Category: Time Synchronisation

All PC’s and networking devices use clocks to maintain an internal system time. These clocks, called Real Time Clock chips (RTC) provide time and date information. The chips are battery backed so that even during power outages, they can maintain time. However, personal computers are not designed to be perfect clocks, their design has been optimized for mass production and low-cost rather than maintaining accurate time.

These internal clocks are prone to drift and although for many application this can be quite adequate, often machines need to work together on a network and if the computers drift at different rates the computers will become out of sync with each other and problems can arise particularly with time sensitive transactions.

Network Time Protocol (NTP) is one of the Internet’s oldest protocols still used, invented by Dr David Mills from the University of Delaware, it has been in utilized since 1985. NTP is a protocol designed to synchronize the clocks on computers and networks across the Internet or Local Area Networks (LANs).

NTP (version 4) can maintain time over the public Internet to within 10 milliseconds (1/100th of a second) and can perform even better over LANs with accuracies of 200 microseconds (1/5000th of a second) under ideal conditions.

NTP works within the TCP/IP suite and relies on UDP, a less complex form of NTP exists called Simple Network Time Protocol (SNTP) that does not require the storing of information about previous communications, needed by NTP. It is used in some devices and applications where high accuracy timing is not as important.

Many operating systems including Windows, UNIX and LINUX can utilize NTP and SNTP  and time synchronisation with NTP is relatively simple, it synchronises time with reference to a reliable clock source. This source could be relative (a computer’s internal clock or the time on a wrist-watch) or absolute (A UTC – Universal Coordinated Time – clock source that is accurate as is humanely possible).
All Microsoft Windows versions since 2000 include the Windows Time Service (w32time.exe) which has the ability to synchronise the computer clock to an NTP server.
 
There are a large number of Internet hosted NTP servers that synchronise with external UTC references such as time.nist.gov or ntp.my-inbox.co.uk but it must be noted that Microsoft and others recommend that an external source is used to synchronise your machines, as Internet based references can’t be authenticated. Specialist NTP time servers are available that can synchronise time on networks using either the MSF (or equivalent) or GPS signal.

The most widely used are the GPS time servers which use the GPS system to relay accurate time. The GPS system consists of a number of satellites providing accurate positioning and location information. Each GPS satellite can only do this by utilising an atomic clock which in turn can be can be used as a timing reference.

A typical GPS receiver can provide timing information to within a few nanoseconds of UTC as long as there is an antenna situated with a good view of the sky.

There are a number of national time and frequency radio transmissions that can be used to synchronise a NTP server. In Britain the signal (called MSF) is broadcast by the National Physics Laboratory in Cumbria which serves as the United Kingdom’s national time reference, there are also similar systems in Colorado, US (WWVB) and in Frankfurt, Germany (DCF-77). These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

Atomic Clocks have been around for over fifty years or so. They are clocks that use an atomic resonance frequency as its timekeeping element rather than conventional oscillating crystals such as quartz.

Most atomic clocks use the resonance of the atom caesium-133 which resonates at an exact frequency of 9,192,631,770 every second. Since 1967 the International System of Units (SI) has defined the second as that number of cycles from caesium -133 which makes atomic clocks (sometimes called caesium oscillators) the standard for time measurements.

Because the resonance of the caesium-133 atom is so precise, this makes atomic clocks accurate to less than 2 nanoseconds per day, which equates to about one second in 1.4million years.

As atomic clocks are so accurate and can maintain a continuous and stable time scale, a universal time, UTC (Coordinated Universal Time or Temps Universel Coordonné), has been developed and supports such features as leap seconds – added to compensate for the slowing of the Earth’s rotation.

However, atomic clocks are extremely expensive and are generally only to be found in large-scale physics laboratories. However, NTP (Network Time Protocol), the standard means for achieving time synchronisation on computer networks,  can synchronise to an atomic clock by using either the Global Positioning System (GPS) network or specialist radio transmissions.

The most widely used is the GPS (Global Positioning System), developed by the United States military. GPS incorporates at least 24 communication satellites in high orbit providing accurate positioning and location information. Each GPS satellite can only do this by utilising an atomic clock which in turn can be can be used as a timing reference.

A GPS time server is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components.  Each GPS satellite transmits in two frequencies L2 for the military use and L1 for use by civilians transmitted at 1575 MHz, Low-cost GPS antennas and receivers are now widely available.

