RTP and Leap Seconds
RFC 7164
| Document | Type |
RFC - Proposed Standard
(March 2014; No errata)
Updates RFC 3550
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-gross-avtcore-leap-second, draft-gross-leap-second | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Magnus Westerlund | ||
| Shepherd write-up | Show (last changed 2013-11-18) | ||
| IESG | IESG state | RFC 7164 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Richard Barnes | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions | ||
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]
RFC 7164 RTP and Leap Seconds March 2014
In 1972, the civil time standard, Coordinated Universal Time (UTC),
was redefined in terms of TAI and the concept of leap seconds was
introduced to allow UTC to remain synchronized with the rotation of
the Earth.
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