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Versions: (draft-lonnofors-simple-partial-notify) 00 01 02 03 04 05 06 07 08 09 10 RFC 5263

SIMPLE WG                                                    M. Lonnfors
Internet-Draft                                          J. Costa-Requena
Expires: October 19, 2004                                    E. Leppanen
                                                            H. Khartabil
                                                                   Nokia
                                                          April 20, 2004


  Session Initiation Protocol (SIP) extension for Partial Notification
                        of Presence Information
                  draft-ietf-simple-partial-notify-02

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 19, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   A Presence service can have constraints for delivering presence
   information to devices with low data processing capabilities, small
   display, and limited battery power. Limitations can also be caused by
   the interface between the terminal and the network, i.e. radio links
   with high latency and low bandwidth. This memo presents a solution
   that aids in reducing the impact of those constrains and to increase
   transport efficiency, by introducing a mechanism called partial



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   notification.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Introduction to the partial notification mechanism . . . . . .  4
     3.1   Basic presence agent operation . . . . . . . . . . . . . .  4
     3.2   Operation with partial notification  . . . . . . . . . . .  4
   4.  Client and server operations . . . . . . . . . . . . . . . . .  5
     4.1   Content-type for partial notifications . . . . . . . . . .  5
     4.2   Watcher generation of SUBSCRIBE requests . . . . . . . . .  5
     4.3   Presence agent processing of SUBSCRIBE requests  . . . . .  6
     4.4   Presence agent generation of partial notifications . . . .  6
     4.5   Watcher processing of NOTIFY requests  . . . . . . . . . .  7
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
     6.1   Confidentiality  . . . . . . . . . . . . . . . . . . . . . 13
     6.2   Message Integrity and Authenticity . . . . . . . . . . . . 13
     6.3   Outbound Authentication  . . . . . . . . . . . . . . . . . 13
     6.4   Replay Prevention  . . . . . . . . . . . . . . . . . . . . 14
     6.5   Denial of Service Attacks Against Third Parties  . . . . . 14
     6.6   Denial Of Service Attacks Against Servers  . . . . . . . . 14
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   8.1   Normative references . . . . . . . . . . . . . . . . . . . . 14
   8.2   Informative references . . . . . . . . . . . . . . . . . . . 15
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
       Intellectual Property and Copyright Statements . . . . . . . . 17






















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1.  Introduction

   A presence event package for the Session Initiation Protocol (SIP)
   [4] allow users ('watchers') to subscribe to other users'
   ('presentities') presence information. The presence information is
   composed of multiple pieces of data that are delivered to the
   watcher. The size of the presence information document can be large
   (i.e. the presence document can contain an arbitrary number of
   elements called presence tuples that convey data). As specified in
   RFC2778 [3] and presence event package for the SIP [4] a Presence
   Agent (PA) always delivers in presence notifications all the presence
   data that has been authorized for a certain watcher. This is done
   regardless of what presence data has changed compared to last
   notification. It may not be reasonable to send the complete presence
   information over low bandwidth and high latency links when only part
   of the presence information has actually changed. This may end up
   degrading the presence service and causing bad perception at the
   watcher side.

   There are some mechanisms, such as signaling compression (SigComp)
   [10] and content indirection [9] that can be used to help in this
   problem. However these solutions set additional requirements on basic
   network functionalities such as security. Some of the existing
   solutions enforce certain requirements on the network and terminals
   for supporting compression mechanism, while other solutions require
   having a specific server to store the requested presence information
   until the terminal fetches it using another protocol (e.g. HTTP) and,
   therefore, increases possible security concerns.

   This draft presents a solution to problems described above, called
   partial notifications.

   In general, the partial notification approach means that the presence
   server delivers to the watchers only those parts of the presence
   information that have changed compared to the presence information
   sent in the previous notifications. This reduces the amount of data
   that needs be transported over the network.

   This mechanism utilizes the presence event package for SIP [4] and
   the partial PIDF MIME type [2].

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.




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   This document makes use of the vocabulary defined in RFC2778 [3],
   RFC3265 [7], presence event package for the SIP [4], and partial PIDF
   format [2].

