Category: quantum physics

Using Time and Frequency Transmissions to Synchronise a Computer Network

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Computer network synchronisation is often perceived as a headache for many system administrators but keeping accurate time is essential for any network to remain secure and reliable. Failing to have an accurate synchronised network can lead to all sorts of errors when dealing with time sensitive transactions.

The protocol NTP (Network Time Protocol) is the industry standard for time synchronisation. NTP distributes a single time source to an entire network ensuring all machines are running the exact same time.

One of the most problematic areas in synchronising a network is in the selection of the time source. Obviously if you are spending time getting a network synchronised then the time source would have to be a UTC (Coordinated Universal Time) as this is the global timescale used by computer networks all over the world.

UTC is available across the internet of course but internet time sources are not only notoriously inaccurate but using the internet as a time source will leave computer system open to security threats as the source is external to the firewall.

A far better and secure method is to use a dedicated NTP time server. The NTP server sits inside the firewall and can receive a secure time signal from highly accurate sources. The most commonly used these days is the GPS network (Global Positioning System) this is because the GPS system is available literally anywhere on the planet. Unfortunately it does require a clear view of the sky to ensure the GPS NTP server can ‘see’ the satellite.

There is another alternative however, and that is to use the national time and frequency transmissions broadcast by several national physics laboratories. These have the advantage in that being long wave signals they can be received indoors. Although it must be noted these signals are not broadcast in every country and the range is finite and susceptible to interference and geographical features.

Some of the main transmissions broadcast are known as: the UK’s MSF signal, Germany’s DCF-77 and the USA’s WWVB.

The Atomic Clock and the Network Time Server

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The atomic clock is the culmination of mankind’s obsession of telling accurate time. Before the atomic clock and the nanosecond accuracy they, employ time scales were based on the celestial bodies.

However, thanks to the development of the atomic clock it has now been realised that even the Earth in its rotation is not as accurate a measure of time as the atomic clock as it loses or gains a fraction of a second each day.

Because of the need to have a timescale based somewhat on the Earth’s rotation (astronomy and farming being two reasons) a timescale that is kept by atomic clocks but adjusted for any slowing (or acceleration) in the Earth’s spin. This timescale is known as UTC (Coordinated Universal Time) as employed across the globe ensuring commerce and trade utilise the same time.

Computer networks use network time servers to synchronise to UTC time. Many people refer to these time server devices as atomic clocks but that is inaccurate. Atomic clocks are extremely expensive and highly sensitive pieces of equipment and are only usually to be found in universities or national physics laboratories.

Fortunately national physics laboratories like NIST (National Institute for Standards and Time – USA) and NPL (National Physical Laboratory – UK) broadcast the time signal from their atomic clocks. Alternatively the GPS network is another good source of accurate time as each GPS satellite has onboard its own atomic clock.

The network time server receives the time from an atomic clock and distributes it using a protocol such as NTP (Network Time Protocol) ensuring the computer network is synchronised to the same time.

Because network time servers are controlled by atomic clocks they can keep incredibly accurate time; not losing a second in hundreds if not thousands of years. This ensures that the computer network is both secure and unsusceptible to timing errors as all machines will have the exact same time.

The NTP Server and Understanding Timescales

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There are several timescale used throughout the world. Most NTP servers and other network time servers use UTC as a base source however, there are others:

When we are asked the time it is very unlikely we would respond with ‘for which timescale’ yet there are several timescales used all over the globe and each is based on different methods of keeping track of the time.
GMT

Greenwich Mean Time (GMT) is the local time on the Greenwich meridian based on the hypothetical mean sun. As the Earth’s orbit is elliptical and its axis is tilted, the actual position of the sun against the background of stars appears a little ahead or behind the expected position. The accumulated timing error varies through the year in a smoothly periodic manner by up to 14 minutes slow in February to 16 minutes fast in November. The use of a hypothetical mean sun removes this effect. Before 1925 astronomers and navigators measured GMT from noon to noon, starting the day 12 hours later than in civil usage which was also commonly referred to as GMT. To avoid confusion astronomers agreed in 1925 to change the reference point from noon to midnight, and a few years later adopted the term Universal Time (UT) for the “new” GMT. GMT remains the legal basis of the civil time for the UK.

UT

Universal Time (UT) is mean solar time on the Greenwich meridian with 0 h UT at mean midnight, and since 1925 has replaced GMT for scientific purposes. By the mid-1950s astronomers had much evidence of fluctuations in the Earth’s rotation and decided to divide UT into three versions. Time derived directly from observations is called UT0, applying corrections for movements of the Earth’s axis, or polar motion, gives UT1, and removing periodic seasonal variations generates UT2. The differences between UT0 and UT1 are of the order of thousandths of a second. Today, only UT1 is still widely used as it provides a measure of the rotational orientation of the Earth in space..