There are also a number of national time and frequency radio transmissions that can be used to synchronise a NTP server. In Britain the signal (called MSF) is broadcast by the National Physics Laboratory in Cumbria which serves as the United Kingdom’s national time reference, there are also similar systems in Colorado, US (WWVB) and in Frankfurt, Germany (DCF-77). These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

Using a GPS NTP server or a radio based NTP time server, network time clients, can be synchronized to within a few milliseconds of UTC depending on network traffic.

On occasion we all need to know the time and we have a multitude of different devices to tell us it; from our mobile phones and wrist watches to the office wall clock or the chimes on the radio news.

But how accurate are all these clocks and does it matter if they are all telling different times? For our day-to-day business it probably doesn’t matter too much if the office wall clock is faster than your wrist-watch your boss probably won’t fire you for being a minute late.

But in some environments accuracy and synchronisation are vital where a minute can make all the difference in something being sold or not or even something being stolen!

Time synchronisation in modern computer networks is essential. It not only provides the only frame of reference between all devices, it is critical in everything from securing, planning and debugging a network to providing a time stamp for applications such as data acquisition or email.

Most PC’s and network devices internal clocks, called Real Time Clock chips (RTC) providing time and date information. The chips are battery backed so that even during power outages, they can maintain time.

However, personal computers are not designed to be perfect clocks, their design has been optimized for mass production and low-cost rather than maintaining accurate time.

Therefore these internal clocks are prone to drift and although for many application this is can be quite adequate, often machines that work together on a network will become out of sync with each other and problems can arise particularly with time sensitive transactions. Can you imagine buying an airline seat only to be told at the airport that the ticket was sold twice because it was purchased afterwards on a computer that had a slower clock?

NTP time servers (Network Time Protocol) use a single time reference to synchronise all machines on the network to that time. This time reference can be either relative (a computer’s internal clock or the time on a wrist-watch perhaps) or absolute such as an atomic clock that relays UTC time (Universal Coordinated Time) and is as accurate as is humanely possible.

Atomic clocks are the most absolute time-keeping devices accurate to a second every 1.4 million years. However, atomic clocks are extremely expensive and are generally only to be found in large-scale physics laboratories. However, NTP can synchronise networks to UTC time via an atomic clock by using either the Global Positioning system (GPS) network or specialist radio transmissions (MTF in the UK). 

While some organisations have to synchronise their networks to UTC such as airlines and the stock exchange, a network can be synchronised to any time and still function, but there really is no substitute for UTC time. Not only is it more efficient to have network synchronised with the rest of the world, a UTC time source is vital in providing security against fraud, data loss and legal exposure and without it, organizations can be vulnerable and lose credibility.

NTP (version 4) can maintain time over the public Internet to within 10 milliseconds (1/100th of a second) and can perform even better over LANs with accuracies of 200 microseconds (1/5000th of a second) under ideal conditions.

Note: it is strongly recommended by Microsoft and others, that external based timing should be used rather than Internet based, as these can’t be authenticated. Specialist NTP servers are available that can synchronise time on networks using either the MSF (or equivalent) or GPS time server signal.

All PC’s and networking devices use clocks to maintain an internal system time. These clocks, called Real Time Clock chips (RTC), provide time and date information. They are battery backed so that even during power outages, they can maintain time. However, personal computers are not designed to be perfect clocks – their design has been optimized for mass production and low-cost rather than maintaining an accurate time.

These internal clocks are prone to drift and although for many application this is can be quite adequate for some applications, but machines on a network that drift at different rates, become out of sync with each other and problems can arise, particularly with time-sensitive transactions.

NTP servers (Network Time Protocol) use a single time reference to synchronise all machines on the network to a time reference. This time reference can be either relative (a computer’s internal clock or the time on a wrist-watch perhaps) or absolute such as a UTC (Universal Coordinated Time) clock source like an atomic clock that is as accurate as is humanely possible.

For some applications a relative time source is sufficient, however in many environments, such as airlines and the stock exchange it is essential for time to be absolute. Imagine buying an airline seat only to be told at the airport that the ticket was sold twice because it was purchased afterwards on a computer that had a slower clock!