3.  Introduction to the partial notification mechanism

   This chapter briefly introduces the regular functionality of the
   presence service, and gives an overview of the partial notification
   solution. This section is information in nature and it does not
   provide any normative statements.

3.1  Basic presence agent operation

   The presence service normally operates so that a watcher sends a SIP
   SUBSCRIBE request targeted to the presentity. The request is routed
   to the presence agent where the presentity's presence information is
   stored. The SUBSCRIBE request can include an Accept header field that
   indicates the supported content types.

   The presence agent receives the SUBSCRIBE request and if there is no
   Accept header indicating the supported content types or the Accept
   header contains the default PIDF content type, the PA will generate
   presence notifications using the default PIDF format [6]. The PIDF
   document can contain one or multiple tuples and presence document
   level information. The tuples include a set of elements defined in
   RFC2778 [3] for representing the presence information. NOTIFY
   requests, built according to RFC 3265 [7], carry in the body of the
   request a presence document containing presence information. Unless
   otherwise specified, the presence document contains the full state
   corresponding to the presence status of the presentity, as
   determinated by the PA local policy and authorization rules.

3.2  Operation with partial notification

   The partial notification mechanism enables the watcher to request
   those parts of the presence information that have changed since the
   last notifications was sent. The presence agent will send only the
   changed presence information since the last notification.

   A watcher that wants to receive partial notifications according to
   this specification, creates a SIP SUBSCRIBE request similar to that
   of a regular presence subscription. However, the SIP SUBSCRIBE
   request contains an Accept header field whose value contains the
   "application/pidf-partial+xml" tag. Besides the Accept header field,
   there is no other difference between a regular presence subscription
   and a subscription requesting partial notifications.

   When the presence agent receives the subscription, it examines the



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   Accept header field value and decides to use the partial
   notifications mechanism specified in this memo. The presence agent
   builds NOTIFY requests that contain the Accept header field set to
   "application/pidf-partial+xml". The first NOTIFY request that
   contains presence information will contain a full presence document.
   This is identified by the "state" attribute set to "full" in the XML
   presence document. Subsequent NOTIFY requests will contain partial
   notifications, identified by the "state" attribute set to "partial"
   in the XML presence document.

   This means that if a partial notification contains new tuples (tuples
   which have new tuple ids compared to the full presence document) they
   are added to the local full presence document. If it contains tuples
   which have existing tuple ids it means that those tuples are updated.
   If "removed" element in the XML document contains existing tuple ids
   it means that those tuples are removed. The watcher updates the local
   copy accordingly. This behavior is described in detail in Section 4.

   Partial notifications, within the scope of this document, apply only
   to <tuple> level XML elements and all possible elements that are
   contained in these elements, i.e., tuples are considered to be atomic
   data elements. This means that, if a notification contains an update
   to an existing tuple, the updated tuple replaces the existing one.
   The SIP presence event package [4] provides instructions to process
   all the data elements which are located outside <tuple> elements.
   This typically means that every notification will include all those
   XML elements (for example the <note> element).

4.  Client and server operations

   This document assumes, that unless otherwise specified in this
   document, the regular watcheer and presence agent behavior is applied
   as defined in the SIP presence event package [4].

4.1  Content-type for partial notifications

   Entities supporting the partial notification extension described in
   this document MUST support the 'application/pidf-partial+xml'
   content-type specified in the PIDF extension for partial presence
   [2].

4.2  Watcher generation of SUBSCRIBE requests

   A SUBSCRIBE request can be used to negotiate the preferred content
   type to be used in the notifications. The Accept header field is used
   for this purpose as specified in RFC2161 [5]. When a watcher wants to
   allow the presence agent to send partial notifications the watcher
   MUST include an Accept header field in a SUBSCRIBE request. The value



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   of the Accept header file MUST contain 'application/pidf-partial+xml'
   (in addition to 'application/pid+xml' required by the SIP  presence
   event package [4]). The watcher MAY include a "q" parameter to each
   accept value to indicate the weight of the accept value, i.e., the
   most preferred accept value.

