Category: timing source

Five Reasons Why You Should Never Use an Internet Timing Source

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Time synchronisation is now an integral part of network administration. Networks that are not synchronised to UTC time (Coordinated Universal Time) become isolated; unable to process time sensitive transactions or communicate securely with other networks.

UTC time has been developed to allow the entire globe to communicate under a single time-frame and it is based on the time told by atomic clocks.

To synchronise to UTC time many network administrators simply connect to an Internet timing source and assume they are receiving a secure source of UTC time. However, there are pitfalls to this and any network that requires security should NEVER use the Internet as a timing source:

1.    To use an internet timing source a port needs to be forwarded in the firewall. This ‘hole’ to allow the timing information to pass through can be utilised by anybody else too.
2.    NTP (Network Time Protocol) has an inbuilt security measure called authentication that ensures a timing source is exactly who it says it is, this can’t be utilised over the Internet.
3.    Internet timing sources are wholly inaccurate. A survey by Nelson Minar of MIT (Massachusetts  Institute of Technology) discovered less than half were close enough to UTC time to be described as reliable (some where minutes and even hours out!).
4.    Distance across the Internet can render even an extremely accurate Internet timing source useless as the distance to client could cause delay.
5.    A dedicated time server will use a radio of GPS timing signal which can be audited to guarantee its accuracy, providing security and legal protection; internet timing sources cannot.

Dedicated NTP time servers not only offer greater protection and security than Internet time sources. They also offer unbridled accuracy with both the GPS and time and frequency radio transmissions (such as MSF, DCF or WWVB) accurate to within a few milliseconds of UTC time.

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.

NTP GPS Server Synchronisation Solution

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Time synchronisation is now a critical aspect of network management enabling time sensitive applications to be conducted from across the globe. Without correct synchronisation computer systems would be unable to communicate with each other and transactions such as seat reservation, Internet auctions and online banking would be impossible.

For effective time synchronisation the global timescale UTC (Coordinated Universal Time) is a prerequisite. While a computer network can be synchronised to any single time source, UTC is employed by computer networks all over the world. By synchronising to a UTC time source a computer network can therefore be synchronised to every other computer network across the globe that also use UTC as their time source.

Receiving a reliable UTC time source is not as easy as it sounds. Many network administrators opt to use a UTC Internet time source. Whilst many of these time sources are accurate enough, they can be too far away to provide reliability and there are plenty of Internet time sources that are vastly inaccurate.

Another reason why Internet time sources should not be used as a source of time synchronisation is because an Internet time source is outside of a firewall and leaving a gap in the firewall to receive timing information can leave a system open to abuse.

So that UTC time can be opted as a civil time throughout the world several national physics laboratories broadcast a UTC timing signal that can be received and utilised as a network time source. Unfortunately, however, these time signals are not available in every country and even in those areas where a signal exists; they can be quite often obstructed by interference and local topography.

Another method for receiving a source of UTC time is to use the GPS satellite network. Strictly speaking the Global Positioning System (GPS ) does not relay UTC but it is a time based on International Atomic Time (TAI) with a predefined offset. A GPS NTP clock can simply convert the GPS time into UTC for synchronisation purposes.

The main advantage of using GPS is that a GPS signal is available anywhere on the planet providing that there is a clear view of the sky above (GPS transmissions are broadcast via line-of-sight) so UTC synchronisation can be conducted anywhere.

Common NTP Server Time Reference Problems

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The NTP server (Network Time Protocol) is one of the most used but least understood computer networking hardware items.

A NTP Server is just a time server that uses the protocol NTP. Other time protocols do exist but NTP is by far the most widely used. The terms ‘NTP server’, ‘time server’ and ‘network time server’ are interchangeable and often the terms ‘radio clock’ or ‘GPS time server’ are used but these simply describe the method which the time servers receive a time reference.

NTP servers receive a time source that they can then distribute amongst a network. NTP will check a devices system clock and advance or retreat the time depending on how much it has drifted. By regularly checking the system clock with the time server, NTP can ensure the device is synchronised.

The NTP server is a simple device to install and run. Most connect to a network via an Ethernet cable and the software included is easily configured. However, there are some common troubleshooting problems associated with NTP servers and in particular with receiving timing sources:

A dedicated NTP server will receive a time signal from various sources. The Internet is probably the most common sources of UTC time (Coordinated Universal Time), however, using the Internet as a timing source can be a cause for several time server problems.

