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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: April 25, 2005                                      E. Leppanen
                                                            H. Khartabil
                                                                   Nokia
                                                        October 25, 2004


  Session Initiation Protocol (SIP) extension for Partial Notification
                        of Presence Information
                  draft-ietf-simple-partial-notify-03

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
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   This Internet-Draft will expire on April 25, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   By default, presence delivered using the Presence Event Package for
   the Session Initiation Protocol is represented in the Presence
   Information Data Format (PIDF).  A PIDF document contains a set of
   elements, each representing a different aspect of the presence being



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   reported.  When any subset of the elements change, even a just a
   single element, a new document containing the full set of elements is
   delivered.  This memo defines an extension allowing delivery of a new
   document type that contains the data that has actually changed.

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  . . . . .  5
     4.4   Presence agent generation of partial notifications . . . .  5
     4.5   Watcher processing of NOTIFY requests  . . . . . . . . . .  6
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.1   Normative references . . . . . . . . . . . . . . . . . . . . 13
   8.2   Informative references . . . . . . . . . . . . . . . . . . . 14
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
       Intellectual Property and Copyright Statements . . . . . . . . 16

























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1.  Introduction

   A presence event package for 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 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 force certain requirements on the network and terminals for
   supporting a 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 document defines a partial notification approach where 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 a
   new MIME type for carrying partial Presence Information Data Format
   documents [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.

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



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   extension for Partial Presence [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 informational in nature.  It does not
   contain 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 XML elements.  The PIDF document
   include a set of elements defined in RFC2778 [3] for representing the
   presence information.  This PIDF document will be carried in the body
   of a NOTIFY request constructed as per RFC3265 [7].  During basic
   operation, the presence document always contains the full state
   corresponding to the presence status of the presentity, as determined
   by the PA local policy and authorization rules.

3.2  Operation with partial notification

   The partial notification mechanism allows a watcher to request that,
   whenever possible, notifications contain only presence information
   that has actually changed.  A watcher that wants to receive partial
   notifications according to this document, 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-diff+xml" tag.

   When the presence agent receives the subscription, it examines the
   Accept header field value and if "application/pidf-diff+xml" value is
   present, it can decide to use the partial notifications mechanism
   specified in this memo.  The presence agent builds NOTIFY requests
   that contain the Content-Type header field set to
   "application/pidf-diff+xml".  The first NOTIFY request that contains
   presence information will contain a full presence document.
   Subsequent NOTIFY requests can contain partial notifications.  This
   behavior is described in detail in Section 4.



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4.  Client and server operations

   Unless otherwise specified in this document, the regular watcher 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-diff+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 its SUBSCRIBE request.
   The value of the Accept header file MUST contain
   'application/pidf-diff+xml' (in addition to 'application/pidf+xml'
   required by the SIP  presence event package [4]).  The watcher MAY
   include a "q" parameter with each Accept value to indicate the
   relative preference of that value.

4.3  Presence agent processing of SUBSCRIBE requests

   The presence agent receives subscriptions from watchers and generates
   notifications according to the 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 indicated
   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

   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.  This is done as specified in RFC
   3856 by sending a NOTIFY request that contains a
   'application/pidf+xml' formatted body.  After this if the PA wants to
   send partial notifications it MUST wait until it has received a final
   response from the last NOTIFY request containing a full state
   presence document.



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   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-diff+xml'.

   When the PA the first generates partial notifications, the PA SHOULD
   include only that presence information that have changed compared to
   the previous notification.  It is up to the PA's local policy to
   determine what is considered as a change to the previous state.  In
   partial notifications the PA MUST include a "version" attribute and
   for the first partial notification the PA MUST initialize version to
   value one.

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

   o  The PA MUST construct the presence information according to the
      PIDF diff format [2].  All the informaton that  has been added to
      presence document is listed inside <add> elements.  All
      information that has been removed from presence decument is listed
      inside <remove> elements and all information that has been changed
      is listed under <replace> elements.

   o  The PA MUST include a "version"  attribute in the presence
      document.  The PA MUST increment the version number by one
      compared to the earlier successfully send presence document to the
      watcher associated with a certain subscription.

