[ntp:questions] Internet-Draft on how to deal with leap seconds (UTC-SLS)

Markus Kuhn n06W03+mgk25 at cl.cam.ac.uk
Wed Jan 18 22:39:47 UTC 2006

A new Internet-Draft with implementation guidelines on how to handle UTC
leap seconds in Internet protocols was posted today on the IETF web

  "Coordinated Universal Time with Smoothed Leap Seconds (UTC-SLS)",
  Markus Kuhn, 18-Jan-06. (36752 bytes)


Background information, FAQ, etc.:



  Coordinated Universal Time (UTC) is the international standard timescale
  used in many Internet protocols. UTC features occasional single-second
  adjustments, known as "leap seconds". These happen at the end of
  announced UTC days, in the form of either an extra second 23:59:60 or a
  missing second 23:59:59. Both events need special consideration in
  UTC-synchronized systems that represent time as a scalar value. This
  specification defines UTC-SLS, a minor variation of UTC that lacks leap
  seconds. Instead, UTC-SLS performs an equivalent "smooth" adjustment,
  during which the rate of the clock temporarily changes by 0.1% for 1000
  seconds. UTC-SLS is a drop-in replacement for UTC. UTC-SLS can be
  generated from the same information as UTC. It can be used with any
  specification that refers to UTC but lacks provisions for leap seconds.
  UTC-SLS provides a robust and interoperable way for networked UTC-
  synchronized clocks to handle leap seconds. By providing UTC-SLS instead
  of UTC to applications, operating systems can free most application and
  protocol designers from any need to even know about UTC leap seconds.

Please have a careful look at the full specification and rationale.


Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain

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