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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                                     Nokia Research Center
Expires: March 19, 2004                                 J. Costa-Requena
                                                             E. Leppanen
                                                            H. Khartabil
                                                                   Nokia
                                                      September 19, 2003


              Partial Notification of Presence Information
                  draft-ietf-simple-partial-notify-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

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

Copyright Notice

   Copyright (C) The Internet Society (2003). 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. Other limitations can be caused
   by the interface between the terminal and the network, i.e. over
   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 efficiency, by introducing a mechanism called partial
   notification.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Introduction of the partial notification mechanism . . . . . .  4
   3.1 Normal presence server operation . . . . . . . . . . . . . . .  4
   3.2 Operation of the partial notification  . . . . . . . . . . . .  4
   4.  Client and server operations . . . . . . . . . . . . . . . . .  5
   4.1 Content-type for partial notifications . . . . . . . . . . . .  5
   4.2 Watcher generating SUBSCRIBE requests  . . . . . . . . . . . .  5
   4.3 Notifier processing of SUBSCRIBE requests  . . . . . . . . . .  5
   4.4 Notifier generating partial notifications  . . . . . . . . . .  5
   4.5 Watcher processing of partial notifications  . . . . . . . . .  6
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   5.1 URN sub-namespace registration for
       'urn:ietf:params:xml:ns:pidf-partial'  . . . . . . . . . . . .  8
   6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
       Normative references . . . . . . . . . . . . . . . . . . . . . 14
       Informative references . . . . . . . . . . . . . . . . . . . . 15
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
       Intellectual Property and Copyright Statements . . . . . . . . 17



























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1. Introduction

   SIP extensions for presence [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). It may not be
   reasonable to send the complete presence information over low
   bandwidth and high latency links when only part of that information
   changes. This may end up degrading the presence service and causing
   bad perception at the watcher side.

   Presence based applications in wireless terminals have certain
   limitations because it is envisioned that the presence service may
   demand high bandwidth. Requirements for wireless environments can be
   found in [12].

   There are some mechanisms, such as signaling compression [14] and
   content indirection [11], [10] that might be used to help in this
   problem. However, none of the existing solutions are optimal because
   they 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 (HTTP) and therefore increases possible
   security concerns.

   This draft presents a solution to these problems, called Partial
   Notifications. Requirements for this mechanism are presented in [3].
   Other set of requirements can be found from [12]. The idea is already
   identified by the SIP Extensions for Presence document [4] as a
   potential solution.

   In general, the partial notification approach means that the Presence
   Server (PS) delivers to the watchers only those parts of the presence
   information that have changed compared to the presence information
   sent in the previous notification. Note that partial notification is
   not IMPP compliant.

   This document introduces a new MIME-Type 'application/pidf-
   partial+xml'.

2. Conventions

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",



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   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

3. Introduction of the partial notification mechanism

   This chapter briefly introduces the current functionality of the
   presence service, and gives an overview of the partial notification
   solution and new items needed to implement it.

3.1 Normal presence server operation

   The presence service normally operates so that the watcher sends the
   SIP SUBSCRIBE request targeted to the presentity. The request is
   routed up to the presence server responsible for terminating the
   request. The SUBSCRIBE request MAY include an Accept header field for
   indicating the supported content types [5].

   The PS receives the SUBSCRIBE request and if there is no Accept
   header indicating the supported content types or Accept header
   contains default PIDF content type , the PS will generate the
   presence notification using the default PIDF format [6]. The PIDF may
   contain one or multiple tuples and presence document level
   information. The tuples include a set of elements defined in the
   presence model [2] for representing the presence information. The
   presence information is sent to the watcher in the body of the NOTIFY
   request according to [7]. By default, the presence information
   contains the full state corresponding to the presence status of the
   presentity, as determinated by the PS local policy and authorization
   rules.

3.2 Operation of the partial notification

   The mechanism for implementing the partial notification consists of
   defining a new content type. The new content type is named as
   'application/pidf-partial+xml'. It is similar to PIDF [6] except that
   it adds new XML attributes to <presence> element in order to enable
   the partial notifications. The new XML attributes are "version" and
   "state". Content type also introduces new XML element called
   "removed".

