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.

Most time servers use Network Time Protocol and like other Internet based protocols NTP contains a packet header. A packet header, put simply, is just is a formatted unit of data that describes the information contained in the packet.

The NTP packet header consists of a number of 32-bit words. Here is a list of the most common packet header terms and their meaning:

IP address – the address of the NTP Time Server

NTP Version – which version of NTP (currently version 4 is the most recent)

Reference timestamp (the prime epoch ) used by NTP to work out the time from this set point (normally January 01 1900

Round trip delay (the time it takes request to arrive and come back in milliseconds)

Local clock offset – time difference between host and client

Leap indicator (if there is to be a leap second that day –normally only on 31 December)

Mode3  -  a three bit integer which values represent: 0=reserved, 1=symmetric active, 2= symmetric passive, 3=client, 4=server, 5=broadcast, 6=NTP control message, 7=reserved for private use.

Stratum level – which stratum level the NTP server is (a stratum 1 server receives the time from an atomic clock source a stratum 2 server receives the time from a stratum 1 server)

Poll Interval (How many requests is made and their intermittence)

Precision – how accurate in milliseconds is the system clock

Root Delay – This is a signed fixed-point number indicating the total roundtrip delay to the primary reference source at the root

Root dispersion (in milliseconds)- The root dispersion is the maximum (worst case) difference between the local system clock and the root of the NTP tree (stratum 1 clock)

Ref ID – 32 bit identifying the reference clock

Originate time stamp (time before synchronisation request)

Receive timestamp – the time the host/NTO time Server got the request

Transmit timestamp – the time the host sent back the request

Valid  response– is the system clock  synchronised or not

Network Time Protocol (NTP) was, invented by Dr David Mills from the University of Delaware, it has been in utilized since 1985 and is still in constant development. NTP is a protocol designed to synchronize the clocks on computers and networks across the Internet or Local Area Networks (LANs). Most networks are synchronised via NTP to a UTC time source (coordinated universal time)

UTC is based on the time told by atomic clocks and is used globally as standardized time source.

NTP (version 4) can maintain time over the public Internet to within 10 milliseconds (1/100th of a second)  of UTC time 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, time synchronisation with NTP is relatively simple, it synchronises time with reference to a reliable UTC source and then distributes this time to all machines and devices on a network.

Microsoft and others recommend that only external based timing should be used rather than Internet based, as these can’t be authenticated and can leave a system open to abuse, especially since an Internet timing source is beyond the firewall. Specialist NTP servers are available that can synchronise time on networks using either the MSF, DCF or WWVB radio transmission. These signals are broadcast on long wave by several national physics laboratories.

In the UK, the MSF national time and frequency radio transmissions used to synchronise an NTP server 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. The antenna 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.

A radio referenced NTP server is easily installed and can provide an organization with a precise time reference enabling the synchronization of entire networks. The NTP server will receive the time signal and then distribute it amongst the network devices.

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.

Computer networks rely on timekeeping for nearly all their applications, from sending an email to saving data, a timestamp is necessary for computer to keep track. All routers and switches need to run at the same rate, out of sync devices can lead to data being lost and even entire connections.

For some transactions it is necessary for computers to be perfectly synchronised, even a few seconds difference between machines can have serious effects, such as finding an airline ticket you had booked had been sold moments later to another customer or you could draw your savings out of a cash machine and when your account is empty you could quickly going to another machine and withdraw it all again.

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. However, 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.

Time servers are like other computer servers in the sense they are usually located on a network. A time server gathers timing information, usually from an external hardware source and then synchronises the network to that time.

Most time servers use NTP (Network Time Protocol) which 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 utilises an external timing reference and then synchronises all devices on the network to that time.

There are various sources that a NTP time server can use as a timing reference. The Internet is an obvious source, however, internet timing references from the Internet such as nist.gov and windows.time can not be authenticated, leaving the time server and therefore the network vulnerable to security threats.

Often time servers are synchronised to a UTC (Coordinated Universal time) source which is the global standard time scale and allows computers all over the world to synchronised to exactly the same time. This has obvious importance in industries where exact timing is crucial such as the stock exchange or airline industry.

