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rfc:rfc5264

Network Working Group A. Niemi Request for Comments: 5264 M. Lonnfors Category: Standards Track Nokia

                                                           E. Leppanen
                                                            Individual
                                                        September 2008
            Publication of Partial 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.

Abstract

 The Session Initiation Protocol (SIP) Extension for Event State
 Publication describes a mechanism with which a presence user agent is
 able to publish presence information to a presence agent.  Using the
 Presence Information Data Format (PIDF), each presence publication
 contains full state, regardless of how much of that information has
 actually changed since the previous update.  As a consequence,
 updating a sizeable presence document with small changes bears a
 considerable overhead and is therefore inefficient.  Especially with
 low bandwidth and high latency links, this can constitute a
 considerable burden to the system.  This memo defines a solution that
 aids in reducing the impact of those constraints and increases
 transport efficiency by introducing a mechanism that allows for
 publication of partial presence information.

Niemi, et al. Standards Track [Page 1] RFC 5264 Partial Publication September 2008

Table of Contents

 1. Introduction ....................................................2
 2. Definitions and Document Conventions ............................3
 3. Overall Operation ...............................................3
    3.1. Presence Publication .......................................3
    3.2. Partial Presence Publication ...............................4
 4. Client and Server Operation .....................................5
    4.1. Content-Type for Partial Publications ......................5
    4.2. Generation of Partial Publications .........................5
    4.3. Processing of Partial Publications .........................7
         4.3.1. Processing <pidf-full> ..............................7
         4.3.2. Processing <pidf-diff> ..............................7
 5. Security Considerations .........................................8
 6. Examples ........................................................8
 7. Acknowledgements ...............................................12
 8. References .....................................................12
    8.1. Normative References ......................................12
    8.2. Informative References ....................................13

1. Introduction

 The Session Initiation Protocol (SIP) Extension for Event State
 Publication [RFC3903] allows Presence User Agents ('PUA') to publish
 presence information of a user ('presentity').  The Presence Agent
 (PA) collects publications from one or several presence user agents,
 and generates the composite event state of the presentity.
 The baseline format for presence information is defined in the
 Presence Information Data Format (PIDF) [RFC3863] and is by default
 used in presence publication.  The PIDF uses Extensible Markup
 Language (XML) [W3C.REC-xml], and groups data into elements called
 tuples.  In addition, [RFC4479], [RFC4480], [RFC4481], [RFC4482], and
 [RFC5196] define extension elements that provide various additional
 features to PIDF.
 Presence publication by default uses the PIDF document format, and
 each publication contains full state, regardless of how much of the
 presence information has actually changed since the previous update.
 As a consequence, updating a sizeable presence document especially
 with small changes bears a considerable overhead and is therefore
 inefficient.  Publication of information over low bandwidth and high
 latency links further exacerbates this inefficiency.
 This memo specifies a mechanism with which the PUA is after an
 initial full state publication able to publish only those parts of
 the presence document that have changed since the previous update.
 This is accomplished using the partial PIDF [RFC5262] document format

Niemi, et al. Standards Track [Page 2] RFC 5264 Partial Publication September 2008

 to communicate a set of presence document changes to the PA, who then
 applies the changes in sequence to its version of the presence
 document.
 This memo is structured in the following way: Section 3 gives an
 overview of the partial publication mechanism, Section 4 includes the
 detailed specification, Section 5 includes discussion of security
 considerations, and Section 6 includes examples of partial
 publication.

2. Definitions and Document 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, BCP 14
 [RFC2119], and indicate requirement levels for compliant
 implementations.
 This document makes use of the vocabulary defined in the Model for
 Presence and Instant Messaging [RFC2778], the Event State Publication
 Extension to SIP [RFC3903], and the PIDF Extension for Partial
 Presence [RFC5262].

3. Overall Operation

 This section introduces the baseline functionality for presence
 publication, and gives an overview of the partial publication
 mechanism.  This section is informational in nature.  It does not
 contain any normative statements.

