Time Synchronisation

This article explains the origins and workings of atomic clocks and how they are used to synchronise computer networks all over the world using NTP servers.

In conventional electronic clocks time is kept by running an electrical current through an oscillator which produces a repetitive electrical signal this is then governed by a quartz crystal to keep precision. These crystal oscillators are far more accurate than mechanical clocks but will still drift, perhaps over a second a week.

For day-to-day use crystal oscillators are a fine way to keep track of time; in the everyday running of our lives, a second makes very little difference, however, as light or radio waves can travel 300,000 miles in a second, some high technologies such as satellite navigation or global communication, require far more accuracy to be possible.

Atomic clocks are a timekeeping device that uses the known atomic resonance frequency of an atom to keep time. The first truly accurate atomic clock was built in 1955 at the National Physical Laboratory in the UK and was based on the caesium atom -133 which oscillates at exactly 9,192,631,770 every second.

This oscillation is actually a repetitive signal from the microwave radiation emitted by electrons in an atom when they change energy levels. Much of an atomic clock is designed to create the correct state to cause and augment oscillations.
Although other atoms can be used, the oscillation (9,192,631,770 a second) of the caesium -133 atom is now accepted by the International System of Units as being the definition of one second.

Atomic clocks are generally very large and constitute many highly technical apparatus such as vacuums and require whole teams of scientists to maintain and monitor the clocks. Much of which goes into compensating for unwanted side-effects such as frequencies of other atoms in the clock and even gravitational dilation (where according to Einstein’s theory clocks at different heights run differently because of the differences in the gravitational field) This makes atomic clocks highly expensive.

Fortunately many large scale national physical laboratories transmit radio time signals from their atomic clocks which can be used to synchronise standard crystal oscillators too.

Atomic clocks are also the basis of GPS (Global Positioning System) as each satellite contains an atomic clock as accurate time is integral for positioning (a position anywhere is made up of a direction, a velocity and time).
GPS signals can also be used to capture a time signal. This is now the most common way computer networks retain accurate time which is also essential in many communications and applications.

Most computer networks use a NTP server (Network Time Protocol) to synchonise their devices to an atomic time signal received via the GPS network.

A universal timescale, UTC (Coordinated universal Time), has been developed based on the time told by atomic clocks, TAI (International Atomic Time). UTC accounts for the slowing of the Earths rotation by adding leap seconds to TAI so as to prevent the gradual drift of night into day (although that would take 40,000 years or so) and allows the whole world to communicate using the same timescale.

Network Time Protocol (NTP) was designed and developed over twenty five years ago but is still in use and constantly updated. It was developed when the Internet was in its infancy as a way to synchronise time across the world wide web.

NTP is now the standard time synchronisation protocol with networks all ove the world using it to ensure their computers and devices are all synchronised.

Most NTP time servers are synchronised to the universal timescale UTC (Coordinated Universal Time) which was developed in the 1970’s after the introduction advancement of atomic clocks.

Not every NTP time server is synchronised to a UTC source. NTP can synchronise to any time source even the highly inaccurate system clock on most computers or indeed a wrist watch or wall clock.

But the benefits of having a network synchronised to UTC are many fold. UTC allows computers all over the world to communicate using the same timescale, allowing time sensitive transactions to take place. As timestamps are an integral part of all computer processes and applications it also ensures a higher level of security to a network.

Receiving a UTC time source is relatively simple. some NTP time servers use an Internet based timing source although these are not recommended as they can vary in accuracy and can’t be authenticated by NTP software making a system vulnerable to attack.

However, a NTP time server can receive a UTC timing reference via a radio receiver (only available in certain countries) or the GPS network.

Using a GPS or radio referenced source for a NTP time server means networks can maintain an accuracy to within a few milliseconds of UTC time.

NTP time servers are relatively inexpensive and extremely simple to set up.

This article explains the origins and workings of atomic clocks and how they are used to synchronise computer networks all over the world using NTP servers.

In conventional electronic clocks time is kept by running an electrical current through an oscillator which produces a repetitive electrical signal this is then governed by a quartz crystal to keep precision. These crystal oscillators are far more accurate than mechanical clocks but will still drift, perhaps over a second a week.

For day-to-day use crystal oscillators are a fine way to keep track of time; in the everyday running of our lives, a second makes very little difference, however, as light or radio waves can travel 300,000 miles in a second, some high technologies such as satellite navigation or global communication, require far more accuracy to be possible.

Atomic clocks are a timekeeping device that uses the known atomic resonance frequency of an atom to keep time. The first truly accurate atomic clock was built in 1955 at the National Physical Laboratory in the UK and was based on the caesium atom -133 which oscillates at exactly 9,192,631,770 every second.

This oscillation is actually a repetitive signal from the microwave radiation emitted by electrons in an atom when they change energy levels. Much of an atomic clock is designed to create the correct state to cause and augment oscillations.
Although other atoms can be used, the oscillation (9,192,631,770 a second) of the caesium -133 atom is now accepted by the International System of Units as being the definition of one second.

Atomic clocks are generally very large and constitute many highly technical apparatus such as vacuums and require whole teams of scientists to maintain and monitor the clocks. Much of which goes into compensating for  unwanted side-effects such as frequencies of other atoms in the clock and even gravitational dilation (where according to Einstein’s theory clocks at different heights run differently because of the differences in the gravitational field)  This makes atomic clocks highly expensive.

Fortunately many large scale national physical laboratories transmit radio time signals from their atomic clocks which can be used to synchronise standard crystal oscillators too.

Atomic clocks are also the basis of GPS (Global Positioning System) as each satellite contains an atomic clock as accurate time is integral for positioning (a position anywhere is made up of a direction, a velocity and time).
GPS signals can also be used to capture a time signal. This is now the most common way computer networks retain accurate time which is also essential in many communications and applications.

Most computer networks use a NTP server (Network Time Protocol) to synchonise their devices to an atomic time signal received via the GPS network.

A universal timescale, UTC (Coordinated universal Time), has been developed based on the time told by atomic clocks, TAI (International Atomic Time). UTC accounts for the slowing of the Earths rotation by adding leap seconds to TAI so as to prevent the gradual drift of night into day (although that would take 40,000 years or so) and allows the whole world to communicate using the same timescale.