Calendaring Extensions to WebDAV (CalDAV): Time Zones by Reference
RFC 7809

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Internet Engineering Task Force (IETF)                          C. Daboo
Request for Comments: 7809                                         Apple
Updates: 4791                                                 March 2016
Category: Standards Track
ISSN: 2070-1721

   Calendaring Extensions to WebDAV (CalDAV): Time Zones by Reference

Abstract

   This document defines an update to the Calendaring Extensions to
   WebDAV (CalDAV) calendar access protocol (RFC 4791) to allow clients
   and servers to exchange iCalendar data without the need to send full
   time zone data.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7809.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Daboo                        Standards Track                    [Page 1]
RFC 7809               CalDAV Time Zone Extension             March 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Time Zones by Reference . . . . . . . . . . . . . . . . . . .   3
     3.1.  New Server Behavior . . . . . . . . . . . . . . . . . . .   4
   4.  New Client Behavior . . . . . . . . . . . . . . . . . . . . .   7
   5.  New WebDAV Properties . . . . . . . . . . . . . . . . . . . .   8
     5.1.  CALDAV:timezone-service-set . . . . . . . . . . . . . . .   8
     5.2.  CALDAV:calendar-timezone-id . . . . . . . . . . . . . . .   9
   6.  XML Element Definitions . . . . . . . . . . . . . . . . . . .   9
     6.1.  CALDAV:calendar-query XML Element . . . . . . . . . . . .   9
     6.2.  CALDAV:timezone-id XML Element  . . . . . . . . . . . . .  10
   7.  Additional Message Header Fields  . . . . . . . . . . . . . .  10
     7.1.  CalDAV-Timezones Request Header Field . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  11
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  CalDAV-Timezones . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The CalDAV [RFC4791] calendar access protocol allows clients to
   access calendar data stored on a server in the iCalendar [RFC5545]
   data format.  In iCalendar, calendar data that uses local time in any
   of its date and/or time values is specified as a date-time value in
   combination with a time zone identifier ("TZID" property parameter).
   The time zone identifier refers to a time zone definition (a
   "VTIMEZONE" component) that has all of the rules required to
   determine local-time UTC offsets for the corresponding time zone.  In
   many cases, these "VTIMEZONE" components can be larger, octet-wise,
   than the events or tasks that make use of them.  However, iCalendar
   currently requires all iCalendar objects ("VCALENDAR" components)
   that refer to a time zone via its identifier to also include the
   corresponding "VTIMEZONE" component.  This leads to inefficiencies in
   the CalDAV protocol because large amounts of "VTIMEZONE" data are
   continuously being exchanged, and for the most part these time zone
   definitions are unchanging.  This is particularly problematic for
   mobile or limited devices, with limited network bandwidth, CPU, and
   energy resources.

Daboo                        Standards Track                    [Page 2]
RFC 7809               CalDAV Time Zone Extension             March 2016