3.1. Presence Publication

 Event State Publication is specified in [RFC3903].
 The publication of presence information consists of a presence user
 agent sending a SIP PUBLISH request [RFC3903] targeted to the
 address-of-record of the presentity, and serviced by a presence agent
 or compositor.  The body of the PUBLISH request carries full event
 state in the form of a presence document.
 The compositor processes the PUBLISH request and stores the presence
 information.  It also assigns an entity-tag that is used to identify
 the publication.  This entity-tag is returned to the PUA in the
 response to the PUBLISH request.
 The PUA uses the entity-tag in the following PUBLISH request for
 identifying the publication that the request is meant to refresh,
 modify or remove.  Presence information is stored in an initial

Niemi, et al. Standards Track [Page 3] RFC 5264 Partial Publication September 2008

 publication, and maintained using the refreshing and modifying
 publications.  Presence information disappears either by explicitly
 removing it or when it meets its expiration time.

3.2. Partial Presence Publication

 The partial publication mechanism enables the PUA to update only
 parts of its presence information, namely those sections of the
 presence document that have changed.  The initial publication always
 carries full state.  However, successive modifying publications to
 this initial presence state can communicate state deltas, i.e., one
 or more changes to the presence information since the previous
 update.  Versioning of these partial publications is necessary to
 guarantee that the changes are applied in the correct order.  The
 PUBLISH method [RFC3903] already accomplishes this using entity-tags
 and conditional requests, which guarantee correct ordering of
 publication updates.
    Note that the partial PIDF format [RFC5262] contains the 'version'
    attribute that could be used for versioning as well.  However, we
    chose not to introduce an additional versioning mechanism to
    partial publish, since that would only add ambiguity and a
    potentially undefined error case if the two versioning mechanisms
    were to somehow contradict.
 To initialize its publication of presence information, the PUA first
 publishes a full state initial publication.  The consequent modifying
 publications can carry either state deltas or full state.  Both
 initial and modifying partial presence publications are accomplished
 using the 'application/pidf-diff+xml' content type [RFC5262], with
 the former using the <pidf-full> root element, and the latter using
 the <pidf-diff> or <pidf-full> root elements, respectively.
 While the <pidf-full> encapsulates a regular PIDF document, the
 <pidf-diff> can contain one or more operations for adding new
 elements or attributes (<add> elements), replacing elements or
 attributes whose content has changed (<replace> elements), or
 indications of removal of certain elements or attributes (<remove>
 elements).  The PUA is free to decide the granularity by which
 changes in presence information are communicated to the composer.  It
 may very well happen that there are enough changes to be communicated
 that it is more efficient to send a full state publication instead of
 a set of state deltas.
 When the presence compositor receives a partial publication, it
 applies the included patch operations in sequence.  The resulting
 changed (or patched) presence document is then submitted to the
 composition logic in the same manner as with a full state presence

Niemi, et al. Standards Track [Page 4] RFC 5264 Partial Publication September 2008

 publication.  Similarly, any changes to the publication expiration
 apply to the full, patched presence publication.  In other words,
 there is no possibility to roll back to an earlier version, except by
 submitting a full state publication.

4. Client and Server Operation

 Unless otherwise specified in this document, the presence user agent
 and presence agent behavior are as defined in [RFC3903].

4.1. Content-Type for Partial Publications

 The entities supporting the partial publication extension described
 in this document MUST support the 'application/pidf-diff+xml' content
 type defined in the partial PIDF format [RFC5262], in addition to the
 baseline 'application/pidf+xml' content type defined in [RFC3863].
 Listing the partial PIDF content type in the Accept header field of a
 SIP response is an explicit indication of support for the partial
 publication mechanism.  The PUA can learn server support either as a
 result of an explicit query, i.e., in a response to an OPTIONS
 request, or by trial-and-error, i.e., after a 415 error response is
 returned to an attempted partial publication.

4.2. Generation of Partial Publications

 Whenever a PUA decides to begin publication of partial presence
 information, it first needs to make an initial publication.  This
 initial publication always carries full state.  After the initial
 publication, presence information can be updated using modifying
 publications; the modifications can carry state deltas as well as
 full state.  Finally, the publication can be terminated by explicit
 removal, or by expiration.
 Both the initial and modifying publications make use of the partial
 presence document format [RFC5262], and all follow the normal rules
 for creating publications, as defined in RFC 3903 [RFC3903], Section
 4.
 If the initial PUBLISH request returns a 415 (Unsupported Media
 Type), it means that the compositor did not understand the partial
 publication format.  In this case, the PUA MUST follow normal
 procedures for handling a 400-class response, as specified in Section
 8.1.3.5 of [RFC3261].  Specifically, the PUA SHOULD retry the
 publication using the default PIDF content type, namely 'application/
 pidf+xml'.  In addition, to find out a priori whether a specific
 presence compositor supports partial presence publication, the PUA
 MAY use the OPTIONS method, as described in [RFC3261].

