Rubidium Oscillators Additional Precision for NTP Serve (Part 2)

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Continued…

However, there are some occasions when a time server can lose connection with the atomic clock and not receive the time code for a prolonged period of time. Sometimes this may be because of downtime by the atomic clock controllers for maintenance or that nearby interference is blocking the transmission.

Obviously the longer the signal is down the more potential drift may occur on the network as the crystal oscillator in the NTP server is the only thing keeping time. For most applications this should never be a problem as the most prolonged period of downtime is not normally more than three or four hours and the NTP server would not have drifted by much in that time and the occurrence of this downtime is quite rare (maybe once or twice a year).

However, for some ultra precise high end applications rubidium crystal oscillators are beginning to be used as they don’t drift as much as quartz. Rubidium (often used in atomic clocks themselves instead of caesium) is far more accurate an oscillator than quartz and provides better accuracy for when there is no signal to a NTP time server allowing the network to maintain a more accurate time.

Rubidium itself is an alkali metal, similar in properties to potassium. It is very slightly radioactive although poses no risk to human health (and is often used in medicine imaging by injecting it into a patient). It has a half life of 49 billion years (the time it takes to decay by half – in comparison some of the most lethal radioactive materials have half-lives of under a second).

The only real danger posed by rubidium is that it reacts rather violently to water and can cause fire

Dealing with Time across the Globe

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No matter where we are in the world we all need to know the time at some point in the day but while each day lasts for the same amount of time no matter where you are on Earth the same timescale is not used globally.

The impracticality of Australians having to wake up at 17.00 or those in the US having to start work at 14.00 would rule out suing a single timescale, although the idea was discussed when the Greenwich was named the official prime meridian (where the dateline officially is) for the world some 125 years ago.

While the idea of a global timescale was rejected for the above reasons, it was later decided that 24 longitudinal lines would split the world up into different timezones. These would emanate from GMT around with those on the opposite side of the planet being +12 hours.

However, by the 1970’s a growth in global communications meant that a universal timescale was finally adopted and is still in much use today despite many people having never heard of it.

UTC, Coordinated Universal Time, is based on GMT (Greenwich Meantime) but is kept by a constellation of atomic clocks. It also accounts for variations in earth’s rotation with additional seconds known as ‘leap seconds’ added once of twice a year to counteract the slowing of the Earth’s spin caused by gravitational and tidal forces.

While most people have never heard of UTC or use it directly its influence on our lives in undeniable with computer networks all synchronised to UTC via NTP time servers (Network Time Protocol).

Without this synchronisation to a single timescale many of the technologies and applications we take for granted today would be impossible. Everything from global trading on stocks and shares to internet shopping, email and social networking are only made possible thanks to UTC and the NTP time server.

Atomic Clocks the Key to Network Synchronisation

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Sourcing the correct time for network synchronisation is only possible thanks to atomic clocks. Compared to standard timing devices and atomic clock is millions of times more accurate with the latest designs providing accurate time to within a second in a 100,000 years.

Atomic clocks use the unchanging resonance of atoms during different energy states to measure time providing an atomic tick that occurs nearly 9 billion times a second in the case of the caesium atom. In fact the resonance of caesium is now the official definition of a second having been adopted by the International System of Unit (SI).

Atomic clocks are the base clocks used for the international time, UTC (Coordinated Universal Time). And they also provide the basis for NTP servers to synchronise computer networks and time sensitive technologies such as those used by air traffic control and other high level time sensitive applications.

Finding an atomic clock source of UTC is a simple procedure. Particularly with the presence of online time sources such as those provided by Microsoft and the National Institute for Standards and Time (windows.time.com and nist.time.gov).

However, these NTP servers are what are known as stratum 2 devices that mean they are connected to another device which in turn gets the time from an atomic clock (in other words a second-hand source of UTC).

While the accuracy of these stratum 2 servers is unquestionable, it can be affected by the distance the client is from the time servers, they are also outside the firewall meaning that any communication with an online time server requires an open UDP (User Datagram Protocol) port to allow the communication.

This can cause vulnerabilities in the network and are not used for this reason in any system that requires complete security. A more secure (and reliable) method of receiving UTC is to use a dedicated NTP time server. These time synchronisation devices receive the time direct from atomic clocks either broadcast on long wave by places like NIST or NPL (National Physical Laboratory – UK). Alternatively UTC can be derived from the GPS signal broadcast by the constellation of satellites in the GPS network (Global Positioning System).

NTP Servers and the Different Time Sources

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NTP servers are essential devices for computer network time synchronisation. Ensuring a network coincides with UTC (Coordinated Universal Time) is vital in modern communications such as the Internet and is the primary function of the network time server (NTP server).

As their name suggests, these time servers use the protocol NTP (Network Time Protocol) to handle the synchronisation requests. NTP is already installed in many operating systems and synchronisation is possible without an NTP server by utilising an Internet time source, this can be unsecure and inaccurate for many network needs.

