Time Synchronisation

UTC – Coordinated Universal Time (from the French: Universel Temps Coordonné) is a global timescale based on Greenwich Meantime (GMT – from the Greenwich Meridian line where the sun is above at 12 noon). But accounts for the natural slowing of the Earth’s rotation. It is used globally in commerce, computer networks via a NTP server, air-traffic control and the World’s stock exchanges to name but a few of its applications.

UTC is really the only solution for time synchronisation needs. While it is just as possible to synchronise a computer network with an NTP server to a time other than UTC it is pointless. As UTC is utilised by computer networks all across the globe by using a UTC time source that means your network can synchronise with every other network in the world that is synchronised to UTC.

UTC is most commonly received from across the Internet, however, this can only be recommended for small network users where either accuracy or security is an issue. An Internet based UTC source is external to the firewall so will leave a potential hole for malicious users to exploit.

Two secure methods of receiving UTC are commonly available. These are either the GPS network (Global Positioning System) or specialist radio transmission broadcast on long wave from several of the world’s national physics laboratories. The two methods have both advantages and disadvantages which need to be ascertained before a method is selected.

A radio transmission such as the UK’s MSF, the German DCF-77 or the USA’s WWVB signal are vulnerable to local topography although many of these signals can be picked up indoors. Whilst not every country transmits a UTC radio signal around the neighbouring countries that do it is possible to still receive it.

GPS on the other hand is available literally anywhere on the globe. The signal comes directly from above and as long as the antenna has a good clear view of the sky it can be received anywhere. However, as the antenna has to be on a roof looking up this can have logistical problems (particularly for very tall buildings).

Specialist dedicated network time servers are available that can actually receive both methods of UTC but whether using GPS or a radio transmissions synchronisation of a network to within a few milliseconds is possible.

1. The business world is now more global than ever with as much likelihood of  your customer’s being from the other side of the planet as from around the corner. Any transactions conducted virtually across the Internet require adequate time synchronisation otherwise your company can be open to abuse or fraud, customers may claim they paid you at a certain time but how do you ascertain if they have without adequate synchronisation?

2. Does your system conduct time sensitive transactions? Computers have only one reference between events and that is time. If a network is not synchronised then many events and transactions may fail to happen. This can have a knock-on effect as one transaction or event fails so do others and without adequate synchronisation it may be quite a while before anyone realises the errors.

3. Do you have valuable or sensitive data? A lack of synchronisation can often lead to data loss. Storage and retrieval is also time reliant so if a computer believes the time data should have been saved has past then it may assume the data is already saved. The problem can be exaggerated if the data is continually updated as the inaccurate timestamps may mean that certain updates are not completed.

4. Is security important to your business? A lack of time synchronisation can leave a computer network open to malicious users, hackers and even fraud. If computers on a network are running different times then this can be exploited by malicious users and without time synchronisation you may not even know they have been there. A perfectly synchronised network will also offer legal protection with a NTP server (Network Time Protocol) being auditable and unquestioned in a court of law.

5. Is the credibility of your company important? A lack of synchronisation can be extremely costly not just in time and money but also in the credibility of your company. Without synchronisation a network will be vulnerable to mistakes and while these may be easily rectified once a customer has to complain word will soon get out.

Running a synchronised network adhering to Universal Coordinated Time (UTC) the world’s standard timescale is fairly simple. Dedicated NTP time servers that receive a UTC time source from either a radio transmission or the GPS network (Global Positioning System).are readily available, simple to set up, accurate and secure.

A NTP server is really just a time server that utilises Network Time Protocol (NTP). Whilst other time protocols do exist, NTP is by far the most commonly used and is utilised in over ninety percent of time servers.

NTP server and time server are therefore interchangeable terms but describe the same thing: a device used to receive and distribute a timing signal.