Niemi, et al. Standards Track [Page 5] RFC 5264 Partial Publication September 2008

 To construct a full-state publication, the PUA uses the following
 process:
 o  The Content-Type header field in the PUBLISH request MUST be set
    to the value 'application/pidf-diff+xml'.
 o  The document in the body of the request is populated with a <pidf-
    full> root element that includes the 'entity' attribute set to
    identify the presentity.
 o  Under the <pidf-full> root element exists all of the children of a
    PIDF [RFC3863] <presence> element.  This document contains the
    full state of which the PUA is aware, and MAY include elements
    from any extension namespace.
 To construct a partial publication, the following process is
 followed:
 o  The Content-Type header field in the PUBLISH request MUST be set
    to the value 'application/pidf-diff+xml'.
 o  The document in the body of the request is populated with a <pidf-
    diff> root element that includes the 'entity' attribute
    identifying the presentity.
 o  Under the <pidf-diff> root element exists a set of patch
    operations that communicate the changes to the presentity's
    presence information.  These operations MUST be constructed in
    sequence, and as defined in the partial PIDF format [RFC5262].
 The PUA is free to decide the granularity by which changes in the
 presentity's presence information are communicated to the presence
 compositor.  In order to reduce unnecessary network traffic, the PUA
 SHOULD batch several patch operations in a single PUBLISH request.
    A reasonable granularity might be to batch state changes resulting
    from related UI events together in a single PUBLISH request.  For
    example, when the user sets their status to "Away", several things
    including freetext notes, service availability, and activities
    might change as a result.
 If the size of the delta state becomes more than the size of the full
 state, the PUA SHOULD instead send a modifying publication carrying
 full state, unless this size comparison is not possible.
    To an implementation that generates state deltas directly out of
    its internal events, it may not be trivial to determine the size
    of the corresponding full state.

Niemi, et al. Standards Track [Page 6] RFC 5264 Partial Publication September 2008

4.3. Processing of Partial Publications

 For each resource, the compositor maintains a record for each of the
 publications.  These are indexed using the entity-tag of the
 publications.
 Processing of publications generally follows the guidelines set in
 [RFC3903].  In addition, processing PUBLISH requests that contain
 'application/pidf-diff+xml' require some extra processing that is
 dependant on whether the request contains full or partial state.

4.3.1. Processing <pidf-full>

 If the value of the Content-Type header field is 'application/
 pidf-diff+xml', and the document therein contains a <pidf-full> root
 element, the publication contains full presence information, and the
 next step applies:
 o  The compositor MUST take the received presence document under the
    <pidf-full> as the local presence document, replacing any previous
    publications.
 If any errors are encountered before the entire publication is
 completely processed, the compositor MUST reject the request with a
 500 (Server Internal Error) response, and revert back to its
 original, locally stored presence information.

4.3.2. Processing <pidf-diff>

 If the value of the Content-Type header field is 'application/
 pidf-diff+xml', and the document in the body contains a <pidf-diff>
 root element, the publication contains partial presence information
 (state delta), and the next steps apply:
 o  If the publication containing the <pidf-diff> root element is a
    modifying publication (i.e., contains an If-Match header field
    with a valid entity-tag), the compositor MUST apply the included
    patch operations in sequence against its locally stored presence
    document.
 o  Else, the publication is an initial publication, for which only
    <pidf-full> is allowed.  Therefore, the publication MUST be
    rejected with an appropriate error response, such as a 400
    (Invalid Partial Publication).
 If a publication carrying partial presence information expires
 without the PUA refreshing it, the compositor MUST clear the entire,
 full state publication.

Niemi, et al. Standards Track [Page 7] RFC 5264 Partial Publication September 2008

    This means that the compositor does not keep a record of the
    applied patches, and consequently (unlike some versioning
    systems), the compositor does not roll back to an earlier version
    if a particular partial publication were to expire.
 If the compositor encounters errors while processing the
 'application/pidf-diff+xml' document, it MUST reject the request with
 a 400 (Bad Request) response.  In addition, the compositor MAY
 include diagnostics information in the body of the response, using an
 appropriate error condition element defined in Section 5.1. of
 [RFC5261].
 If any other errors are encountered before the entire partial
 publication is completely processed, including all of the patch
 operations in the 'application/pidf-diff+xml' body, the compositor
 MUST reject the request with a 500 (Server Internal Error) response,
 and revert back to its original, locally stored presence information.