4.3  Presence agent processing of SUBSCRIBE requests

   The presence agent receives the subscriptions from watchers and
   generates the notifications according to SIP presence event package
   [4]. If the watcher has indicated the supported content types in the
   Accept header field of the SUBSCRIBE request, the presence agent
   compares the values included in the Accept header field with the
   supported ones, and decides which one to use. If the watcher has
   decisionindicated preferred accept values by means of "q" parameters,
   the presence agent SHOULD base the decision on those preferences,
   unless otherwise indicated by the presence agent local policy.

4.4  Presence agent generation of partial notifications

   If the presence agent decides to send notifications according to this
   specification that include a presence document, the presence agent
   MUST build a presence document according to the PIDF extension for
   Partial Presence [2] and MUST set the Content-Type header field to
   the value 'application/pidf-partial+xml'.

   Tuple ids are used to match tuples across subsequent notifications.
   Presence agent MUST use the same tuple ids for tuples which are
   identical between subsequent notifications and MUST allocate
   different tuple ids for tuples which are different from previously
   sent tuples. Presence agents MUST keep tuple ids consistent until the
   next full state presence documentis delivered. The decision on
   whether tuple ids are the same or different is left up to PA's local
   policy.

   Once a subscription is accepted and installed, the PA MUST deliver
   the full state of the presence information in the first notification
   that contains a presence document. In this case, the PA MUST set the
   "state" attribute of the <presence> element in the presence document
   to value "full". PA MUST also include a "version" attribute and it
   MUST be initialized to value zero.

   When the PA generates subsequent notifications, PA SHOULD include
   only those tuples that have changed compared to the previous
   notification. It is up to the PA local policy to determine what is
   considered as a change to the previous state. When the presence
   document does not include a full presence state, the PA MUST set the
   "state" attribute value of the <presence> element to "partial".



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   The PA MUST ensure that all tuple ids used in the presence document
   are unique. This applies to all tuple ids in <tuple> elements and in
   <t_id> elements under the <removed> element.

   The PA SHOULD construct the partial presence document according to
   the following logic:

   o  The PA MUST construct the presence information according to the
      Presence event package [4], with the exception that only the
      changed tuples are included in the presence document. The PA MUST
      also add all newly created tuples, if any,  to the presence
      information.

   o  The PA MUST include a "version" and "state" attributes in the
      presence document. The PA MUST increment the version number by one
      compared to the earlier delivered presence document to the watcher
      associated with a certain subscription.

   o  When there are changes (e.g. in the authorization) which lead to
      removal of tuples from the previously delivered presence
      information the PA MUST construct a partial notification document
      that lists the tuple ids of the removed tuples in the "removed"
      element.

   o  The PA MUST include  all the presence information outside the
      <tuple> elements in each notification, i.e., all the notifications
      which convey partial presence documents MUST always have that
      data.

   In case the PA receives a subscription refresh or termination request
   from existing subscription (with any value in the Expires header
   field) and the PA decides to include a body into the following NOTIFY
   request the PA MUST build a NOTIFY request that contains a full
   presence document (i.e. the attribute "state" is set to "full" and
   the attribute "version" is set to value 0).

4.5  Watcher processing of NOTIFY requests

   If the PA decided to use the partial notifications, then the watcher
   will receive a NOTIFY request with the Content-Type header field
   value set to 'application/pidf-partial+xml' .

   The watcher will receive the full presence document in the first
   notification. In this case, the "state" attribute of the <presence>
   element in the presence document is set to the value "full". When the
   watcher receives the full presence document it MUST perform the
   following actions:




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   o  The watcher MUST discard all previously received presence
      information from that particular presentity in the context of
      current subscription.

   o  The watcher MUST initialize an internal version counter, related
      to the particular presentity or subscription, to the value of
      "version" attributeof the <presence> element included in the
      presence document.

   o  The watcher MUST store the values of all tuple ids together with
      the content received in the notification. This constitutes the
      watcher's local copy of the full presence document.

   o  If the presence document contains a <removed> element the watcher
      MUST ignore the content of that element.

