Category: timing source

UTC A global Timescale

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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.

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.

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.

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.

Network Time Server Keeping Control of Time

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Computer networking can seem an intimidating undertaking. However, a computer network is really just a number of machines connected together for ease of data transfer and security. They can be very small such as two computers in a home network to really large networks consisting of hundreds and thousands of machines.

When a computer or device is connected to a network then there is only one point of reference that the computers can use to establish the order of events and applications and that is time.

Time, in the form of time stamps are used by most applications and this is when problems in computer networks can occur.

Computers tell the time by using a software clock. This is based on a system clock that keeps time when the computer is off. However, computers internal clocks are wholly inaccurate. They tend to drift up to several seconds a week. On a network when there is more than one machine, this can cause severe problems if the machines are drifting at different rates.

Emails may arrive before they have been sent and the whole network can be vulnerable to security threats and even fraud!

A network time server is used to synchronize a computer network to a single time source. This time source can be anything from an internal clock on a computer to the time told by a wrist watch. However, to ensure perfect accuracy and to keep a network synchronized to the rest of the world then a UTC time source should be used.

UTC (Coordinated Universal Time) is a global timescale based on the time told by atomic clocks. A network time server can receive a UTC time source from across the Internet (although unsecured), via the GPS (global positioning system) network or via specialist radio transmission from national physics laboratories.

Most network time servers use NTP (Network Time Protocol) to distribute the timing reference throughout the network. NTP is not the only timing protocol designed to do this although it is, however, by far the most widely used.

GPS Time Server and NTP (Network Time Protocol)?

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We are all used to Satellite Navigation by now. More and more people are installing those little black boxes into their cars and throwing away their old paper road maps. The advantages of satellite navigation are many fold – from constant updates keeping the maps current to being able to pin point your location miles from any landmarks or road signs but GPS has more uses than merely triangulating a position for direction finding, it can be utilized to provide time and frequency information worldwide.

Since the early 1990’s the Global Positioning system (GPS) has been the worlds’ only fully functioning Global Navigational Satellite System (GNSS). Run by the American military, GPS (sometimes referred to as NAVSTAR) has allowed accurate timing and location finding all over the world.

To accurately pinpoint a location, all GNSS systems require an absolute time source, that is a time source as accurate as humanely possible such as that from an atomic clock. Without knowing exactly what the time is a GNSS satellite would not be able to accurately pin point a location (as the Earth, satellites and people are all moving about a location can only be defined by a position and time). Because of the distance of the satellites away from the Earth, even an inaccuracy of a second or two could mean a sat nav’s location could be miles out.

For this reason each satellite has a highly accurate atomic clock onboard which can also be used by NTP (Network Time Protocol) servers to synchronise computer networks. GPS is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components.

A GPS receiver decodes the signal sent from the GPS antenna to a computer readable protocol which can be utilised by most time servers and operating systems including, Windows, LINUX and UNIX.

The GPS receiver also outputs a precise pulse every second that GPS NTP servers and computer time servers may utilise to provide ultra-precise timing. The pulse-per-second timing on most receivers is accurate to within 0.001 of a second of UTC (Coordinated Universal Time or Temps Universel Coordonné).

GPS is ideal in providing NTP time servers or stand-alone computers with a highly accurate external reference for synchronisation. Even with relatively low cost equipment, accuracy of hundred nanoseconds (a nanosecond = a billionth of a second) can be reasonably achieved using GPS as an external reference.

In 2002, the European Space Agency and European Union agreed to build Europe’s own GNSS called Galileo. To compete with the new and more advanced GNSS technologies the GPS programme is currently being upgraded and it is expected that when Galileo begins relaying signals both systems will become interoperable allowing even more accuracy in timing and positioning.

Using WWVB as a Timing Reference for NTP Servers

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Atomic clocks are incredibly expensive and generally they are normally only to be found in large scale physics laboratories such as MIT (Massachusetts Institute of Technology), NIST (National Institute of Standards and Technology (Colorado) or the National Physical Laboratory in the UK.

Fortunately many national laboratories broadcast the UTC (Coordinated Universal Time) time from their atomic clocks via a radio transmission.

In the US the national timing broadcast is called WWVB and is broadcast by NIST (National Institute fro Standards and Time) in Fort Collins, Colorado. The WWVB broadcast is used by millions of people throughout North America to synchronize consumer electronic products like wall clocks, clock radios, and wristwatches. In addition, WWVB is used for high-level applications such as network time synchronization utilizing NTP.

The time code contains the year, day of year, hour, minute, second, and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds.

WWVB broadcasts on 2.5, 5, 10, 15, and 20 MHz and for most users in the United States, the received accuracy should be less than 10 milliseconds (1/100 of a second).

While many NTP servers now use GPS to receive a timing reference, the advantage of using a radio transmission is that a signal can be received indoors (a GPS antenna needs a good view of the sky).

However, the radio signal has a finite range and can be blocked by skyscrapers, mountains and dense conurbations. 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.

Similar national timing transmissions are broadcast from other countries in the UK the signal is referred to as MSF and is broadcast by the National Physical Laboratory in Cumbria, other systems are broadcast in Frankfurt, Germany (DCF-77), Japan (JJY) and France (TDF)