Category: chronology

Computers, Communications, Atomic Clocks and the NTP Server

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Time synchronisation on computer networks is often conducted by the NTP server. NTP time servers do not generate any timing information themselves but are merely methods of communicating with an atomic clock.

The precision of an atomic clock is widely talked about. Many of them can maintain time to nanosecond precision (billionths of a second) which means they won’t drift beyond a second in accuracy in hundreds of millions of years.

However, what is less understood and talked about is why we need to have such accurate clocks, after-all the traditional methods of keeping time such as mechanical clocks, electronic watches and using the rotation of the Earth to keep track of the days has proved reliable for thousands of years.

However, the development of digital technology over recent years has been nearly solely reliant on the ultra high precision of an atomic clock. One of the most widely used applications for atomic clocks is in the communications industry.

For several years now telephone calls taken in most industrialized countries are now transmitted digitally. However, most telephone wires are simply copper cables (although many telephone companies are now investing in fibre optics) which can only transmit one packet of information at a time. Yet telephone wires have to carry many conversations down the same wires at the same time.

This is achieved by computers at the exchanges switching from one conversation to another thousands of times every second and all this has to be controlled by nano-second precision otherwise  the calls will become out of step and get jumbled – hence the need for. Atomic clocks; mobile phones, digital TV and Internet communications use similar technology.

The accuracy of atomic clocks is also the basis for satellite navigation such as GPS (global positioning system). GPS satellites contain an onboard atomic clock that generates and transmits a time signal. A GPS receiver will receive four of theses signals and use the timing information to work out how long the transmissions took to reach it and therefore the position of the receiver on Earth.

Current GPS systems are accurate to a few metres but to give an indication of how vital precision is, a one second drift of a GPS clock could see the GPS receiver be inaccurate by over 100 thousand miles (because of the  huge distances light and therefore transmissions take in one second).

Many of these technologies that depend on atomic clocks utilise NTP servers as the preferred way to communicate with atomic clocks making the NTP time server one of the most crucial pieces of equipment in the communication industries.

The NTP Time Server Essential Network Protection

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There are a myriad of hardware and software methods of protecting computers. Anti-virus software, firewalls, spyware and routers to name but a few yet perhaps the most important tools for keeping a network safe is often the most overlooked.

One of the reasons for this is that the network time server’s often referred to as the NTP time server (after the protocol Network Time Protocol) primary task is time synchronisation and not security.

The NTP server’s primary task is to retrieve a time signal from a UTC source (Coordinated Universal Time) which it then distributes it amongst the network, checking the clock on each system device and ensuring its running in synchronisation with UTC.

Here is where many network administrators fall down. They know that time synchronisation is vital for computer security. Without it, errors can not be logged (or even spotted) network attacks can’t be countered, data can be lost and if a malicious user does get into the system it is near impossible to discover what they were up to without all machines on a network corresponding to the same time.

However, the NTP server is where many network administrators think they can save a little money. ‘Why bother?’ ‘They say, ‘when you can log on to an Internet NTP server for free.’

Well, as the old saying goes there is no such thing as a free lunch or as it goes a free source of UTC time. Using internet time providers may be free but this is where many computer networks leave themselves open to abuse.

To utilise an internet source of time such as Microsoft’s, NIST or one of those on the NTP pool project may be free but they are also outside a networks firewall and these is where many network administrators come unstuck.

Bringing Atomic Clock Precision to your Desktop

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Atomic clocks have been a huge influence on our modern lives with many of the technologies that have revolutionised the way we live our lives relying on their ultra precise time keeping abilities.

Atomic clocks are far different to other chronometers; a normal watch or clock will keep time fairly accurately but will lose second or two each day. An atomic clock on the other hand will not lose a second in millions of years.

In fact it is fair to say that an atomic clock doesn’t measure time but is the foundations we base our perceptions of time on. Let me explain, time, as Einstein demonstrated, is relative and the only constant in the universe is the speed of light (though a vacuum).

