Posts by: Stuart

NTP Server History Acquiring Precision

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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.

The NTP Server and the Atomic Clock Reason for Precision

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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.

NTP Server running a network (Part 2)

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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.

NTP Server running a network (Part 1)

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NTP servers are a vital tool for any business that needs to communicate globally and securely. NTP servers distribute Coordinated Universal Time (UTC), the world’s global timescale based on the highly accurate time told by atomic clocks.

NTP (Network Time Protocol) is the protocol used to distribute the UTC time across a network it also ensures all time is accurate and stable. However, there are many pitfalls in setting up a NTP network, here are the most common:

Using the correct time source

Attaining the most suitable time source is fundamental in setting up a NTP network. The time source is going to be distributed amongst all machines and devices on a network so it is vital that it is not only accurate but also stable and secure.

Many system administrators cut corners with a time source. Some will decide to use an Internet based time source although these are not secure as the firewall will require an opening and also many internet sources are either wholly inaccurate or too far away to afford any useful precision.

There are two highly secure methods of receiving a UTC time source. The first is to utilise the GPS network which although doesn’t transmit UTC, GPS time is based on International atomic time and is therefore easy for NTP to convert. GPS time signals are also readily available all over the globe.

The second method is to use the long wave radio signals broadcast by some national physical laboratories. These signals, however, are not available in every country and they have a finite range and are susceptible to interference and local topography.

It could be the last Leap Second tonight as there are calls to have it scrapped

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At midnight on tonight an extra second will be added as recommended by the International Earth rotation and Reference systems Service (IERS). That means for the last minute of 2008 there will 61 seconds.

Leap Seconds have been added nearly every year since the inception of UTC (Coordinated Universal Time) in the 1970’s. The extra second is added to ensure UTC keeps in synch with GMT (Greenwich Meantime or sometimes called UT1). GMT is the traditional 24 hour clock system where a day is defined as the rotation of the Earth which takes 86,400 seconds for a complete revolution.

Unfortunately the Earth can often be a little tardy in its spin and if the extra seconds were no added at the end of the year to compensate eventually the two systems (UTC and GMT) would drift apart. In a millennium the time difference would only be an hour but many argue to a have a time system that does no correspond to the movement of the heavens would be irrational and occupations such as farming and astronomy would be made more difficult.

However, not everybody sees it that way wit some arguing that as te entire world’s computer networks are synchronised to UTC using NTP servers then the fudging of the extra second causes untold amounts of trouble.

Now a group within the International Telecommunications Union, called has recommended abolishing the leap second. Group member Elisa Felicitas Arias, of the International Bureau of Weights and Measures in Paris, France, argues that a timescale that doesn’t need regular tweaking is essential in an increasingly interconnected world. What’s more, she says, ships and aircraft now navigate via GPS rather than the old time system. GPS runs on a version of atomic time.

Next year, member states of the ITU are due to vote on the proposal. If 70 per cent support the idea, an official decision will be made at the World Radio Conference in 2011. According to a report co-authored by Felicitas Arias, most member states support the idea. The UK, however, is against reworking its laws, which include the solar timescale Greenwich Mean Time. Without the UK abolition may be difficult, says Felicitas Arias.

“In theory, adding a second is as easy as flipping a switch; in practice, it rarely works that way,” says Dennis McCarthy of the US Naval Research Laboratory, which provides the time standard used by the US military. Most likely to be affected are IT systems that need precision of less than a second. In 1998 – two leap seconds ago – cellphone communications blacked out over part of the southern US. Different regions of service had slipped into slightly different times, preventing proper relaying of signals.

All quotes attributed to the BBC

Keeping Track of the Worlds Time and Difficulties in Synchronisation

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Until 1967 the second was defined using the motion of the Earth which rotates once on its axis every 24 hours, and there are 3,600 seconds in that hour and 86,400 in 24.

That would be fine if the earth was punctual but in fact it is not. The Earth’s rotation rate changes every day by thousands of nanoseconds, and this is due in a large part to wind and waves spinning around the Earth and causing drag.

Over the course of thousands of days, these changes in the rate of rotation can result in the Earth’s spin getting out of synch with the high-precision atomic clocks that we use to keep the UTC system (Coordinated Universal Time) ticking over. For this reason the Earth’s rotation is monitored and timed using the far off flashes from a type of collapsed star called a quasar that flash with an ultra precise rhythm many millions of light years away. By monitoring the Earth’s spin against these far away objects it can be worked out how much the rotation has slowed.

Once a second of slowing has been built up, The International Earth Rotation Service (IERS), recommends a Leap Second to be added, usually at the end of the year.

Other complications arise when it comes to synchronising the Earth to one timescale. In 1905, Albert Einstein’s theory of relativity showed that there is no such thing as absolute time. Every clock, everywhere in the universe, ticks at a different rate. For GPS, this is an enormous issue because it turns out that the clocks on the satellites drift by almost 40,000 nanoseconds per day relative to the clocks on the ground because they are high above the Earth’s surface (and therefore in a weaker gravitational field) and are moving fast relative to the ground.

