Category: timing source

NTP or SNTP That is the Question?

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While there are several protocols available for time synchronisation the majority of network time is synchronised using either NTP or SNTP.

Network Time Protocol (NTP) and Simple Network Time Protocol (SNTP) have been around since the inception of the Internet (and in the case of NTP, several years beforehand) and are by far the most popular and widespread time synchronisation protocols.

However, the difference between the two is slight and deciding which protocol is best for a ntp time server or a particular time synchronisation application can be troublesome.

As its name suggests, SNTP is a simplified version of Network Time Protocol but the question is often asked: ‘what exactly is the difference?’

The main difference between the two versions of the protocol is in the algorithm that is used. NTP’s algorithm can query multiple reference clocks an calculate which is the most accurate.

SNTP use for low processing devices – it is suited to less powerful machines, do not require the high level accuracy of NTP. NTP can also monitor any offset and jitter (small variations in waveform resulting from voltage supply fluctuations, mechanical vibrations or other sources) whilst SNTP does not.

Another major difference is in the way the two protocols adjust for any drift in network devices. NTP will speed up or slow down a system clock to match the time of the reference clock coming into the NTP server (slewing) while SNTP will simply step forward or backward the system clock.

This stepping of the system time can cause potential problems with time sensitive applications especially of the step is quite large.

NTP is used when accuracy is important and when time critical applications are reliant on the network. However, its complex algorithm is not suited to simple machines or those with less powerful processors. SNTP on the other hand is best suited for these simpler devices as it takes up less computer resources, however it is not suited for any device where accuracy is critical or where time critical applications are reliant on the network.

Atomic Clock to be attached to International Space Station

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One of the world’s most accurate atomic clocks is to be launched into orbit and attached to the International Space Station (ISS) thanks to an agreement signed by the French space agency.

The PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite) atomic clock is to attached to the ISS in an effort to more accurately test Einstein’s theory of relatively as well as increasing the accuracy of Coordinated Universal Time (UTC) amongst other geodesy experiments.

PHARAO is a next generation caesium atomic clock with an accuracy that corresponds to less than a second’s drift every 300,000 years. PHARAO is to be launched by the European Space Agency (ESA) in 2013.

Atomic clocks are the most accurate timekeeping devices available to mankind yet they are susceptible to changes in gravitational pull, as predicted by Einstein’s theory, as time itself is slewed by the Earth’s pull. By placing this accurate atomic clock into orbit the effect of Earth’s gravity is lessened allowing PHARAO to be more accurate than Earth based clock.

While atomic clocks are not new to orbit, as many satellites; including the GPS network (Global Positioning System) contain atomic clocks, however, PHARAO will be among the most accurate clocks ever launched into space, allowing it to be used for far more detailed analysis.

Atomic clocks have been around since the 1960’s but their increasing development has paved the way for more and more advanced technologies. Atomic clocks form the basis of many modern technologies from satellite navigation to allowing computer networks to communicate effectively across the globe.

Computer networks receive time signals from atomic clocks via NTP time servers (Network Time Protocol) which can accurately synchronise a computer network to within a few milliseconds of UTC.

NTP Servers and the Different Time Sources

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NTP servers are essential devices for computer network time synchronisation. Ensuring a network coincides with UTC (Coordinated Universal Time) is vital in modern communications such as the Internet and is the primary function of the network time server (NTP server).

As their name suggests, these time servers use the protocol NTP (Network Time Protocol) to handle the synchronisation requests. NTP is already installed in many operating systems and synchronisation is possible without an NTP server by utilising an Internet time source, this can be unsecure and inaccurate for many network needs.

Network time servers receive a far more accurate and secure time signal. There are two methods of receiving the time using a time server: utilising the GPS network or receiving long wave radio transmissions.

Both these methods of receiving a time source are secure as they are external to any network firewall. They are also accurate as both sources of time are generated directly by atomic clocks rather than an Internet time service that are normally NTP devices connected to a third party atomic clock.

The GPS network provides an ideal source of time for NTP servers as the signals are available anywhere. The only downside of using the GPS network is that a view of the sky is required to lock-on to a satellite.

Radio referenced time sources are more flexible in that the long wave signal can be received indoors. They are limited in strength and not every country has a time signal although some signals such as the German DCF and the USA WVBB are available in neighbouring states.

Atomic Clocks and Gravity

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We couldn’t live our lives without them. They affect almost every aspect of our daily lives and many of the technologies that we take for granted in today’s world, just couldn’t function without them. In fact, if you are reading this article on the Internet the there is a chance you are using one right now.

Without knowing it, atomic clocks govern all of us. From the Internet; to mobile phone networks and satellite navigation, without atomic clocks none of these technologies would be possible.

Atomic clocks govern all computer networks using the protocol NTP (network time protocol) and network time servers, computer systems around the world remain in perfect synchronisation.

