rfc4481.txt

有关IMS SIP及Presence应用的RFC文档包

Network Working Group                                     H. Schulzrinne
Request for Comments: 4481                                   Columbia U.
Category: Standards Track                                      July 2006


                    Timed Presence Extensions to the
               Presence Information Data Format (PIDF) to
     Indicate Status Information for Past and Future Time Intervals

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.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   The Presence Information Data Format (PIDF) defines a basic XML
   format for presenting presence information for a presentity.  This
   document extends PIDF, adding a timed status extension
   (<timed-status> element) that allows a presentity to declare its
   status for a time interval fully in the future or the past.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology and Conventions .....................................2
   3. Timed-Status Element ............................................3
   4. Example .........................................................4
   5. The XML Schema Definition .......................................5
   6. IANA Considerations .............................................6
      6.1. URN Sub-Namespace Registration for
           'urn:ietf:params:xml:ns:pidf:timed-status' .................6
      6.2. Schema Registration for Schema
           'urn:ietf:params:xml:ns:pidf:timed-status' .................7
   7. Security Considerations .........................................7
   8. References ......................................................7
      8.1. Normative References .......................................7
      8.2. Informative References .....................................7
   Contributor's Address ..............................................8
   Acknowledgements ...................................................8




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RFC 4481                     Timed Presence                    July 2006


1.  Introduction

   Traditionally, presence information, e.g., represented as Presence
   Information Data Format [3] (PIDF) and augmented by Rich Presence
   Information Data format [9] (RPID), describes the current state of
   the presentity.  However, a watcher can better plan communications if
   it knows about the presentity's future plans.  For example, if a
   watcher knows that the presentity is about to travel, it might place
   a phone call earlier.

   In this document, we use terms defined in RFC 2778 [7].  In
   particular, a "presentity", abbreviating presence entity, provides
   presence information to a presence service.  It is typically a
   uniquely-identified person.

   RPID already allows a presentity to indicate the period when a
   particular aspect of its presence is valid.  However, the <status>
   element in the PIDF <tuple> does not have this facility, so that it
   is not possible to indicate that a presentity will be OPEN or CLOSED
   in the future, for example.

   It is also occasionally useful to represent past information since it
   may be the only known presence information; it may give watchers an
   indication of the current status.  For example, indicating that the
   presentity was at an off-site meeting that ended an hour ago
   indicates that the presentity is likely in transit at the current
   time.

   It is unfortunately not possible to simply add time range attributes
   to the PIDF <status> element, as PIDF parsers without this capability
   would ignore these attributes and thus not be able to distinguish
   current from future presence status information.

   This document defines the <timed-status> element that describes the
   status of a presentity that is either no longer valid or covers some
   future time period.

2.  Terminology and Conventions

   The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT,
   RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted
   as described in BCP 14, RFC 2119 [1].









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RFC 4481                     Timed Presence                    July 2006


3.  Timed-Status Element

   The <timed-status> element is a child of the <tuple> element and MUST
   NOT appear as a child of a PIDF <status> element or another
   <timed-status> element.  More than one such element MAY appear within
   a PIDF <tuple> element.

   Sources of <timed-status> information should avoid elements that
   overlap in time, but since overlapping appointments are common in
   calendars, for example, receivers MUST be able to render such
   overlapping <timed-status> indications.


   The <timed-status> element MUST be qualified with the 'from'
   attribute and MAY be qualified with an 'until' attribute to describe
   the time when the status assumed this value and the time until which
   this element is expected to be valid.  If the 'until' attribute is
   missing, the information is assumed valid until the tuple is
   explicitly overridden or expires as defined by the publication
   mechanism used.  The time range MUST NOT encompass the present time,
   i.e., the PIDF <timestamp> value, as that would provide an
   unnecessary and confusing alternate mechanism to describe presence.
   Thus, the 'from' attribute for tuples without an 'until' attribute
   MUST refer to the future.

   During composition, a presence agent (PA) may encounter a stored
   <timed-status> element that covers the present time.  The PA MAY
   either discard that element or MAY convert it to a regular <status>
   element if it considers that information more credible.

   The <timed-status> element may contain the <basic> and <note>
   elements, as well as any other element that is appropriate as a PIDF
   <status> extension and that has a limited validity period.  Examples
   include the PIDF-LO [8] extensions for location objects.

   This extension chose absolute rather than relative times, since
   relative times would be too hard to keep properly updated when
   spacing notifications, for example.  Originators of presence
   information MUST generate time values in the <timed-status> elements
   that are fully in the past or future relative to local real
   (wallclock) time and the time information contained in the optional
   PIDF <timestamp> element.









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RFC 4481                     Timed Presence                    July 2006


4.  Example

   An example combining PIDF and timed-status is shown below:

   <presence xmlns="urn:ietf:params:xml:ns:pidf"
     xmlns:ts="urn:ietf:params:xml:ns:pidf:timed-status"
       entity="pres:[e-mail]">

     <tuple id="c8dqui">
       <status>
         <basic>open</basic>
       </status>
       <ts:timed-status from="2005-08-15T10:20:00.000-05:00"
          until="2005-08-22T19:30:00.000-05:00">
          <ts:basic>closed</ts:basic>
       </ts:timed-status>
       <contact>sip:[e-mail]</contact>
     </tuple>
     <note>I'll be in Tokyo next week</note>
   </presence>































Schulzrinne                 Standards Track                     [Page 4]

RFC 4481                     Timed Presence                    July 2006


5.  The XML Schema Definition

   The XML [4] schema [5][6] is shown below.

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:ts="urn:ietf:params:xml:ns:pidf:timed-status"
   xmlns:pidf="urn:ietf:params:xml:ns:pidf"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   targetNamespace="urn:ietf:params:xml:ns:pidf:timed-status"
   elementFormDefault="qualified" attributeFormDefault="unqualified">

     <xs:import namespace="urn:ietf:params:xml:ns:pidf"/>

     <xs:annotation>
        <xs:documentation>
          Describes timed-status tuple extensions for PIDF.
        </xs:documentation>
     </xs:annotation>
     <xs:element name="timed-status" type="ts:timed-status"/>
     <xs:complexType name="timed-status">
       <xs:sequence>
         <xs:element name="basic" type="pidf:basic" minOccurs="0"/>
         <xs:element name="note" type="pidf:note" minOccurs="0"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
           maxOccurs="unbounded"/>