digest [4]. Furthermore, XCAP servers MUST implement HTTP over
TLS [5]. 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
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presence document manipulation operations, and that only authorized
clients are allowed to perform them.
13. IANA Considerations
There are an IANA consideration associated with this specification.
13.1 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 presence documents in Session
Initiation Protocol (SIP) based presence systems.
14. Acknowledgements
The authors would like to thank Jonathan Rosenberg, Aki Niemi,
Krisztian Kiss, Jose Costa-Requena and George Foti for their
comments.
15. References
15.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)",
draft-rosenberg-simple-xcap-02 (work in progress), February
2004.
[3] Sugano, H., "CPIM presence information data format",
draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003.
[4] Franks, J., "HTTP Authentication: Basic and Digest Access
Authentication", RFC 2617, June 1999.
[5] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
15.2 Informative References
[6] Bray, T., "Extensible Markup Language (XML) 1.0 (Second
edition)", W3C REC REC-xml-20001006, October 2000.
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[7] Day, M., "A model for presence and instant messaging", RFC
2778, February 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: Extension to the
Presence Information Data Format",
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.
[12] Niemi, A., "An Event State Publication Extension for Session
Initiation Protocol (SIP)", draft-ietf-sip-publish-03.txt
(work in progress), February 2004.
Authors' Addresses
Markus Isomaki
Nokia Research Center
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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