5. Security Considerations

 This specification relies on protocol behavior defined in [RFC3903].
 General security considerations related to Event State Publication
 are extensively discussed in that specification and all the
 identified security considerations apply to this document in
 entirety.  In addition, this specification adds no new security
 considerations.

6. Examples

 The following message flow (Figure 1) shows an example of a presence
 system that applies the partial publication mechanism.
 First, the PUA sends an initial publication that contains full state.
 In return, it receives a 200 OK response containing an entity-tag.
 This entity-tag serves as a reference with which the initial full
 state can be updated using partial publications containing state
 deltas.
 Then at some point the resource state changes, and the PUA assembles
 these changes into a set of patch operations.  It then sends a
 modifying publication containing the patch operations, using the
 entity-tag as a reference to the publication against which the
 patches are to be applied.  The compositor applies the received patch
 operations to its local presence document in sequence, and returns a
 200 OK, which includes a new entity-tag.

Niemi, et al. Standards Track [Page 8] RFC 5264 Partial Publication September 2008

                                           Presence Agent /
                   PUA                        Compositor
                    | (M1) PUBLISH                |
                    |---------------------------->|
                    | (M2) 200 OK                 |
                    |<----------------------------|
                    |                             |
                    |                             |
                    |                             |
                    | (M3) PUBLISH                |
                    |---------------------------->|
                    | (M4) 200 OK                 |
                    |<----------------------------|
                    |                             |
                   _|_                           _|_
              Figure 1: Partial Publication Message Flow
 Message details:
 (M1): PUA -> Compositor
       PUBLISH sip:resource@example.com SIP/2.0
       ...
       Event: presence
       Expires: 3600
       Content-Type: application/pidf-diff+xml
       Content-Length: 1457
       <?xml version="1.0" encoding="UTF-8"?>
       <p:pidf-full xmlns="urn:ietf:params:xml:ns:pidf"
              xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
              xmlns:r="urn:ietf:params:xml:ns:pidf:rpid"
              xmlns:c="urn:ietf:params:xml:ns:pidf:caps"
              entity="pres:someone@example.com">
        <tuple id="sg89ae">
         <status>
          <basic>open</basic>
          <r:relationship>assistant</r:relationship>
         </status>
         <c:servcaps>
          <c:audio>true</c:audio>
          <c:video>false</c:video>
          <c:message>true</c:message>
         </c:servcaps>
         <contact priority="0.8">tel:09012345678</contact>
        </tuple>

Niemi, et al. Standards Track [Page 9] RFC 5264 Partial Publication September 2008

        <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>
          <r:activity>meeting</r:activity>
         </status>
         <r:homepage>http://example.com/~pep/</r:homepage>
         <r:icon>http://example.com/~pep/icon.gif</r:icon>
         <r:card>http://example.com/~pep/card.vcd</r:card>
         <contact priority="0.9">sip:pep@example.com</contact>
        </tuple>
        <note xml:lang="en">Full state presence document</note>
        <r:person>
         <r:status>
          <r:activities>
           <r:on-the-phone/>
           <r:busy/>
          </r:activities>
         </r:status>
        </r:person>
        <r:device id="urn:esn:600b40c7">
         <r:status>
          <c:devcaps>
           <c:mobility>
            <c:supported>
             <c:mobile/>
            </c:supported>
           </c:mobility>
          </c:devcaps>
         </r:status>
        </r:device>
       </p:pidf-full>

Niemi, et al. Standards Track [Page 10] RFC 5264 Partial Publication September 2008