Atomic clocks are the most absolute time-keeping devices. They work on the principle that the atom, caesium-133, has an exact number of cycles of radiation every second (9,192,631,770). This has proved so accurate the International System of Units (SI) has now defined the second as the duration of 9,192,631,770 cycles of radiation of the caesium-133 atom and the development of UTC (Coordinated Universal Time) now means computers all over the workld can be synchronized to the same time.

However, atomic clocks are extremely expensive and are generally only to be found in large-scale physics laboratories. However, NTP servers can synchronise networks to an atomic clock by using either the Global Positioning system (GPS) network or specialist radio transmissions (MTF in the UK).  It must be noted that Microsoft and others strongly recommend that external based timing should be used rather than Internet based, as these can’t be authenticated. Specialist NTP servers are available that can synchronise time on networks using either the MSF (or equivalent) or GPS time server signal.

GPS is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components.  Each GPS satellite transmits in two frequencies L2 for the military use and L1 for use by civilians transmitted at 1575 MHz, Low-cost GPS antennas and receivers are now widely available.

The radio signal transmitted by the satellite can pass through windows but can be blocked by buildings so the ideal location for a GPS antenna is on a rooftop with a good view of the sky. The more satellites it can receive from the better the signal. However, roof-mounted antennas can be prone to lighting strikes or other voltage surges so a suppressor is highly recommend being installed inline on the GPS cable.

The cable between the GPS antenna and receiver is also critical. The maximum distance that a cable can run is normally only 20-30 metres but a high quality coax cable combined with a GPS amplifier placed in-line to boost the gain of the antenna can allow in excess of 100 metre cable runs.

There are also a number of national time and frequency radio transmissions that can be used to synchronise a NTP server. In Britain the signal (called MSF) is broadcast by the National Physics Laboratory in Cumbria which serves as the United Kingdom’s national time reference, there are also similar systems in Colorado, US (WWVB) and in Frankfurt, Germany (DCF-77).

A radio based NTP server usually consists of a rack-mountable time server, and an antenna, consisting of a ferrite bar inside a plastic enclosure, which receives the radio time and frequency broadcast. It should always be mounted horizontally at a right angle toward the transmission for optimum signal strength. Data is sent in pulses, 60 a second. These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

Both a GPS NTP server and MSF time server can provide an affordable and efficient way to accurately synchronise computer networks using NTP.

On occasion, we all need to know the time and we have a multitude of different devices to tell us it, from our mobile phones and wrist watches to the office wall clock or the chimes on the radio news. But how accurate are all these clocks and does it matter if they are all telling different times?

For our day-to-day business it probably doesn’t matter too much. If the office wall clock is a faster than your wrist-watch your boss probably won’t fire you for being a minute late but when it comes to solving criminal cases, timing is everything!

Take the case of Joan Beddeson, a 71-year-old found murdered in her home in Macclesfield. The chief suspect, her former lover who owed the victim over a quarter of a million pounds, 64-year-old John Crittenden, denied the killing, claiming he was at home in bed with his wife at the time of the murder.

However, police had discovered a credit card statement that showed that Crittenden had bought fuel in Worcester just hours before the killing and was then spotted on a camera 12 minutes later travelling up the motorway towards Macclesfield. Later that night the same car was recorded coming back down the motorway leaving Crittenden with a 45 minute window to commit his crime.

However, during his trial Crittenden, who admitted buying the fuel, denied travelling up the motorway and claimed the cameras were not accurate. However, the cameras were all synchronised using a NTP time server (Network Time Protocol) to Universal Coordinated Time (UTC) and was so accurate that Crittenden’s lawyers had no defence and he was convicted of the murder and sent to prison for life.

Time synchronisation is not just important in securing convictions it can also prove somebody’s innocence! When a woman was found murdered in Maryland US, the police thought they had found the perpetrators when the victim’s bank card was being used at an ATM. A check at a local CCTV camera provided footage of the three suspects using the machine and although the quality was quite grainy, once aired on America’s Most Wanted the three suspects were soon rounded up.

However, it emerged that the time recorded by the camera was three minutes off the time recorded by the ATM and the three people held were an entirely innocent family, not connected with he murder at all.

The investigators conceded that if the camera had been synchronised to a reliable source like the ATM machine, then the wrongful arrest would not have been made.

The cases above underline the importance of reliable time synchronisation. Even if a business is not involved in the detection of crime, failing to synchronise a computer network can leave a system vulnerable to fraud, data loss and even legal exposure and without it, organizations can be vulnerable and lose credibility.