   The "version" attribute is a sequence number that is progressively
   incremented for each watcher when notification is sent. The "state"
   attribute indicates the nature of the presence information included
   in the notified document, whether it contains full or partial state
   corresponding to the cases when the full presence information or only
   changed parts of the presence information are delivered. The use of
   these attributes is similar to the watcher information template
   package [9].



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   In the scope of this document the partial updates apply only to
   <tuple> level XML elements and everything what is contained inside
   these elements, in other words: tuples are considered to be atomic
   data elements. This means that when an update is send to a tuple it
   is assumed that the whole tuple is completely replaced by the new
   one. All the data which is located outside the  <tuple> elements must
   be processed as specified in [4]. Usually this means that all those
   XML elements (for example the <note> element) must be included in
   every notification.

4. Client and server operations

   This document assumes that unless otherwise specified in this
   document the normal subscriber and notifier behavior is applied as
   defined in [4]. The watcher has the same behavior as a subscriber.

4.1 Content-type for partial notifications

   The entities supporting the partial notification extension described
   in this document MUST support the 'application/pidf-partial+xml'
   content-type.

4.2 Watcher generating SUBSCRIBE requests

   The SUBSCRIBE request can be used to negotiate the preferred content
   type to be used in the notifications. The Accept header is used for
   this purpose as specified in [5]. When watcher wants to allow PS to
   send partial notifications it MUST include the Accept header value
   'application/pidf-partial+xml' in the SUBSCRIBE request. The qvalue
   parameter of the Accept header can be used to indicate the most
   preferred content type to be used.

4.3 Notifier processing of SUBSCRIBE requests

   The Presence Server receives the subscriptions from the watchers and
   generates the notifications according to [4]. If the watcher has
   indicated the supported content types in the Accept header the
   Presence Server compares the content types included in the Accept
   header with the supported ones, and decides which one to use. If the
   watcher has used the qvalue parameter of the Accept header for the
   content types the decision should be based on them. Otherwise the
   decision is made according to the local policy of the server.

4.4 Notifier generating partial notifications

   If the content type negotiation between the watcher and the PS
   resulted in the agreement to use partial notifications, then the PS
   MUST use the 'application/pidf-partial+xml' content type in the



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   NOTIFY requests.

   The PS MUST deliver the full state of the presence information
   according to [4] in the first notification. In this case, the "state"
   attribute of the <presence> element in the presence document MUST be
   set to the value "full". The "version" attribute MUST also be present
   and it MUST be initialized to value zero.

   When the PS generates subsequent notifications, the presence document
   includes only the tuples that have changed compared to the previous
   notification. It is up to the local policy to determine what is
   considered as a change to the previous state. The "state" attribute's
   value MUST be set to "partial".

   The PS constructs the presence document according to the following
   logic:

   o  The delivered presence information is constructed according to [4]
      in such a way that only the changed tuples are delivered. New
      tuples are also be added to the presence information, if any.

   o  The "version" and "state" attributes are also included in the
      presence document. The version number is incremented by one
      compared to the earlier delivered presence document to the watcher
      associated with a certain subscription. The version number should
      follow the COUNTER32 format so that after reaching the maximum
      value it starts from zero [15].

   o  When there are changes (e.g. in the authorization) which lead to
      removal of tuples from the previously delivered presence
      information the PS lists the IDs of the removed tuples in the
      "removed" element.

   o  All the presence information outside the <tuple> elements MUST be
      included in each notification, i.e., all the notifications which
      convey partial notifications MUST always have that data.


4.5 Watcher processing of partial notifications

   If the negotiation between the watcher and the PS resulted in the
   agreement to use the partial notifications, then the watcher receives
   'application/pidf-partial+xml' content type in the NOTIFY requests.

   The watcher receives the full state of the presence information
   according to [4] in the first notification using the partial
   notifications. In this case, the "state" element of the presence
   document has the value "full". When the watcher receives the full



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   state notification it MUST perform the following actions:

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

   o  The watcher MUST initialize an internal version counter, related
      that particular presentity or subscription, to the "version" value
      received in the notification.

   o  The watcher MUST store the values of all tuple IDs together with
      the content received in the notification.

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

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

   o  The Watcher compares tuple IDs to the tuple IDs received in the
      previous notifications. If a tuple ID in the notification matches
      an existing tuple ID, the existing tuple is replaced with the
      newly received in the notification. If the tuple ID does not match
      to those received in the earlier notifications, it is stored as a
      new tuple.

   o  If the presence document includes the "removed" element the tuples
      which IDs are listed are removed from the local storage.

   o  Tuples whose IDs are missing in the NOTIFY remain unchanged.