   The PA MUST NOT send a new NOTIFY request that contains a partial
   presence document (not a re-transmission) for the same Request-URI,
   until it has received a final response from the watcher for the
   previous one or the previous NOTIFY request has timed out.

   The PA always ends a sequence of partial notifications when it
   receives any SUBSCRIBE request (refresh or termination) within the
   associated subscription.  The PA sends a NOTIFY request to this
   SUBSCRIBE request as specified in RFC3856 [4].

4.5  Watcher processing of NOTIFY requests

   Watcher processes all NOTIFY requests that contain
   'application/pidf+xml' content type as specified in RFC3856 [4].

   When the watcher receives the first partial notification the watcher
   MUST initialize an internal version counter, related to this
   subscription, to the value of the "version" included in the presence
   document.  This version counter is scoped to the subscription.  When



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   the watcher receives the first partial presence document the watcher
   MUST modify its local copy according to the following logic:

   o  The watcher MUST apply the changes to its local copy of the full
      presence document indicated in the received
      'application/pidf-diff+xml' document as specified in PIDF diff
      format [2].

   o  The watcher MUST increment local version counter by one.

   When the watcher receives a subsequent partial presence document the
   watcher MUST compare the received "version" attribute with the local
   version counter.  If the version number is incremented by one, the
   watcher MUST modify its local presence document following the same
   processing rules as for the first partial notification.

   If the watcher receives a partial 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 "version" attribute value equal
   or lower than the locally stored version number, it is considered a
   PA failure and the watcher SHOULD discard the document without
   further processing.

   If the PA changes the content type used in notifications within the
   existing subscription the watcher MUST discard all the previously
   received presence information (except local version counter) 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-diff+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/pidff+xml' content type.  The following notifications
   only include the delta of the presence information from the previous
   NOTIFY request.



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       Watcher                   Presence Agent                  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@example.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-diff+xml;q=1
            Contact: <sip:user@watcherhost.example.com>
            Expires: 600
            Content-Length: 0

      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



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            From: <sip:watcher@example.com>;tag=xfg9
            Call-ID: 2010@watcherhost.example.com
            CSeq: 17766 SUBSCRIBE
            Event: presence
            Expires: 600
            Contact: <sip:server.example.com>
            Content-Length: 0

          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 the full presence 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@example.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+xml
            Content-Length: [replace with real content length]

      <?xml version="1.0" encoding="UTF-8"?>
      <presence xmlns="urn:ietf:params:xml:ns:pidf"
             xmlns:pe="urn:ietf:params:xml:ns:pidf:person"
             xmlns:de="urn:ietf:params:xml:ns:pidf:device"
             xmlns:rs="urn:ietf:params:xml:ns:pidf:status:rpid-status"
             xmlns:rt="urn:ietf:params:xml:ns:pidf:rpid-tuple"
             xmlns:ci="urn:ietf:params:xml:ns:pidf:cipid"
             xmlns:sc="urn:ietf:params:xml:ns:pidf:status:servcaps"
             xmlns:dc="urn:ietf:params:xml:ns:pidf:status:devcaps"
             entity="pres:someone@example.com">

       <tuple id="sg89ae">
        <status>
         <basic>open</basic>
         <rs:relationship>assistant</rs:relationship>
        </status>
        <sc:servcaps>
         <sc:video>false</sc:video>
         <sc:audio>true</sc:audio>



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         <sc:message>true</sc:message>
        </sc:servcaps>

        <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>
         <rs:activity>meeting</rs:activity>
        </status>
        <ci:homepage>http://example.com/~pep/</ci:homepage>
        <ci:icon>http://example.com/~pep/icon.gif</ci:icon>
        <ci:card>http://example.com/~pep/card.vcd</ci:card>