Specialist NTP time servers (Network Time Protocol) are available and can synchronise a computer network and all its devices to an accurate clock source such as an atomic clock using either  the GPS or a specialist radio transmission, allowing networks to be accurately synchronized to Universal Coordinated Time (UTC).

Mankind has always been preoccupied with measuring and recording the passage of time. Timekeeping has been essential for the development of civilisations; from knowing when to plant or harvest crops to identifying important events in the year.

Time has historically been measured in relation to the movement of the Earth; a day, is one revolution of the planet; while a year is an entire orbit of the Sun. Calendars were developed from as far back as 20,000 years ago when hunter-gatherers scratched lines and gouged holes in sticks and bones to possibly count the days between phases of the moon.

Civilizations from the Ancient Egyptians to the Roman Empire have used differing methods to discover what day of the year it is. However, measuring time as it passed throughout the day had always proved difficult to early mankind. Sundials were perhaps the first time pieces and they can trace their origin back over five thousand years; when obelisks were built, possibly to allow the telling of time by the cast of their shadows.

However, the time told on a sundial was based on the movement of the sun in the sky, which would differ throughout the seasons and of course would not work on cloudy days or at night. Other methods such as water clocks or the hourglass would simply act as crude timers. Telling the time of day would prove difficult with people relying on comparisons as time references such as: “As long as it would take a man to walk a quarter mile.”

People were reliant on these methods and others such as bell ringing to indicate important moments until the 14th century, when mechanical clocks first appeared which were driven by weight and regulated by a verge-and-foliot escapement (a gear system that advancing the gear train at regular intervals or ‘ticks’). These clocks were far more reliable than sundials or other methods allowing accurate and reliable telling of the time of day for the first time in human history.

The next step forward in horology came in the 17th century when the pendulum was developed to help clocks maintain their accuracy. Clock making soon became widespread and it was not for another three hundred years that the next revolutionary step in horology would take place; with the development of electronic clocks. These were based on the movement of a vibrating crystal (usually quartz) to create an electric signal with an exact frequency.

While electronic clocks were far more accurate than mechanical clocks it wasn’t until the development of Atomic Clocks and around fifty years ago that modern technologies such as communication satellites, GPS and global computer networks became possible.

Most atomic clocks use the resonance of the atom caesium-133 which vibrates exactly at a frequency of 9,192,631,770 every second. Since 1967 the International System of Units (SI) has defined the second as that number of cycles from this atom which makes atomic clocks (sometimes called caesium oscillators) the standard for time measurements.

Atomic clocks are accurate to less than 2 nanoseconds per day, which equates to about one second in 1.4 million years. Because of this accuracy, a universal time scale UTC (Coordinated Universal Time or Temps Universel Coordonné) has been developed that maintains a continuous and stable time scale and supports such features as leap seconds – added to compensate for the slowing of the Earth’s rotation.

However, atomic clocks are extremely expensive and are generally only to be found in large-scale physics laboratories. However, NTP servers (Network Time Protocol), the standard means for achieving time synchronisation on computer networks,  can synchronise networks to an atomic clock by using either the Global Positioning System (GPS) network or specialist radio transmissions.

The development of atomic clocks, GPS and NTP time servers has been vital for modern technologies, allowing computer networks all over the world to be synchronized to UTC.

An accurate time source is needed for many computer applications. Every Personal Computer comprises of an internal Clock, it is beneficial to check the date and time settings on your PC daily. For critical application, you should synchronise the time base with a highly accurate external time source.

Personal Computers are not designed to be perfect clocks. Their design has been optimised for mass production and low-cost rather than maintaining accurate time. Where time is crucial to the application, there are a number of precise external references available that enable computers to maintain accurate system time. This article looks at the various sources of time references to show how they can be utilised to maintain synchronised time on your computer.

Working to a synchronised time base is essential in computer networks. Without any external reference, individual computers will start to drift, anything from a few seconds to a few minutes each day. Clearly such a situation would not be acceptable when processing transactions or performing time critical tasks.

On the Internet this problem has been solved by introducing the Network Time Protocol (NTP). The NTP protocol supports the distribution of accurate time from a highly precise time server to network time clients. Most modern operating systems have the ability to synchronise time with an NTP server. Generally all that is required is the IP address or domain name of Stratum 1 or Stratum 2 NTP servers.