Measuring time with any real precision is therefore difficult as even the gravity on Earth skews time, slowing it down. It is also almost impossible to base time on any point of reference. Historically we have always used the revolution of the earth and reference to the celestial bodies as a basis for our time telling (24 hours in a day = one revolution of the Earth, 365 days = one revolution of the earth around the Sun etc).

Unfortunately the Earth’s rotation is not an accurate frame of reference to base our time keeping on. The earth slows down and speeds up in its revolution meaning some days are longer than others.

Atomic clocks
however, used the resonance of atoms (normally caesium) at particular energy states. As these atoms vibrate at exact frequencies (or an exact number of times) this can be used as a basis for telling time. So after the development of the atomic clock the second has been defined as over 9 billion resonance ’ticks’ of the caesium atom.

The ultra precise nature of atomic clocks is the basis for technologies such as satellite navigation (GPS), air traffic control and internet trading. It is possible to use the precise nature of atomic clocks to synchronise computer networks too. All that is needed is a NTP time server (Network Time Protocol).
NTP servers receive the time from atomic clocks via a broadcast signal or the GPS network they then distribute it amongst a network ensuring all devices have the exact same, ultra precise time.

The World in Perfect Synchronization

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Synchronization is something we are familiar with everyday of our lives. From driving down the highway to walking crowded street; we automatically adapt our behaviour to synchronize with those around us. We drive in the same direction or walk the same thoroughfares as other commuters as failing to do so would make our journey a lot more difficult (and dangerous).

When it comes to timing, synchronisation is even more important. Even in our day to day dealings we expect a reasonable amount of synchronisation from people. When a meeting starts at 10am we expect everybody to be there within a few minutes.

However, when it comes to computer transactions across a network, accuracy in synchronisation becomes even more important where accuracy to a few seconds is too inadequate and synchronisation to the millisecond becomes essential.

Computers use time for every transaction and process they do and you only have to think back to the furore caused by the millennium bug to appreciate the importance computer’s place on time. When there is not precise enough synchronisation then all sorts of errors and problems can occur, particularly with time sensitive transactions.

Its not just transactions that can fail without adequate synchronisation but time stamps are used in computer log files so if something goes wrong or if a malicious user has invaded (which is very easy to do without adequate synchronisation) it can take a long time to discover what went wrong and even longer to fix the problems.

A lack of synchronisation can also have other effects such as data loss or failed retrieval it can also leave a company defenceless in any potential legal argument as a badly or unsynchronised network can be impossible to audit.

Millisecond synchronisation is however, not the headache many administrators assume it is going to be. Many opt to take advantage of many of the online timeservers that are available on the internet but in doing so can generate more problems than it solves such as having to leave the UDP port open in the firewall (to allow the timing information through) not-to-mention no guaranteed level of accuracy from the public time server.

A better and simpler solution is to use a dedicated network time server that uses the protocol NTP (Network Time Protocol). A NTP time server will plug straight into a network and use the GPS (Global Positioning System) or specialist radio transmissions to receive the time direct from an atomic clock and distribute it amongst the network.

The Concept of Time

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Time is something that we are all familiar with, it governs our lives even more so than money and we are constantly ‘at war’ with time as we battle to conduct our daily tasks before it runs out.

Yet when we start to examine time we discover that the concept of time we begin to realise that a non-ending linear distance between different events that we call time is purely a human invention.

Of course time exists but it certainly doesn’t follow the rules that the human concept of time does. It is not never ending or constant and changes and warps depending on speed of observers and the pull of gravity. In fact it was Einstein’s theories on relativity that gave human kind its first glimpse as to what time really is and how it affects our daily lives.

Einstein described a four-dimensional space-time, where time and space are inextricably woven together. This space-time gets warped and bent by gravity slowing time (or our perception of it). Einstein also, he suggested that the speed of light was the only constant in the universe and time altered depending on the relative speed to it.

When it comes to keeping track of time, Einstein’s theories can hamper any attempts at chronology. If both gravity and relative speed can affect time then it becomes difficult to measure time accurately.