   In case the watcher receives a partial notification with the
   "version" attribute value higher than the locally stored value by
   more than one, the watcher assumes that one or more NOTIFY were lost
   and SHOULD either refresh the subscription within the existing dialog
   in order to receive a complete update (full state) of the presence
   information or terminate the subscription. If the watcher receives a
   notification with "state" attribute value "partial" and the "version"
   attribute value equal or smaller than the one in the previous
   notification, it is considered a PS failure and the watcher SHOULD
   either refresh or terminate the subscription.

   All information received in the notification which is located outside
   the <tuple> element must be processed as specified in [4] i.e., the



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   watcher must replace the existing data with data received in the
   latest notification.

   In case the PS changes the content type used in notifications within
   the existing dialog the watcher must discard all previously received
   presence information from that particular presentity and process the
   new content as specified for that content type.

5. IANA Considerations

   This memo calls for IANA to register a new XML namespace URN per [8].
   A new content type 'application/pidf-partial+xml' is defined to
   represent an XML MIME for the partial presence information content.
   This specification follows the guidelines of RFC3023 [13].

5.1 URN sub-namespace registration for
    'urn:ietf:params:xml:ns:pidf-partial'

   URI:
   uurn:ietf:params:xml:ns:pidf-partial

   Description:
   This is the XML namespace for XML elements defined by [[[RFCXXXX]]]
   to describe the 'application/pidf-partial+xml' content type for
   partial notifications.

   Registrant Contact:
   IETF, SIMPLE working group, <simple@ietf.org>
   Mikko Lonnfors, <mikko.lonnfors@nokia.com>

   XML:




















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     BEGIN
         <?xml version="1.0"?>
         <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
         "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
         <html xmlns="http://www.w3.org/1999/xhtml
         <head>
              <meta http-equiv="content-type"
              content="text/html;charset=iso-8859-1"/>
              <title>PIDF extension for partial notifications</title>
         </head>
         <body>
             <h1>Namespace for PIDF extension for partial
      notifications</h1>
             <h2>application/pidf-partial+xml</h2>
             <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
          </body>
          </html>
         END

6. Examples

   The following message flow show an example applying the partial
   notifications mechanism. The document of the 'application/
   pidf-partial+xml' format mentioned in the message details is
   constructed according to the XML schema described in the chapter
   Section 7.

   The watcher sends a SUBSCRIBE request including the default presence
   format (PIDF) and the content type for the partial notification in
   the Accept header field. The watcher uses the qvalue parameter to set
   the preference for receiving partial notifications. The PS accepts
   the subscription and based on the qvalue information 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 Server                  PUA
            | F1 SUBSCRIBE              |                         |
            |-------------------------->|                         |
            | F2 200 OK                 |                         |
            |<--------------------------|                         |
            | F3 NOTIFY                 |                         |
            |<--------------------------|                         |
            | F4 200 OK                 |                         |
            |-------------------------->|                         |
            |                           |                         |



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            |                           |   Update presence       |
            |                           |<----------------------- |
            |                           |                         |
            | F5 NOTIFY                 |                         |
            |<--------------------------|                         |
            | F6 200 OK                 |                         |
            |-------------------------->|                         |


         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/cpim-pidf+xml;q=0.3, application/pidf-partial+xml;q=1
            Contact: user@watcherhost.example.com
            Expires: 600

         F2 200 OK   example.com server->watcher

      The Presence Server accepts the subscription and based on the qvalue
      information in the Accept header uses the partial notitifcations.
      (See that the value 'application/pidf-partial+xml' in the Content-Type header).

            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


         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



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            From: sip:resource@example.com;tag=ffd2
            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: ..

            PIDF-PARTIAL+XML Document with FULL STATE information:

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

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

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

      F5 NOTIFY example.com server -> watcher

      It is the local policy issue to construct the 'PIDF-partial+xml'



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      formated document including the delta from the previous NOTIFY.
      Note that the tuple which id was "r1230d" was deleted.

            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: ...

