Date and Time on the Internet: Timestamps
RFC 3339

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Network Working Group                                           G. Klyne
Request for Comments: 3339                        Clearswift Corporation
Category: Standards Track                                      C. Newman
                                                        Sun Microsystems
                                                               July 2002

               Date and Time on the Internet: Timestamps

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 (2002).  All Rights Reserved.

Abstract

   This document defines a date and time format for use in Internet
   protocols that is a profile of the ISO 8601 standard for
   representation of dates and times using the Gregorian calendar.

Table of Contents

   1. Introduction ............................................ 2
   2. Definitions ............................................. 3
   3. Two Digit Years ......................................... 4
   4. Local Time .............................................. 4
   4.1. Coordinated Universal Time (UTC) ...................... 4
   4.2. Local Offsets ......................................... 5
   4.3. Unknown Local Offset Convention ....................... 5
   4.4. Unqualified Local Time ................................ 5
   5. Date and Time format .................................... 6
   5.1. Ordering .............................................. 6
   5.2. Human Readability ..................................... 6
   5.3. Rarely Used Options ................................... 7
   5.4. Redundant Information ................................. 7
   5.5. Simplicity ............................................ 7
   5.6. Internet Date/Time Format ............................. 8
   5.7. Restrictions .......................................... 9
   5.8. Examples ............................................. 10
   6. References ............................................. 10
   7. Security Considerations ................................ 11

Klyne, et. al.              Standards Track                     [Page 1]
RFC 3339       Date and Time on the Internet: Timestamps       July 2002

   Appendix A. ISO 8601 Collected ABNF ....................... 12
   Appendix B. Day of the Week ............................... 14
   Appendix C. Leap Years .................................... 14
   Appendix D. Leap Seconds ..............................,... 15
   Acknowledgements .......................................... 17
   Authors' Addresses ........................................ 17
   Full Copyright Statement .................................. 18

1. Introduction

   Date and time formats cause a lot of confusion and interoperability
   problems on the Internet.  This document addresses many of the
   problems encountered and makes recommendations to improve consistency
   and interoperability when representing and using date and time in
   Internet protocols.

   This document includes an Internet profile of the ISO 8601 [ISO8601]
   standard for representation of dates and times using the Gregorian
   calendar.

   There are many ways in which date and time values might appear in
   Internet protocols:  this document focuses on just one common usage,
   viz. timestamps for Internet protocol events.  This limited
   consideration has the following consequences:

   o  All dates and times are assumed to be in the "current era",
      somewhere between 0000AD and 9999AD.

   o  All times expressed have a stated relationship (offset) to
      Coordinated Universal Time (UTC).  (This is distinct from some
      usage in scheduling applications where a local time and location
      may be known, but the actual relationship to UTC may be dependent
      on the unknown or unknowable actions of politicians or
      administrators.  The UTC time corresponding to 17:00 on 23rd March
      2005 in New York may depend on administrative decisions about
      daylight savings time.  This specification steers well clear of
      such considerations.)

   o  Timestamps can express times that occurred before the introduction
      of UTC.  Such timestamps are expressed relative to universal time,
      using the best available practice at the stated time.

   o  Date and time expressions indicate an instant in time.
      Description of time periods, or intervals, is not covered here.

Klyne, et. al.              Standards Track                     [Page 2]
RFC 3339       Date and Time on the Internet: Timestamps       July 2002

2. Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this