Coordinated Universal Time (UTC – from the  French Temps Universel Coordonné) is an international timescale based on the time told by atomic clocks. Atomic clocks are accurate to within a second in several million years. They are so accurate that International Atomic Time, the time relayed by these devices, is even more accurate than the spin of the Earth.

The Earth’s rotation is affected by the gravity of the moon and can therefore slow or speed up. For this reason, International Atomic Time (TAI from the French Temps Atomique International) has to have ‘Leap seconds’ added to keep it in line with the original timescale GMT (Greenwich meantime) also referred to as UT1, which is based on solar time.

This new timescale known as UTC is now used all over the world allowing computer networks and communications to be conducted at opposite sides of the globe.

UTC is governed not by an individual country or administration but a collaboration of atomic clocks all over the world which ensures political neutrality and also added accuracy.

UTC is transmitted in numerous ways across the globe and is utilised by computer networks, airlines and satellites to ensure accurate synchronisation no matter what the location on the Earth.

In the USA NIST (National Institute of Standards and Technology) broadcast UTC from their atomic clock in Fort Collins, Colorado. The National Physics Laboratories of the UK and Germany have similar systems in Europe.

The internet is also another source of UTC time. Over a thousand time servers across the web can be used to receive a UTC time source, although many are not precise enough for most networking needs.

Another, secure and more accurate method of receiving UTC is to use the signals transmitted by the USA’s Global Positioning System. The satellites of the GPS network all contain atomic clocks that are used to enable positioning. These clocks transmit the time which can be received using a GPS receiver.

Many dedicated time servers are available that can receive a UTC time source from either the GPS network or the National physics Laboratory’s transmissions (all of which are broadcast at 60 kHz longwave).

Most time servers use NTP (Network Time Protocol) to distribute and synchronise computer networks to UTC time.

Network Time Protocol seems to have been around for ever. In fact it is indeed one of the Internet’s oldest protocols having been developed in the 1980’s by Professor David Mills and his team from Delaware University.

In a laid-back world it perhaps doesn’t matter if computer networks are not synchronised. The only consequences of timing errors could be that an email arrives before it was sent but in industries such as airline seat reservation, the stock exchange or satellite communication, fractions of a second can cause serious errors such as selling seats more than once, the loss of millions of dollars or even fraud.

Computers are logical machines and as time is linear to a computer any event that happens on one machine must happen before news of that event reaches another. When networks are not synchronised computers struggle to deal with events that have obviously occurred (such as an email being sent) but according to their clock and time stamp it hasn’t yet, just think back to the millennium bug where it was feared clocks would jump back to 1900!

For this very reason NTP was developed.  NTP uses an algorithm (Marzullo’s algorithm) to synchronise the time with the current version of NTP can maintain time over the public Internet to within 10 milliseconds and can perform even better over LANs. NTP time servers work within the TCP/IP suite and rely on UDP (User Datagram Protocol).

NTP servers are normally dedicated NTP devices that use a single time reference to synchronise a network to. This time reference is most often a UTC (Coordinated Universal Time) source. UTC is a global time scale distributed by atomic clocks via the Internet, specialist long wave radio transmissions or via the GPS (Global Positioning System) network.

The NTP algorithm uses this time reference to determine the amount to advance or retreat the system or network clock. NTP analyses the timestamp’s values including the frequency of errors and its stability. A NTP server will maintain an estimate the quality of both the reference clocks and itself.

NTP is hierarchical. The distance from the timing reference is divided into strata. Stratum 0 is the atomic clock reference; Stratum 1 is the NTP server, while Stratum 2 is a server that receives timing information from the NTP server. NTP can support almost limitless strata although the further away from the timing reference you go the less accurate it will be.

As each stratum level can both receive and send timing signals, the advantage of this hierarchical system is that thousands of machines can be synchronised with only the need for one NTP server.

NTP contains its a security measure called authentication. Authentication verifies that each timestamp has come from the intended time reference by analysing a set of encryption keys that are sent with the time reference.  NTP analyses it and confirms whether it has come from the time source by verifying it against a set of trusted keys in its configuration files.

