RTP and Leap Seconds
draft-ietf-avtcore-leap-second-00
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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
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 23, 2012.
Copyright Notice
Copyright (c) 2012 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 Expires December 23, 2012 [Page 1]
Internet-Draft RTP Leap Seconds June 2012
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
Gross & van Brandenburg Expires December 23, 2012 [Page 2]
Internet-Draft RTP Leap Seconds June 2012
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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