   When the watcher receives subsequent notifications and the notifier
   has not changed the used content type, and the "state" attribute of
   the <presence> element includes the value "partial", the watcher MUST
   construct the presence information according to the following logic:

   o  The watcher MUST compare the "version" attribute of the <presence>
      element with the version information of a previously received
      presence document. If the version number is incremented by one,
      the watcher MUST continue handling the content present in the
      notification.

   o  The watcher MUST compare the tuple ids with the tuple ids received
      in previous notifications. If a tuple id in the current
      notification matches an existing tuple id, the existing tuple is
      replaced with the newly received tuple. If the tuple id does not
      match any tuple received in the earlier notifications, the watcher
      MUST store it as a new tuple.

   o  The watcher MUST remove from the local storage those tuples whose
      tuple ids are listed in the "removed" element of the presence
      document.

   o  Tuples whose tuple ids are not listed in the presence document
      included in the NOTIFY remain unchanged

   If the watcher receives a presence document whose "version" attribute
   value higher by more than one with the locally stored value the
   watcher assumes that one or more NOTIFYs were lost. The watcher
   SHOULD either refresh the subscription in order to receive a full
   presence document or terminate the subscription. If the watcher
   receives a presence document with the "state" attribute set to
   "partial" and the "version" attribute value is equal or lower than



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   the one received in the presence docment of a previous notification,
   it is considered a PA failure and the watcher SHOULD discard the
   document without further processing.

   All the information located outside the <tuple> element must be
   processed as specified in the SIP presence event package [4] i.e.,
   the watcher MUST replace the existing data with data received in the
   latest notification.

   If the PA changes the content type used in notifications within the
   existing subscription the watcher MUST discard all the previously
   received presence information from that particular presentity and
   process the new content as specified for that content type.

5.  Examples

   The following message flow shows an example applying the partial
   notifications mechanism.

   A watcher sends a SUBSCRIBE request declaring support for the default
   presence format ('application/pidf+xml)) and the for the partial
   notification ('application/pidf-partial+xml') in the Accept header
   field value. The watcher uses the "q" parameter to set the preference
   for receiving partial notifications. The PA accepts the subscription
   and, based on the "q" parameter value, selects to send partial
   notifications in NOTIFY requests. The first NOTIFY request includes
   the full state of presence information represented in the
   'application/pidf-partial+xml' content type. The following
   notifications only include the delta of the presence information from
   the previous NOTIFY request.

       Watcher                   Presence Agent                  PUA
            | F1 SUBSCRIBE              |                         |
            |-------------------------->|                         |
            | F2 200 OK                 |                         |
            |<--------------------------|                         |
            | F3 NOTIFY                 |                         |
            |<--------------------------|                         |
            | F4 200 OK                 |                         |
            |-------------------------->|                         |
            |                           |                         |
            |                           |   Update presence       |
            |                           |<----------------------- |
            |                           |                         |
            | F5 NOTIFY                 |                         |
            |<--------------------------|                         |
            | F6 200 OK                 |                         |
            |-------------------------->|                         |



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         Message Details

      F1 SUBSCRIBE   watcher->example.com server

            SUBSCRIBE sip:resource@example.com SIP/2.0
            Via: SIP/2.0/TCP watcherhost.example.com;
              branch=z9hG4bKnashds7
            To: sip:resource@example.com
            From: <sip:watcher@somewhere.com> ;tag=xfg9
            Call-ID: 2010@watcherhost.example.com
            CSeq: 17766 SUBSCRIBE
            Max-Forwards: 70
            Event: presence
            Accept: application/pidf+xml;q=0.3,
              application/pidf-partial+xml;q=1
            Contact: sip:user@watcherhost.example.com
            Expires: 600

      The PA accepts the subscription and generates a 200 OK
      response to the SUBSCRIBE request

         F2 200 OK   example.com server->watcher

            SIP/2.0 200 OK
            Via: SIP/2.0/TCP watcherhost.example.com;
              branch=z9hG4bKnashds7
              ;received=192.0.2.1
            To: <sip:resource@example.com>;tag=ffd2
            From: <sip:watcher@somewhere.com>;tag=xfg9
                  Call-ID: 2010@watcherhost.example.com
            CSeq: 17766 SUBSCRIBE
            Event: presence
            Expires: 600
            Contact: sip:server.example.com

          The PA, based on the "q" parameter value in the Accept
          header of the SUBSCRIBE request (F1), decides to  use
          partial notifications. The PA creates a first NOTIFY
          request that includes a partical notification document that
          contains the full state.

