This article describes how a time server can use specialist radio transmissions as a time source to provide accurate atomic clock time to a computer network using the protocol NTP.
Network Time Protocol (NTP) is one of the Internet’s oldest
protocols still used, invented by Dr David Mills from the University of
Delaware, it has been in utilized since 1985. NTP is a protocol designed to
synchronize the clocks on computers and networks across the Internet or Local
Area Networks (LANs).
NTP (version 4) can maintain time over the public Internet
to within 10 milliseconds (1/100th of a second) and can perform even
better over LANs with accuracies of 200 microseconds (1/5000th of a
second) under ideal conditions.
NTP works within the TCP/IP suite and relies on UDP, a less
complex form of NTP exists called Simple Network Time Protocol (SNTP) that does
not require the storing of information about previous communications, needed by
NTP. It is used in some devices and applications where high accuracy timing is
not as important.
Time
synchronisation with NTP is relatively simple, it synchronises time with reference to a
reliable clock source. This source could be relative (a computer’s internal
clock or the time on a wrist-watch
) or absolute (A UTC - Universal Coordinated
Time - clock source that is accurate as is humanely possible).
It is strongly recommended by Microsoft and others, that
external based timing should be used rather than Internet based, as these can’t
be authenticated. Specialist NTP servers are available that can synchronise time on networks
using either the MSF (or equivalent) or GPS signal.
Atomic clocks
are the most absolute time-keeping devices; however, they are extremely
expensive and are generally only to be found in large-scale physics
laboratories. However, NTP can
synchronise networks to an atomic clock by using either the Global
Positioning system (GPS) network or specialist radio transmission (MSF in
Britain).
The MSF
national time and frequency radio transmissions used to synchronise an
NTP server is broadcast by the National Physics Laboratory in Cumbria which serves as the , the radio signal has a finite range and is vulnerable to
interference.
A radio referenced NTP server is easily installed and can
provide an organization with a precise time reference enabling the
synchronization of entire networks
About the author
Richard N Williams is a technical author and a
specialist in the telecommunications and network time synchronisation industry
helping to develop dedicated time server products. Please visit us for
more information about a GPS time server or other NTP products.
Tags: absolute time, accuracies, atomic clock time, atomic clocks, clock source, global positioning system, internal clock, local area networks, network time protocol, ntp servers, physics laboratories, radio transmission, radio transmissions, sntp, time clock, time server, time source, time synchronisation, universal coordinated time, university of delaware
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