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NTP Server Configuration for Windows and Linux

Network Time Protocol has been developed to keep computers synchronized. All computers are prone to drift and accurate timing is essential for many time critical applications.

A version of NTP is installed on most versions of Windows (although a stripped down version called SNTP –Simplified NTP- is in older versions) and Linux but is free to download from NTP.org.

When synchronising a a network it is preferable to use a dedicated NTP server that receives a timing source from an atomic clock either via specialist radio transmissions or the GPS network. However, many Internet time references are available, some more reliable than others, although it must be noted Internet based time sources can’t be authenticated by NTP, leaving your computer vulnerable to threats.

NTP is hierarchical and arranged into stratum. Stratum 0 is timing reference, while stratum 1 is a server connected to a stratum 0 timing source and a stratum 2 is a computer (or device) attached to a stratum 1 server.

The Basic configuration of NTP is done using the /etc/ntp.conf file you have to edit it and place the IP address of stratum 1 and stratum 2 servers. Here is an example of a basic ntp.conf file:

server xxx.yyy.zzz.aaa prefer (time server address such as time.windows.com)

server 123.123.1.0

server 122.123.1.0 stratum 3

Driftfile /etc/ntp/drift

The most basic ntp.conf file will list 2 servers, one that it wishes to synchronise too and an IP address for itself. It is good housekeeping to have more than one server for reference in case one goes down.

A server with the tag ‘prefer’ is used for a trusted source ensuring NTP will always use that server when possible. The IP address will be used in case of problems when NTP will synchonise with itself is. The drift file is where NTP builds a record of the system clock’s drift rate and automatically adjusts for it.

NTP will adjust your system time but only slowly. NTP will await at least ten packets of information before trusting the time source. To test NTP simply change your system clock by half an hour at the end of the day and the time in the morning should be correct.

Atomic Clock Synchronization using WWVB

Accurate time using Atomic Clocks is available across North America using the WWVB Atomic Clock time signal transmitted from Fort Collins, Colorado; it provides the ability to synchronize the time on computers and other electrical equipment.

The North American WWVB signal is operated by NIST - the National Institute of Standards and Technology. WWVB has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from WWVB a lot of bounce, and this single station can therefore cover the entire continental United States plus much of Canada and Central America.

The time codes are sent from WWVB using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: • 0.2 seconds of reduced power means a binary zero • 0.5 seconds of reduced power is a binary one. • 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated NTP time servers that are tuned to receive the WWVB time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

It could be the last Leap Second tonight as there are calls to have it scrapped

At midnight on tonight an extra second will be added as recommended by the International Earth rotation and Reference systems Service (IERS). That means for the last minute of 2008 there will 61 seconds.

Leap Seconds have been added nearly every year since the inception of UTC (Coordinated Universal Time) in the 1970’s. The extra second is added to ensure UTC keeps in synch with GMT (Greenwich Meantime or sometimes called UT1). GMT is the traditional 24 hour clock system where a day is defined as the rotation of the Earth which takes 86,400 seconds for a complete revolution.

Unfortunately the Earth can often be a little tardy in its spin and if the extra seconds were no added at the end of the year to compensate eventually the two systems (UTC and GMT) would drift apart. In a millennium the time difference would only be an hour but many argue to a have a time system that does no correspond to the movement of the heavens would be irrational and occupations such as farming and astronomy would be made more difficult.

However, not everybody sees it that way wit some arguing that as te entire world’s computer networks are synchronised to UTC using NTP servers then the fudging of the extra second causes untold amounts of trouble.

Now a group within the International Telecommunications Union, called has recommended abolishing the leap second. Group member Elisa Felicitas Arias, of the International Bureau of Weights and Measures in Paris, France, argues that a timescale that doesn’t need regular tweaking is essential in an increasingly interconnected world. What’s more, she says, ships and aircraft now navigate via GPS rather than the old time system. GPS runs on a version of atomic time.

Next year, member states of the ITU are due to vote on the proposal. If 70 per cent support the idea, an official decision will be made at the World Radio Conference in 2011. According to a report co-authored by Felicitas Arias, most member states support the idea. The UK, however, is against reworking its laws, which include the solar timescale Greenwich Mean Time. Without the UK abolition may be difficult, says Felicitas Arias.

“In theory, adding a second is as easy as flipping a switch; in practice, it rarely works that way,” says Dennis McCarthy of the US Naval Research Laboratory, which provides the time standard used by the US military. Most likely to be affected are IT systems that need precision of less than a second. In 1998 – two leap seconds ago – cellphone communications blacked out over part of the southern US. Different regions of service had slipped into slightly different times, preventing proper relaying of signals.

