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Versions: 00

INTERET-DRAFT                                          J.Costa-Requena
draft-lonnofors-simple-partial-notify-00.txt              Eva Leppanen
Expires: July 2003                                     Hisham Khartabi
                                                        Mikko Lonnfors
                                                                 Nokia
                                                          January 2003



               Partial Notification of Presence Information



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.



Abstract

   A Presence service implemented using SIMPLE has some 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 increasing efficiency, by introducing
   a new MIME-type æpartial notificationsÆ and a Require header
   extension æpartial-notificationÆ.





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Table of Contents

   1 Introduction....................................................2
      1.1 Existing mechanisms........................................3
   2 Conventions used in this document...............................4
   3 Introduction of the partial notification solution...............4
      3.1 Normal presence server operation...........................5
      3.2 Operation of the partial notification......................5
   4 Client and server operations....................................5
         4.1.1 Watcher generating SUBSCRIBE requests.................6
         4.1.2 Notifier processing of SUBSCRIBE requests.............6
         4.1.3 NOTIFY body for partial notifications.................7
         4.1.4 Notifier generation of partial notifications..........7
         4.1.5 Watcher processing of partial notifications...........8
   5 IANA considerations.............................................9
   6 Examples.......................................................10
         6.1.1 Subscription with partial notification as optional...10
         6.1.2 Subscription with partial notification as requirement14
   7 XML Schema.....................................................18
   8 Security Considerations........................................20
   9 Acknowledgements...............................................20
   10 References....................................................20
   11 Author's Addresses............................................22


1 Introduction

   SIP extensions for presence [1] allow users (öwatchersö) to subscribe
   to other users (öpresentitiesö) presence information. The presence
   information is composed of multiple pieces of data that is delivered
   to the watcher. The size of the presence information can be large
   (i.e. 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 in degrading the
   presence service and causing bad perception at the watcher side.
   Thus, it is necessary to provide solutions to overcome this problem
   for the sake of success of the presence service.

   Presence based applications in wireless terminals have certain
   limitations because it is envisioned that the presence service may
   demand high bandwidth. It is foreseen that the presence information
   may have a considerable size, especially if large content is included
   in presence information. Requirements of wireless environments can
   also be found in [2].

   There are some mechanisms which might be used to help the problem,
   such as signaling compression [3] and content indirection [4] and


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   [5]. However, none of the existing solutions are optimal because they
   set additional requirements on basic network functionalities such as
   charging and 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 another approach as a solution to the problem,
   namely ôPartial Notificationsö. The idea is already identified by the
   SIP Extensions for Presence document [1] as a potential solution. In
   general, the partial notification approach means that the Presence
   Server (PS) delivers to the watchers only that part of the presence
   information that has changed compared to the previous notification.
   (See also [2] for requirements). Note that the ôPartial
   Notificationsö are not IMPP compliant.

   This document introduces a new MIME-Type 'application/pidf-
   partial+xml' and a Require-header extension 'partial-notification'.


1.1 Existing mechanisms

   The SIMPLE Working Group has already proposed a set of mechanisms in
   order to accommodate excessive message size when messages are
   delivered over links with limited bandwidth.

   - SigComp[3]: Signalling compression.
   This mechanism provides a reasonable message size reduction because
   of the text-based nature of SIP. However, this approach has certain
   limitations when the messages contain binary content and it does not
   reduce the size after the compression process. This approach also
   requires having additional functionality in the terminal and in the
   server. (I.e. the SigComp dictionaries require additional memory that
   is a scarce resource in small devices, especially when the dictionary
   includes binary content).

   - Content Indirection [4],[5]:
   Consists of sending a URL pointing to the content. This approach
   solves the problem of excessive message size sent in the presence
   notifications. The notification only includes a URL pointing to the
   location where the content is stored. The watcher receiving the URL
   has the option to use amore appropriate data protocol such as HTTP to
   fetch the content every time a notification is received.

   The inconvenience with this mechanism is that the URL has an
   expiration time and after expiry, the URL becomes obsolete. There are
   also security concerns since the URL should also include some


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   security credentials for authentication purposes when fetching the
   content. In addition to this, the terminal has to fetch the content
   after receiving the notification, causing delays in receiving the
   presence information. In some systems this may also complicate the
   charging system.