 (M2): Compositor -> PUA
       SIP/2.0 200 OK
       ...
       SIP-ETag: 61763862389729
       Expires: 3600
       Content-Length: 0
 (M3): PUA -> Compositor
       PUBLISH sip:resource@example.com SIP/2.0
       ...
       Event: presence
       SIP-If-Match: 61763862389729
       Expires: 3600
       Content-Type: application/pidf-diff+xml
       Content-Length: 778
       <?xml version="1.0" encoding="UTF-8"?>
       <p:pidf-diff xmlns="urn:ietf:params:xml:ns:pidf"
                    xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
                    xmlns:r="urn:ietf:params:xml:ns:pidf:rpid"
                    entity="pres:someone@example.com">
        <p:add sel="presence/note" pos="before"><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 note element</note>
        </tuple>
        </p:add>
        <p:replace sel="*/tuple[@id='r1230d']/status/basic/text()"
         >open</p:replace>
        <p:remove sel="*/r:person/r:status/r:activities/r:busy"/>
        <p:replace sel="*/tuple[@id='cg231jcr']/contact/@priority"
         >0.7</p:replace>
       </p:pidf-diff>

Niemi, et al. Standards Track [Page 11] RFC 5264 Partial Publication September 2008

 (M4): Compositor -> PUA
       SIP/2.0 200 OK
       ...
       SIP-ETag: 18764920981476
       Expires: 3600
       Content-Length: 0

7. Acknowledgements

 The authors would like to thank Atle Monrad, Christian Schmidt,
 George Foti, Fridy Sharon-Fridman, and Avshalom Houri for review
 comments.

8. References

8.1. Normative References

 [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3903]      Niemi, A., "Session Initiation Protocol (SIP)
                Extension for Event State Publication", RFC 3903,
                October 2004.
 [RFC3863]      Sugano, H., Fujimoto, S., Klyne, G., Bateman, A.,
                Carr, W., and J. Peterson, "Presence Information Data
                Format (PIDF)", RFC 3863, August 2004.
 [RFC3261]      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.
 [RFC5262]      Lonnfors, M., Costa-Requena, J., Leppanen, E., and H.
                Khartabil, "Presence Information Data Format (PIDF)
                Extension for Partial Presence", RFC 5262, September
                2008.
 [RFC5261]      Urpalainen, J., "An Extensible Markup Language (XML)
                Patch Operations Framework Utilizing XML Path Language
                (XPath) Selectors", RFC 5261, September 2008.

Niemi, et al. Standards Track [Page 12] RFC 5264 Partial Publication September 2008

8.2. Informative References

 [RFC2778]      Day, M., Rosenberg, J., and H. Sugano, "A Model for
                Presence and Instant Messaging", RFC 2778,
                February 2000.
 [RFC4479]      Rosenberg, J., "A Data Model for Presence", RFC 4479,
                July 2006.
 [RFC4480]      Schulzrinne, H., Gurbani, V., Kyzivat, P., and J.
                Rosenberg, "RPID: Rich Presence Extensions to the
                Presence Information Data Format (PIDF)", RFC 4480,
                July 2006.
 [RFC4481]      Schulzrinne, H., "Timed Presence Extensions to the
                Presence Information Data Format (PIDF) to Indicate
                Status Information for Past and Future Time
                Intervals", RFC 4481, July 2006.
 [RFC4482]      Schulzrinne, H., "CIPID: Contact Information for the
                Presence Information Data Format", RFC 4482,
                July 2006.
 [RFC5196]      Lonnfors, M. and K. Kiss, "Session Initiation Protocol
                (SIP) User Agent Capability Extension to Presence
                Information Data Format (PIDF)", RFC 5196, September
                2008.
 [W3C.REC-xml]  Bray, T., Paoli, J., Sperberg-McQueen, C., and E.
                Maler, "Extensible Markup Language (XML) 1.0 (2nd
                ed)", W3C REC-xml, October 2000,
                <http://www.w3.org/TR/REC-xml>.

Niemi, et al. Standards Track [Page 13] RFC 5264 Partial Publication September 2008

Authors' Addresses

 Aki Niemi
 Nokia
 P.O. Box 407
 NOKIA GROUP, FIN 00045
 Finland
 Phone: +358 71 8008000
 EMail: aki.niemi@nokia.com
 Mikko Lonnfors
 Nokia
 Itamerenkatu 11-13
 Helsinki
 Finland
 Phone: +358 71 8008000
 EMail: mikko.lonnfors@nokia.com
 Eva Leppanen
 Individual
 Lempaala
 Finland
 EMail: eva.leppanen@saunalahti.fi

Niemi, et al. Standards Track [Page 14] RFC 5264 Partial Publication September 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Niemi, et al. Standards Track [Page 15]

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