All quotes attributed to the BBC

Keeping Track of the Worlds Time and Difficulties in Synchronisation

Until 1967 the second was defined using the motion of the Earth which rotates once on its axis every 24 hours, and there are 3,600 seconds in that hour and 86,400 in 24.

That would be fine if the earth was punctual but in fact it is not. The Earth’s rotation rate changes every day by thousands of nanoseconds, and this is due in a large part to wind and waves spinning around the Earth and causing drag.

Over the course of thousands of days, these changes in the rate of rotation can result in the Earth’s spin getting out of synch with the high-precision atomic clocks that we use to keep the UTC system (Coordinated Universal Time) ticking over. For this reason the Earth’s rotation is monitored and timed using the far off flashes from a type of collapsed star called a quasar that flash with an ultra precise rhythm many millions of light years away. By monitoring the Earth’s spin against these far away objects it can be worked out how much the rotation has slowed.

Once a second of slowing has been built up, The International Earth Rotation Service (IERS), recommends a Leap Second to be added, usually at the end of the year.

Other complications arise when it comes to synchronising the Earth to one timescale. In 1905, Albert Einstein’s theory of relativity showed that there is no such thing as absolute time. Every clock, everywhere in the universe, ticks at a different rate. For GPS, this is an enormous issue because it turns out that the clocks on the satellites drift by almost 40,000 nanoseconds per day relative to the clocks on the ground because they are high above the Earth’s surface (and therefore in a weaker gravitational field) and are moving fast relative to the ground.

And as light can travel Forty-thousand feet in that time, you can see the problem. Einstein’s equations first written down in 1905 and 1915 are used to correct for this time-shift, allowing GPS to work, planes to navigate safely and GPS NTP servers to receive the correct time.

MSF Technical Information

The MSF transmission from Anthorn (latitude 54° 55′ N, longitude 3° 15′ W) is the principal means of disseminating the UK national standards of time and frequency which are maintained by the National Physical Laboratory. The effective monopole radiated power is 15 kW and the antenna is substantially omnidirectional. The signal strength is greater than 10 mV/m at 100 km and greater than 100 μV/m at 1000 km from the transmitter. The signal is widely used in northern and western Europe. The carrier frequency is maintained at 60 kHz to within 2 parts in 1012.

Simple on-off carrier modulation is used, the rise and fall times of the carrier are determined by the combination of antenna and transmitter. The timing of these edges is governed by the seconds and minutes of Coordinated Universal Time (UTC), which is always within a second of Greenwich Mean Time (GMT). Every UTC second is marked by an ‘off’ preceded by at least 500 ms of carrier, and this second marker is transmitted with an accuracy better than ±1 ms.

The first second of the minute begins with a period of 500 ms with the carrier off, to serve as a minute marker. The other 59 (or, exceptionally, 60 or 58) seconds of the minute always begin with at least 100 ms ‘off’ and end with at least 700 ms of carrier. Seconds 01-16 carry information for the current minute about the difference (DUT1) between astronomical time and atomic time, and the remaining seconds convey the time and date code. The time and date code information is always given in terms of UK clock time and date, which is UTC in winter and UTC+1h when Summer Time is in effect, and it relates to the minute following that in which it is transmitted.

Dedicated MSF NTP Server devices are available that can connect directly to the MSF transmission.

Information Courtesy of NPL

Happy Christmas from all at Galleon Systems

Here at Galleon Systems, one of Europe’s leading suppliers of NTP server systems, we would like to wish all our customers, suppliers and even our competitors a Merry Christmas and a Happy New Year. We hope 2009 is a successful year for you all.

Atomic Clock Synchronisation using MSF

Accurate time using Atomic Clocks is available across Great Britain and parts of northern Europe using the MSF Atomic Clock time signal transmitted from Cumbria, UK; it provides the ability to synchronize the time on computers and other electrical equipment.

The UK MSF signal is operated by NPL – the National Physical Laboratory. MSF has high transmitter power (50,000 watts), a very efficient antenna and an extremely low frequency (60,000 Hz). For comparison, a typical AM radio station broadcasts at a frequency of 1,000,000 Hz. The combination of high power and low frequency gives the radio waves from MSF a lot of bounce, and this single station can therefore cover most of Britain and some of continental Europe.

The time codes are sent from MSF using one of the simplest systems possible, and at a very low data rate of one bit per second. The 60,000 Hz signal is always transmitted, but every second it is significantly reduced in power for a period of 0.2, 0.5 or 0.8 seconds: • 0.2 seconds of reduced power means a binary zero • 0.5 seconds of reduced power is a binary one. • 0.8 seconds of reduced power is a separator. The time code is sent in BCD (Binary Coded Decimal) and indicates minutes, hours, day of the year and year, along with information about daylight savings time and leap years.