   - Embedded URL in Presence Content:
   Include a URL, that points to the binary content, in the
   notification. This approach is similar to the previous Content
   Indirection approach but instead of sending the URL for the whole
   presence document, the URL included in the presence information is
   pointing only to some pieces of information (e.g. images or other
   binary content).

   This mechanism would be the most suitable one because if it were used
   in conjunction with the compression mechanism, it would lead into a
   reduced size of the message to be delivered in the notification. The
   inconveniences with this approach are the security, charging and
   performance problems identified for the 'Content Indirection'
   approach. Another inconvenience is that he watcher receives the
   notification and thereafter has to fetch the content that is included
   in the presence document with URLs.

2 Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [6].


3 Introduction of the partial notification solution

   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.

   The motivation for introducing a partial notification mechanism, in
   addition to the existing solutions described in Section 1.1, is to
   mitigate the excessive message size in certain circumstances
   (notifications with large un-compressed content). The approach is
   Presence Server (PS) centric in a sense that the watcher, also
   referred to as subscriber in this document, initiates the negotiation
   in order to inform the Presence server (PS) about its ability to
   receive partial notifications. The PS is the ultimate element that
   decides whether the partial notification capability is used or not in
   the particular subscription.




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3.1 Normal presence server operation

   The presence service normally operates so that the watcher sends the
   SIP SUBSCRIBE method targeted to the presentity. The request is
   routed up to the PS responsible for storing the presence information
   of the presentity. The SUBSCRIBE request MAY include an Accept-header
   field for indicating the supported content types [7].

   The PS receives the SUBSCRIBE request and if there is no Accept
   header indicating supported content types, PS will generate the
   presence notification using the default PIDF format [8]. PIDF may
   contain one or multiple 'tuples' and presence document level
   information. The 'tuples' include a set of elements defined in the
   presence model [9] for representing the presence information. The
   presence information is sent to the watcher in the body of the NOTIFY
   request according to [10]. By default, the presence information
   contains the full state corresponding to the presence status of the
   presentity, as allowed by the PS local policy.


3.2 Operation of the partial notification

   The proposed mechanism for implementing the partial notification
   consists of defining a new content type as extension to the existing
   'PIDF' format [8]. The new content type is named as
   'application/pdif-partial+xml' and it adds new elements in addition
   to the existing 'PIDF' schema in order to enable the partial
   notifications. The new elements are 'version' and 'state'.

   The 'version' information is a sequence number that is progressively
   incremented for each watcher when notification is sent. The 'state'
   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 watcher information template package
   [11].

   In addition the 'content-type' header of the NOTIFY request also
   refers to the format type included in the document (i.e. 'CPIM-
   PIDF+xml' or 'PIDF-partial+xml').


4 Client and server operations

   This document assumes that unless otherwise specified in this
   document normal subscriber and notifier behavior is applied as
   defined in [12]. The watcher has the same behavior as a subscriber.



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4.1.1 Watcher generating SUBSCRIBE requests

   The SUBSCRIBE request can be used to negotiate the prefered content
   type to be used in the notifications. The 'Accept' header is used for
   this purpose as specified in [7]. When sending a SUBSCRIBE request,
   the watcher has the following options:

   - Watcher may omit the æAcceptÆ header or place default content type
   as a value of æAcceptÆ header. In this case the watcher is willing to
   receive only the default presence format.

   - Watcher may add the æAcceptÆ header with values: application/cpim-
   pidf+xml and application/pidf-partial+xml. In this case the watcher
   is able to process both the default content type and the partial
   notification content type.



   Therefore, the watcher can indicate the content types that it is
   willing to receive in the NOTIFY using the 'Accept' header. At least
   the default content type specified for the Presence service MUST be
   indicated. If the æAcceptÆ header is omitted the default content type
   (PDIF[8]) MUST be used by the Presence Server.

   The watcher MAY include a æRequireÆ header field with the value
   æpartial-notificationÆ if the watcher wants to be sure that the PS
   supports and uses the extensions defined in this specification. If PS
   does understand the extension indicated in the æRequireÆ header field
   the PS SHOULD reject the subscription or alternatively accept the
   subscription and send back an error response.

   The æSupportedÆ header achieves the same result as the æAcceptÆ
   header field. Since the æAcceptÆ header MUST be present in a
   SUSBSCRIBE request that requires a NOTIFY request with a content type
   that is not the default one, the field presence of æSupportedÆ header
   is considered to be redundant, but it is not strictly disallowed.