And as light can travel Forty-thousand feet in that time, you can see the problem. Einstein’s equations first written down in 1905 and 1915 are used to correct for this time-shift, allowing GPS to work, planes to navigate safely and GPS NTP servers to receive the correct time.

MSF Technical Information

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The MSF transmission from Anthorn (latitude 54° 55′ N, longitude 3° 15′ W) is the principal means of disseminating the UK national standards of time and frequency which are maintained by the National Physical Laboratory. The effective monopole radiated power is 15 kW and the antenna is substantially omnidirectional. The signal strength is greater than 10 mV/m at 100 km and greater than 100 μV/m at 1000 km from the transmitter. The signal is widely used in northern and western Europe. The carrier frequency is maintained at 60 kHz to within 2 parts in 1012.

Simple on-off carrier modulation is used, the rise and fall times of the carrier are determined by the combination of antenna and transmitter. The timing of these edges is governed by the seconds and minutes of Coordinated Universal Time (UTC), which is always within a second of Greenwich Mean Time (GMT). Every UTC second is marked by an ‘off’ preceded by at least 500 ms of carrier, and this second marker is transmitted with an accuracy better than ±1 ms.

The first second of the minute begins with a period of 500 ms with the carrier off, to serve as a minute marker. The other 59 (or, exceptionally, 60 or 58) seconds of the minute always begin with at least 100 ms ‘off’ and end with at least 700 ms of carrier. Seconds 01-16 carry information for the current minute about the difference (DUT1) between astronomical time and atomic time, and the remaining seconds convey the time and date code. The time and date code information is always given in terms of UK clock time and date, which is UTC in winter and UTC+1h when Summer Time is in effect, and it relates to the minute following that in which it is transmitted.

Dedicated MSF NTP Server devices are available that can connect directly to the MSF transmission.

Information Courtesy of NPL

2008 Will be a second longer Leap Second to be added to UTC

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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
https://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

Atomic Clocks and the NTP Server Using Quantum Mechanics to Tell the Time

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Telling the time is not as straight forward as most people think. In fact the very question, ‘what is the time?’ is a question that even modern science can fail to answer. Time, according to Einstein, is relative; it’s passing changes for different observers, affected by such things as speed and gravity.

Even when we all live on the same planet and experience the passing of time in a similar way, telling the time can be increasingly difficult. Our original method of using the Earth’s rotation has since been discovered to be inaccurate as the Moon’s gravity causes some days to be longer than 24 hours and a few to be shorter. In fact when the early dinosaurs were roaming the Earth a day was only 22 hours long!

Whilst mechanical and electronic clocks have provided us with some degree accuracy, our modern technologies have required far more accurate time measurements. GPS, Internet trading and air traffic control are just three industries were split second timing is incredibly important.

So how do we keep track of time? Using the Earth’s rotation has proven unreliable whilst electrical oscillators (quartz clocks) and mechanical clocks are only accurate to a second or two per day. Unfortunately for many of our technologies a second inaccuracy can be far too long. In satellite navigation, light can travel 300,000 km in just over a second, making the average sat-nav unit useless if there was one second of inaccuracy.

The solution to finding an accurate method of measuring time has been to examine the very small – quantum mechanics. Quantum mechanics is the study of the atom and its properties and how they interact. It was discovered that electrons, the tiny particles that orbit atoms changed the path that they orbit and released a precise amount of energy when they do so.

In the case of the caesium atom this occurs nearly nine billion times a second and this number never alters and so can be used as an ultra reliable method of keeping track of time. Caesium atoms are use din atomic clocks and in fact the second is now defined as just over 9 billion cycles of radiation of the caesium atom.

Atomic clocks are the foundation for many of our technologies. The entire global economy relies on them with the time relayed by NTP time servers on computer networks or beamed down by GPS satellites; ensuring the entire world keeps the same, accurate and stable time.

An official global timescale, Coordinated Universal Time (UTC) has been developed thanks to atomic clocks allowing the whole world to run the same time to within a few thousandths of a second from each other.

GPS Time Server Receiving Time from Space

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GPS time servers are network time servers that receive a timing signal from the GPS network and distribute it amongst all devices on a network ensuring that the entire network is synchronised.

GPS is an ideal time source as a GPS signal is available anywhere on the globe. GPS stands for Global Positioning System, the GPS network is owned by the US military and controlled and run by the US air force (space wing). It is however, since the late 1980’s been opened up to the world’s civilian population as tool to aid navigation.

The GPS network is actually a constellation of 32 satellites that orbit the Earth, they do not actually provide positioning information (GPS receivers do that) but transmit from their onboard atomic clocks a timing signal.

This timing signal is what is used to work out a global position by triangulating 3-4 timing signals a receiver can work out how far and therefore the position you are from a satellite. In essence then, a global positioning satellite is just an orbiting clock and it is this information that is broadcast that can be picked up by a GPS time server and distributed amongst a network.

Whilst strictly speaking GPS time is not the same as the global timescale UTC (coordinated universal time), a GPS time server will automatically convert the time format into UTC.

A GPS time server can provide unbridled accuracy with networks able to maintain accuracy to within a few milliseconds of UTC.