On Implementing Time
draft-ietf-ntp-implementation-guidance-00
NTP Working Group A. Malhotra
Internet-Draft Boston University
Intended status: Informational K. Teichel
Expires: May 22, 2020 PTB
M. Hoffmann
W. Toorop
NLnet Labs
November 19, 2019
On Implementing Time
draft-ietf-ntp-implementation-guidance-00
Abstract
This document describes the properties of different types of clocks
available on digital systems. It provides implementors of
applications with guidance on choices they have to make when working
with time to provide basic functionality and security guarantees.
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This Internet-Draft will expire on May 22, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Scope of the document . . . . . . . . . . . . . . . . . . . . 3
3. Expressing Time . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Absolute Time . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Relative Time . . . . . . . . . . . . . . . . . . . . . . 4
4. Keeping Time: Different Clocks . . . . . . . . . . . . . . . 4
4.1. Native Clock . . . . . . . . . . . . . . . . . . . . . . 4
4.2. World Clock . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Approaches . . . . . . . . . . . . . . . . . . 6
6. Accessing the Native Clock on Selected Operating Systems . . 7
6.1. POSIX . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.2. Microsoft Window . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
It is hard to overstate the importance of time in modern digital
systems. The functionality and security of applications (distributed
or local to one system) and that of network protocols generally hinge
on some notion of time. For implementation, these applications and
protocols have to choose one of the types of clocks available on
their system, each of which has its own specific properties.
However, currently many of these applications seem to be oblivious to
the implications of choosing one or the other clock for
implementation. This behavior can be attributed to:
a. the lack of clear understanding of the distinct properties of
these clocks,
b. trade-offs of using one or the other for an application, and
c. availability and compatibility of these clocks on different
systems.
This document discusses a) and b).
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