Category: time server

Windows Time Server Synchronising Your Network With NTP

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Nearly all a computers activity involves time whether logging a timestamp for when a network was accessed to sending an email, knowing the time is crucial for computer applications.

All computers have an on-board clock that provides time and date information. These Real Time Clock (RTC) chips are battery backed so that even when off they can maintain time, however these RTC chips are mass produced and cannot maintain accurate time and tend to drift.

For many applications this can be quite adequate, however if a computer is on a network and needs to talk to other machines, failing to be synchonised to the correct time can mean many time-sensitive transactions can not be completed and can even leave the network open to security threats.

All versions of Windows Server since 2000 have included a time synchronization facility, called Windows Time Service (w32time.exe), built into the operating system. This can be configured to operate as a network time server synchronizing all machines to a specific time source.

Windows Time Service uses a version of NTP (Network Time Protocol), normally a simplified version, of the Internet protocol which is designed to synchronise machines on a network, NTP is also the standard for which most computer networks across the global use to synchronise with.

Choosing the correct time source is vitally important. Most networks are synchronized to UTC (Coordinated Universal Time) source. UTC is a global standardized time based on atomic clocks which are the most accurate time sources.

UTC can be obtained over the Internet from such places as (us Naval Observatory) or (Microsoft) but it must be noted that internet time sources can not be authenticated which can leave a system open to abuse and Microsoft and others advise using an external hardware source as a reference clock such as a specialized NTP server.

NTP servers receive their time source from either a specialist radio transmission from national physics laboratories which broadcast UTC time taken from an atomic clock source or by the GPS network which also relays UTC as a consequence of needing it to pin point locations.

NTP can maintain time over the public Internet to within 1/100th of a second (10 milliseconds) and can perform even better over LANs.

Keeping accurate time on Linux

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If you want to be sure that your computer clock is accurate you can configure your system to use NTP (Network Time Protocol), one of the oldest Internet protocols and the industry standard for time synchronisation.

NTP on will synchronise your computer’s clock to a pool of time servers around the world that are official ‘timekeepers’. It is best to choose the closest to you so response time is minimized and to use more than one in case one goes down. There are more than 1.500 servers to choose from, but some areas are better served than others. Many servers on the internet are extremely inaccurate and Internet time references should not be used as a replacement for a dedicated time server.

However, for basic time synchronisation purposes, Internet providers will suffice. The first step should be to select three servers close to you – preferably in your country, or if there aren’t enough, in your ‘zone. Go to ntp home and browse through the tree of zones and servers to select which ones are best for you. The follow these commands to configure:

1. Configure /etc/ntp.conf
Edit this file with a text-editor. Replace
server <example-server-name>
with your servers, such as:


2. Synchronise your clock manually
If your clock is drifting too NTP might refuse to synchronise it, but it can be done manually:

ntpdate (server name that you choose)

3. Make your ntp daemon executable

chmod +x /etc/rc.d/rc.ntpd

4. Start NTP now without rebooting
Again, a simple command:

/etc/rc.d/rc.ntpd start

Basic Time Server Information

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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 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.

Six Reasons why you need a Dedicated Network Time Server!

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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.

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.

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.

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

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.

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.

A Beginners Guide To The NTP Server

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Computer networking is one of the most difficult aspects of information and communications technology (ICT). The logistics of connecting terminals, routers, printers and all the other devices can leave many administrators with a constant headache.

One of the most important aspects that often gets overlooked and can have disastrous consequences is that of time synchronization.

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

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

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

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

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

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

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

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

NTP GPS Server for Time Critical Applications

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The GPS (Global Positioning System) is a Global Navigational Satellite System (GNSS) controlled and run by the United States of America.

GNSS systems work by using satellites several thousand miles above the Earth’s surface that beam timing information down to a GNSS receiver (like the satellite navigation unit in our cars). It is this information that is used by the GPS receiver to triangulate an exact position. They can only do this by having onboard their own highly accurate atomic clock as the distance the satellites are away from the Earth, even an inaccuracy of a second or two could mean a sat navigation’s location could be miles out.

As a consequence of having this accurate time sources, GPS and the new breed of GNSS systems can all be used to receive an absolute or UTC (Universal Coordinated Time) time source. This time source can be used by computer networks running a NTP server (Network Time Protocol) to synchronise all machines and devices to the same time.

NTP is a protocol designed to synchronise computers and network devices to an external timing reference.

GPS is an ideal time and frequency reference 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 and dedicated NTP GPS servers are now relatively low cost.

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.

A NTP GPS Server 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.

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.