4.1.2 Notifier processing of SUBSCRIBE requests

   The Presence Server receives the subscriptions from the watchers and
   generates the notifications according to [1]. The watcher might have
   indicated the supported formats of the presence document by listing
   the content types in the 'Accept' header. The Presence Server MUST
   compare the content types included in the 'Accept' header with
   supported ones, and decide which one to use according to its local
   policy. There are the following cases:



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   - There is no æAcceptÆ header field present in the request or the
   æAcceptÆ header field contains the default content type. In this
   case, the subscription processing proceeds as defined in [1].

   - The æAcceptÆ header field contains both æapplication/cpim-pidf+xmlÆ
   and æapplication/pidf-partial+xmlÆ. Choosing either of these content
   types is up to the local configuration as defined in [1]

  - The æAcceptÆ header field contains both æapplication/cpim-pidf+xmlÆ
  and æapplication/pidf-partial+xmlÆ the  æRequireÆ header field
  includes æpartial-notificationÆ. If the PS does not support the
  æpartial-notificationÆ extension, then it rejects the request as
  defined in [1]. If the PS supports the extension, it MUST use the
  æapplication/pidf-partial+xmlÆ content type in all subsequent NOTIFY
  requests. The semantics for the æRequireÆ header with value æpartial-
  notificationÆ apply to the content type included in the æAcceptÆ
  header with value æapplication/pidf-partial+xmlÆ.

     Note: If Accept-header field does not include æapplication/pidf-
     partial+xmlÆ but a Require-header field with æpartial-notificationÆ
     was present, the PS rejects the subscription.


4.1.3 NOTIFY body for partial notifications

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


4.1.4 Notifier generation of partial notifications

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

   The PS MUST deliver the full state of the presence information
   according to [1] in the first notification. In this case, the 'state'
   element of the presence document MUST be set to the value 'full'. The
   æversionÆ 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. Except in the case when the tuples are removed, the
   complete presence document is sent. It is up to the local
   configuration to determine what is considered as change to previous
   state. The 'state' element's value MUST be set to 'partialÆ.



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

   The delivered presence information is constructed according to [1] in
   such a way that only changed tuples are delivered. There might also
   be new tuples added to the presence information because presentity
   has published more information or because authorization policy has
   been changed.

   In addition, the version number and state element 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 that after reaching the maximum value it
   starts from zero [13].

   When there are changes (e.g. in the authorisation) which lead to the
   removal of a tuple from the previously delivered presence information
   the PS sends the full presence information by setting the value
   'full' for the 'state' element, and restarting the version numbering
   again. The decision to send æfullÆ state is up to the local policy.


4.1.5 Watcher processing of partial notifications

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

   The watcher receives the full state of the presence information
   according to [1] in the first notification. In this case, the 'state'
   element of the presence document has the value 'full'. When the
   watcher receives full state notifications it MUST perform the
   following actions:

   - Watcher MUST discard all previously received presence information
   from that particular presentity.

   - Watcher MUST initialize internal version counter, related that
   particular presentity or subscription, to the value received in the
   notification

   - Watcher MUST store the values of all tuple IDs together with the
   content received in the notification.

   When the watcher receives subsequent notifications, the presence
   document includes only those tuples that have changed compared to the


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   previous notification. The 'state' element includes the value of
   'partial' telling to the watcher that the notification includes
   partial information. The watcher MUST construct the presence
   information according to the following logic:

   - The version number of the presence document SHOULD be compared with
   the version number of the previously received presence document. If
   the version number is incremented by one, the watcher SHOULD continue
   handling the content present in the notification.

   - The Watcher MUST compare tuple IDs to tuple IDs received in
   previous notifications. If a tuple ID in the notification matches an
   existing tuple ID, the existing tuple must be replaced with the newly
   received in the notification. If the tuple ID does not match to the
   ones received in earlier notifications, it will be stored as new
   tuple.

   - The missing tuples means that they remained unchanged.

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


   OPEN ISSUE: Handling of <note> element. PIDF and application/pidf-
   partial+xml can have <note> elements located as child elements to
   <presence> element. It must be specified how these elements are
   handled when partial notifications are send to watchers. The simplest
   approach is to send them with the complete information even if they
   did not change.



