RTP and Leap Seconds
draft-ietf-avtcore-leap-second-01

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Document Type Active Internet-Draft (avtcore WG)
Last updated 2012-10-19
Replaces draft-gross-leap-second, draft-gross-avtcore-leap-second
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AVTCore                                                         K. Gross
Internet-Draft                                              AVA Networks
Updates: 3550 (if approved)                           R. van Brandenburg
Intended status: Standards Track                                     TNO
Expires: April 22, 2013                                 October 19, 2012

                          RTP and Leap Seconds
                   draft-ietf-avtcore-leap-second-01

Abstract

   This document discusses issues that arise when RTP sessions span
   Universal Coordinate Time (UTC) leap seconds.  It updates RFC 3550 to
   describe how RTP senders and receivers should behave in the presence
   of leap seconds.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 22, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Leap seconds  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  UTC behavior during leap second . . . . . . . . . . . . . . 4
     3.2.  NTP behavior during leap second . . . . . . . . . . . . . . 4
     3.3.  POSIX behavior during leap second . . . . . . . . . . . . . 4
     3.4.  Summary of leap-second behaviors  . . . . . . . . . . . . . 4
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 5
     4.1.  RTP Sender Reports and Receiver Reports . . . . . . . . . . 5
     4.2.  RTP Packet Playout  . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   In some media networking applications, RTP streams are referenced to
   a wall-clock time (absolute date and time).  This is accomplished
   through use of the NTP timestamp field in the RTCP sender report (SR)
   to create a mapping between RTP timestamps and the wall clock.  When
   a wall-clock reference is used, the play-out time for RTP packets is
   referenced to the wall clock.  Smooth and continuous media play out
   requires a smooth and continuous time base.  The time base used by
   the wall clock may include leap seconds which are not rendered
   smoothly.

   This document provides recommendations for smoothly rendering
   streamed media referenced to common wall clocks which do not have
   smooth or continuous behavior in the presence of leap seconds.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [1] and indicate
   requirement levels for compliant implementations.

3.  Leap seconds

   The world time standard is International Atomic Time (TAI) which is
   based on vibrations of cesium atoms in an atomic clock.  The more
   common Universal Coordinated Time (UTC) is based on the rotation of
   the Earth.  In 1971 UTC was redefined in terms of TAI and the concept
   of leap seconds was introduced to allow UTC to remain synchronized
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