However, authentication is unavailable from timing sources from across the Internet which is why Microsoft and Novell amongst others strongly recommend only external time references are used such as a dedicated GPS NTP server or one that receives the national time and frequency long wave transmission.

Security
Having inaccurate time or running a network that is not synchronised can leave a computer system vulnerable to security threats and even fraud. Timestamps are the only point of reference for a computer to track applications and events. If these are inaccurate all sorts of problems can occur such as emails arriving before they were sent. It also makes possible such time sensitive transactions as e-commerce, online reservation and trading in stocks and share where exact timing with a network time server is essential and prices can fall or rise by millions in a second.

Protection:
Failure to synchronise a computer network can allow hackers and malicious uses the opportunity to get at your system, even fraudsters can take advantage. Even those machines that are synchronised can fall victim, especially when the use the Internet as a timing reference which allows an open door for malicious users to inject a virus into your network. Using Radio or GPS atomic clocks provide accurate time behind your firewall maintaining you security.

Accuracy:
NTP Time Servers ensure that all networked computers are synchronized automatically to the accurate time and date, now and in the future, automatically updating the network during daylight saving and leap seconds.

Legality:
If computer data is ever to be used in a court of law then it essential that the information comes from a network that is synchronised. If the system is not then the evidence may be inadmissible.

Happy users:
Stop users complaining about incorrect time on their workstations

Control:
You have control of the configuration. For example you can automatically changes the time forward and back each Spring and Autumn for daylight saving time or set your server time to be locked to UTC time only or any time zone you choose.

The GPS (Global Positioning System) network has been around for over thirty years but it was only since 1983 when a Korean airliner was accidentally shot down did the US military, who own and control the system, agree to open it up for civilian use in the hope of preventing such tragedies.

The GPS system is currently the world’s only global navigational satellite system (GNSS) although Europe and China are currently developing their own (Galileo and GLONASS). GPS, or to give it its official name Navstar GPS is based on a constellation of between 24 and 32 Medium Earth Orbit satellites.

These satellites transmit messages via precise microwave signals. These messages contain the time the message was sent, a precise orbit for the satellite sending the message and the general system health and rough orbits of all GPS satellites.

To work out a position a GPS receiver is required. This receives the signal from 4 (or more) satellites. Because the satellites broadcast their position and the time the message was sent, the GPS receiver can use the timing signal and distance information to workout by process of triangulation exactly where it is in the world.

GPS and other GNSS systems can only pinpoint the location so accurately because each relays timing information from an onboard atomic clock. Atomic clocks are so accurate that they either lose or gain a second in millions of years. It is only this accuracy that makes GPS positioning possible because as the signal transmitted by the satellites travel at the speed of light (up to 180,000 miles an second) a one second inaccuracy could make place positioning thousands of miles in the wrong place.

Because of this onboard atomic clock and high level of timing accuracy, a GPS satellite can be used as a source for UTC (Coordinated Universal Time). UTC is a global timescale based on the time told by atomic clocks and used across the globe to allow computer networks to all synchronize to the same time.

Computer networks use NTP time servers (network time protocol) to synchronise their systems. An  NTP server connected to a GPS antenna can receive a UTC time signal from the satellite and then distribute amongst the network.

Utilizing the GPs for timing information is one of the most accurate and secure methods of receiving a UTC source with accuracies of a few milliseconds quite feasibly possible.

Q. What is NTP?
A. NTP – Network Time Protocol is an Internet protocol for time synchronisation, whilst other time synchronisation protocols are available NTP is by far the most widely used having been around since the mid 1980’s when the Internet was still in its infancy.

Q. What is UTC?
A.  UTC – Coordinated Universal Time is a global timescale based on the time told by atomic clocks. Because these clocks are so accurate every year or so ‘leap seconds’ have to be added as UTC is even more accurate than the Earth’s rotation which slows and speeds up thanks to the Moon’s gravity.

Q. What is a Network Time Server?
A. A network time server also known as a NTP time server is a network device that receives a UTC time signal and then distributes it among the other devices on a network. The time protocol NTP then ensures that all machines are kept synchronised to that time.

