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
( 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
Schulzrinne Standards Track [Page 1]
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
element in the PIDF 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 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 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].
Schulzrinne Standards Track [Page 2]
RFC 4481 Timed Presence July 2006
3. Timed-Status Element
The element is a child of the element and MUST
NOT appear as a child of a PIDF element or another
element. More than one such element MAY appear within
a PIDF element.
Sources of 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 indications.
The 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 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
element that covers the present time. The PA MAY
either discard that element or MAY convert it to a regular
element if it considers that information more credible.
The element may contain the and
elements, as well as any other element that is appropriate as a PIDF
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 elements
that are fully in the past or future relative to local real
(wallclock) time and the time information contained in the optional
PIDF element.
Schulzrinne Standards Track [Page 3]
RFC 4481 Timed Presence July 2006
4. Example
An example combining PIDF and timed-status is shown below:
open
closed
sip:someone@example.com
I'll be in Tokyo next week
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.
Describes timed-status tuple extensions for PIDF.
Schulzrinne Standards Track [Page 5]
RFC 4481 Timed Presence July 2006
6. IANA Considerations
This document calls for IANA to register a new XML namespace URN and
schema per [2].
6.1. URN Sub-Namespace Registration for
'urn:ietf:params:xml:ns:pidf:timed-status'
URI: urn:ietf:params:xml:ns:pidf:timed-status
Description: This is the XML namespace for XML elements defined by
RFC 4481 to describe timed-status presence information extensions
for the status element in the PIDF presence document format in the
application/pidf+xml content type.
Registrant Contact: IETF, SIMPLE working group, simple@ietf.org;
Henning Schulzrinne, hgs@cs.columbia.edu
XML:
BEGIN
Timed Presence Extensions to the Presence
Information Data Format (PIDF) to Indicate Status
Information for Past and Future Time Intervals
Namespace for timed-status presence extension
urn:ietf:params:xml:ns:pidf:timed-status
See
RFC4481.