Firstly Internet timing sources can’t be authenticated; authentication is NTP’s in-built security measure and ensures that a timing reference is coming from where it says it is. On a similar note to use an Internet timing source would mean that a gap would have to be created in the network firewall, this can obviously cause its own security issues.

Internet timing sources are also notoriously inaccurate. A survey by MIT (Massachusetts Institute of Technology) found less than a quarter of Internet timing sources were any where near accurate and often those that were, were too far away from clients to provide a reliable timing source.

The most common, secure and accurate method for receiving timing source is the GPS system (Global Positioning System). While a GPs signal can be received anywhere on the planet there are still common installation issues.

A GPS antenna has to have a good clear view of the sky; this is because the GPs satellite broadcast their signal by line of sight. He signal can not penetrate buildings and therefore the antenna has to be situated on the rood. Another common issue with a GPS time server is that they need to be left for at least 49 hours to ensure the GPS receiver gets a good satellite fix. Many users find that they are receiving an intermittent signal this is normally due to impatience and not letting the GPS system obtain a solid fix.

The other secure and reliable method for receiving a timing signal is the national radio transmissions. In the UK this is called MSF but similar systems exist in the US (WWVB), Germany (DCF) and several other countries. There are usually less problems faced when using the MSF/DCF/WWVB signal.

Although the radio signal can penetrate buildings it is susceptible to interference from topography and other electrical appliances.  Any issues with a MSF time server can normally be resolved by moving the server to another locale or often just angling the server so its ib-built antenna is perpendicular to the transmission.

Time Server FAQ on British Time

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Time servers are used throughout UK industry. Many of which receive the MSF signal from the National Physical Laboratoruy in Cumbria. Here are some FAQ’s about British time and the MSF signal:

Who decides when clocks should go forward or back for summer time?

If you live in Europe, the time at which summer time begins and ends is given in the relevant EU Directive and UK Statutory Instrument as 1 a.m. Greenwich Mean Time (GMT).

Does ‘midnight’ belong to the day before or the day after?

The use of the word midnight is heavily dependent on its context but 00.00 (often called 12 am) is the start of the next day. There are no standards established for the meaning of 12 a.m. and 12 p.m. and often a 24 hour time is less confusing.

Is there an approved way to represent dates and times?

The standard notation for the date is the sequence YYYY-MM-DD or YY-MM-DD although in the USA it is the convention to have days and months the other way around.

When did the new millennium really begin?

A millennium is any period of a thousand years. So you could say that the next millennium begins now. The third millennium of the Christian Era began at the start of the year 2001 A.D.

How do you know atomic clocks keep better time?

If you look at several atomic clocks all set to the same time you’ll find that they still agree within ten millionths of a second after a week.

What is the accuracy of the ‘speaking clock’?

Even allowing for the delay in the telephone network, you can probably expect the starts of the seconds pips to be accurate seconds markers within about one-tenth of a second.

Why did my radio-controlled clock move to summer time at 2 a.m., one hour late?

Battery powered radio-controlled clocks typically check the time only every hour or two, or even less, This is to conserve the battery.

Why does my radio-controlled clock receive the MSF signal less well at night?

Users of the MSF service receive predominantly a ‘ground wave’ signal. However, there is also a residual ‘sky wave’ which is reflected off the ionosphere and is much stronger at night, this can result in a total received signal that is either stronger or weaker.

Is there a permanent one-hour difference between MSF time and DCF-77 time?

Since 1995 October 22 there has been a permanent one-hour difference between British time (as broadcast by MSF) and Central European Time, as broadcast by DCF-77 in Germany.

What does MSF stand for?

MSF is the three-letter call sign used to designate the UK’s 60 kHz standard-frequency and time signal.

Thanks to the National Physical Laboratory for their help with this blog.

History of Timekeeping from Stonehenge to the NTP Server

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Keeping track of time has been as integral part of helping human civilisation to develop. It could be argued that the greatest step that mankind took was in the development of farming, allowing humans to free up more time to develop sophisticated cultures.

However, farming was fundamentally reliant on timekeeping. Crops are seasonal and knowing when to plant them is the key to all horticulture. It is believed that ancient monuments such as Stonehenge were elaborate calendars helping the ancients to identify the shortest and longest days (solstice).

As human civilisation developed, telling increasingly accurate time became more and more important. And identifying days of the year was one thing but calculating how far into a day was another.

Timing was extremely inaccurate up until the middle ages. People would rely on comparisons of time as a time reference such as how long it took to walk a mile or the time of day would be estimated from when the sun was highest (noon).