And they will continue to do so for several million years as atomic clocks are so accurate they can maintain time to within a second for well over 100 million years. However, atomic clocks can be made even more accurate and a French team of scientists are planning to do just that by launching an atomic clock into space.

Atomic clocks are limited to their accuracy on Earth because of the effects of he gravitational pull of the planet on time itself; as Einstein suggested time itself is warped by gravity and this warping slows down time on Earth.

However, a new type of atomic clock named PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbit) is to be placed aboard the ISS (international space station) out of reach from the worst effects of Earth’ gravitational pull.

This new type of atomic clock will allow hyper accurate synchronization with other atomic clocks, here on Earth (which in effect will make synchronization to an NTP server even more precise).

Pharao is expected to reach accuracies of around one second each 300 million years and will allow further advances in time reliant technologies.

A Brief History of Computer Time

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Telling the time is something may of us learn when we are very small children. Knowing what time it is is an essential part of our society and we couldn’t function without it. Just imagine if we didn’t tell the time – when would you go to work? When would you leave and how would it be possible to meet other people or arrange any kind of function.

While telling the time is crucial to us, it is even more vital for computers who use time as the only point of reference and amongst computer networks time synchronisation is vital. Without recording the passing of time, computers couldn’t function as there would be no reference to order programs and functions.
But the way computers tell the time and date is far different to the way we record it. Rather than record a separate time, date and year – computer systems use a single number. This number is based on the number of seconds from a set point in time – known as the prime epoch.

When this epoch is, depends on the operating system or programming language in question. For instance, Unix systems have a prime epoch which starts at 1 January 1970 and the number of seconds from the epoch are counted in a 32 bit integer. Other operating systems, such as Windows, use a similar system but the epoch is different (Windows starts on 1 January 1601).

There are, however, disadvantages to this integer system. For instance as the Unix system is a 32-bit integer which started in 01 Jan 1970, by 19 January 2038 the integer will have exhausted every possible number and will have to return to zero’s. This could cause problems with systems reliant on Unix in a problem reminiscent of the Millennium bug.
There are other issues involving computer time also. Because of the global requirements of the Internet all computer time is now based on UTC (Coordinated Universal Time). However, UTC is altered on occasion by adding Leap Seconds to ensure the time matches the rotation of the Earth (the Earth’s rotation is never exact due to gravitational forces) so leap second handling has to be encompassed into a computer time systems.

Computer time is often associated with NTP (Network Time Protocol) which is used to synchronise computers often using a network time server.

Time Synchronisation on a Windows 7 Network

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Windows 7 is the latest instalment in the Microsoft operating system family. Following on from the much maligned Windows Vista, Windows 7 has a much warmer reception from critics and consumers.

Time synchronisation on Windows 7 is extremely straight forward as the protocol NTP (Network Time Protocol) is built-in to Windows 7 and the operating system automatically synchronises the computer’s clock by connecting to the Microsoft time service

This is useful for many home users but the synchronisation across the Internet is not secure enough for a computer network for the following reason:

To connect to any Internet time source such as a post is required to be left open in the firewall. As with any open port in a network firewall this can be used as a point of entry by a malicious user or some malicious software.

The time synchronisation facility in Windows 7 can be turned off and is quite simple to do by opening the time and date dialogue box and uncheck the synchronization box.

However, time synchronisation on a network is vital so if the Internet time service is turned off it needs to be replaced with a secure and accurate source of time.

By far the best way of doing this is to use a time source that’s external to the network (and the firewall).

The simplest, safest and most accurate way of synchronizing a Windows 7 network is to use a dedicated NTP server. These devices use a time reference from either a radio frequency (usually distributed by national physics laboratories such as Britain’s NPL and America’s NIST) or from the GPS satellite network.

Because both these reference sources come from atomic clock sources they are incredibly accurate too and a Windows 7 network that consists of hundreds of machines can be synchronised to within a few milliseconds of the global timescale UTC (Coordinated Universal Time) by utilising just one NTP time server.

Common Time Synchronization Pitfalls Finding UTC

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Time synchronization can be a headache for many network administrators attempting to synchronize a network for the first time. There are many pitfalls that an unaware network administrator can fall into when attempting to get every machine on a network to synchronize to the same time.

The first problem many network administrators make is the selection of the time source. UTC (Coordinated Universal Time) is a global timescale and is used throughout the world as a basis for time synchronization as it doesn’t rely on time zones enabling the global community to base itself on one timescale.

UTC is also controlled by a constellation of atomic clocks which ensures its accuracy; however, it is regularly adjusted to ensure that it matches mean solar time by the addition of leap seconds which are added to counter the natural slowing of the Earth’s rotation.

UTC is readily available as a time reference from a number of sources. The Internet is a popular location to receive a UTC time source. However, an Internet time source is located through the network firewall and security issues can arise from having to leave the UDP port open to receive the time requests.

Internet time sources can also be inaccurate and as NTP’s own security system known as NTP authentication cannot work across the Internet further security issues can arise.

