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ntp_intro(7)
NAME
  ntp_intro - Network Time Protocol (NTP) introductory information

DESCRIPTION
  The Tru64 UNIX software supports two time services:

    ·  Network Time Protocol (NTP)

    ·  Time Synchronization Protocol (TSP)

  Because it can be traced to clocks of high absolute accuracy, NTP provides
  a more accurate time service than TSP. By contrast, TSP synchronizes time
  to the average of the network host times.  TSP is an acceptable time
  service if your system is not on the Internet and does not have access to a
  highly accurate time server; otherwise, NTP is recommended.

  Network Time Protocol

  The Network Time Protocol (NTP) provides accurate, dependable, and
  synchronized time for hosts on both wide area networks (like the Internet)
  and local area networks. In particular, NTP provides synchronization
  traceable to clocks of high absolute accuracy, and avoids synchronization
  to clocks keeping bad time.

  Hosts running NTP periodically exchange datagrams querying each other about
  their current estimate of the time.  Using the round-trip time of the
  packet, a host can estimate the one-way delay to the other host.  (The
  assumption is that the delay is roughly equal in both directions.) By
  measuring the one-way delay and examining the timestamps that are returned
  with the NTP packet, a host computes the difference between its clock time
  and that of the host it queried.

  A host queries a remote host several times over a period and feeds the
  results from the multiple samples to a digital-filtering algorithm.  The
  algorithm provides a more accurate estimate of the delay, clock offset, and
  clock stability than could be obtained with a single sample.

  NTP messages also contain information about the accuracy and reliability of
  the time sources.  An NTP host connected directly to a highly accurate time
  source, such as a radio receiver tuned to a time code signal broadcast by a
  government agency, is called a stratum 1 server.  Every other NTP host
  adopts a stratum number that is one higher than the host from which it sets
  its own time.	 For example, a host synchronized to a stratum 1 server
  becomes a stratum 2 host.  Stratum determination is done automatically, and
  the stratum of a host can vary as its connectivity changes.

  A host running NTP combines various information to decide which of the
  hosts it queried provides the time it believes to be the most accurate.
  This information includes the output of the digital-filtering algorithm and
  the stratum numbers of the hosts it queried.	By communicating with several
  other hosts, an NTP host can usually detect those hosts that are keeping
  bad time, and is able to stay synchronized even if some of the other hosts
  become unavailable for long periods.

  In practice, NTP is able to synchronize clocks to within a few milliseconds
  even over wide area networks spanning thousands of miles. To obtain even
  greater accuracy, use the NTP_TIME kernel option.  See System
  Administration for more information.

  You can optionally use a high-resolution clock, enabling the time returned
  by the clock_gettime routine to be extrapolated between the clock ticks.
  The granularity of the time returned will be in microseconds. To use the
  high-resolution clock, use the MICRO_TIME kernel option.

  For detailed information on NTP, see Network Time Protocol (Version 3) (RFC
  1305).

  Time Synchronization Protocol

  The Time Synchronization Protocol (TSP) is the protocol used by the
  /usr/sbin/timed daemon.  In its simplest application, the TSP servers on a
  broadcast network (for example, an Ethernet) periodically broadcast TSP
  packets.  The hosts on the network elect one of the hosts on the network
  running TSP as a master.  The master then controls the further operation of
  the protocol until it fails and a new master is elected.  The master
  collects time values from the other hosts and computes the average of all
  the times reported.  It then sets its own clock to this average, and tells
  the other hosts to synchronize their clocks with it.

  TSP quickly synchronizes all participating hosts.  However, because TSP
  does not trace time back to sources of known accuracy, it is unable to
  correct for systematic errors.  If a clock drifts significantly, or if a
  mistake is made in setting the time on a participating host, the average
  time calculated and distributed by the master can be affected
  significantly.

  For information on setting up the network time services, refer to Network
  Administration: Services.

SEE ALSO
  Commands:ntp(1), ntpdate(8), ntptrace(8), timedsetup(8), xntpdc(8)

  Functions: ctime(3)

  Files: ntp.conf(4), ntp.drift(4), ntp.keys(4)

  Daemons: timed(8), xntpd(8)

  Network Time Protocol (Version 3) (RFC 1305)

  Network Administration: Services System Administration

Index for Section 7

Alphabetical listing for N

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