RTP and Leap Seconds
draft-ietf-avtcore-leap-second-00
AVTCore K. Gross
Internet-Draft AVA Networks
Updates: 3550 (if approved) R. van Brandenburg
Intended status: Standards Track TNO
Expires: December 23, 2012 June 21, 2012
RTP and Leap Seconds
draft-ietf-avtcore-leap-second-00
Abstract
This document discusses issues that arise when RTP sessions span
(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
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This Internet-Draft will expire on December 23, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Leap seconds . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. UTC behavior during leap second . . . . . . . . . . . . . . 3
3.2. NTP behavior during leap second . . . . . . . . . . . . . . 4
3.3. POSIX behavior during leap second . . . . . . . . . . . . . 4
4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. RTP Sender Reports and Receiver Reports . . . . . . . . . . 5
4.2. RTP Packet Playout . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
In some applications, RTP streams are referenced to a walllock time
(absolute date and time). This is typically accomplished through use
of the NTP timestamp field in the RTCP sender report (SR) to create a
mapping between RTP timestamps and the wallclock. When a wallclock
reference is used, the playout time for RTP packets is referenced to
the wallclock. Smooth and continuous media playout requires a smooth
and continuous timebase. The timebase used by the wallclock may
include leap seconds which, in many cases, are not rendered smoothly.
This document provides recommendations for smoothly rendering
streamed media referenced to common wallclocks which may 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 [RFC2119] and indicate
requirement levels for compliant implementations.
3. Leap seconds
Leap seconds are intended to keep UTC time synchronized with the
rotation of the earth. Leap seconds are scheduled by the
International Earth Rotation and Reference Systems Service. Leap
seconds may be scheduled at the last day of any month but are
preferentially scheduled for December and June and secondarily March
and September.[TF.460-6] Because earth's rotation is unpredictable,
leap seconds are typically not scheduled more than six months in
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