RFC 5263

Network Working Group                                        M. Lonnfors
Request for Comments: 5263                              J. Costa-Requena
Category: Standards Track                                    E. Leppanen
                                                            H. Khartabil
                                                          September 2008

            Session Initiation Protocol (SIP) Extension for
              Partial Notification of Presence Information

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   By default, presence delivered using the presence event package for
   the Session Initiation Protocol (SIP) 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
   reported.  When any subset of the elements change, even just a single
   element, a new document containing the full set of elements is
   delivered.  This memo defines an extension allowing delivery of only
   the presence data that has actually changed.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Introduction to the Partial Notification Mechanism . . . . . .  3
     3.1.  Basic Presence Agent Operation . . . . . . . . . . . . . .  3
     3.2.  Operation with Partial Notification  . . . . . . . . . . .  3
   4.  Client and Server Operations . . . . . . . . . . . . . . . . .  4
     4.1.  Content-Type for Partial Notifications . . . . . . . . . .  4
     4.2.  Watcher Generation of SUBSCRIBE Requests . . . . . . . . .  4
     4.3.  Presence Agent Processing of SUBSCRIBE Requests  . . . . .  4
     4.4.  Presence Agent Generation of Partial Notifications . . . .  5
     4.5.  Watcher Processing of NOTIFY Requests  . . . . . . . . . .  6
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14

1.  Introduction

   A presence event package for Session Initiation Protocol (SIP) [3]
   allows 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
   RFC 2778 [9] and the presence event package for SIP [3], 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.

   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 is transported over the network.

   This mechanism utilizes the presence event package for SIP [3] and a
   new MIME type for carrying partial Presence Information Data Format
   documents [2].

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2.  Conventions

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

   This document makes use of the vocabulary defined in RFC 2778 [9],
   RFC 3265 [6], the presence event package for SIP [3], and the PIDF
   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 [5].  The PIDF
   document can contain one or multiple XML elements.  The PIDF document
   includes a set of elements defined in RFC 2778 [9], and its
   extensions for representing the presence information.  This PIDF
   document will be carried in the body of a NOTIFY request constructed
   as per RFC 3265 [6].  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

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   contains the "application/pidf-diff+xml" tag as well as the
   "application/pidf+xml" tag.

   When the presence agent receives the subscription, it examines the
   Accept header field value and if the "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 presence documents.
   This behavior is described in detail in Section 4.

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 [3].

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 RFC 3261 [4].  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 field MUST contain 'application/
   pidf-diff+xml' (in addition to 'application/pidf+xml' required by the
   SIP presence event package [3]).  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 [3].  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

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   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 partial
   notification that contains a presence document having <pidf-full>
   root element.  If the presence agent decides to send notifications
   that include a presence document according to this specification, 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 using the 'application/pidf-diff+xml' MIME type, the PA MUST
   include a "version" attribute; for the first partial notification
   (within a given subscription), the PA MUST initialize version to
   value one (1).  This version counter is scoped to the subscription,
   and is incremented by one within each partial notification.  The
   version value is only reset when the given subscription is
   terminated.  It is not reset when the subscription is refreshed.

   When the PA generates a partial presence document, the PA SHOULD
   include only that presence information that has changed compared to
   the previous notifications.  It is up to the PA's local policy to
   determine what is considered as a change to the previous state.

   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 extension for Partial Presence [2].  All the information that
      has been added to the presence document is listed inside <add>
      elements.  All information that has been removed from the presence
      document 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 sent presence document in the
      PIDF extension for Partial Presence [2] format to the watcher
      associated with a certain subscription.

   The PA MUST NOT send a new NOTIFY request that contains a partial
   notification 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.

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   When the PA receives a SUBSCRIBE request (refresh or termination)
   within the associated subscription, it SHOULD send a NOTIFY request
   containing the full presence document.

   If the PA has used other than the 'application/pidf-diff+xml' content
   type in notifications within the existing subscription, and changes
   to deliver partial notifications, the PA MUST deliver the full state
   of the presence information containing a presence document having
   <pidf-full> root element as the first partial notification.

4.5.  Watcher Processing of NOTIFY Requests

   Watcher processes all NOTIFY requests that contain 'application/
   pidf+xml' content type as specified in RFC 3856 [3].

   When the watcher receives the first notification containing the
   'application/pidf-diff+xml' MIME body 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.  The watcher MUST also store
   the received full presence document as its local copy.

   When the watcher receives a subsequent 'application/pidf-diff+xml'
   encoded presence document the watcher MUST compare the received
   "version" attribute with the local version counter.  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.  Otherwise, the watcher MUST modify its locally
   stored information according to the following logic:

   o  If the root element of the presence document is <pidf-full>, the
      watcher must replace its local copy of the presence document with
      the presence document received in the 'application/pidf-diff+xml'
      body and set the internal version value to the value of the
      "version" attribute included in the presence document.

   o  If the root element of the presence document is <pidf-diff> and
      the received version number is incremented by one compared with
      the local version counter, 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
      extension for Partial Presence [2].  The watcher MUST increment
      the local version counter by one.