         F3 NOTIFY  example.com server-> watcher

            NOTIFY sip:user@watcherhost.example.com SIP/2.0
            Via: SIP/2.0/TCP server.example.com;
              branch=z9hG4bKna998sk
            To: <sip:watcher@somewhere.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2



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            Call-ID: 2010@watcherhost.example.com
            Event: presence
            Subscription-State: active;expires=599
            Max-Forwards: 70
            CSeq: 8775 NOTIFY
            Contact: sip:server.example.com
            Content-Type: application/pidf-partial+xml
            Content-Length: [replace with real content length]

            <?xml version="1.0" encoding="UTF-8"?>
            <pidf-part:presence xmlns="urn:ietf:params:xml:ns:pidf"
                xmlns:pidf-part="urn:ietf:params:xml:ns:pidf-partial"
                entity="pres:someone@example.com" version="0"
                state="full">

              <tuple id="sg89ae">
                <status><basic>open</basic>
                </status>
                <contact priority="0.8">tel:09012345678
                </contact>
              </tuple>

              <tuple id="cg231jcr">
                <status><basic>open</basic>
                </status>
                <contact priority="1.0">
                      im:pep@example.com</contact>
              </tuple>
              <tuple id="r1230d">
                <status><basic>closed</basic>
                </status>
                <contact priority="0.9">
                      sip:pep@example.com</contact>
              </tuple>
            </pidf-part:presence>

         F4 200 OK watcher-> example.com server

            SIP/2.0 200 OK
            Via: SIP/2.0/TCP server.example.com;
              branch=z9hG4bKna998sk
              ;received=192.0.2.2
            To: <sip:watcher@somewhere.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8775 NOTIFY

            At a later time, the presentity's presence information



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            changes: the tuple id "cg231jcr" has changed its
            status, a new tuple id "wsqw798jcr" is added and the
            tuple id "r1230d" is deleted from the presence
            document. The PA generates a NOTIFY request
            that includes a partial presence document that includes
            the deleted tuple

      F5 NOTIFY example.com server -> watcher

            NOTIFY sip:user@watcherhost.example.com SIP/2.0
            Via: SIP/2.0/TCP server.example.com;
              branch=z9hG4bKna998sl
            To: <sip:watcher@somewhere.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8776 NOTIFY
            Event: presence
            Subscription-State: active;expires=543
            Max-Forwards: 70
            Contact: sip:server.example.com
            Content-Type: application/pidf-partial+xml
            Content-Length: [replace with real content length]

            <?xml version="1.0" encoding="UTF-8"?>
            <pidf-part:presence xmlns="urn:ietf:params:xml:ns:pidf"
                xmlns:pidf-part="urn:ietf:params:xml:ns:pidf-partial"
               entity="pres:someone@example.com" version="1"
               state="partial">

              <tuple id="cg231jcr">
                <status><basic>closed</basic>
                </status>
                <contact priority="1.0">
                      im:pep@example.com</contact>
                <note xml:lang="en">This is an update of existing
                tuple sent in previous notification</note>
              </tuple>

              <tuple id="wsqw798jcr">
                <status><basic>open</basic>
                </status>
                <contact priority="0.4">
                      im:mac@hut.com</contact>
                <note xml:lang="en">This is a completely new
                tuple not sent in previous notification</note>
              </tuple>

           <pidf-part:removed><pidf-part:t_id>r1230d</pidf-part:t_id>



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           </pidf-part:removed>

            </pidf-part:presence>

         F6 200 OK watcher-> example.com server

            SIP/2.0 200 OK
            Via: SIP/2.0/TCP server.example.com;
              branch=z9hG4bKna998sl
             ;received=192.0.2.2
            To: <sip:watcher@somewhere.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8776 NOTIFY



6.  Security Considerations

   This specification relies on presence event package for the SIP [4]
   and it does not introduce any new protocol functionality. Partial
   notifications can reveal information what has changed compared to
   last time when notification was sent. This can make it easier for
   eavesdropper to know what kind of changes are happening in
   presentity's presence information. However, same information can be
   found if presence event package is used with baseline PIDF [6]. Thus,
   this specification does not introduce any new security considerations
   compared to presence event package for the SIP [4].