The world time standard (UTC):

Although TAI provides a continuous, uniform, and precise time scale for scientific reference purposes, it is not convenient for everyday use because it is not in step with the Earth’s rate of rotation. A time scale that corresponds to the alternation of day and night is much more useful, and since 1972, all broadcast time services distribute time scales based on Coordinated Universal Time (UTC). UTC is an atomic time scale that is kept in agreement with Universal Time. Leap seconds are occasionally

Information courtesy of the National Physical Laboratory UK.

NTP Server Configuration for Windows and Linux

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Network Time Protocol has been developed to keep computers synchronized. All computers are prone to drift and accurate timing is essential for many time critical applications.

A version of NTP is installed on most versions of Windows (although a stripped down version called SNTP –Simplified NTP- is in older versions) and Linux but is free to download from NTP.org.

When synchronising a a network it is preferable to use a dedicated NTP server that receives a timing source from an atomic clock either via specialist radio transmissions or the GPS network. However, many Internet time references are available, some more reliable than others, although it must be noted Internet based time sources can’t be authenticated by NTP, leaving your computer vulnerable to threats.

NTP is hierarchical and arranged into stratum. Stratum 0 is timing reference, while stratum 1 is a server connected to a stratum 0 timing source and a stratum 2 is a computer (or device) attached to a stratum 1 server.

The Basic configuration of NTP is done using the /etc/ntp.conf file you have to edit it and place the IP address of stratum 1 and stratum 2 servers. Here is an example of a basic ntp.conf file:

server xxx.yyy.zzz.aaa prefer (time server address such as time.windows.com)

server 123.123.1.0

server 122.123.1.0 stratum 3

Driftfile /etc/ntp/drift

The most basic ntp.conf file will list 2 servers, one that it wishes to synchronise too and an IP address for itself. It is good housekeeping to have more than one server for reference in case one goes down.

A server with the tag ‘prefer’ is used for a trusted source ensuring NTP will always use that server when possible. The IP address will be used in case of problems when NTP will synchonise with itself is. The drift file is where NTP builds a record of the system clock’s drift rate and automatically adjusts for it.

NTP will adjust your system time but only slowly. NTP will await at least ten packets of information before trusting the time source. To test NTP simply change your system clock by half an hour at the end of the day and the time in the morning should be correct.

Atomic Clock Synchronization using WWVB

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Accurate time using Atomic Clocks is available across North America using the WWVB Atomic Clock time signal transmitted from Fort Collins, Colorado; it provides the ability to synchronize the time on computers and other electrical equipment.

The North American WWVB signal is operated by NIST – the National Institute of Standards and Technology. WWVB 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 WWVB a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America.

The time codes are sent from WWVB 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 NTP time servers that are tuned to receive the WWVB 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).

Atomic Clocks The Future of Time

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Methods of keeping track of time have altered throughout history with ever increasing accuracy has being the catalyst for change.

Most methods of timekeeping have traditionally been based on the movement of the Earth around the Sun. For millennia, a day has been divided into 24 equal parts that have become known as hours. Basing our timescales on the rotation of the Earth has been adequate for most of our historical needs, however as technology advances, the need for an ever increasingly accurate timescale has been evident.

The problem with the traditional methods became apparent when the first truly accurate timepieces – the atomic clock was developed in the 1950’s. Because these timepieces  was based on the frequency of atoms and were accurate to within a second every million years it was soon discovered that our day, that we had always presumed as being precisely 24 hours, altered from day to day.

The affects of the Moon’s gravity on our oceans causes the Earth to slow and speed up during its rotation – some days are longer than 24 hours whilst others are shorter. Whilst this minute differences in the length of a day have made little difference to our daily lives it this inaccuracy has implications for many of our modern technologies such as satellite communication and global positioning.

A timescale has been developed to deal with the inaccuracies in the Earth’s spin – Coordinated Universal Time (UTC). It is based on the traditional 24-hour Earth rotation known as Greenwich Meantime (GMT) but accounts for the inaccuracies in the earth’s spin by having so-called ‘Leap Seconds’ added (or subtracted).

As UTC is based on the time told by atomic clocks it is incredibly accurate and therefore has been adopted as the World’s civilian timescale and is used by business and commerce all over the globe.

Most computer networks can be synchronised to UTC by using a dedicated NTP time server.

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.

Keeping Time with the Rest of the World

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A time server is a common office tool but what is it for?

We are all used to having a different time from the rest of the world. When America is waking up, Honk Kong is going to bed which is why the world is divided into time zones. Even in the same time-zone there can still be differences. In mainland Europe for instance most countries are an hour ahead of the UK because of Britain’s seasonal clock changing.

However, when it comes to global communication, having different times all over the world can cause problem particularly if you have to conduct time sensitive transactions such as buying or selling shares.

