Receiving the Time with Time Servers and the MSF transmitter

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MSF is the name given to the dedicated time broadcast provided by the National Physical Laboratory in the UK, It is an accurate and reliable source of UK civil time, based on the time scale UTC (Coordinated Universal Time).

MSF is used throughout the UK and indeed other parts of Europe to receive a UTC time source which can be used by radio clocks and to synchronise computer networks by using a NTP time server.

It is available 24 hours a day across the whole of the UK although in some areas the signal can be weaker and it is susceptible to interference and local topography. The signal operates on a frequency of 60 kHz and carries a time and date code which relays the following information in binary format: Year, month, day of month,  day of week,  hour,  minute,  British Summer Time (in effect or imminent) and DUT1 (the difference between UTC and UT1 which is based on the Earths rotation)

The MSF signal is transmitted from Anthorn Radio Station in Cumbria but was only recently moved there after residing in Rugby, Warwickshire since it was started in the 1960’s. The signal’s carrier frequency is at 60 kHz, controlled by caesium atomic clocks at the radio station.

Caesium atomic clocks are the most reliably accurate atomic clocks anywhere, neither losing nor gaining a second in several millions of years.

To receive the MSF signal simple radio clocks can be used to display the exact UTC time or alternatively MSF referenced time servers can receive the long-wave transmission and distribute the timing information around computer networks using NTP (Network Time Protocol).

The only real alternative to the MSF signal in the UK is to use the onboard caesium clocks of the GPS network (Global Positioning System) that relay accurate time information that can be used as a UTC time source.

Six Reasons why you need a Dedicated Network Time Server!

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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 Atomic Clock and the NTP Time Server

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Most people have heard of atomic clocks, their accuracy and precision are well known. An ato0mic clock has the potential to keep time for several hundred million years and not lose a second in drift. Drift is the process where clocks lose or gain time because of the inaccuracies in the mechanisms that make them work.

Mechanical clocks, for instance, have been around for hundreds of years but even the most expensive and well engineered will drift at least a second a day. Whilst electronic clocks are more accurate they also will drift by about a second a week.

Atomic clocks have no comparison when it comes to time keeping. Because an atomic clock is based on the oscillation of an atom (in most cases the caesium 133 atom) which has an exact and finite resonance (caesium is 9,192,631,770 every second) this makes them accurate to within a billionth of a second (a nanosecond).

While this type of accuracy is unparalleled it has made possible technologies and innovations that have changed the world. Satellite communication is only possible thanks to the time keeping of atomic clocks, so is satellite navigation. As the speed of light (and therefore radio waves) travel at over 300,000km a second an inaccuracy of a second could see a navigation system be hundreds of thousands of miles out.

Precise accuracy is also essential in many modern computer applications. Global communication, particularly financial transactions have to be done precisely. In Wall Street or the London stock exchange a second can see the value of stock rise or fall by millions. Online reservation also requires the accuracy and perfect synchronisation only atomic clocks can provide otherwise tickets could be sold more than once and cash machines could end up paying out your wages twice if you found a cash machine with a slow clock.

Whilst this may sound desirable to the more dishonest of us, it doesn’t take much imagination to understand what problems a lack of accuracy and synchronisation could cause. For this reason an International timescale based on the time told by atomic clocks has been developed.

UTC (Coordinated Universal Time) is the same everywhere and can account for the slowing of the Earth’s rotation by adding leap seconds to keep UTC inline with GMT (Greenwich Meantime). All computer networks that participate in global communication need to be synchronised to UTC. Because UTC is based on the time told by atomic clocks it is the most precise timescale possible. For a computer network to receive and keep synchronised to UTC  it first needs access to an atomic clock. These are expensive and large pieces of equipment and are generally only to be found in large scale physics laboratories.

Fortunately the time told by these clocks can still be received by a network time server wither by utilising time and frequency long wave broadcasts transmitted by national physics laboratories or from the GPS (Global Positioning system). NTP (network time protocol) can then distribute this UTC time to the network and use the time signal to keep all devices on the network perfectly synchronised to UTC.

Global Positioning System (GPS) Operation and Implementation

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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.