The timing signal utilised by most NTP servers is a UTC time source. UTC (Coordinated Universal Time) is a global time scale based on the time told by atomic clocks. By utilising UTC a NTP server can in affect, synchronise a network to the same time as millions of other computer networks from around the world. This has made possible many online global transactions that just simply wouldn’t be possible without UTC.

The timing signal is received by the NTP server (or time server) via a number of ways; the Internet, national time and frequency transmission (long wave) or the GPS (global positioning system) network. Once received the time server (NTP server) checks the authenticity of this signal (except from Internet sources where authentication is not possible), evaluates its accuracy then distributes it amongst the network.

To prevent a possible overload of time requests to the time server, machines that receive a time signal from the NTP server, can themselves be used as a time reference and the machines that receive a time signal from those can again be used as a reference. This hierarchy is called stratum levels. A NTP server is a stratum 1 device, a machine that receives a signal directly from the time server is a stratum 2 device and if a machine receives a signal from that it becomes stratum 3.

A time server is an integral part of any network system. It ensures all machines on a network or keeping the exact same time, failure to do so could lead to all sorts of problems, particularly with time sensitive transactions.

Most computer networks are synchronised to UTC (coordinated Universal Time). UTC is a global time scale and used throughout the world. It is also highly precise as it is based on the time told by atomic clocks.

Atomic clocks are ideal sources of time as they do not drift whilst the standard electrical oscillators on our PC clocks can drift by a second every week. This drift can cause untold problems which is why most networks are synchronised to a time server that receives a time signal from an atomic clock.

Atomic clock time signals can be received from a myriad of sources. The Internet is an obvious choice but unless security and precision is not an issue then it is not recommended for any commercial networks as using an Internet times source can leave a system open to security threats.

For security and accuracy there are two options to synchronise to an atomic clock. One is to use a GPS time server that receives the time-code from the GPS system. The other method is to use a time server that can receive the long wave radio transmissions broadcast from several national physics laboratories.

To receive and distribute and authenticated UTC time source there are currently two types of NTP server, the GPS NTP server and the radio referenced NTP server. While both these systems distribute UTC in identical ways the way they receive the timing information differs.

A GPS NTP 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.

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. This can provide difficulties in installation in larger buildings if the server is too far from the antenna.

An alternative solution is to use a radio referenced NTP time server. These rely on a number of national time and frequency radio transmissions that that broadcast UTC time. 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 the USA (WWVB) and in France, Germany and Japan.

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.

NTP GPS server is a time server that uses the protocol NTP (Network Time Protocol) receives its authoritative time source from the GPS satellite network (Global Positioning System).

Other varieties of time server exist most if not all dedicated devices use NTP as it is universally excepted as the most superlative time protocol, there are however numerous ways a network time server (whether NTP or not) can receive a time signal.

The internet is a common source for timing information although very few administrators who have a dedicated time server device would use the Internet. This is because external time sources across the Internet are the wrong side of a uses firewall and therefore pose a potential security risk not-to-mention many Internet timing sources are not very accurate and also most are stratum 2 devices and therefore further away from the original time source than a stratum 1 dedicated NTP server (stratum 0 devices are atomic clocks).

The other methods a dedicated NTP server (often called network time server) can receive a timing signal is via GPS or radio transmissions that are broadcast from national physics laboratories.

Radio signal are a good source of UTC time (coordinated universal time) as they are maintained and run by organisations such NPL (National Physical Lab. UK) or NIST (National Institute for Standards and Time – US). However, these long wave transmissions are not broadcast in every country and the signals are susceptible to local interference and topography.

On the other hand a dedicated NTP GPS server receives its time signal from the GPS satellite system (each satellite contains an atomic clock). These signals offer excellent accuracy and furthermore are available everywhere on the planet where there is a clear view of the sky.

A GPS time server is really a communication device. Its purpose is to receive a timing signal and then distribute it amongst all devices on a network. Time server s are often called different things from network time server, GPS time server, radio time server and NTP server.