We long ago abandoned the idea of using the celestial bodies and Earth’s rotation as a reference for our timekeeping as it was recognised in the early twentieth century that Earth’s rotation wasn’t at all accurate or reliable. Instead, we have depended n the oscillations of atoms to keep track of time. Atomic clocks measure atomic ticks of particular atoms and our concept of time is based on these ticks with every second being equal to over 9 billion oscillation of the caesium atom.

Even though we now base time on atomic oscillations, technologies such as GPS satellites (Global Positioning System) still have to counter the effects of lower gravity. In fact the effects of time can be monitored so accurately thanks to atomic clocks that those at different altitudes above sea level run at slightly differing speeds which has to be compensated for.

Atomic clocks can also be used to synchronise a computer network ensuring that they are running as accurately as possible. Most NTP time servers operate by utilising and distributing the time signal broadcast by an atomic clock (either through GPS or long wave) using the protocol NTP (Network Time Protocol).

Why the Need for NTP

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Network Time Protocol is an Internet protocol used to synchronize computer clocks to a stable and precise time reference. NTP was originally developed by Professor David L. Mills at the University of Delaware in 1985 and is an Internet standard protocol and is used in most network time servers, hence the name NTP server.

NTP was developed to solve the problem of multiple computers working together and having the different time. Whilst, time usually just advances, if programs are running on different computers time should advance even if you switch from one computer to another. However, if one system is ahead of the other, switching between these systems would cause time to jump forward and back.

As a consequence, networks may run their own time, but as soon as you connect to the Internet, effects become visible. Just Email messages arrive before they were sent, and are even replied to before they were mailed!

Whilst this sort of problem may seem innocuous when it comes to receiving email, however, in some environments a lack of synchronisation can have disastrous results this is why air traffic control was one of the first applications for NTP.

NTP uses a single time source and distributes it amongst all devices on a network it does this by using an algorithm that works out how much to adjust a system clock to ensure synchronisation.

NTP works on a hierarchical basis to ensure there are no network traffic and bandwidth problems. It uses a single time source, normally UTC (coordinated universal time) and receives time requests from the machines on the top of the hierarch which then pass the time on further down the chain.

Most networks that utilise NTP will use a dedicated NTP time server to receive their UTC time signal. These can receive the time from the GPS network or radio transmissions broadcast by national physics laboratories. These dedicated NTP time servers are ideal as they receive time direct from an atomic clock source they are also secure as they are situated externally and therefore do not require interruptions in the network firewall.

NTP has been an astronomical success and is now used in nearly 99 per cent of time synchronisation devices and a version of it is included in most operating system packages.

NTP owes much of its success to the development and support it continues to receives nearly three decades after its inception which is why t is now used throughout the world in NTP servers.

Increased Accuracy of Dual NTP Server Systems

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The NTP time server has revolutionised the synchronisation of computer networks over the last twenty years. NTP (Network Time Protocol) is the software  that  is responsible for distributing time from the time server to the entire network, adjusting machines for drift and assuring accuracy.

NTP can reliable maintain system clocks to within a few millimetres of UTC (Coordinated Universal Time) or whatever timescale it is fed with.

However NTP can only be as reliable as the time source that it receives and as UTC  is the global civil timescale it depends on where the UTC source comes from.

National time and frequency transmissions from physics labs like NIST in the USA or NPL in the UK are extremely reliable sources of UTC and NTP time servers are designed specifically for them. However, the time signals are not guaranteed, they can drop off throughout the day and are susceptible to interference; they are also regularly turned of for maintenance.

For most applications a few hours of your network relying on crystal oscillators will probably not cause too much problems in synchronisation. However, GPS (Global Positioning System) is far more reliable source for UTC time in that a GPS satellite is always overhead. They do require a line-of-sight reception which means an antenna has to go on the roof or outside an open window.

For applications where accuracy and reliability are essential the safest solution is to invest in a dual system NTP time server, these device can receive both the radio transmissions such  as MSF, DCF-77 or WWVB and the GPS signal.

On a dual system NTP server, NTP will take both time sources and to synchronise a network to ensuring increased accuracy and reliability.