5 IANA considerations

   This memo calls for IANA to register a new XML namespace URN as
   defined in [14].

   A new content type æapplication/pidf-partial+xmlÆ is defined to
   represent an XML MIME for the partial presence information content.
   This specification follows the guidelines of RFC3023 [15].



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   It may also be needed an IANA registration for the value æpartial-
   notificationÆ of the æRequireÆ header as a SIP extension and the
   required information for this registration, as specified in RFC3261
   [7], is:

      Name: partial-notification

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


   Description: This option tag is used in the æRequireÆ header field by
   a UAC to ensure that partial notifications are honored at the PS.

   Registrant Contact:   IETF, SIMPLE working group, <simple@ietf.org>


   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 flows show examples when applying the proposed partial
   notification extension. The document of the æpidf-partial+xmlÆ format
   mentioned in the message details is constructed according to the XML
   schema described in the chapter 6.2.

6.1.1 Subscription with partial notification as optional

   The watcher sends a SUBSCRIBE request including the default presence
   format (PIDF) and the PDIF partial extension using the æAcceptÆ


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   header field. The PS accepts the subscription and based on a local
   policy it selects to send partial notifications in NOTIFY requests
   according to the logic described in this document. The first NOTIFY
   request includes the full state of presence information represented
   in the æapplication/pidf-partial+xmlÆ contenttypeÆ. 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                 |                         |
         |-------------------------->|                         |
         |                           |                         |
         |                           |   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, application/pidf-partial+xml
         Contact: user@watcherhost.example.com
         Expires: 600
         Content-Length: 0
      F2 200 OK   example.com server->watcher

   The Presence Server accepts the subscription and based on the local
   policy it applies the partial notitifcation. (See æContent-TypeÆ=
   æapplication/pidf-partial+xmlÆ).


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         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
         Content-Length: 0


      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
         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 æFULL STATEÆ information:
         <?xml version="1.0" encoding="UTF-8"?>
         <impp:presence xmlns:impp="urn:ietf:params:xml:ns:pidf-partial"
          entity="pres:someone@example.com" version=ö1ö state=öfullö>

           <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@nokia.com</impp:contact>
           </impp:tuple>
         </impp:presence>

      F4 200 OK watcher-> example.com server

         SIP/2.0 200 OK


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         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
         Content-Length: 0


   F5 NOTIFY example.com server -> watcher

   It is the local policy issue to construct the æPIDF-partial+xmlÆ
   formated document including the delta from the previous NOTIFY.


         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 æPARTIAL STATEÆ information:
         <?xml version="1.0" encoding="UTF-8"?>
         <impp:presence xmlns:impp="urn:ietf:params:xml:ns:pidf-partial"
          entity="pres:someone@example.com" version=ö2ö state=öpartialö>

           <impp:tuple id="cg231jcr">
             <impp:status><impp:basic>closed</impp:basic></impp:status>
             <impp:contact priority="1.0">
                   im:pep@nokia.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>


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      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
         Content-Length: 0



6.1.2 Subscription with partial notification as requirement

   The watcher sends SUBSCRIBE request including æpartial-notificationÆ
   extension in the æRequireÆ header field. The PS does not support the
   æpartial-notificationÆ extension, so it rejects the subscription. The
   watcher re-subscribed without including the ærequireÆ header field.


     Watcher                 Presence Server                  PUA
         | F1 SUBSCRIBE              |                         |
         |-------------------------->|                         |
         | F2 420 Bad Extension        |                         |
         |<--------------------------|                         |
         | F3 SUBSCRIBE              |                         |
         |-------------------------->|                         |
         | F4 200 OK                 |                         |
         |<--------------------------|                         |
         | F5 NOTIFY                 |                         |
         |<--------------------------|                         |
         | F6 200 OK                 |                         |
         |-------------------------->|                         |
         |                           |                         |
         |                           |   Update presence       |
         |                           |<----------------------- |
         |                           |                         |
         | F7 NOTIFY                 |                         |
         |<--------------------------|                         |
         | F8 200 OK                 |                         |
         |-------------------------->|                         |



      Message Details:

   F1 SUBSCRIBE   watcher->example.com server


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         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
         Require: partial-notification
         Contact: sip:user@watcherhost.example.com
         Expires: 600

         Content-Length: 0


      F2 420 Bad Extension   example.com server->watcher

   The Presence Server does not support the extension indicated in the
   æRequireÆ header and the subscription is rejected.