For this purpose it was clear by the early 1970’s that a global timescale was required. It was introduced on 1 January 1972 and was called UTC – Coordinated Universal Time. UTC is kept by atomic clock but is based on Greenwich Meantime (GMT – often called UT1) which is itself a timescale based on the rotation of the Earth. Unfortunately the Earth varies in its spin so UTC accounts for this by adding a second once or twice a year (Leap Second).

Whilst controversial to many, leap seconds are needed by astronomers and other institutions to prevent the day from drifting otherwise it would be impossible to work out the position of the stars in the night sky.

UTC is now used all over the world. Not only is it the official global timescale but is used by hundreds of thousands of computer networks all over the world.

Computer networks use a network time server to synchronise all devices on a network to UTC. Most time servers use the protocol NTP (Network Time Protocol) to distribute time.

NTP time servers receive the time from atomic clocks by either long-wave radio transmissions from national physics laboratories or from the GPS network (Global Positioning System). GPS satellites all carry an onboard atomic clock that beams the time back to Earth. Whilst this time signal is not strictly speaking UTC (it is known as GPS time) because of the accuracy of the transmission it is easily converted to UTC by a GPS NTP server.

How an Atomic Clock Works

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Atomic clocks are used for thousands of applications all over the world. From controlling satellites to even synchronising a computer network using a NTP server, atomic clocks have changed the way we control and govern time.

In terms of accuracy an atomic clock is unrivalled. Digital quartz clocks may keep accurate time for a week, not losing more than a second but an atomic clock can keep time for millions of years without drifting as much.

Atomic clocks work on the principle of quantum leaps, a branch of quantum mechanics which states that an electron; a negatively charged particle, will orbit a nucleus of an atom (the centre) in a certain plain or level. When it absorbs or releases enough energy, in the form of electromagnetic radiation, the electron will jump to a different plane – the quantum leap.

By measuring the frequency of the electromagnetic radiation corresponding to the transition between the two levels, the passage of time can be recorded. Caesium atoms (caesium 133) are preferred for timing as they have 9,192,631,770 cycles of radiation in every second. Because the energy levels of the caesium atom (the quantum standards) are always the same and is such a high number, the caesium atomic clock is incredibly precise.

The most common form of atomic clock used in the world today is the caesium fountain. In this type of clock a cloud of atoms is projected up into a microwave chamber and allowed to fall down under gravity. Laser beams slow these atoms down and the transition between the atom’s energy levels are measured.

The next generation of atomic clocks are being developed use ion traps rather than a fountain. Ions are positively charged atoms which can be trapped by a magnetic field. Other elements such as strontium are being used in these next generation clocks and it is estimated that the potential accuracy of a strontium ion trap clock could be 1000 times that of the current atomic clocks.

Atomic clocks are utilised by all sorts of technologies; satellite communication, the Global Positioning System and even Internet trading is reliant on atomic clocks. Most computers synchronise indirectly to an atomic clock by using a NTP server. These devices receive the time from an atomic clock and distribute around their networks ensuring precise time on all devices.

Synchronising to an Atomic Clock

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Atomic clocks are the pinnacle of time keeping devices. Modern atomic clocks can keep time to such accuracy that in 100,000,000 years (100 million) they do not lose even a second in time. Because of this high level of accuracy, atomic clocks are the basis for the world’s timescale.

To allow global communication and time sensitive transactions such as the buying of stacks and shares a global timescale, based on the time told by atomic clocks, was developed in 1972. This timescale, Coordinated Universal Time (UTC) is governed and controlled by the International Bureau of weights and Measures (BIPM) who use a constellation of over 230 atomic clocks from 65 laboratories all over the world to ensure high levels of accuracy.

Atomic clocks are based on the fundamental properties of the atom, known as quantum mechanics.  Quantum mechanics suggest that an electron (negatively charged particle) that orbits an atom’s nucleus can exist in different levels or orbit planes depending if they absorb or release the correct amount of energy. Once an electron has absorbed or released enough energy in can ‘jump’ to another level, this is known as a quantum jump.

The frequency between these two energy states is what is used to keep time. Most atomic clocks are based on the caesium atom which has 9,192,631,770 periods of radiation corresponding to the transition between the two levels. Because of the accuracy of caesium clocks the BIPM now considers a second to be defined as 9,192,631,770 cycles of the caesium atom.

Atomic clocks are used in thousands of different applications where precise timing is essential. Satellite communication, air traffic control, internet trading and GPs all require atomic clocks to keep time. Atomic clocks can also be used as a method of synchronising computer networks.

A computer network using a NTP time server can use either a radio transmission or the signals broadcast by GPS satellites (Global Positioning System) as a timing source. The NTP program (or daemon) will then ensure all devices on that network will be synchronised to the time as told by the atomic clock.

By using a NTP server synchronised to an atomic clock, a computer network can run the identical coordinated universal time as other networks allowing time sensitive transactions to be conducted from across the globe.