Keeping Time: Network Synchronisation

The worst part of a power cut is running around the house setting all the clocks and timers back to the correct time, it can take ages and you will always forget one, however, as long as you have a wrist watch it should be quite easy to get your clocks all telling the same time. But what time is your wrist watch set too and who regulates that time?

Complete precision and accuracy in time telling is not essential for our day-to-day lives and neither is synchronisation, our computer may be a few minutes slower than our wall clock but it will make little difference when we send an email.

However, what if the person we sent the email to has a computer clock that is even slower? They may end up sending a reply before they have technically received it. Computers are easily fooled if timestamps run backwards – remember the millennium bug!

For this reason it is important for computers, particularly those that deal with time sensitive or financial applications, to be telling the same time; otherwise global stocks could be bought whilst already sold-out or an airline seat, already purchased could be bought again by a buyer with a slower computer clock.

The regulation of time didn’t start until after the development of atomic clocks when the oscillation of the caesium atom became the standard definition of a second (9,192,631,770 a second).

The time told by these atomic clocks was so accurate a new timescale was developed called International Atomic Time (TAI). However, it was discovered that the traditional method of telling time, based on the revolution of the Earth (ie 24 hours in a day) and this new timescale soon became out of sync with each other as the gravity from the moon alters the revolution of the Earth, slowing it down.

This difference in the Earths spin is only minute but enough people argued (mainly astronomers) that if it was not compensated for, night would eventually creep into day (albeit in many thousands of years) and it would be difficult to keep track of the celestial bodies.

A compromise was called for and the new timescale, Universal Coordinated Time (UTC) was developed that accounted for the slowing of the Earth’s spin by adding leap seconds every year or so.

UTC has meant that modern technologies and applications such as the Global Positioning System, satellite communication, live television broadcasts and global trading have become possible.

Computer networks can receive UTC time and keep all their devices synchronised to it by using a NTP server (Network Time Protocol). NTP servers can receive UTC time from an atomic clock source via the Internet, a national radio transmission or through the GPS network.