RTP and Leap Seconds
RFC 7164

Internet Engineering Task Force (IETF)                          K. Gross
Request for Comments: 7164                                  AVA Networks
Updates: 3550                                         R. van Brandenburg
Category: Standards Track                                            TNO
ISSN: 2070-1721                                               March 2014

                          RTP and Leap Seconds

Abstract

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

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/rfc7164.

Copyright Notice

   Copyright (c) 2014 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.

Gross & van Brandenburg      Standards Track                    [Page 1]
RFC 7164                  RTP and Leap Seconds                March 2014

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Leap Seconds  . . . . . . . . . . . . . . . . . . . . . . . .   2
     3.1.  UTC Behavior during a Positive Leap Second  . . . . . . .   3
     3.2.  NTP Behavior during a Positive Leap Second  . . . . . . .   3
     3.3.  POSIX Behavior during a Positive Leap Second  . . . . . .   3
     3.4.  Example of Leap-Second Behaviors  . . . . . . . . . . . .   4
   4.  Receiver Behavior during a Leap Second  . . . . . . . . . . .   5
   5.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Sender Reports  . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  RTP Packet Playout  . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8

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 sender report (SR) to
   create a mapping between RTP timestamps and the wall clock.  When a
   wall-clock reference is used, the playout time for RTP packets is
   referenced to the wall clock.  Smooth and continuous media playout
   requires a smooth and continuous time base.  The time base used by
   the wall clock may include leap seconds that are not rendered
   smoothly.

   This document updates RFC 3550 [1] by providing recommendations for
   smoothly rendering streamed media referenced to common wall clocks
   that 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 RFC 2119 [2] and
   indicate requirement levels for compliant implementations.

3.  Leap Seconds

   The world's scientific time standard is International Atomic Time
   (TAI), which is based on vibrations of cesium atoms in an atomic
   clock.  The world's civil time is based on the rotation of the Earth.

Gross & van Brandenburg      Standards Track                    [Page 2]