The time is transmitted using 53 bits and 7 separators, and therefore takes 60 seconds to transmit. A clock or watch can contain an extremely small and relatively simple antenna and receiver to decode the information in the signal and set the clock’s time accurately. All that you have to do is set the time zone, and the atomic clock will display the correct time.

Dedicated time servers that are tuned to receive the MSF time signal are available. These devices connect o a computer network like any other server only these receive the timing signal and distribute it to other machines on the network using NTP (Network Time Protocol).

Correcting Network Time

Distributed networks rely completely on the correct time. Computers need timestamps to order events and when a collection of machines are working together it is imperative they run the same time.

Unfortunately modern PC’s are not designed to be perfect timekeepers. Their system clocks are simple electronic oscillators and are prone to drift. This is not normally a problem when the machines are working independently but when they are communicating across a network all sorts of problems can occur.

From emails arriving before they have been sent to entire system crashes, lack of synchronisation can causes untold problems across a network and it is for this reason that network time servers are used to ensure the entire network is synchronised together.

Network time servers come in two forms – The GPS time server and the radio referenced time server. GPS NTP servers use the time signal broadcast from GPS satellites. This is extremely accurate as it is generated by an atomic clock on board the GPS satellite. Radio referenced NTP servers use a long wave transmission broadcast by several national physics laboratories.

Both these methods are a good source of Coordinated Universal Time (UTC) the world’s global timescale. UTC is used by networks across the globe and synchronising to it allows computer networks to communicate confidently and partake of time sensitive transactions without error.

Some administrators use the Internet to receive a UTC time source. Whilst a dedicated network time server is not required to do this it does have security drawbacks in that a port is needed to be left open in the firewall for the computer to communicate with the NTP server, this can leave a system vulnerable and open to attack. Furthermore, Internet time sources are notoriously unreliable with many either too inaccurate or too far away to serve any useful purpose.

Why the Need for NTP

Network Time Protocol is an Internet protocol used to synchronize computer clocks to a stable and precise time reference. NTP was originally developed by Professor David L. Mills at the University of Delaware in 1985 and is an Internet standard protocol.

NTP was developed to solve the problem of multiple computers working together and having the different time. Whilst, time usually just advances, if programs are running on different computers time should advance even if you switch from one computer to another. However, if one system is ahead of the other, switching between these systems would cause time to jump forward and back.

As a consequence, networks may run their own time, but as soon as you connect to the Internet, effects become visible. Just Email messages arrive before they were sent, and are even replied to before they were mailed!

Whilst this sort of problem may seem innocuous when it comes to receiving email, however, in some environments a lack of synchronisation can have disastrous results this is why air traffic control was one of the first applications for NTP.

NTP uses a single time source and distributes it amongst all devices on a network it does this by using an algorithm that works out how much to adjust a system clock to ensure synchronisation.

NTP works on a hierarchical basis to ensure there are no network traffic and bandwidth problems. It uses a single time source, normally UTC (coordinated universal time) and receives time requests from the machines on the top of the hierarch which then pass the time on further down the chain.

Most networks that utilise NTP will use a dedicated network time server to receive their UTC time signal. These can receive the time from the GPS network or radio transmissions broadcast by national physics laboratories. These dedicated NTP time servers are ideal as they receive time direct from an atomic clock source they are also secure as they are situated externally and therefore do not require interruptions in the network firewall.

New Waterproof GPS Mushroom Antenna

Galleon Systems’ new mushroom GPS antenna provide increased reliability in receiving GPS timing signals for NTP time servers.
The new Exactime 300 GPS Timing and Synchronization Receiver boasts waterproof protection, anti-UV, anti-acidity and anti-alkalinity properties to ensure reliable and continual communication with the GPS network.

The attractive white mushroom is smaller than conventional GPS antennas and sits just 77.5mm or 3.05-inch in height and is easily fitted and installed thanks to the inclusion of a full installation guide and CD manual.

Whilst an ideal unit for a GPS NTP time server this industry standard antenna is also ideal for all GPS receiving needs including: Marine Navigation, Control Vehicle Tracking and NTP synchronisation
The main features of the Exactime 300 mushroom antenna are:

• Built-in patch antenna • 12 parallel tracking channels • Fast TTFF (Time to first fix) and low power consumption • On-board, rechargeable battery sustained Real-Time Clock and control • parameters memory for fast satellite acquisition during power-up • Interference filter to major VHF channels of marine radar • WAAS compliant with EGNOS support • Perfect Static Drift for both of speed and course •  Magnetic Declination compensation • Is protected against reverse polarity voltage • Support RS-232 or RS-422 interface, Support 1 PPS output.