Time synchronisation is often described as a ‘headache’ by network administrators. Keeping computers on a network all running the same time is increasingly important in modern network communications particularly if a network has to communicate with another network running independently.

For this reason UTC (Coordinated Universal Time) has been developed to ensure all networks are running the same accurate timescale. UTC is based on the time told by atomic clocks so it is highly precise, never losing even a second. Network time synchronisation is however, relatively straight forward thanks to the protocol NTP (Network Time Protocol).

UTC time sources are widely available with over a thousand online stratum 1 servers available on the Internet. The stratum level describes how far away a time server is to an atomic clock (an atomic clock that generates UTC is known as a stratum 0 device). Most time servers available on the Internet are in fact not stratum 1 devices but stratum in that they get their time from a device that in turn receives the UTC time signal.

For many applications this can be accurate enough but as these timing sources are on the Internet there is very little you can do to ensure both their accuracy and their precision. In fact even if an Internet source is highly accurate the distance away form it can cause delays int eh time signal.

Internet time sources are also unsecure as they are situated outside of the firewall forcing the network to be left open for the time requests. For this reason network administrators serious about time synchronisation opt to use their own external stratum 1 server.

These devices, often called a NTP server, receive a UTC time source from a trusted and secure source such as a GPS satellite then distribute it amongst the network. The NTP server is far more secure than an Internet based time source and are relatively inexpensive and highly accurate.

Time synchronisation is extremely important for modern computer networks. In some industries time synchronisation is absolutely vital especially when you are dealing with technologies such as air traffic control or marine navigation where hundreds of lives could be put at risk by lack of precise time.

Even in the financial world, correct time synchronisation is vital as millions can be added or wiped off share prices every second. For this reason the entire world adheres to a global timescale known as coordinated universal time (UTC). However, adhering to UTC and keeping UTC precise are two different things.

Most computer clocks are simple oscillators that will slowly drift either faster or slower. Unfortunately this means that no matter how accurate they are set on Monday they will have drifted by Friday. This drift may be only a fraction of a second but it soon won’t take long for the originally UTC time to be over a second out.

In many industries this may not mean a matter of life and death of the loss of millions in stocks and shares but lack of time synchronisation can have unforeseen consequences such as leaving a company less protected from fraud. However, receiving and keeping true UTC time is quite straight forward.

Dedicated network time servers are available that uses the protocol NTP (Network Time Protocol) to continually check the time of a network against a source of UTC time. These devices are often referred to as an NTP server, time server or network time server. The NTP server constantly adjusts all devices on a network to ensure that the machines are not drifting from UTC.

UTC is available from several sources including the GPS network. This is an ideal source of UTC time as it is secure, reliable and available everywhere on the planet. UTC is also available via specialist national radio transmissions which are broadcast from national physics laboratories although they are not available everywhere.

When we take a glance at our watches or the office clock we often take for granted that the time we are given is correct. We may notice if our watches are ten minutes fast or slow but take little heed if they are a second or two out.

Yet for thousands of years mankind has strode to get ever increasingly accurate clocks the benefits of which are plentiful today in our age of satellite navigation, NTP servers, the Internet and global communications.

To understand how accurate time can be measured it is first important to understand the concept of time itself. Time as it has been measured on Earth for millennia is a different concept to time itself which as Einstein informed us was part of the fabric of the universe itself in what he described as a four dimensional space-time.

Yet we have historically measured time based not on the passing of time itself but the rotation of our planet in relation to the Sun and the Moon. A day is divided into 24 equal parts (hours) each of which is divided into 60 minutes and the minute is divided into 60 seconds.

However, it has now been realised that measuring time this way can not be considered accurate as the Earth’s rotation varies from day to day. All sorts of variable such as tidal forces, hurricanes, solar winds and even the amount of snow at the poles effects the speed of the Earth’s rotation. In fact when the dinosaurs first started roaming the Earth, the length of a day as we measure it now would have only been 22 hours.

We now base our timekeeping on the transition of atoms using atomic clocks with a second based on 9,192,631,770 periods of the radiation emitted by the hyperfine transition of a unionized caesium atom in the ground state. Whilst this may sound complicated it really is just an atomic ‘tick’ that never alters and therefore can provide a highly accurate reference to base our time on.

Atomic clocks use this atomic resonance and can keep time that is so accurate a second isn’t lost in even a billion years. Modern technologies all take advantage of this precision enabling many of the communications and global trade we benefit from today with the utilisation of satellite navigation, NTP servers and air traffic control changing the way we live our lives.