         SIP/2.0 420 OK
         Via: SIP/2.0/TCP watcherhost.example.com;branch=z9hG4bKnashds7
           ;received=192.0.2.1
         To: sip:resource@example.com
         From: sip:watcher@somewhere.com;tag=xfg9
         Call-ID: 2010@watcherhost.example.com
         CSeq: 17766 SUBSCRIBE
         Event: presence
         Expires: 600
         Unsupported: partial-notification
         Contact: sip:server.example.com
         Content-Length: 0


      F3 SUBSCRIBE watcher -> example.com server

   The watcher makes subscribtion without any requirements for partial
   notification. The default presence service and PDIF format [1] are
   applied.

         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: 17767 SUBSCRIBE
         Max-Forwards: 70
         Event: presence


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         Contact: sip:user@watcherhost.example.com
         Expires: 600
         Content-Length: 0


      F4 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
         From: sip:watcher@somewhere.com;tag=xfg9
         Call-ID: 2010@watcherhost.example.com
         CSeq: 17767 SUBSCRIBE
         Event: presence
         Expires: 600
         Contact: sip:server.example.com
         Content-Length: 0



      F5 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
         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/cpim-pidf+xml
         Content-Length: ..

         CPIM-PIDF+XML formatted document:
         <?xml version="1.0" encoding="UTF-8"?>
         <impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
          entity="pres:someone@example.com">

           <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">


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                   im:pep@nokia.com</impp:contact>
           </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=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
         Content-Length: 0


   F7 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/cpim-pidf+xml
         Content-Length: ...

         New CPIM-PIDF+XML formatted_document:
         <?xml version="1.0" encoding="UTF-8"?>
         <impp:presence xmlns:impp="urn:ietf:params:xml:ns:cpim-pidf"
          entity="pres:someone@example.com">

           <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>closed</impp:basic></impp:status>
             <impp:contact priority="1.0">
                   im:pep@nokia.com</impp:contact>


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             <impp:note xml: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>



      F8 200 OK
         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
         Content-Length: 0


7 XML Schema

   The XML schema for the æpidf-partial+xmlÆ 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: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:element name="presence" type="tns:presence"/>

     <xs:complexType name="presence">
       <xs:sequence>
         <xs:element name="tuple" type="tns:tuple"
            maxOccurs="unbounded"/>
         <xs:element name="note" type="tns:note" minOccurs="0"


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            maxOccurs="unbounded"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
            maxOccurs="unbounded"/>
       </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:complexType>

     <xs:complexType name="tuple">
       <xs:sequence>
         <xs:element name="status" type="tns:status"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
            maxOccurs="unbounded"/>
         <xs:element name="contact" type="tns:contact" minOccurs="0"/>
         <xs:element name="note" type="tns:note" minOccurs="0"
            maxOccurs="unbounded"/>
         <xs:element name="timestamp" type="xs:dateTime" minOccurs="0"/>
       </xs:sequence>
       <xs:attribute name="id" type="xs:ID" use="required"/>
     </xs:complexType>

     <xs:complexType name="status">
       <xs:sequence>
         <xs:element name="basic" type="tns:basic" minOccurs="0"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
            maxOccurs="unbounded"/>
       </xs:sequence>
     </xs:complexType>
      <xs:simpleType name="basic">
       <xs:restriction base="xs:string">
         <xs:enumeration value="open"/>
         <xs:enumeration value="closed"/>
       </xs:restriction>
     </xs:simpleType>

     <xs:complexType name="contact">
       <xs:simpleContent>
         <xs:extension base="xs:anyURI">
           <xs:attribute name="priority" type="tns:qvalue"/>
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>


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     <xs:complexType name="note">
       <xs:simpleContent>
         <xs:extension base="xs:string">
           <xs:attribute ref="xml:lang"/>
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>

     <xs:simpleType name="qvalue">
       <xs:restriction base="xs:decimal">
         <xs:pattern value="0(.[0-9]{0,3})?"/>
         <xs:pattern value="1(.0{0,3})?"/>
       </xs:restriction>
     </xs:simpleType>

