From the Sundial to the Time Server a Brief History of Horology

Keeping track of time is something most people take for granted, yet the science of timekeeping has a long and fascinating history.

Keeping track of time was always based on the relationship between the Earth, Moon and Sun. The first timekeeping devices are thought to be monuments like Stone Henge in the UK that would recognise the winter or summer solstice allowing early man to calculate when to plant crops.

Dividing the day up into hours and being able to keep track of them has proved more difficult to civilisations.

The first timing devices were sundials, obelisks and water clocks but it wasn’t until the development of mechanical clocks in the middle-ages that time-telling started to become more accurate.

Mechanical clocks continued to develop until the turn of the twentieth century when they were bettered in accuracy by electronic oscillators that would use the resonance of a crystal (often quartz) to keep a stable time.

While electronic clocks provided accuracy to within a second a day, the atomic clock that uses the resonance of an atom (in most cases caesium -133) and was developed in the 1950’s demonstrated millisecond accuracy – not losing a second in several thousands of years.

Now atomic clocks are approaching nano-second accuracy (one second every billion years) with new developments like strontium. The atomic clock has also made horologists realise that basing a time system on the movement of the Earth and celestial bodies is unreliable as the Earth slows and speeds up.

UTC (coordinated universal time) was developed to combat this by adding leap seconds to keep atomic time in line with GMT (Greenwich Meantime). Now computer networks all over the world can synchronise to UTC and atomic clocks by using a time server.

A time server will receive a time from an atomic clock source and synchronise an entire network to this time. Without time servers, atomic clocks and UTC, technologies such as satellite communication, the Internet and global trading would be near impossible.

Time Server Fundamentals: UTC and Atomic Clocks

The atomic clock was developed in the 1950’s and represented a huge step forward in chronology. Before the atomic clock, electronic oscillators, as used in most digital clocks and watches, were providing the best accuracy although these would drift several seconds a month.

The atomic clock used the resonance of the atom caesium -133 which had an exact oscillation of 9,192,631,770 times a second. Because of this exact oscillation atomic clocks soon offered nearnano-second accuracy in that it would take several million years before they would drift by a second.

Atomic clocks were deemed so accurate that the International System of Units (SI) defined the second as this number of oscillations of the caesium atom.

As time-telling became so accurate it was soon discovered that the rotation of the Earth was not as precise as the clocks and that to keep atomic time relevant to Greenwich Meantime (GMT) and to stop night from slowly drifting into day a new timescale was developed calledUTC (Coordinated Universal Time) which accounted for the slowing of the Earth’s spin by adding ‘Leap Seconds’.

UTC is now globally used and allows the entire world to synchronise to the same timescale. This is particularly relevant for computer networks that often have to communicate with other networks across the globe.

UTC can be received by using a time server that can either synchronise to a timing reference across the Internet or for better accuracy an d security a time server can receiveUTC time from the GPS network via a GPS antenna or by receiving national timing broadcasts, transmitted form several countries.

By using a time server that receives UTC time a computer network can be accurate to within a few milliseconds of UTC allowing cross-global communication.

Synchronisation and Time Server Basics

A time server is a computer device that obtains a timing reference from a  particular source and transfers it to a network and its clients.

A time server does not rely on a system clock for timing information (all though they can be set to) as the internal clocks in PCs are prone to drift. Instead a time server will request timing information from an authoritative source and synchronises to it.

Most time servers use NTP (network Time Protocol) to synchronise devices and networks using the information gathered by the time server.

Most network administrators prefer to get their timing reference from a hardware source, preferably one that relays UTC (Coordinated Universal Time) a global timescale based on the time told by atomic clocks.

Apart from Internet time sources, of which many  are inaccurate and can’t be authenticated there are two other methods to receive UTC time: the GPS network and national time and frequency transmissions.

A GPS time server will receive the timing information via an roof-mounted antenna whilst a radio receiving time server will utilise the national broadcasts of the US (WWVB), the UK (MSF), Germany (DCF), France (TDF) and Japan (JJY).

These broadcasts can’t be received everywhere and are vulnerable to local geography and interference.

GPS receivers are available everywhere on the planet so long as the antenna has a clear view of the sky.

Some dedicated time servers can receive both radio and GPS signals and can utilise both as a timing source, providing even more accuracy.

A time server receiving UTC time through either method can realistically provide accuracy to within a few milliseconds (1/1000th of a second) and can perform even better over LANs/WANs.

The Need for a Dedicated Time Server

As important as telling the time is for the smooth running of our daily lives, it is even more essential for computer networks. Everything from sending and receiving email to debugging a network is dependent on a timestamp. If timestamps on machines differ then all sorts of complications can arise from email arriving before it was sent to systems being left vulnerable to attacks and even fraud.

Computer networks use Network Time Protocol (NTP) to synchronise their networks to an authoritative time source. The ideal sources are those that relay UTC (Coordinated Universal Time). UTC was developed after the invention of atomic clocks and is a global timescale that allows computer networks and devices all over the world to synchronise to the exact same time.

There are different ways to receive UTC most commonly is from an Internet source. However, Internet timing sources vary in accuracy and are affected by distance and bandwidth problems. Also, Microsoft and others suggest they should not be used as they can’t be authenticated. This is a security measure used by NTP to ensure that a servers is what it is supposed to be.

Fortunately a dedicated time server can receive a UTC source from either a specialist radio broadcast (available in certain countries only – including France, Germany, UK, USA and Japan) or the GPS network (available anywhere on Earth).

Not only can a dedicated time server provide accuracy to within a few milliseconds of UTC it can also be authenticated by NTP ensuring security.

Dedicated time servers are relatively inexpensive and simple to install and can allow networks of hundreds and even thousands to be synchronised to UTC.