Fortunately the development of clocks during the middle of the last millennium meant that for the first time humans could tell with some degree of precision the time of day. As clocks developed so did their accuracy and civilisation became more efficient as events could be more accurately synchronised.

When electronic clocks arrived at the turn of the last century, accuracy was further increased and new technologies started to develop but it wasn’t until the rise of the atomic clock that the modern world really took shape.

Atomic clocks have enabled technologies such as satellites, computer networks and GPS tracking possible as they are so accurate – to within a second every hundred million years.

The atomic clocks were even discovered to be even more accurate than the spin of the Earth that varies, thanks to the Moon’s gravity and extra seconds have to be added to the length of a day – The leap second.

Atomic clocks mean that a global timescale accurate to within a thousandth of second has been developed called UTC – Coordinated Universal Time.

Computer networks to communicate with each other from across the globe in perfect synchronisation to UTC if they use a NTP time server.

An NTP server will synchronise an entire computer network to within a few milliseconds of UTC time allowing global communications and transactions.

Atomic clocks are still being developed the latest strontium clocks are promising accuracy to within a second every billion years.

Time Server History and The changing ways of recording time

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The NTP server or network time server as it is often called is the culmination of centuries of horology and chronology. The history of keeping track of time has not been as smooth as you may think.

What month was the Russian October revolution? I’m sure you have guessed that it is a trick question, in fact if you trace the days back to the October revolution that changed the shape of Russia in 1917 you will find it didn’t start until November!

One of the first decisions the Bolsheviks, who had won the revolution, chose to make was to join the rest of eh world by taking up the Gregorian calendar. Russia was last to do adopt the calendar, which is still in use throughout the world today.

This new calendar was more sophisticated that the Julian calendar which most of Europe had been using since the Roman Empire. Unfortunately the Julian calendar did not allow for enough leap years and by the turn of the century this had meant that the seasons had drifted, so-much-so, that when Russia finally adopted the calendar on after Wednesday, 31 January 1918 the following day became Thursday, 14 February 1918.

So whilst the October revolution occurred in October in the old system, to the new Gregorian calendar it meant it had taken place in November.

Whilst the rest of Europe adopted this more accurate calendar earlier than the Russians they still also had to correct the seasonal drift, so in 1752 when Britain changed systems they lost eleven days which according to the populist painter of the time, Hogarth, caused rioters to demand the return of their lost eleven days.

This problem of inaccuracy in keeping track of time was thought to be solved in the 1950’s when the first atomic clocks were developed. These devices were so accurate that they could keep time for a million years without losing a second.

However, it was soon discovered that these new chronometers were in fact too accurate – compared with the Earth’s rotation anyway. The problem was that while atomic clocks could measure the length of a day to the nearest millisecond, a day is never the same length.

The reason being is that the Moon’s gravity affects the Earth’s rotation causing a wobble. This wobble has the effect of slowing down and speeding up the Earth’s spin. If nothing was done to compensate for this then eventually the time told by atomic clocks (International Atomic Time- TAI) and the time based on the Earth’s rotation used by farmers, astronomers and you and I (Greenwich Meantime- GMT) would drift that eventually noon would become midnight (albeit in many millennia).

The solution has been to devise a timescale that is based on atomic time but also accounts for this wobble of the Earth’s rotation. The solution was called UTC (Coordinated Universal Time) and accounts for the Earth’s variable rotation by having ‘leap seconds’ occasionally added. There have been over thirty leap seconds added to UTC since its inception in the 1970’s.

UTC is now a global timescale used throughout the world by computer networks to synchronise too. Most computer networks use a NTP server to receive and distribute UTC time.

Time Server Top Tips for Time Synchronisation

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Time synchronisation is an integral part of modern computer networking particularly with the Internet and online communication having become so dominant.

Communicating with machines across the globe requires exact time synchronisation otherwise many of the online tasks we take for granted would not be possible. Time in the form of timestamps is the only form of reference a computer has to identify the order of events. So with time sensitive transactions time synchronisation is pivotal.

Here are some tips to ensure your network is running precise and accurate time as possible:

NTP (Network Time Protocol) is the world’s leading time synchronisation software. There are other time protocols but NTP is the most widely used and best supported.

Most computer networks across the globe are synchronised to UTC (Coordinated Universal Time). This is a global timescale based on the time told by atomic clocks. Always use a UTC source to synchronise too.

Always use an external hardware source as a timing reference as time sources from the Internet can not be authenticated. Authentication is a security measure used by NTP to ensure a timing reference is coming from where it says it is from. Also using an Internet timing source means that the reference is outside your networks firewall, this can cause added security risks.