   Presence related security considerations are extensively discussed in
   the presence event package for the SIP [4] and all those identified
   security consideration apply to this document as well. Issues
   described in the presence event package for the SIP [4] are briefly
   reviewed below.

6.1  Confidentiality

   Confidentiality considerations identified in the presence event
   package for the SIP [4] apply here without any changes.

6.2  Message Integrity and Authenticity

   Message Integrity and Authenticity identified in the presence event
   package for the SIP [4] apply here without any changes.

6.3  Outbound Authentication

   Outbound Authentication considerations identified in the presence



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   event package for the SIP [4] apply here without any changes.

6.4  Replay Prevention

   Replay Prevention considerations identified in the presence event
   package for the SIP [4] apply here without any changes.

6.5  Denial of Service Attacks Against Third Parties

   Denial of Service Attacks Against Third Parties considerations
   identified in the presence event package for the SIP [4] apply here
   without any changes.

6.6  Denial Of Service Attacks Against Servers

   Denial Of Service Attacks Against Servers considerations identified
   in the presence event package for the SIP [4] apply here without any
   changes.

7.  Acknowledgements

   The authors would like to thank Jyrki Aarnos, Jonathan Rosenberg,
   Dean Willis, Kriztian Kiss, Juha Kalliokulju, Miguel Garcia, Anders
   Kristensen, Yannis Pavlidis, Ben Cambell, and Tim Moran for their
   valuable comments.

8.  References

8.1  Normative references

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Lonnfors, M., Khartabil, H. and E. Leppanen, "Presence
        Information Data Format (PIDF) Extension for Partial Presence",
        draft-ietf-simple-partial-pidf-format-01 (work in progress),
        January 2004.

   [3]  Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
        Instant Messaging", RFC 2778, February 2000.

   [4]  Rosenberg, J., "A Presence Event Package for the Session
        Initiation Protocol (SIP)",  draft-ietf-simple-presence-10 (work
        in progress), January 2003.

   [5]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.



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   [6]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and
        J. Peterson, "CPIM presence information data format",
        draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003.

   [7]  Roach, A., "SIP-Specific Event Notification", RFC 3265, June
        2002.

8.2  Informative references

   [8]   Rosenberg, J., "A Watcher Information Event Template-Package
         for the Session Initiation Protocol (SIP)",
         draft-ietf-simple-winfo-package-05 (work in progress), January
         2003.

   [9]   Olson, S., "Mechanism for Content Indirection in Session
         Initiation Protocol (SIP) Messages",
         draft-ietf-sip-content-indirect-mech-03 (work in progress),
         February 2003.

   [10]  Price, R., "Signaling Compression (SigComp)", RFC 3320, January
         2003.


Authors' Addresses

   Mikko Lonnfors
   Nokia
   Itamerenkatu 11-13 00180
   Helsinki
   Finland

   Phone: +358 71 8008000
   EMail: mikko.lonnfors@nokia.com


   Jose Costa-Requena
   Nokia
   Valimotie 9 00380
   Helsinki
   Finland

   Phone: +358 71 8008000
   EMail: jose.costa-requena@nokia.com








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   Eva Leppanen
   Nokia
   P.O BOX 785
   Tampere
   Finland

   Phone: +358 7180 77066
   EMail: eva-maria.leppanen@nokia.com


   Hisham Khartabil
   Nokia
   P.O. Box 321
   Helsinki
   Finland

   Phone: +358 7180 76161
   EMail: hisham.khartabil@nokia.com

































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