In an age of atomic clocks and the NTP server time keeping is now more accurate then ever with ever increasing precision having allowed many of the technologies and systems we now take for granted.

Whilst timekeeping has always been a preoccupation of mankind, it has only been in the last few decades that true accuracy has been possible thanks to the advent of the atomic clock.

Before atomic time, electrical oscillators like those found in the average digital watch were the most accurate measure of time and whilst electronic clocks like these are far more precise than their predecessors – the mechanical clocks, they can still drift by up to a second a week.

But why does time need to be so precise, after all, how important can a second be? In the day-to-day running of our lives a second isn’t that important and electronic clocks (and even mechanical ones) provide adequate timekeeping for our needs.

In our day-to-day lives a second makes little difference but in many modern applications a second can be an age.

Modern satellite navigation is one example. These devices can pinpoint a location anywhere on earth to within a few metres. Yet they can only do this because of the ultra-precise nature of the atomic clocks that control the system as the time signal sent from the navigation satellites travels at the speed of light which is nearly 300,000 km a second.

As light can travel such a vast distance in a second any atomic clock governing a satellite navigation system that was just one second out it would the positioning would be inaccurate by thousands of miles, rendering the positioning system useless.

There are many other technologies that require similar accuracy and also many of the ways we trade and communicate. Stocks and shares fluctuate up and down every second and global trade requires that everybody all over the world has to communicate using the same time.

Most computer networks are controlled by using a NTP server (Network Time Protocol). These devices allow computer networks to all use the same atomic clock based timescale UTC (coordinated universal time). By utilising UTC via a NTP server, computer networks can be synchronised to within a few milliseconds of each other.

Organising Strata

Stratum levels describe the distance between a device and the reference clock. For instance an atomic clock based in a physics laboratory or GPS satellite is a stratum 0 device. A stratum 1 device is a time server that receives time from a stratum 0 device so any dedicated NTP server is stratum 1. Devices that receive the time from the time server such as computers and routers are stratum 2 devices.

NTP can support up to 16 stratum levels and although there is a drop-off in accuracy the further away you go stratum levels are designed to allow huge networks to all receive a time from a single NTP server without causing network congestion or a blockage in the bandwidth.

When using a NTP server it is important to not overload the device with time requests so the network should be divided with a select number of machines taking requests from the NTP server (the NTP server manufacturer can recommend the number of requests it can handle). These stratum 2 devices can ten be used as time references for other devices (which become stratum 3 devices) on very large networks these can then be used as time references themselves.

Here at Galleon Systems, one of Europe’s leading suppliers of NTP server systems, we would like to wish all our customers, suppliers and even our competitors a Merry Christmas and a Happy New Year. We hope 2009 is a successful year for you all.

Accurate time using Atomic Clocks is available across Great Britain and parts of northern Europe using the MSF Atomic Clock time signal transmitted from Cumbria, UK; it provides the ability to synchronize the time on computers and other electrical equipment.

The UK MSF signal is operated by NPL – the National Physical Laboratory. MSF has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from MSF a lot of bounce, and this single station can therefore cover most of Britain and some of continental Europe.

The time codes are sent from MSF using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: • 0.2 seconds of reduced power means a binary zero • 0.5 seconds of reduced power is a binary one. • 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated time servers that are tuned to receive the MSF time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

To receive and distribute and authenticated UTC time source there are currently two types of NTP server, the GPS NTP server and the radio referenced NTP server. While both these systems distribute UTC in identical ways the way they receive the timing information differs.

A GPS NTP time server is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components.  Each GPS satellite transmits in two frequencies L2 for the military use and L1 for use by civilians transmitted at 1575 MHz, Low-cost GPS antennas and receivers are now widely available.

The radio signal transmitted by the satellite can pass through windows but can be blocked by buildings so the ideal location for a GPS antenna is on a rooftop with a good view of the sky. The more satellites it can receive from the better the signal. However, roof-mounted antennas can be prone to lighting strikes or other voltage surges so a suppressor is highly recommend being installed inline on the GPS cable.

The cable between the GPS antenna and receiver is also critical. The maximum distance that a cable can run is normally only 20-30 metres but a high quality coax cable combined with a GPS amplifier placed in-line to boost the gain of the antenna can allow in excess of 100 metre cable runs. This can provide difficulties in installation in larger buildings if the server is too far from the antenna.