Accuracy in Timekeeping Atomic clocks and Time Servers

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The development of atomic clocks throughout the twentieth century has been fundamental to many of the technologies we employ everyday. Without atomic clocks many of the innovations of the twentieth century would simply not exist.

Satellite communication, global positioning, computer networks and even the Internet would not be able to function in the way we are used to if it wasn’t for atomic clocks and their ultra-precision in timekeeping.

Atomic clocks are incredibly accurate chronometers not losing a second in millions of years. In comparison digital clocks may lose a second every week and the most intricately accurate mechanical clocks lose even more time.

The reason for an atomic clock’s incredible precision is that it is based on an oscillation of a single atom. An oscillation is merely a vibration at a particular energy level in the case of most atomic clocks they are based on the resonance of the caesium atom which oscillates at exactly 9,192,631,770 times every second.

Many technologies now rely on atomic clocks for their unbridled accuracy. The global positing system is a prime example. GPS satellites all have onboard an atomic clock and it is this timing information that is used to work out positioning. Because GPS satellites communicate using radio waves and they travel at the speed of light (180,000 miles a second in a vacuum), tiny inaccuracies in the time could make positioning inaccurate by hundreds of miles.

Another application that requires the use of atomic clocks is in computer networks. When computers talk to each other across the globe it is imperative that they all use the same timing source. If they didn’t, time sensitive transactions such as Internet shopping, online reservations, the stock exchange and even sending an email would be near to impossible. Emails would arrive before they were sent and the same item on an Internet shopping site could be sold to more than one person.

For this reason a global timescale called UTC (Coordinated Universal Time) based on the time told by atomic clocks has been developed. UTC is delivered to computer networks via times servers. Most time servers utilise NTP (network time protocol) to distribute and synchronize the networks.

NTP time servers can receive UTC time from a number of sources most commonly the onboard atomic clocks of the GPS system can be used as a UTC source by a time server connected to a GPS antenna.

Another method that is quite commonly used by NTP time servers is to utilise the long wave radio transmission broadcast by several countries’ national physics laboratories.  Whilst not available everywhere and quite susceptible to local topography the broadcasts do provide a secure method of receiving timing source.

If neither of these methods is available then a UTC timing source can be received from the Internet although accuracy and security are not guaranteed.

NTP Time Server Frequently Asked Questions

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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.

Receiving a Time Source

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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.

A Brief History of NTP Time

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NTP (network time protocol) is an Internet protocol. Protocols are simply a set of instructions that a computer will follow and NTP has been designed and developed to synchronize computer networks.

It was developed in the 1985 by Professor David Mills from the University of Delaware when the Internet was still in its infancy. Professor Mills realised the need for synchronisation amongst computers when they were talking to each other.

NTP uses Marzullo’s Algorithm which is an agreement algorithm used to select sources for estimating accurate time from a number of noisy time sources.  NTP works by distributing a single time source. Whilst this time reference can be anything such as a wrist watch, it makes little sense to synchronise a network to anything other than UTC time.

UTC (Coordinated Universal Time) is a global time scale based on the time told by atomic clocks. Atomic clocks boast such high levels of accuracy that they do not lose or gain a second in over a million years.

By synchronizing to a UTC time source a network can in affect be synchronised to every other network that uses UTC time.

Once a time source has been selected the NTP daemon (or service on Windows) not only distributes the time reference it also continually checks for accuracy and errors.

NTP is a hierarchical system. The distance from a time server is referred to as a stratum level. A stratum 0 server is a time source itself such as an atomic clock, a stratum 1 server is the NTP time server whilst a stratum 2 server is  a device that receives the time from the time server and stratum 3 servers receive the time signal via a stratum 2 server.

Arranging the network into strata means that a NTP time server can distribute time to hundreds or even thousands of machines without the network or time server itself becoming congested with traffic.  Although it must be noted that the lower down the stratum level a device a fall in accuracy can be expected.

The actual UTC time signal can be received from a number of ways. From across the Internet although this can cause security issues as the time signal can’t be authenticated which is NTP’s inbuilt security measure. It is far safer to receive a time signal from a radio signal broadcast by several national physics laboratories or even the GPS network  whose onboard atomic clocks can be utilised as a timing source if the NTP time server is fitted with a GPS receiver.