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   o  If the root element of the presence document is <pidf-diff> and
      the received "version" value is higher by more than one compared
      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 encounters a processing error while processing the
   received 'application/pidf-diff+xml' encoded presence document, look
   at Section 5.1 of [8].  In this case, the watcher SHOULD renew the
   subscription.  The watcher MAY also fall back to normal presence
   operations by not inserting 'application/pidf-diff+xml' in a new
   SUBSCRIBE request.  It is hardly reasonable to signal this error to
   the notifier even if the error exists in the notifier process.

   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.  The local version counter MUST NOT be
   discarded because if the PA changes back to 'application/
   pidf-diff+xml', the MIME type version counter will continue to
   increase from the last version value.

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 for the partial
   notification format ('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.  The following
   notifications only include information about delta of the presence
   information from the previous NOTIFY requests.

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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;
            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,
            Contact: <sip:user@watcherhost.example.com>
            Expires: 3600
            Content-Length: 0

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      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;
            To: <sip:resource@example.com>;tag=ffd2
            From: <sip:watcher@example.com>;tag=xfg9
            Call-ID: 2010@watcherhost.example.com
            CSeq: 17766 SUBSCRIBE
            Event: presence
            Expires: 3600
            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 the first NOTIFY request that
      includes the full presence document.

         F3 NOTIFY  example.com server -> watcher

            NOTIFY sip:user@watcherhost.example.com SIP/2.0
            Via: SIP/2.0/TCP server.example.com;
            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=3599
            Max-Forwards: 70
            CSeq: 8775 NOTIFY
            Contact: <sip:server.example.com>
            Content-Type: application/pidf-diff+xml
            Content-Length: ...

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

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

       <tuple id="cg231jcr">
        <contact priority="1.0">im:res@example.com</contact>

       <tuple id="r1230d">
        <contact priority="0.9">sip:resource@example.com</contact>

       <note xml:lang="en">Full state presence document</note>

       <dm:person id="fdkfj">

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       <dm:device id="u00b40c7">


         F4 200 OK watcher -> example.com server

            SIP/2.0 200 OK
            Via: SIP/2.0/TCP server.example.com;
            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 information about the changes.

      F5 NOTIFY example.com server -> watcher

            NOTIFY sip:user@watcherhost.example.com SIP/2.0
            Via: SIP/2.0/TCP server.example.com;
            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=3543
            Max-Forwards: 70
            Contact: <sip:server.example.com>
            Content-Type: application/pidf-diff+xml
            Content-Length: ...

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

       <p:add sel="presence/note" pos="before"><tuple id="ert4773">
        <contact priority="0.4">mailto:res@example.com</contact>
        <note xml:lang="en">This is a new tuple inserted
              between the last tuple and note element</note>


       <p:replace sel="*/tuple[@id='r1230d']/status/basic/text()"

       <p:remove sel="*/dm:person/r:activities/r:busy"/>

       <p:replace sel="*/tuple[@id='cg231jcr']/contact/@priority"


      F6 200 OK watcher-> example.com server

            SIP/2.0 200 OK
            Via: SIP/2.0/TCP server.example.com;
            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

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6.  Security Considerations

   This specification relies on the presence event package for SIP [3].
   Partial notifications can reveal information about what has changed
   compared to the previous notification.  This can make it easier for
   an 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

   A third party can inject a NOTIFY request with partial state that
   will cause the watcher to think it has missed a partial notification
   and to request a new full presence 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 this attack against the partial notification mechanism.

   Presence-related security considerations are extensively discussed in
   the presence event package for SIP [3] and all those identified
   security considerations apply to this document as well.  Issues
   described in the presence event package for SIP [3], including
   confidentiality, message integrity and authenticity, outbound
   authentication, replay prevention, Denial-of-Service (DoS) attacks
   against thirst parties and DoS attacks against servers all apply here
   without any change.

   It is RECOMMENDED that TLS [7] be used between elements to provide
   hop-by-hop confidentially protection.  Furthermore, S/MIME MAY be
   used for integrity and authenticity of SUBSCRIBE and NOTIFY requests.
   This is described in Section 23 of RFC 3261.

7.  Acknowledgments

   The authors would like to thank Jari Urpalainen, 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.

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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., Leppanen, E., and J. Urpalainen,
        "Presence Information Data Format (PIDF) Extension for Partial
        Presence", RFC 5262, August 008.

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

   [4]  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.

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

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

   [7]  Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1",
        RFC 4346, April 2006.

   [8]  Urpalainen, J., "An Extensible Markup Language (XML) Patch
        Operations Framework Utilizing XML Path Language (XPath)
        Selectors", RFC 5261, September 2008.

8.2.  Informative References

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

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Authors' Addresses

   Mikko Lonnfors
   P.O. Box 321

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

   Jose Costa-Requena
   P.O. Box 321

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

   Eva Leppanen

   EMail: eva.leppanen@saunalahti.fi

   Hisham Khartabil

   Phone: +61 416 108 890
   EMail: hisham.khartabil@gmail.com

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Full Copyright Statement

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   specification can be obtained from the IETF on-line IPR repository at

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   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at

Lonnfors, et al.            Standards Track                    [Page 16]