A far better solution for getting a source of UTC is to use either the Global Positioning System (GPS) or the long wave radio transmissions broadcast by several national physics laboratories such as NIST in the USA and the UK’s NPL.

Dedicated NTP time servers can receive these secure and authenticated signals and then distribute them amongst all devices on a network.

How Satellite Navigation Works

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Satellite navigational systems, or sat navs, have changed the way we navigate our way around the high roads. Gone are the days when travellers had to have a glove box full of maps and gone too is the need to stop and ask a local for directions.

Satellite navigation means that we an now go from point A to point B confident our systems will take us there and while sat nav systems are not fool proof (we must have all read the stories of people driving over cliffs and into rivers etc), it has certainly revolutionised our wayfinding.

Currently there is only one Global Navigational Satellite System (GNSS) the American run Global Positioning System (GPS). Although, a rival European System (Galileo) is set to go online sometime after 2012 and a both a Russian (GLONASS) and Chinese (COMPASS) system are being developed.

However, all these GNSS networks will operate using the same technology as employed by GPS, and in fact, current GPS systems should be able to utilise these future systems without much alteration.

The GPS system is basically a constellation of satellites (currently there are 27). These satellites each contain onboard an atomic clock (actually two are on most GPS satellites but for the purpose of this explanation only one need be considered). The signals that are transmitted from the GPS satellite contain several pieces of information sent as one integer:

* The time the message was sent

* The orbital position of the satellite (known as the ephemeris)

* The general system health and orbits of the other GPS satellites (known as the almanac)

A satellite navigation receiver, the kind found on the dashbopard of your car, receives this information and using the timing information works out the exact distance from the receiver to the satellite. By using three or more of these signals the exact position can be triangulated (four signals are actually required as height above sea level has to be worked out too).

Because the triangulation works out when the time signal was sent and how long it took to arrive at the receiver, the signals have to be incredibly accurate. Even a second of inaccuracy could see the navigational information out but thousands of kilometres as light, and therefore radio signals, can travel nearly 300,000 km each second.

Currently the GPS satellite network can provide navigational accuracy to within 5 metres which goes to show just how accurate atomic clocks can be.

Setting up Windows XP as an NTP Server

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A network time server or NTP server (Network Time Protocol), is a central computer or server on a network that controls the time and synchronises all machines on that network to it.

Windows XP can be set up to operate as an NTP server to synchronise the rest of the computers and devices on a network. Setting up a Windows XP machine to act as a NTP server involves editing the registry, however, editing an operating system registry can lead to potential problems and should only be conducted by somebody with experience of registry editing.

To configure Windows XP as an NTP server the first thing to do is to open the registry editor in Windows. This is done by clicking the Start button and selecting “Run” from the menu. Enter “regedit” in the run menu and press return. This should open the Windows registry editor.

Select the: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer\ folder in the left hand pane. This folder holds the values for the NTP server.

Right-click the “Enabled” key in the right window pane and select “Properties”. This should open a dialog box where you can alter the value of the registry key. Enter “1” in the window, setting the value to “True” which turns the XP computer into a time server.

Close the registry and open the DOS command prompt by clicking the Windows Start button, selecting “Run”. Then type “cmd” in the text box and press return.

Type “Net stop w32time” into the command prompt and press “Enter.” Now type “net start w32time” this will restart the time server for Windows XP.

However, the XP machine, which is now set as a NTP server, will merely distribute the time it currently holds. If this time is inaccurate then it will inaccurate time that is distributed amongst the network.

To ensure an accurate and secure source of time is used then a dedicated NTP time server that receives the time from an atomic clock source should be used.

Europes GPS System is starting to Take Shape

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Following years of wrangling and uncertainty, the European equivalent to the GPS (Global Positioning System), is finally beginning to take shape. The European Galileo system, which will complement the current USA system, is a step closer to completion.

Galileo, which will be the first operational global navigational satellite system (GNSS) outside the United States will provide positioning information for satellite navigation machines and timing information for GPS NTP servers (Network Time Protocol).

The system, being designed and manufactured by the European Space Agency (ESA) and the European Union (EU) and when it is operational it is expected to improve the availability and accuracy of timing and navigation signals transmitted from space.

They system has been dogged in political wrangling and uncertainty since its inception nearly a decade ago. Objections from the US that they will lose the ability top switch off GPS in times of military need; and economic restraints across Europe, meant that the project was nearly shelved several times.

However, the first four satellites are being finalised in a laboratory in southern England. These In-Orbit Validation (IOV) satellites will form a mini-constellation in the sky and prove the Galileo concept by transmitting the first signals so the European system can become a reality.

The rest of the satellite network should follow shortly after and. Galileo should eventually comprise over 30 of them which means that users of satellite navigation systems of GPS NTP time servers should get quicker fixes be able to locate their positions with an error of one metre compared with the current GPS-only error of five.