An alternative solution is to use a radio referenced NTP time server. These rely on a number of national time and frequency radio transmissions that that broadcast UTC time. In Britain the signal (called MSF) is broadcast by the National Physics Laboratory in Cumbria which serves as the United Kingdom’s national time reference, there are also similar systems in the USA (WWVB) and in France, Germany and Japan.

A radio based NTP server usually consists of a rack-mountable time server, and an antenna, consisting of a ferrite bar inside a plastic enclosure, which receives the radio time and frequency broadcast. It should always be mounted horizontally at a right angle toward the transmission for optimum signal strength. Data is sent in pulses, 60 a second. These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

New Year’s celebrations will have to wait another second this year as the International Earth Rotation and Reference Systems Service (IERS) have decided to 2008 is to have Leap Second added.

IERS announced in Paris in July that a positive Leap Second was to be added to 2008, the first since Dec. 31, 2005. Leap Seconds were introduced to compensate for the unpredictability of the Earth’s rotation and to keep UTC (Coordinated Universal Time) with GMT (Greenwich Meantime).

The new extra second will be added on the last day of this year at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time — 6:59:59 pm Eastern Standard Time. 33 Leap Seconds have been added since 1972

NTP server systems controlling time synchronisation on computer networks are all governed by UTC (Coordinated Universal Time). When an additional second is added at the end of the year UTC will automatically be altered as the additional second. #

Whether a NTP server receives a time signal fro transmissions such as MSF, WWVB or DCF or from the GPS network the signal will automatically carry the Leap Second announcement.

Notice of Leap Second from the International Earth Rotation and Reference Systems Service (IERS)

SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE

SERVICE DE LA ROTATION TERRESTRE
OBSERVATOIRE DE PARIS
61, Av. de l’Observatoire 75014 PARIS (France)
Tel.      : 33 (0) 1 40 51 22 26
FAX       : 33 (0) 1 40 51 22 91
e-mail    : services.iers@obspm.fr

http://hpiers.obspm.fr/eop-pc

Paris, 4 July 2008

Bulletin C 36

To authorities responsible for the measurement and distribution of time

UTC TIME STEP
on the 1st of January 2009

A positive leap second will be introduced at the end of December 2008.
The sequence of dates of the UTC second markers will be:

2008 December 31,     23h 59m 59s
2008 December 31,     23h 59m 60s
2009 January   1,      0h  0m  0s

The difference between UTC and the International Atomic Time TAI is:

from 2006 January 1, 0h UTC, to 2009 January 1  0h UTC  : UTC-TAI = – 33s
from 2009 January 1, 0h UTC, until further notice       : UTC-TAI = – 34s

Leap seconds can be introduced in UTC at the end of the months of December

A GPS time server is really a communication device. Its purpose is to receive a timing signal and then distribute it amongst all devices on a network. Time server s are often called different things from network time server, GPS time server, radio time server and NTP server.

Most time servers use the protocol NTP (Network Time Protocol). NTP is one of the Internet’s oldest protocols and is used by the majority of machines that use a time server. NTP is often installed, in a basic form, in most operating systems.

A GPS time server, as the names suggests, receives a timing signal from the GPS network. GPS satellites are really nothing more than orbiting clocks. Onboard each GPS satellite is an atomic clock. The ultra-precise time from this clock is what is transmitted from the satellite (along with the satellite’s position).

A satellite navigation system works by receiving the time signal from three or more satellites and by working out the position of the satellites and how long the signals took to arrive, it can triangulate a position.

A GPS time server needs even less information and only one satellite is required in order to receive a timing reference. A GPS time server’s antenna will receive a timing signal from one of the 33 orbiting satellites via line of sight, so the best place to fix the antenna is the roof.

Most dedicated GPS NTP time servers require a good 48 hours to locate and get a steady fix on a satellite but once they have it is rare for communication to be lost.

The time relayed by GPS satellites is known as GPS time and although it differs to the official global timescale UTC (Coordinated Universal Time) as they are both based on atomic time (TAI) GPS time is easily converted by NTP.

A GPS time server is often referred to as a stratum 1 NTP device, a stratum 2 device is a machine that receives the time from the GPS time server. Stratum 2 and stratum 3 devices can also be used as a time servers and in this way a single GPS time server can operate as a timing source for an unlimited amount of computers and devices as long as the hierarchy of NTP is followed.