     <!-- Global Attributes -->
     <xs:attribute name="mustUnderstand" type="xs:boolean" default="0">
       <xs:annotation>
         <xs:documentation>
         This attribute may be used on any element within an optional
         PIDF extension to indicate that the corresponding element must
         be understood by the PIDF processor if the enclosing optional
         element is to be handled.
         </xs:documentation>
       </xs:annotation>
     </xs:attribute>
   </xs:schema>


8 Security Considerations

   The security considerations for the presence are considered in [2],
   and RFC 2779 [5] also outlines them. Furthermore, the PDIF [8]
   document includes additional security requirements to be considered
   in the data format for the partial notifications.
9 Acknowledgements

   The authors would like to thank Kriztian Kiss, Juha Kalliokulju and
   Tim Moran for their valuable comments.


10 References

   [1] Rosenberg, J., et al, "SIP Extensions for Presence", draft-ietf-
   simple-presence-07.txt. Internet Draft, May 2002, Work in progress.

   [2] K.Kiss, ôRequirements for Presence Service based on 3GPP
   specifications and wireless environment characheristicsö draft-kiss-


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   simple-presence-wireless-reqs-01.txt. Internet Draft, October 2002.
   Work in progress.

   [3] Price, R., et al, öSignaling Compression (SigComp)ö, RFC 3320,
   Internet Engineering Task Force, January 2003.

   [4] Olson, S.,ö A Mechanism for Content Indirection in Session
   Initiation Protocol (SIP) Messagesö, draft-ietf-sip-content-indirect-
   mech-01. Internet Draft, November 2002, Work in progress.

   [5] Khartabil. H.,ö Congestion safety and Content Indirectionö,
   draft-khartabil-sip-congestionsafe-ci-01.txt, Internet Draft, October
   2002, Work in progress.

   [6] S. Bradner, "Key words for use in RFCs to indicate requirement
      levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

   [7] J. Rosenberg, et al. ôSIP: Session Initiation Protocolö. RFC
   3261, Internet Engineering Task Force, June 2002.

   [8] H. Sugano, S. Fujimoto, et al, "CPIM presence information data
   format," draft-ietf-impp-cpim-pidf-05.txt. Internet Draft, May 2002.
   Work in progress.

   [9] M. Day, J. Rosenberg, H. Sugano, "A Model for Presence and
   Instant Messaging", RFC 2778, Internet Engineering Task Force,
   February 2000.

   [10] Roach, A., "SIP-Specific Event Notification", RFC 3265, Internet
   Engineering Task Force, June 2002.

   [11] Rosenberg, J.,ö A Watcher Information Event Template-Package for
   the Session Initiation Protocol (SIP)ö, draft-ietf-simple-winfo-
   package-04.txt, Internet Draft, December 2002. Work in progress.

   [12] Day, M., Aggarwal, S., Mohr, G., Vincent,K., "Instant Messaging/
   Presence Protocol Requirements", RFC 2779, Internet Engineering Task
   Force, February 2000.

   [13] K. McCloghrie et al, ôStructure of Management Information
   Version 2 (SMIv2)ö, RFC 2578, STD 58, April 1999.

   [14] Mealling, M., "The IETF XML Registry", draft-mealling-iana-
   xmlns-registry-04, June 2002, work in progress.

   [15] M. Murata, S. S. Laurent, and D. Kohn, "XML media types," RFC
   3023, Internet Engineering Task Force, Jan. 2001.




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11 Author's Addresses

   Jose Costa-Requena
   Nokia
   Valimotie 9
   00380 HELSINKI
   Finland
   Tel: +358-71-8008000
   E-mail: jose.costa-requena@nokia.com

   Mikko Lonnfors
   Nokia Research Center
   P.O. Box 407
   FIN-00045 NOKIA GROUP
   Finland
   Tel: +358 50 4836402
   Email: mikko.lonnfors@nokia.com

   Eva Leppanen
   Nokia
   P.O Box 785
   FIN-33101 Tampere
   FINLAND
   Tel: +358 7180 77066
   Email: eva-maria.leppanen@nokia.com

   Hisham Khartabil
   Nokia
   P.O. Box 321
   FIN-00045
   NOKIA GROUP
   FINLAND
   Email: hisham.khartabil@nokia.com
   Tel: + 358 7180 76161

















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