Time Synchronisation

Accurate time using Atomic Clocks is available across Great Britain and parts of northern Europe using the MSF Atomic Clock time signal transmitted from Cumbria, UK; it provides the ability to synchronize the time on computers and other electrical equipment.

The UK MSF signal is operated by NPL – the National Physical Laboratory. MSF has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from MSF a lot of bounce, and this single station can therefore cover most of Britain and some of continental Europe.

The time codes are sent from MSF using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: 0.2 seconds of reduced power means a binary zero 0.5 seconds of reduced power is a binary one. 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated time servers that are tuned to receive the MSF time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

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

The North American WWVB signal is operated by NIST – the National Institute of Standards and Technology. WWVB has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from WWVB a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America.

The time codes are sent from WWVB using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: 0.2 seconds of reduced power means a binary zero 0.5 seconds of reduced power is a binary one. 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated NTP time servers that are tuned to receive the WWVB time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

NTP (Network Time Protocol) is an internet based protocol designed to synchronise the clocks on a computer network. It is the main time synchronisation software used in computer networks and is also packaged with most operating systems.

An NTP server is a dedicated device that receives a single time source then distributes it amongst all devices on a network. The protocol NTP monitors the drift of the internal clocks on a network and corrects for them.

An NTP server can receive a time source from either a national physical laboratory such as the UK’s National Physical Laboratory (NPL), however, these time signals are broadcast via long wave radio and have  finite range.

GPS NTP servers are designed to receive the time source generated by the atomic clocks onboard GPS satellites (Global Positioning System). GPS is available anywhere on the planet as a time source as long as there is a clear view of the sky.

Without correct synchronisation all sorts of potential problems can occur such as leaving a computer system vulnerable to fraud, malicious users and hackers. An unsynchronised computer network may also lose data and be difficult to audit.

A global timescale called UTC (Coordinated Universal Time) has been developed to ensure the entire world uses the same timescale. The NTP server utilise UTC ensuring the computer network is telling the same time as every other computer network.

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

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

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

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

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

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

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

In selecting a timing source to synchronise a computer network to using a NTP server (Network Time Protocol) it is important that the time source is accurate, secure and a source of UTC (Coordinated Universal Time). UTC is a global timescale used by computer networks, business and commerce across the globe.

Whilst UTC is freely available across the Internet it is neither accurate nor secure (being as it is external to your firewall).  Also Internet time sources cannot be authenticated which is NTP’s own method of ensuring a time source is what it says it is. There are two secure, accurate and reliable methods for receiving UTC via a NTP server and both come with their own advantages and drawbacks.

The first method is to use the GPS network (Global Positioning System).The main advantage of using the signals transmitted from a GPS satellite’s onboard atomic clock is that a signal is available anywhere on the planet. However it does come with a downside. As the signals are all line-of-sight it means that the GPS antenna needs to be placed on a roof to ensure connectivity with a satellite.

An alternative to the GPS signal but equally as accurate and reliable is to make use of the long wave radio transmissions broadcast by several national physics laboratories. These signals, such as the UK’s MSF, Germany’s DCF-77 and the United States’ WWVB transmissions, can often be picked up inside buildings making them ideal for a solution if a rooftop is unavailable for a GPS antenna. It must be noted that not every country broadcasts such a signal and whilst most transmissions can be picked up in neighbouring countries the signals are vulnerable to interference and local geography.

NTP (Network Time Protocol) is the most prevalent time synchronisation software available. On of the reasons NTP is so successful is the way it organises its clients into a hierarchy.

The hierarchy of NTP is divided into stratum with each strata representing the distance from the original reference clock.  For instance an atomic clock that generates a UTC (coordinated universal time) signal is referred to as a stratum 0 device.

A NTP server that receives a stratum  1 time signal is referred to as a stratum 1 device and a device that receives a time source from a NTP server is a stratum 2 device. NTP can support up to 16 strata although the further away from the reference clock you get (stratum 0) the less accurate the device will be.

However, by arranging the network into stratum and allowing stratum 2 devices to pass on the time to a stratum 3 device (and so on) it reduced the demand on the NTP server and the network. By using a stratum based network, realistically thousands of machines can be synchronised to just one NTP server.

Network Time Protocol is a hierarchical protocol and is divided into stratum which define the distance from the reference clock. A reference clock source that relays UTC (Coordinated Universal Time) time and has little or no delay is known as a stratum-0 device. Stratum-0 servers cannot be used on the network, instead, they are directly connected to computers which then operate as primary time servers.

A primary server that receives a time signal from a stratum 0 device either through the GPS network or national time and frequency transmission is known as a stratum-1 device. On a network a stratum 1 time server supplies the time to other devices on the network which are known as stratum-2 devices. These also can be used as a time source and equipment that connects to a stratum-2 device to receive it become stratum-3 and so on.

NTP can handle up to 16 different stratum levels, although the lower down the hierarchy you go the less accurate the devices become. However, to make the system more reliable, each client can receive a time source from multiple servers. Stratum 2 devices and below can also synchronise with each other. The NTP software monitors continuously the figures of stability and accuracy of all the servers and always chooses a server with the best figures.

Multiple stratum are used an in larger networks because to bombard a single stratum-1 time server with NTP requests from thousands of machines could cause it to overload or block the network itself with workstations/routers etc repeatedly waiting for their time synchronisation requests to go through.

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

In a modern global economy time synchronisation is essential for carrying out time sensitive transactions such as booking an airline ticket to bidding on an Internet auction site. If clocks were not synchronised to the same time you may find your airline seat sold after you had bought it and Ebay’s administrators would not be able to discover whose bid was the latest.

