SIMPLE WG                                                     M. Isomaki
Internet-Draft                                               E. Leppanen
Expires: April 22, 2005                                            Nokia
                                                        October 22, 2004

   An Extensible Markup Language (XML) Configuration Access Protocol
        (XCAP) Usage for Manipulating Presence Document Contents

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   This document is an Internet-Draft and is subject to all provisions
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Copyright Notice

   Copyright (C) The Internet Society (2004).


   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 on

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   which it builds the overall presence state for the presentity.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Conventions  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Relationship with Presence State Published Using SIP
        PUBLISH  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.   Application Usage ID . . . . . . . . . . . . . . . . . . . .   6
   5.   Structure of Manipulated Presence Information  . . . . . . .   6
   6.   Additional Constraints . . . . . . . . . . . . . . . . . . .   6
   7.   Resource Interdependencies . . . . . . . . . . . . . . . . .   6
   8.   Naming Conventions . . . . . . . . . . . . . . . . . . . . .   6
   9.   Authorization Policies . . . . . . . . . . . . . . . . . . .   6
   10.  Example Document . . . . . . . . . . . . . . . . . . . . . .   6
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .   8
   12.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .   8
     12.1   XCAP Application Usage ID  . . . . . . . . . . . . . . .   8
   13.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .   9
   14.  References . . . . . . . . . . . . . . . . . . . . . . . . .   9
   14.1   Normative References . . . . . . . . . . . . . . . . . . .   9
   14.2   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 [7].  The presence data model has been
   specified in [10].  The data model makes a clean separation between
   person, service and device related information.

   A SIP based mechanism, SIP PUBLISH method, has been defined for
   publishing presence state [4].  Using SIP PUBLISH a Presence User
   Agent (PUA) can publish its view of the presence state, independently
   of and without the need to learn about the states set by other PUAs.
   However, SIP PUBLISH has a limited scope and does not address all the
   requirements for setting presence state.  The main issue is that SIP
   PUBLISH creates a soft state which expires after the negotiated
   lifetime unless it is refreshed.  This makes it unsuitable for cases
   where the state should prevail without active devices capable of
   refreshing the state.

   There are three main use cases where setting of permanent presence
   state that is independent of activeness of any particular device is
   useful.  The first case concerns setting person related state.  The
   presentity would often like to set its presence state even for
   periods when it has no active devices capable of publishing
   available.  Good examples are traveling, vacations and so on.  The
   second case is about setting state for services that are open for
   communication even if the presentity does not have a device running
   that service on-line.  Examples of this kind of services include
   e-mail, MMS and SMS.  In these services the presentity is provisioned
   with a server that makes the service persistently available, at least
   in certain form, and it would be good to be able to advertise this to
   the watchers.  Since it is not realistic to assume that all e-mail,
   MMS or SMS servers can publish presence state on their own (and even
   if this were possible, such state would almost never change), this
   has to be done by some other device - and since the availability of
   the service is not dependent on that device, it would be unpractical
   to require that device to be constantly active just to publish such
   availability.  The third case concerns setting the default state of
   person, any service or any device in the absence of any device
   capable of actively publishing such state.  For instance the
   presentity might want to advertise that his or her voice service is
   right now closed, just to let the watchers to know that such service
   might be open at some point.  Again, this type of default state is
   independent of any particular device, and can be considered to be
   rather persistent.

   Even though SIP PUBLISH remains to be the main way of publishing

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   presence state in SIMPLE based presence systems and is espcially well
   suited for publishing dynamic state (which presence mainly is), it
   needs to be complemented by the mechanism described in this document
   to address the use cases presented above.

   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

   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 Section 4.

2.  Conventions

   In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
   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 described in Figure 1.
   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.

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   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.

               +---------------+         +------------+
               |   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

   The protocol interface between XCAP server and the event state
   compositor is not specified here.

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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 Schema of the presence information (PIDF) is defined in CPIM
   Presence Information Data Format [3].  The PIDF also defines a
   mechanism for extending presence information.  See [8], [9], [11] and
   [12] for currently defined PIDF extensions and their XML Schemas.

   The namespace URI for PIDF is 'urn:ietf:params:xml:ns:pidf'.

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.  Resource Interdependencies

   There are no resource interdependencies beyond the possible
   interdependencies defined in CPIM PIDF [3] and XCAP [2] that need to
   be defined for this application usage.

8.  Naming Conventions

   There are no naming conventions beyond the possible conventions
   defined in CPIM PIDF [3] that need to be defined for this application

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 do not own, but the establishment and indication
   of such policies is outside the scope of this document.

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

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   available via 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) [8] and CIPID: Contact Information in
   Presence Information Data Format [9].

   First, the presence document is created.

   Content type:appliation/pidf+xml

   <?xml version="1.0" encoding="UTF-8"?>
         <presence xmlns="urn:ietf:params:xml:ns:pidf"

           <tuple id="8eg92m">
             <contact priority="0.5"></contact>
             <note>I'm available only by e-mail.</note>

           <tuple id="8eg92n">
             <contact priority="1.0"></contact>
             <note>I'm reading mail a couple of times a week</note>


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   HTTP/1.1 201 Created
   Etag: "xyz"

   Next, the note concerning the e-mail is changed.

   /~~/presence/tuple%5b@id=%228eg92n%22%5d/note HTTP/1.1
   If-Match: "xyz"
   Content type:appliation/xcap-el+xml

   <note>I'm reading mails on Tuesdays and Fridays</note>

   HTTP/1.1 200 OK

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 Digest authentication specified in RFC 2617 [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)

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   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, Hisham Khartabil,
   Aki Niemi, Mikko Lonnfors, Oliver Biot, Alex Audu, Krisztian Kiss,
   Jose Costa-Requena, George Foti and Paul Kyzivat for their comments.

14.  References

14.1  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-ietf-simple-xcap-03 (work in progress), July 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

   [5]  Franks, J., "HTTP Authentication: Basic and Digest Access
        Authentication", RFC 2617, June 1999.

   [6]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

14.2  Informative References

   [7]   Rosenberg, J., "A Presence Event Package for the Session
         Initiation Protocol (SIP)", RFC 3856, August 2004.

   [8]   Schulzrinne, H., "RPID: Rich Presence Extensions to the
         Presence Information Data Format (PIDF)",
         draft-ietf-simple-rpid-03.txt (work in progress), March 2004.

   [9]   Schulzrinne, H., "CIPID: Contact Information in Presence
         Information Data Format",  draft-ietf-simple-cipid-03.txt (work
         in progress), July 2004.

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   [10]  Rosenberg, J., "A Data Model for Presence",
         draft-ietf-simple-presence-data-model-00 (work in progress),
         September 2004.

   [11]  Lonnfors, M., "User Agent Capability Extension to Presence
         Information Data Format (PIDF)",
         draft-ietf-simple-prescaps-ext-01 (work in progress), May 2004.

   [12]  Schulzrinne, H., "Timed Presence Extensions to the Presence
         Information Data Format (PIDF) to Indicate Presence Information
         for Past and Future Time Intervals",
         draft-ietf-simple-future-02 (work in progress), July 2004.

Authors' Addresses

   Markus Isomaki
   P.O.BOX 100
   00045 NOKIA GROUP


   Eva Leppanen
   P.O BOX 785
   33101 Tampere


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