Network time servers receive a far more accurate and secure time signal. There are two methods of receiving the time using a time server: utilising the GPS network or receiving long wave radio transmissions.

Both these methods of receiving a time source are secure as they are external to any network firewall. They are also accurate as both sources of time are generated directly by atomic clocks rather than an Internet time service that are normally NTP devices connected to a third party atomic clock.

The GPS network provides an ideal source of time for NTP servers as the signals are available anywhere. The only downside of using the GPS network is that a view of the sky is required to lock-on to a satellite.

Radio referenced time sources are more flexible in that the long wave signal can be received indoors. They are limited in strength and not every country has a time signal although some signals such as the German DCF and the USA WVBB are available in neighbouring states.

Time Synchronisation on a Windows 7 Network

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Windows 7 is the latest instalment in the Microsoft operating system family. Following on from the much maligned Windows Vista, Windows 7 has a much warmer reception from critics and consumers.

Time synchronisation on Windows 7 is extremely straight forward as the protocol NTP (Network Time Protocol) is built-in to Windows 7 and the operating system automatically synchronises the computer’s clock by connecting to the Microsoft time service time.windows.com.

This is useful for many home users but the synchronisation across the Internet is not secure enough for a computer network for the following reason:

To connect to any Internet time source such as time.windows.com a post is required to be left open in the firewall. As with any open port in a network firewall this can be used as a point of entry by a malicious user or some malicious software.

The time synchronisation facility in Windows 7 can be turned off and is quite simple to do by opening the time and date dialogue box and uncheck the synchronization box.

However, time synchronisation on a network is vital so if the Internet time service is turned off it needs to be replaced with a secure and accurate source of time.

By far the best way of doing this is to use a time source that’s external to the network (and the firewall).

The simplest, safest and most accurate way of synchronizing a Windows 7 network is to use a dedicated NTP server. These devices use a time reference from either a radio frequency (usually distributed by national physics laboratories such as Britain’s NPL and America’s NIST) or from the GPS satellite network.

Because both these reference sources come from atomic clock sources they are incredibly accurate too and a Windows 7 network that consists of hundreds of machines can be synchronised to within a few milliseconds of the global timescale UTC (Coordinated Universal Time) by utilising just one NTP time server.

Common Time Synchronization Pitfalls Finding UTC

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Time synchronization can be a headache for many network administrators attempting to synchronize a network for the first time. There are many pitfalls that an unaware network administrator can fall into when attempting to get every machine on a network to synchronize to the same time.

The first problem many network administrators make is the selection of the time source. UTC (Coordinated Universal Time) is a global timescale and is used throughout the world as a basis for time synchronization as it doesn’t rely on time zones enabling the global community to base itself on one timescale.

UTC is also controlled by a constellation of atomic clocks which ensures its accuracy; however, it is regularly adjusted to ensure that it matches mean solar time by the addition of leap seconds which are added to counter the natural slowing of the Earth’s rotation.

UTC is readily available as a time reference from a number of sources. The Internet is a popular location to receive a UTC time source. However, an Internet time source is located through the network firewall and security issues can arise from having to leave the UDP port open to receive the time requests.

Internet time sources can also be inaccurate and as NTP’s own security system known as NTP authentication cannot work across the Internet further security issues can arise.

A far better solution for getting a source of UTC is to use either the Global Positioning System (GPS) or the long wave radio transmissions broadcast by several national physics laboratories such as NIST in the USA and the UK’s NPL.

Dedicated NTP time servers can receive these secure and authenticated signals and then distribute them amongst all devices on a network.

GPS Atomic Clock Time Signals

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It seems that nearly every car dashboard has a GPS receiver perched on the top. They have become incredibly popular as a navigational tool with many people relying on them solely to work their way around the road networks.

The Global Positioning System has been around for quite a few years now but was originally designed and built for US military applications but was extended for civilian use following an airline disaster.

Whilst it is incredibly useful and convenient a tool, the GPS systems is relatively simple in its operation. The navigation works using a constellation of 30 or so satellites (there are quite a few more that are orbiting but no longer operational).

The signals sent from the satellites contain three pieces of information that are received by the sat nav devices in our cars.

That information includes:

* The time the message was sent

* The orbital position of the satellite (known as the ephemeris)

* The general system health and orbits of the other GPS satellites (known as the almanac)

The way the navigational information is worked out is by using the information from four satellites. The time the signals left the each of the satellites is recorded by the sat nav receiver and the distance from each satellite is then worked out using this information. By using the information from four satellites it possible to work out exactly where the satellite receiver is, this process is known as triangulation.

However, working out exactly where you are in the world does rely on complete accuracy in the time signals that are broadcast by the satellites. As signals such as the GPS travel at the speed of light (approximately 300,000 km a second through a vacuum) even a one second inaccuracy could see positioning information out by 300 kilometres! Currently the GPS system is accurate to five metres which demonstrates just how accurate the timing information broadcast by the satellites is.