Most time servers use the protocol NTP (Network Time Protocol). NTP is one of the Internet’s oldest protocols and is used by the majority of machines that use a time server. NTP is often installed, in a basic form, in most operating systems.

A GPS time server, as the names suggests, receives a timing signal from the GPS network. GPS satellites are really nothing more than orbiting clocks. Onboard each GPS satellite is an atomic clock. The ultra-precise time from this clock is what is transmitted from the satellite (along with the satellite’s position).

A satellite navigation system works by receiving the time signal from three or more satellites and by working out the position of the satellites and how long the signals took to arrive, it can triangulate a position.

A GPS time server needs even less information and only one satellite is required in order to receive a timing reference. A GPS time server’s antenna will receive a timing signal from one of the 33 orbiting satellites via line of sight, so the best place to fix the antenna is the roof.

Most dedicated GPS NTP time servers require a good 48 hours to locate and get a steady fix on a satellite but once they have it is rare for communication to be lost.

The time relayed by GPS satellites is known as GPS time and although it differs to the official global timescale UTC (Coordinated Universal Time) as they are both based on atomic time (TAI) GPS time is easily converted by NTP.

A GPS time server is often referred to as a stratum 1 NTP device, a stratum 2 device is a machine that receives the time from the GPS time server. Stratum 2 and stratum 3 devices can also be used as a time servers and in this way a single GPS time server can operate as a timing source for an unlimited amount of computers and devices as long as the hierarchy of NTP is followed.

A time server is a common office tool but what is it for?

We are all used to having a different time from the rest of the world. When America is waking up, Honk Kong is going to bed which is why the world is divided into time zones. Even in the same time-zone there can still be differences. In mainland Europe for instance most countries are an hour ahead of the UK because of Britain’s seasonal clock changing.

However, when it comes to global communication, having different times all over the world can cause problem particularly if you have to conduct time sensitive transactions such as buying or selling shares.

For this purpose it was clear by the early 1970’s that a global timescale was required. It was introduced on 1 January 1972 and was called UTC – Coordinated Universal Time. UTC is kept by atomic clock but is based on Greenwich Meantime (GMT – often called UT1) which is itself a timescale based on the rotation of the Earth. Unfortunately the Earth varies in its spin so UTC accounts for this by adding a second once or twice a year (Leap Second).

Whilst controversial to many, leap seconds are needed by astronomers and other institutions to prevent the day from drifting otherwise it would be impossible to work out the position of the stars in the night sky.

UTC is now used all over the world. Not only is it the official global timescale but is used by hundreds of thousands of computer networks all over the world.

Computer networks use a network time server to synchronise all devices on a network to UTC. Most time servers use the protocol NTP (Network Time Protocol) to distribute time.

NTP time servers receive the time from atomic clocks by either long-wave radio transmissions from national physics laboratories or from the GPS network (Global Positioning System). GPS satellites all carry an onboard atomic clock that beams the time back to Earth. Whilst this time signal is not strictly speaking UTC (it is known as GPS time) because of the accuracy of the transmission it is easily converted to UTC by a GPS NTP server.

From military hardware to GPS time servers

The Global Positioning System was designed and built by the US military in the late 1970’s, although it didn’t achieve initial operational capability until 1993. GPS was originally designed as a military only system but in 1983 after a USSR aircraft shot down a Korean airliner that had accidentally strayed into Soviet airspace, the then President of the United States, Ronald Reagan, vowed the system would be available for civilian use once completed.

Full Operational Capability was declared by the now named NAVSTAR GPS in April 1995 and in 1996 to fulfil his predecessors promise the U.S. President Bill Clinton issued a policy directive declaring GPS to be a dual-use system; one for US military use and one system for civilians.

Currently GPS is the World’s only GNSS (Global Navigational Satellite System) although the Russian GLONASS system that was operational during the Cold War but has since fallen into disrepair is being repaired and a European GNSS known as Galileo is expected to be operational by 2012, other systems developed by China and India are also being developed.