Choosing a NTP Server and Selecting the Best Timing Source for You

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The NTP server is an integral part of the modern computer network. Without Network Time Protocol and NTP time servers many of the modern functionality of computers that we take for granted such as online reservation, Internet trading and satellite communication would be impossible.

Synchronisation in computers is dealt with by NTP.  NTP and NTP servers use a single time reference to synchronise all machines on a network to that time.  This time reference could in fact be anything such as the time on a wrist watch perhaps. However, synchronisation is pointless unless a UTC (coordinated universal time) time source is used as UTC has been developed to allow the whole world to synchronise to the same time, allowing truly global synchronisation.

UTC is based on the time told by atomic clocks although compensation measures such as Leap Seconds are added to UTC to keep it inline with Greenwich Meantime (GMT).

Atomic clocks are very expensive and extremely delicate pieces of equipment and not the sort of thing that can be housed in the office server room. Fortunately a NTP server can receive a UTC time source from several different locations.

The Internet is perhaps the most widely used source of time references. Unfortunately however, there are draw backs in using the Internet for a timing source. Firstly the Internet timing sources can’t be authenticated. Authentication is a security measure used by NTP to check that timing source is genuine. Secondly, to use an Internet timing reference means a hole has to be left open in the network’s firewall, again compromising security. Thirdly, Internet timing sources are notoriously inaccurate and those that aren’t can often be too far away from a client to provide any useful precision.

However, if security and high level of accuracy to UTC time is not required then the Internet can provide a simple and affordable solution.

A far more secure method of receiving a UTC timing reference is to use the specialist national time and frequency transmission broadcast by several countries. The UK (MSF), USA (WWVB), Germany (DCF) and Japan (JJY) all boast a long wave timing signal. While these signals are limited in range and strength, where available they make an ideal timing source as the radio receiver can pick these signals up from inside a building. These transmissions can also be authenticated providing a high level of security.

The third and perhaps simplest solution is to use a GPS NTP server. These use the signals sent from the Global Positioning System which contains timing information. This is ideal as the GPS signal can be received literally anywhere in the world so if there is no radio transmission your area then the GPS network will provide a secure and authenticated solution.

The only downside to GPS is that an antenna has to have a good view of the sky and therefore need to be positioned on the roof. This obviously has logistical drawbacks if the server room is in the basement of a sky-scraper.

In selecting a timing source, the most important thing to remember is where the NTP server is going to be situated. If it is indoors and there is no opportunity to run and antenna to the roof then the radio transmissions would be the best alternative. If there are no radio transmission in your country/area or the signals are blocked by local topography then the GPS is an ideal solution.

However, if accuracy and security are not an issue then the Internet  would be the most obvious solution.

Understanding a NTP GPS Server

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A NTP GPS Server is a type of time server that uses Network Time Protocol (NTP) as a method for synchronizing the time on network devices and computers after receiving a time signal from he GPS network.

The GPS (Global Positioning System) network is a constellation of satellites owned and operated by the USA military. Most people are aware of GPS as an aid for satellite navigation. In actual fact, the basis of the transmissions broadcast by the GPS satellites is a time signal. This time signal is generated by the satellite’s onboard atomic clock. It is this information that a satellite navigation system receives and calculates by triangulation the distance away from the satellites.

This timing signal is what is used by a NTP GPS server as a reference to synchronize a network too. NTP then distributes this time to all routers and computers on that network.

A NTP GPS server comprises of a GPS receiver, GPS antenna and NTP software. The GPS antenna should be situated on a rooftop which will give the best possibility of receiving the transmissions from the satellites.

The GPS receiver then converts this information into timing information that can be read and distributed by NTP.

While the atomic clocks onboard the GPS satellites do not transmit a UTC timing code (Coordinated Universal Time). However, NTP has the ability to convert the atomic clock from the satellites to UTC. This allows computer networks to be synchronized to the same universal time source no matter where they are in the world.

Using a dedicated NTP GPS server a network can be synchronized to within a few milliseconds of UTC time with accuracies of a few hundred nanoseconds made possible over LAN’s.