Security and Synchronisation

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Security is often the most worried about aspect of running a computer network. Keeping unwanted users out whilst allowing freedom for users to access network applications is a full time job. Yet many network administrators fail to pay any heed to one of the most crucial aspects of keeping a network secure – time synchronisation.

Time synchronisation is not just important but it is vital in network security and yet it is staggering how many network administrators disregard it or fail to have their systems properly synchronised.

Ensuring the same and correct time (ideally UTC – Coordinated Universal Time) is on each network machine is essential as any time delays can be an open door for hackers to slip in undetected and what is worse if machines do get hacked are not running the same time it can be near impossible to detect, repair and get the network back up and running.

Yet time synchronisation is one of the simplest of tasks to employ, particularly as most operating systems have a version of the time protocol NTP (Network Time Protocol).

Finding an accurate time server can sometimes be problematic particularly if the network is synchronised across the internet as this can raise other security issues such as having an open port in the firewall and a lack of possible authentication by NTP to ensure the signal is trusted.

However, an easier method for time synchronisation, being both accurate and secure, is to use a dedicated NTP time server (also known as network time server). An NTP server will take a time signal direct from GPS or from the national time and frequency radio transmissions put out by organisations such as NIST or NPL.

By using a dedicated NTP server the network will become a lot securer and if the worst does happen and the system does fall victim to malicious users then having a synchronised network will ensure it is easily solvable.

How to Synchronise a Computer to an Atomic Clock

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Time synchronisation is often a much underrated aspect of computer management. Generally time synchronisation is only crucial for networks or for computers that a take in time sensitive transactions across the internet.

Time synchronisation with modern operating systems such as Windows Vista, XP or the different versions of Linux is relatively easy as most contain the time synchronisation protocol NTP (Network Time Protocol) or a simplified version at least (SNTP).

NTP is an algorithm based program and works by using a single time source that can be distributed amongst the network (or a single computer) and is constantly checked to ensure the network’s clocks is running accurately.

For single computer users, or networks where security and precision are not primary concerns (although for any network security should be a main issue) then the simplest method of synchronising a computer is to use an internet time standard.

With a Windows operating system this can easily be done on a single computer by double clicking the clock icon and then configuring the internet time tab. However, it must be noted that in using an internet based time source such as or windows.time, a port will have to be left open in the firewall which could be taken advantage of by malicious users.

For network users and those not wanting to leave vulnerabilities in their firewall then the most suitable solution is to use a dedicated network time server. Most of these devices also use the protocol NTP but as they receive a time reference externally to the network (usually by way of GPS or long wave radio) the leave no vulnerabilities in the firewall.

These NTP server devices are also far more reliable and accurate than internet time sources as they communicate directly with the signal from an atomic clock rather than being several tiers (in NTP terms known as strata) from the reference clock as most internet time sources are.

Common GPS Queries

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Is the GPS time signal the same as the GPS positioning signal?

Yes. The signals that are broadcast by GPS satellites contain time information and the position of the satellite it came from (and its velocity). The timing information is generated by an onboard caesium atomic clock. It is this information used by satellite navigation devices (sat navs) that enables global positioning. Sat Navs use these signals from multiple satellites to triangulate a position.

How accurate is GPS positioning?

Because the time signal generated by GPS comes from an atomic clock it is accurate to within 16 nanoseconds (16 billionths of a second). As light travels nearly 186 000 miles in a second this equates to around 16 feet (5+metres) which means a GPS positioning system is usually accurate to this much.

Is GPS time the same as UTC?

No. GPS time, like UTC (Coordinated Universal Time)is based on International Atomic Time (TAI) – the time told by atomic clocks. However as the GPS system was developed several decades ago it is now 14 seconds (and soon to be 15) behind UTC because it has missed out on the Leap Seconds added to UTC to calibrate for the Earth’s slowing rotation.

How can I use GPS as a source of UTC then?

Fortunately a GPS time server will convert GPS to the current UTC time, which as od 1 January 2009 will mean it has to add exactly 15 seconds.