On Implementing Time
draft-aanchal-time-implementation-guidance-02

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Last updated 2019-07-08
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NTP Working Group                                            A. Malhotra
Internet-Draft                                         Boston University
Intended status: Informational                                K. Teichel
Expires: January 9, 2020                                             PTB
                                                             M. Hoffmann
                                                               W. Toorop
                                                              NLnet Labs
                                                            July 8, 2019

                          On Implementing Time
             draft-aanchal-time-implementation-guidance-02

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.

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
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   This Internet-Draft will expire on January 9, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://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

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   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.

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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