NTP is a multi-tiered system, each tier being called a stratum. Servers at each tier communicate with each other (peer) and provide time to lower strata. Servers at the top stratum, stratum 1 connect to an atomic clock either over the Internet or by a radio or GPS receiver while a stratum 2 server will connect to a stratum 1.

NTP uses an algorithm (Marzullo’s algorithm) to synchronise time on a network using time scales like UTC (Coordinated Universal Time or Temps Universel Coordonné) and can support such features as leap seconds – added to compensate for the slowing of the Earth’s rotation.

NTP (version 4 being the latest) 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 time servers work within the TCP/IP suite and rely on UDP (User Datagram Protocol). A less complex form of NTP called Simple Network Time Protocol (SNTP) that does not require the storing of information about previous communications, needed by NTP, is used in some devices and applications where high accuracy timing is not as important and is also included as standard in Windows software (although more recent versions of Microsoft Windows have the full NTP installed and the source code is free and readily available on the Internet).

The NTP program (known as a daemon on UNIX and a service on Windows) runs in the background and refuses to believe the time it is told until several exchanges have taken place, each passing a set of tests. If the replies from a server satisfy these ‘protocol specifications’, the server is accepted. It usually takes about five good samples (five minutes) until a NTP server is accepted as a source for synchronisation.

Synchronisation with NTP is relatively simple, it synchronises time with reference to a reliable clock source such as an atomic clock, although these are extremely expensive and are generally only to be found in large-scale physics laboratories, however NTP can use either the Global Positioning system (GPS) network or specialist radio transmission to receive UTC time from these clocks.

A simplified version of NTP called Simple Network Time Protocol (SNTP) exists that does not require the storing of information about previous communications as required by NTP. It is used in some devices and applications where high accuracy timing is not as important and is installed on older versions of Microsoft Windows. Windows since 2000 has included the Windows Time Service (w32time.exe) which uses SNTP to synchronise the computer clock. NTP is also available on UNIX and LINUX (download via NTP.org).

Computer networking is one of the most difficult aspects of information and communications technology (ICT). The logistics of connecting terminals, routers, printers and all the other devices can leave many administrators with a constant headache.
One of the most important aspects that often gets overlooked and can have disastrous consequences is that of time synchronization.

It is imperative that all devices on a network are telling the same time as timestamps, the format a computer relays time to each other, are the only form of reference a computer can use to establish a sequence of events. If different machines on a network are telling different times then unforeseen consequences such as emails arriving before they have technically been sent and other anomalies will make the administrator’s headache even worse.

What’s more a computer network that is not synchronized is open to security threats and even fraud. Fortunately the NTP time server has been around for many years and can ease the headache of time synchronization .

NTP (Network Time Protocol) is one of the oldest protocols used by computer networks. Developed nearly three decades ago NTP is a protocol that checks the time on all devices on network and adds or subtracts enough time to ensure they are all synchronized.

NTP requires a time reference to synchronise the network’s clocks to. Whilst NTP can synchronize a network to any time an authoritative time source is obviously the best solution. UTC (Coordinated Universal Time) is a globally used timescale based on the time told by atomic clocks. As atomic clocks lose less than a second of time in over a thousand years, UTC is by far the best timing source to synchronize a network to. Not only will your network be perfectly synchronized together but also your network will be synchronized to the same time as millions of computer networks all from around the world.

A NTP server can receive a UTC time reference from several sources. The Internet is the most obvious source, however Internet timing sources are notoriously inaccurate and those that are not can be relatively useless if the distance is too far away. Also having placed your NTP server securely behind your firewall it does seem pointless to have to keep a hole open in it to allow the NTP server to poll the timing reference from across the web and leave the entire network vulnerable, particularly as NTP authentication (NTP’s own security measure) is not possible over the Internet.

There are two far more secure and accurate methods of receiving a UTC timing reference. The first is to utilise the national time and frequency transmissions that several countries broadcast from their national physics laboratories. These are usually broadcast via long wave which has an advantage of being able to be picked up inside a server room although many countries do not have such a signal.

However, many NTP servers can utilize the timing signal broadcast by the onboard atomic clocks of the GPS (Global Positioning System) satellites.  This signal is available everywhere but a GPS antenna is required that can get a clear view of the sky.

By utilizing a UTC timing source either through the GPS network of radio transmission a computer network can be synchronized to within a few milliseconds of UTC time.

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

NTP is installed on most versions of Windows (although a stripped down version called SNTP is in older versions) and Linux but regardless is open source an free to download from ntp.org.

To synchronise a network it is preferable to use a dedicated NTP server that receives a timing source from an atomic clock either from specialist national radio transmissions or the US GPS system, although Internet time references are available but some are more reliable than others (and none can be authenticated leaving a system open to attack).

NTP is hierarchical, it is arranged into stratum. Stratum 0 is a timing source (such as an atomic clock) while stratum 1 is a server connected to a stratum 0 server and a stratum 2 is a computer (or device) attached to a stratum 1 server.

There is an understanding that if using a public Internet based time server, stratum 0 servers are not used by most applications as too many requests would disable them. Instead NTP should be configured to receive a timing reference from several stratum 1 and stratum 2 servers (it is good housekeeping to use more than one as it is possible one server could go down).

The most accurate and secure way of synchronising a network is to use a dedicated NTP server. These can receive a timing reference from either the GPS network (as each GPS satellite contains an atomic clock and broadcasts the signal) or a specialist national radio transmission. Both of these signals come from a stratum 0 source and both provide accuracy to within a few milliseconds.