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