GPS is primarily a navigational system that transmits precise timing information via an onboard atomic clock. It is this information and the satellites location that is used to triangulate positioning. However, the GPS signal can also be used by a GPS time server as a timing source.

What is a time server?

A time server is a hardware device that distributes a single time source amongst a network to ensure all computers and devices are synchronised

What is NTP?

Network Time Protocol is a set of software instructions designed to distribute time across computers. NTP uses a complex algorithm to work out d inaccuracies and compensates for them by advancing or retarding the system clock.

What is UTC?

Coordinated Universal Time (UTC) is the offical global timescale. It is used by computer networks throughout the world. It is based on the time told by atomic clocks but compensates for the slowing of the Earth’s rotation by adding Leap Seconds, this also keeps it inline with GMT (Greenwich Meantime) sometimes referred to as UT1.

How does a time server receive UTC?

UTC can be received by either tuning in to a national time and frequency broadcast on long-wave administered by national physics laboratories, although not every country has one. Alternatively as GPS satellites (Global Positioning System) all carry an onboard atomic clock which transmits timing information this can be used also as a timing source for network time servers.

Can’t I use the Internet as a timing source?

You can, and there are many sources of UTC time on the Internet but very few offer any useful accuracy and for those that do the distance away can cause a drop-off in precision. More importantly, Internet time sources are exterior to your firewall and therefore a port needs to be left open to ensure communication, this can be taken advantage of by malicious users. Also Internet timing sources can’t be authenticated; authentication is a security measure that ensures that a timing reference is what it says it is.

Which method is best for me a radio referenced time server or one that utilises the GPS network?

This depends on location. While GPS signals are available everywhere on the planet the antennas do have to have a clear view of the sky to receive the signal, alternatively radio transmissions are limited in their availability although where available the signals can be received indoors.

How accurate are time servers?

A radio referenced network time server can provide UTC time to an accuracy of 100 microseconds, while the GPS network can fare even better with accuracies of a few milliseconds reasonably possible.

NTP time server (Network Time Protocol) abuse is quite often unintentional and fortunately thanks to the NTP pool is less frequent than it was although incidents still happen.

NTP server abuse is any act that violates the access rules of a NTP time server or an act that damages it in any way. Public NTP servers are those servers that can be accessed from across the Internet by devices and routers to use as a timing source to synchronise a network to. Most public NTP time servers are non-profit and set up as acts of generosity, mostly by University’s or other technical centres.

For this reason access rules have to be set up as huge amounts of traffic can generate giant bandwidth bills and can lead to the NTP time server being turned off permanently. Access rules are used to prevent too much traffic from accessing stratum 1 servers, by convention stratum 1 servers should only be accessed by stratum 2 servers which in turn can pass the timing information on down the line.

However, the worst cases of NTP server abuse have been where thousands of devices have sent requests for time, where in the hierarchical nature of NTP only one is needed.

Whilst most acts of NTP abuse are intentional some of the worst abuses of NTP time servers have been committed (albeit unintentionally) by large companies. The first large firm discovered to have been guilty of NTP abuse was Netgear, who, in 2003 released four routers that were all hard coded to use the University of Wisconsin’s NTP server, the resulting DDS (Distributed Denial of Service) reached nearly 150 megabits a second.

Even now, five years on and despite the release of several patches to fix the problem and the University being compensated by Netgear the problem still continues as some people have never patched their routers.

Similar incidents have been committed by SMC and D-Link. D-Link in particular caused controversy as when the matter was drawn to their attention they decided to bring the lawyers in. Only after it was discovered that they violated nearly 50 NTP servers did they attempt resolve the problem (and only after scathing press coverage did they relent).

The easiest way to avoid such problems is to use a dedicated external stratum 1 time server. These devices are relatively inexpensive, simple to install and far more accurate and secure than online NTP servers. These devices receive the time from atomic clocks either from the GPS network (Global Positioning System).