            New PIDF-PARTIAL+XML Document with PARTIAL STATE information:

            <?xml version="1.0" encoding="UTF-8"?>
            <pidf-part:presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
                xmlns:pidf-part="urn:ietf:params:xml:ns:pidf-partial"
                xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
               entity="pres:someone@example.com" pidf-part:version="2" pidf-part:state="partial">

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

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

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



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            From: sip:resource@example.com;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8776 NOTIFY



7. XML Schema

   The XML schema for the 'pidf-partial+xml' data format.


   <?xml version="1.0" encoding="UTF-8"?>
      <xs:schema targetNamespace="urn:ietf:params:xml:ns:pidf-partial"
           xmlns:tns="urn:ietf:params:xml:ns:pidf-partial"
           xmlns:pidf="urn:ietf:params:xml:ns:cpim-pidf"
           xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified">

        <!-- This import brings in the XML language attribute xml:lang-->
        <xs:import namespace="http://www.w3.org/XML/1998/namespace"
          schemaLocation="http://www.w3.org/2001/xml.xsd"/>

       <xs:import namespace="urn:ietf:params:xml:ns:cpim-pidf"/>

        <xs:element name="presence" type="tns:partial-presence"/>

        <xs:complexType name="partial-presence">
        <xs:complexContent>
            <xs:extensionBase=pidf:presence>
                <xs:sequence>
                         <xs:element name="removed" type="tns:removed_tuple" minOccurs="0" maxOccurs="1"/>
               </xs:sequence>
               <xs:attribute name="entity" type="xs:anyURI" use="required"/>
                <xs:attribute name="version" type="xs:nonNegativeInteger" use="required"/>
               <xs:attribute name="state" use="required">
                    <xs:simpleType>
                                <xs:restriction base="xs:string">
                                <xs:enumeration value="full"/>
                                <xs:enumeration value="partial"/>
                                </xs:restriction>
                   </xs:simpleType>
                </xs:attribute>
            </xs:extensionBase>
        </xs:complexContent>
        </complexType>

        <xs:complexType name="removed_tuple">



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        <xs:sequence>
           <xs:element name="t_id" type="xs:ID" minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
        </xs:complexType>

      </xs:schema>



8. Security Considerations

   Presence information may contain highly sensitive information about
   the presentities. Presence related security considerations are
   extensively discussed in [4] and all those identified security
   consideration apply to this document as well. Partial notification
   mechanism does not add anything new which (in term of the security)
   is not already specified in [4] and [5]. Thus no new security
   considerations are introduced here.

9. Acknowledgements

   The authors would like to thank Jyrki Aarnos, Jonathan Rosenberg,
   Dean Willis, Kriztian Kiss, Juha Kalliokulju and Tim Moran for their
   valuable comments.

Normative references

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

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

   [3]  Lonnfors, M., Leppanen, E., Requena, J. and H.  Khartabil,
        "Requirements for Efficient Delivery of Presence Information",
        draft-ietf-simple-presinfo-deliv-reg-00 (work in progress),
        April 2003.

   [4]  Rosenberg, J., "SIP Extensions for Presence",
        draft-ietf-simple-presence-10 (work in progress), January 2003.

   [5]  Rosenberg, J., "SIP: Session Initiation Protocol", RFC 3261,
        June 2002.

   [6]  Sugano, H., "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



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        2002.

Informative references

   [8]   Mealling, M., "The IETF XML Registry",
         draft-mealling-iana-xmlns-registry-05 (work in progress), June
         2002.

   [9]   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.

   [10]  Khartabil, H., "Congestion safety and Content Indirection",
         draft-khartabil-sip-congestionsafe-ci-02 (work in progress),
         March 2003.

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

   [12]  Kiss, K., "Requirements for Presence Service based on 3GPP
         specifications and wireless environment characheristics",
         draft-kiss-simple-presence-wireless-reqs-01 (work in progress),
         February 2003.

   [13]  Murata, M., "XML media types", RFC 3023, January 2001.

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

   [15]  McCloghrie, K., "Structure of Management Information Version 2
         (SMIv2)", RFC 2578, April 1999.


Authors' Addresses

   Mikko Lonnfors
   Nokia Research Center
   Itamerenkatu 11-13 00180
   Helsinki
   Finland

   Phone: +358 50 4836402
   EMail: mikko.lonnfors@nokia.com





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   Jose Costa-Requena
   Nokia
   Valimotie 9 00380
   Helsinki
   Finland

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


   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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