        <contact priority="0.9">sip:pep@example.com</contact>
       </tuple>

       <pe:person>
        <pe:status>
         <rs:activities>
          <rs:activity>on-the-phone</rs:activity>
          <rs:activity>busy</rs:activity>
         </rs:activities>
        </pe:status>
       </pe:person>

       <de:device device-id="urn:esn:600b40c7">
        <de:status>
         <dc:devcaps>
          <dc:supported>
           <dc:fixed/>
          </dc:supported>
         </dc:prescaps>
        </de:status>
       </de:device>
       <note xml:lang="en">Full state presence document</note>
      </presence>

         F4 200 OK watcher-> example.com server




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            SIP/2.0 200 OK
            Via: SIP/2.0/TCP server.example.com;
              branch=z9hG4bKna998sk
              ;received=192.0.2.2
            To: <sip:watcher@example.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8775 NOTIFY
            Content-Length: 0

            At a later time, the presentity's presence information
            changes The PA generates a NOTIFY request
            that includes the changed information

      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@example.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-diff+xml
            Content-Length: [replace with real content length]

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

       <add parent="presence" sel="*[4]">
        <![CDATA[
         <tuple id="ert4773">
          <status>
           <basic>open</basic>
          </status>
          <contact priority="0.4">mailto:pep@example.com</contact>
          <note xml:lang="en">This is a new tuple inserted
              between the last tuple and person element</note>
         </tuple>
        ]] >
       </add>




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       <replace
        sel="presence/tuple[@id="r1230d"]/status/
        basic/text()">open</replace>

       <remove sel="presence/tuple[@id=
       "r1230d"]/rs:activity"/>

        <remove sel="presence/tuple[@id="r1230d"]
        /status/rs:activity"/>

       <replace
        sel="presence/tuple[@id="cg231jcr"]
        /contact/@priority"
        >0.7</replace>

      </pidf-diff>

         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@example.com>;tag=xfg9
            From: <sip:resource@example.com>;tag=ffd2
            Call-ID: 2010@watcherhost.example.com
            CSeq: 8776 NOTIFY
            Content-Length: 0


6.  Security Considerations

   This specification relies on the presence event package for SIP [4].
   Partial notifications can reveal information about what has changed
   compared to the previous notification.  This can make it easier for
   eavesdropper to know what kind of changes are happening in the
   presentity's presence information.  However, the same information can
   be found if the presence event package is used with baseline PIDF
   [6].

   A third party can inject a NOTIFY request with partial state that
   will cause the watcher to think it has missed a partial document and
   to request a new full state document.  This is no worse than what we
   have without this extension since a party that could perform such
   action could also send a NOTIFY with Subscription-State: terminated
   and achieve the same effect without knowing about the extension.
   Partial Notification does not make the situation any worse, and the
   protection mechanisms from the existing system apply to preventing



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   this attack against the partial notification mechanism.

   Presence related security considerations are extensively discussed in
   the presence event package for SIP [4] and all those identified
   security considerations apply to this document as well.  Issues
   described in the presence event package for SIP [4], including
   confidentiality, message integrity and authenticity, outbound
   authentication, replay prevention, DoS attacks against thirst parties
   and DoS attachs againsts servers all apply here without any change

7.  Acknowledgments

   The authors would like to thank Jyrki Aarnos, Jonathan Rosenberg,
   Dean Willis, Kriztian Kiss, Juha Kalliokulju, Miguel Garcia, Anders
   Kristensen, Yannis Pavlidis, Ben Cambell, Robert Sparks, 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-02 (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)", RFC 3856, August 2004.

   [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.

   [6]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and
        J. Peterson, "Presence Information Data Format (PIDF)", RFC
        3863, August 2004.

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






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8.2  Informative references

   [8]   Rosenberg, J., "A Watcher Information Event Template-Package
         for the Session Initiation Protocol (SIP)", RFC 3857, August
         2004.

   [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


   Eva Leppanen
   Nokia
   P.O BOX 785
   Tampere
   Finland

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






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   Hisham Khartabil
   Nokia
   P.O. Box 321
   Helsinki
   Finland

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











































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