LINUX and UNIX operating systems can download the full NTP implementation from the NTP website at www.ntp.org NTP is freely available, open source software, available under the GNU public license.

Mirosoft Windows XP/2000/2003 and Vista system software use a standart SNTP client for Simple Network Time Protocol. This is based on a sub-set of the Network Time Protocol, using a simplified NTP algorithm with many of the more complex high precision routines removed.

The Windows operating systems provide facilities for an IP address or domain name of an Internet or Intranet NTP server to be entered in the time properties tab. The SNTP client will then contact the NTP server periodically in order to update and synchronise system time.

Alternative methods will be required for standalone computers and systems which do not have access to the Internet. These can be provided with a local access to national radio time references which are transmitted free-to-air.

All that is required is a small RS232 serial or USB radio receiver, and the PC can obtain continuous accurate time. The Computer Time synchronises to the received time and frequency radio source.

Radio broadcasts are identified by their ‘call sign’ The UK time transmitter call sign, MSF, is located at Anthorn, Cumbria. Similar arrangements exist in Noth America – call sign WWVB from Colarado. Germany is covered by DCF broadcast from Mineflingen, near Frankfurt. National broadcasts are also available in France, Switzerland, Japan and Canada.

The only shortcoming with national radio time and frequency solutions is that they have a finite transmission range. In general they are limited to geographic boundaries also. Such issues do not apply to the Global Position System (GPS) a satellite based universal navigation system.

Each GPS satellite carries a highly accurate synchronised atomic clock. This enables GPS to provide precise timing information anywhere on the face of the planet. All that is required to receive the transmission is a low cost-cost GPS receiver and antenna with a clear view of the sky. PC connections are similar to the radio transmissions configuration, using a serial or USB port, enabling accurate timing information to be available continuously.

This article is about the Importance of network time synchronisation and how significant it is to have an accurate network time server resource in the business.

Every Computer has a clock that sustains the internal system time. PC clocks have low- cost crystal oscillators that are notoriously prone to drift. Each Computer can drift at different rates.

The time difference can become bigger and bigger over a period of time. This can lead to huge problems within the company. This article conveys the value of network time synchronization and having an accurate network time server source in an organization.

Computer Time: Computer system time is maintained by low cost real time clock and crystal oscillator components. Crystal oscillators are built with very low tolerance, each oscillates at a slightly different rate. The temperature variation make the crystal change its frequency. This is one of the reason why computers are weak in keeping up an accurate time. A Companies Computers need to be synchronized otherwise each computer will drift at a slightly different quantity.

Each computer need a network time that is correctly synchronized otherwise it can cause huge problems, especially in transaction-processing surroundings. Unsynchronized PCs can lead to fraud and other problems that can be caused in an environment where synchronized time is needed. Problems can arise with shared network files, the reason is because the unsynchronized computers are using the same resource.

Network Time Servers: Network Time servers gain precise time from an external time reference and offer (presents) an accurate time source to network time clients. Time server use the Network Time Protocol (NTP), which is a UDP based protection over TCP/IP. There is a number of options that can be used to get an accurate time. GPS (Global Positioning Systems) offers a highly accurate time; all that is needed is a clear view to the sky. Another alternative would be radio frequency. The main countries that provide radio frequency are England (MSF); Germany (DCF-77) and the US (WWVB). Other countries are France (TDF); Canada (CHU); Japan (JJY) and Switzerland (HBG) and it is possible to obtain time from mobile phone network.

Internet Time Servers: There are a lot of Internet based NTP time server resources offered that can be used for network time synchronization. The Internet Time Server can cause Problem for the Company’s Computers. The time server is located outside the firewall, so a port must be left open to access the time server. This does not just lead to Security implications, but also to problems with the time server accuracy, reliability and provision.

Local Dedicated Network Time Server: A local devoted network time server overcome many problems related to Internet based references. The time server is located inside the security firewall and does not need any external access. Also, a local time server can improve accuracy due to reliable network paths between clients and server.

To resume, the network time synchronization is an important factor in Computer network installations. Unlike the internet based network time servers, which are known for they security problems, local dedicated network time servers overcome the security problems by offering secure, accurate and reliable network time synchronisation resolution.