This high level of accuracy is possible because each GPS satellite contains atomic clocks. Atomic clocks are incredibly accurate relying on the unwavering oscillations of atoms to keep time – in fact each GPS satellite will run for over a million years before it will drift by as much as a second (compared to the average electronic watch which will drift by a second in a week or two)

Because of this high level of accuracy the atomic clocks on board GPS satellites can be used as a source of accurate time for the synchronization of computer networks and other devices that require synchronization.

Receiving this time signal requires the use of a NTP GPS server that will synchronize with the satellite and distribute the time to all devices on a network.

Why Bother Using a NTP Time Server?

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Keeping computers synchronized on a network is vitally important, especially if the network in question deals with time sensitive transactions. And failing to keep a network synchronized can cause havoc leading to errors, vulnerabilities and endless problems with debugging.

However with the amount of online time servers available from reputable places such as NIST or Microsoft it is often queried as to why computer networks need to be synchronised to an external NTP time server.

These dedicated NTP devices are often seen as an unnecessary expense and many network administrators simply forgo them and connect to an online time server, after-all, it does the same job doesn’t it?

Actually there are two major reasons why NTP time servers are not only important but essential for most computer networks and to overlook them could be costly in many ways.

Let me explain. The first reason why an external NTP server is important is accuracy. It’s not that internet time sources are generally inaccurate (although many are) but there is the question of distance the time reference has to travel. Furthermore, in times when the connection is lost -whether it’s because of a local connection fault or the time server itself goes down – the network will start to drift until the connection is restored.

Secondly and perhaps most important is the security issues involved in using an Internet time source. The main problem is that if your connection to a time server through the then a open port (UDP 123 fro NTP requests) has to be left open, And as with any open port that can used as a gateway for malicious software and users.

The reason dedicated NTP time servers are essential for computer networks is that they work completely independently and external to the network’s firewall. Instead of accessing a time source across the Internet they use either GPS or radio transmissions to get the time. And in doing so they can provide accurate time all the time without fear of losing a connection or allowing a nasty Trojan through the firewall.

When Time is Money Accuracy Matters

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We live in a fast paced world where time matters. In some industries even a second can make all the difference. Millions of dollars are exchanged hands in the stock exchange each second and share prices can rise or plummet.

Getting the right price at the right time is essential for trading in such a fast paced money market and perfect network time synchronization is the essential to be able to make that happen.

Ensuring every machine that deals in stocks, shares and bonds has the correct time is vital if people are going to trade in the derivatives market but when traders are sat in different parts of the world how can this possibly be achieved.

Fortunately Coordinated Universal Time (UTC), a global timescale developed after the development of atomic clocks, allows the same time to govern every trader, regardless of where they are in the world.

As UTC is based on atomic clock time and is kept accurate by a constellation of these clocks, it is high reliable and accurate. And industries like the stock exchange use UTC to govern the time on their computer networks.

Computer network time synchronization is achieved in computer networks by using the NTP server (Network Time Protocol). NTP servers receive a source of UTC from an atomic clock reference. This is either from the GPS network or through specialist radio transmissions (it is available through the internet too but is not as reliable).

Once received, the NTP server distributes the highly accurate time throughout the network, continually checking each device and workstation to ensure the clock is as precise as possible.

These network time servers can keep entire networks of hundreds and thousands of machines in perfect synchronization – to within a few milliseconds of UTC!

Why we Synchronize the Time

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We live and work in a totally different world to the one that many of us were born into. We are now as likely to buy something from across the internet as stroll down the coal high street. And big business and commerce has changed too with the marketplace becoming truly global and the internet being the most common tool for trade.

Trading globally does provide its problems though as different timescales govern the different countries across the globe. To ensure parity a global timescale was introduced in the 1970’s knows Coordinated Universal Time (UTC). However, as e-commerce advanced so did the need to ensure accurate synchronization to UTC.

The biggest problem is that most clocks and watches, including those inbuilt into computer motherboards, are susceptible to drift. And as different machines will drift at different rates, global communication and e-commerce could be impossible. Just think of the difference a second can make in marketplaces like the stock exchange, where fortunes are won or lost, or when you purchase seat reservations online, what would happen if somebody on a computer with slower clock booked the same seat after you, the computer’s timestamps will show the person booked before you.

Other unforeseen errors can result, even in internal networks, when computers are running different times. Data can get lost, errors can be difficult to log, track down and fix and malicious users can take advantage of the time confusion.

To ensure truly global synchronization, computer networks can synchronize to an atomic clock allowing all computers on a network o remain within a few milliseconds of UTC. Compute networks use NTP servers (Network Time Protocol) to ensure accurate synchronization, most NTP servers receive the atomic clock time from either GPS satellites of radio frequencies.