Publication of Partial Presence Information
RFC 5264

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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