RFC 1059 (rfc1059) - Page 3 of 58

Network Time Protocol (version 1) specification and implementation

RFC 1059                 Network Time Protocol                 July 1988


1.  Introduction

   This document describes the Network Time Protocol (NTP), including
   the architectures, algorithms and protocols to synchronize local
   clocks in a set of distributed clients and servers.  The protocol was
   first described in RFC-958 [24], but has evolved in significant ways
   since publication of that document.  NTP is built on the Internet
   Protocol (IP) [10] and User Datagram Protocol (UDP) [6], which
   provide a connectionless transport mechanism;  however, it is readily
   adaptable to other protocol suites.  It is evolved from the Time
   Protocol [13] and the ICMP Timestamp message [11], but is
   specifically designed to maintain accuracy and robustness, even when
   used over typical Internet paths involving multiple gateways and
   unreliable nets.

   The service environment consists of the implementation model, service
   model and time scale described in Section 2.  The implementation
   model is based on a multiple-process operating system architecture,
   although other architectures could be used as well.  The service
   model is based on a returnable-time design which depends only on
   measured offsets, or skews, but does not require reliable message
   delivery.  The subnet is a self-organizing, hierarchical master-slave
   configuration, with synchronization paths determined by a minimum-
   weight spanning tree.  While multiple masters (primary servers) may
   exist, there is no requirement for an election protocol.

   NTP itself is described in Section 3.  It provides the protocol
   mechanisms to synchronize time in principle to precisions in the
   order of nanoseconds while preserving a non-ambiguous date well into
   the next century.  The protocol includes provisions to specify the
   characteristics and estimate the error of the local clock and the
   time server to which it may be synchronized.  It also includes
   provisions for operation with a number of mutually suspicious,
   hierarchically distributed primary reference sources such as radio
   clocks.

   Section 4 describes algorithms useful for deglitching and smoothing
   clock-offset samples collected on a continuous basis.  These
   algorithms began with those suggested in [22], were refined as the
   results of experiments described in [23] and further evolved under
   typical operating conditions over the last two years.  In addition,
   as the result of experience in operating multiple-server nets
   including radio-synchronized clocks at several sites in the US and
   with clients in the US and Europe, reliable algorithms for selecting
   good clocks from a population possibly including broken ones have
   been developed and are described in Section 4.

   The accuracies achievable by NTP depend strongly on the precision of



Mills