Q. Where does a network time server receive a UTC time from?
A. There are several sources where a UTC time reference can be taken. The Internet is the most obvious with hundreds of different time servers relaying their UTC time signals. However these are notoriously inaccurate depending on many variable the Internet is also not a secure source and not suitable for any computer network where security issues are a concern. The other methods that provide a more accurate, secure and reliable source of UTC time is to either use the transmissions of the GPS (global positioning system) network or the national time and frequency transmissions broadcast on long-wave.

Q. Can I receive a radio time signal from anywhere?
A. Unfortunately not. Only certain countries have a time signal broadcast from their national physics laboratories and these signals are finite and vulnerable to interference. In the USA the signal is broadcast from Colorado and is known as WWVB, in the UK it is broadcast from Cumbria and is called MSF. Similar systems exist in Germany, Japan, France and Switzerland.

Q. What about the GPS signal?
A. A satellite navigation system relies on the time signals from the onboard atomic clocks in the GPS satellites. It is this time signal that is used to triangulate positioning and it can also be received by a network time server fitted with a GPS antenna. GPS is available everywhere in the World but an antenna does need to have a clear view of the sky.

Q. If I have large network then I will need multiple network time servers?
A. Not necessarily. NTP is hierarchical and divided into ‘stratum’ an atomic clock is a stratum 0 device, a time server that receives the clocks signal is a stratum 1 device and a network device that receives a signal from a time server is a stratum 2 device. NTP can support 12 stratum (realistically, although more is possible) and each strata can be used as a device to synchronise to. Therefore a stratum 2 device can synchronise other machine lower down the strata and so on. This means no matter how big a network is, only one network time server would be required.

A NTP Server connects to a computer network with the purpose of synchronising all computers, routers and other devices to the exact same time. NTP servers use Network Time Protocol to adjust the drift of different machines to match the reference time.

NTP servers rely on using a reference clock; most networks that use a NTP server will use a UTC (Coordinated Universal Time) time source. UTC is based on the time told by the incredibly accurate and expensive atomic clocks.

Atomic clocks work on the principle that a single atom (in most cases the caesium -133) will resonate at an exact rate at certain energy levels. The accuracy of atomic clocks is so proficient that UTC was developed to allow international Atomic Time (TAI) and Greenwich Meantime (GMT) to be combined, allowing for the slowing of the Earth’s rotation by adding leap seconds and therefore keeping the Sun at the Earth’s meridian at noon.

Failure to account for this slowing in the Earth’s spin would result in the eventual drift of day and night (albeit in many millennia).
A NTP server can be set to receive a UTC time signal from across the Internet although these can vary tremendously in accuracy and are reliant on reasonably close distances from client and server.

Relying on an Internet based timing references can also leave a network open to malicious users as they can not utilise NTP authentication which is a security measure used to ensure a timing reference is what it says it is.

Many dedicated NTP servers are designed to receive a more accurate and authenticated timing reference. One method utilises radio transmissions that are broadcast by several national physics laboratories such as NIST (National Institute for Standards and Technology) in the US (WWVB signal) and NPL (National Physical Laboratory) in the UK (MSF signal). These signals are broadcast in long wave and can be picked up within the broadcast area although the signals can be blocked by local geographical features.

Another method to receive a UTC timing reference is to use the onboard atomic clocks on GPS (Global Positioning System) network. While GPS is most commonly known as a positioning system the satellite actually relays timing information which is used by GPS receivers to calculate the time it has travelled and therefore the distance.
While the GPS signals are not broadcast in UTC format they are highly accurate and NTP has no problem in converting them.

The NTP server checks the time stamp from the UTC source and uses the information to calculate if the network clocks are drifting and adds or subtracts a second to match the reference clock. The NTP server will do this at set intervals, normally every fifteen minutes to ensure perfect accuracy.

NTP is accurate to within 1/100th of a second (10 milliseconds) over the public Internet and can perform even better over LANs and WANS with accuracies of 1/5000th of a second (200 microseconds) not unheard of.

To ensure further accuracy the NTP service (or daemon on Linux) runs in the background and does not believe the time it is told until after several exchanges and each one has passed a protocol specification (a test), the server is then considered. It usually takes about five good samples) until a NTP server is accepted as a timing source.