Dedicated time servers can receive UTC signals from radio transmissions and the GPs network. These offer the most secure, accurate and reliable method of receiving a UTC time reference.

Networks based in Britain, Germany, the USA and Japan have access to long-wave time and frequency transmissions that are broadcast by national physics labs. These broadcasts are accurate and reliable and often the dedicated time servers that receive them are less expensive than their GPS alternatives.

GPS is available everywhere on the globe as a source of UTC time. GPS antennas do good a good 180 degree view of the sky and require a good 48 hours to receive a stable ‘locked’ satellite fix.

Arrange your network into strata. Stratum levels signify the distance from a timing source. A stratum 0 server is an atomic clock while a stratum 1 server is a dedicated time server that receives the time from a stratum 0 source. Stratum 2 devices are machines that receive their timing source from a stratum 1 server but stratum 2 devices can also be used to pass on timing information. By ensuring you have enough stratum levels you will avoid congestion in your network and time server.

UTC Radio References from Around the World

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UTC (Coordinated Universal Time) is the global civil timescale used by millions of people, businesses and authorities across the globe. UTC is based on the time told by caesium atomic clocks. These clocks are the most reliably accurate chronometers on Earth, able to maintain accurate time for several millions of years whilst neither losing nor gaining a second.

Unfortunately caesium clocks are far too expensive and delicate pieces of machinery to make it practical for us all to have one but fortunately the time that they tell is transmitted by several countries. These nation’s national physics laboratories tend to broadcast the UTC time from these clocks by long-wave.

In the UK the 60 kHz transmission is broadcast by the National Physical Laboratory from a transmitter in Anthorn in Cumbria (it was based in Rugby until 2007). NPL constantly maintain the transmissions and assess its accuracy. Whilst the MSF signal is a British based transmission is possible to receive the signal in some parts of northern Europe and Scandinavia.

However, in mainland Europe, the strongest time and frequency signal is the German transmission broadcast from Frankfurt in Germany. This signal known as the DCF is controlled and maintained by the German National Physics Laboratory. While Switzerland also has its own time and frequency signal, the German DCF signal is by far the most widely used in Europe.

In the USA a similar system is maintained by NIST (National Institute for Standards and Time) and is broadcast from Fort Collins, Colorado. This signal is known as WWVB and is available in most parts of Northern America (including Canada).

Japan maintains its own timing broadcast (JJY) also which is popular in the south pacific and several other countries (such as France) maintain their own signals too although these tend to have only minor coverage.

All these times signals operate in a similar fashion. The strength of the signal is either reduced by between 6 and 10 dB or switched off for a specific amount of time before being restored at the start of each second. The amount of time the signal is reduced indicates a stream of binary numbers with positioning markers.
The signals operate on a 60 kHz frequency and carry a time and date code which relays the following information in binary format: Year, month, day of month,  day of week,  hour,  minute,  DUT1 (the difference between UTC and UT1 which is based on the Earths rotation). The signals also relay information about local time such as British Summer Time.

Keeping accurate time on Linux

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If you want to be sure that your computer clock is accurate you can configure your system to use NTP (Network Time Protocol), one of the oldest Internet protocols and the industry standard for time synchronisation.

NTP on will synchronise your computer’s clock to a pool of time servers around the world that are official ‘timekeepers’. It is best to choose the closest to you so response time is minimized and to use more than one in case one goes down. There are more than 1.500 servers to choose from, but some areas are better served than others. Many servers on the internet are extremely inaccurate and Internet time references should not be used as a replacement for a dedicated time server.

However, for basic time synchronisation purposes, Internet providers will suffice. The first step should be to select three servers close to you – preferably in your country, or if there aren’t enough, in your ‘zone. Go to ntp home and browse through the tree of zones and servers to select which ones are best for you. The follow these commands to configure:

1. Configure /etc/ntp.conf
Edit this file with a text-editor. Replace
server <example-server-name>
with your servers, such as:

server 0.br.pool.ntp.org
server 1.br.pool.ntp.org
server 2.br.pool.ntp.org

2. Synchronise your clock manually
If your clock is drifting too NTP might refuse to synchronise it, but it can be done manually:

ntpdate 0.br.pool.ntp.org (server name that you choose)

3. Make your ntp daemon executable

chmod +x /etc/rc.d/rc.ntpd

4. Start NTP now without rebooting
Again, a simple command:

/etc/rc.d/rc.ntpd start