Posts by: Richard N Williams

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.

IEEE 1588 Time Protocol Promises More Accurate Time Synchronisation

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Despite being around for over twenty years, the current favoured time protocol by most networks, NTP (Network Time Protocol) has some competition.

Currently NTP is used to synchonise computer networks using network time servers (NTP servers). Currently NTP can synchronise a computer network to a few milliseconds.

The Precision Time Protocol (PTP) or IEEE 1588 has been developed for local systems requiring very high accuracy (to nano-second level). Currently this type of accuracy is beyond the capabilities of NTP.

PTP requires a master and slave relation ship in the network. A two-step process is required to synchronise devices using the IEEE 1588 (PTP). First, determination of which device is the master is required then the offsets and natural network delays are measured. PTP uses the Best Master Clock algorithm (BMC) to establish which clock on the network is the most accurate and it becomes the master whilst all other clocks become slaves and synchronise to this master.

IEEE (Institute of Electrical and Electronic Engineers) describes IEEE 1588 or (PTP) as designed to “fill a niche not well served by either of the two dominant protocols, NTP and GPS.  IEEE 1588 is designed for local systems requiring very high accuracies beyond those attainable using NTP. It is also designed for applications that cannot bear the cost of a GPS receiver at each node, or for which GPS signals are inaccessible.” (quoted in Wikipedia)

PTP can provide accuracy to a few nano-seconds but this type of accuracy is not required by most network users however, the target use of PTP appears to be mobile broadband and other mobile technologies as PTP supports time-of-day information, used by billing and service level agreement reporting functions in mobile networks.

Secrets of Time Synchronization Software

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Time synchronization is a crucial aspect of computer networking. Ensuring all machines on a network are synchronised to the global timescale, UTC (Coordinated Universal Time), otherwise time sensitive transactions with other networks would be impossible.

Time synchronization is made easy thanks to the Network Time Protocol (NTP) which was devised in the early days of the Internet for that very purpose. It works be utilising a single time source (usually UTC) which is then distributed amongst all devices on the NTP network.

The UTC time source is often taken from the Internet on networks where security is not a great issue but as this involves leaving an open port in a network firewall for many networks the vulnerability this can leave isn’t worth the risk.

Dedicated network time servers (often referred to as NTP servers) are used by many networks as a secure and even more accurate method of receiving UTC. These devices receive the UTC time direct from an atomic clock source.

Furthermore, these dedicated time servers operate external to the firewall and network and use sources such as GPS or radio frequencies to pick up the time codes.

For ease of synchronisation there are various time synchronisation software packages that run hand-in-hand with NTP and allow, through browser interfaces, easy configuration of the time synchronization throughout the network.

Whilst these time synchronisation software packages aren’t essential in using most NTP servers, the standard software installed in operating systems is often lacking or quite complicated.

Most specialist producers of dedicated network time servers will produce a times service client to allow configuration and these are probably best suited for the device from that suppler. However, there are many freeware and open source time synchronisation software packages that are mostly compatible with many NTP servers.

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 time.windows.com.

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 time.windows.com 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.

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.

Auditable Time Synchronization with an NTP Server

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Time synchronization is crucial for many modern applications. Whilst computer networks all have to be running in perfect time to prevent errors and ensure security other systems require time synchronization for legal reasons.

Average speed cameras, traffic light cameras, CCTV, parking meters and alarm systems to name but a few, all require accurate time synchronization not just to ensure the correct operation of the systems but also to provide an auditable and legal trail for use in prosecutions.

Failure to do so can lead to the system being completely useless as any legal case based around the technology would need to be provable.

For instance, a CCTV network that is not synchronized would not be admissible in court, a defendant could easily claim that an image of them on a camera could not be them as they were not in the vicinity at the time and unless the camera system can be audited and proved to be accurate then reasonable doubt would see any case against the suspect dropped.

For this reason, systems like those mentioned above require complete auditable time synchronisation that can be proven beyond reasonable doubt in a court system.

An auditable system of time synchronization is only possible by using a dedicated NTP time server (Network Time Protocol). NTP servers not only provide an accurate method of synchronization being accurate to a few milliseconds they also provide a full audit trail that can’t be disputed.

NTP server systems use the GPS network or specialist radio transmissions to receive the atomic clock time which is so accurate the chance of it being even a second out from UTC time (Universal Coordinated Time) is over 3 billion to one which is even greater than the accuracy of other legal evidences such as DNA.

GPS Atomic Clock Time Signals

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It seems that nearly every car dashboard has a GPS receiver perched on the top. They have become incredibly popular as a navigational tool with many people relying on them solely to work their way around the road networks.

The Global Positioning System has been around for quite a few years now but was originally designed and built for US military applications but was extended for civilian use following an airline disaster.

Whilst it is incredibly useful and convenient a tool, the GPS systems is relatively simple in its operation. The navigation works using a constellation of 30 or so satellites (there are quite a few more that are orbiting but no longer operational).

The signals sent from the satellites contain three pieces of information that are received by the sat nav devices in our cars.

That information includes:

* 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)

The way the navigational information is worked out is by using the information from four satellites. The time the signals left the each of the satellites is recorded by the sat nav receiver and the distance from each satellite is then worked out using this information. By using the information from four satellites it possible to work out exactly where the satellite receiver is, this process is known as triangulation.

However, working out exactly where you are in the world does rely on complete accuracy in the time signals that are broadcast by the satellites. As signals such as the GPS travel at the speed of light (approximately 300,000 km a second through a vacuum) even a one second inaccuracy could see positioning information out by 300 kilometres! Currently the GPS system is accurate to five metres which demonstrates just how accurate the timing information broadcast by the satellites is.

This high level of accuracy is possible because each GPS satellite contains atomic clocks. Atomic clocks are incredibly accurate relying on the unwavering oscillations of atoms to keep time – in fact each GPS satellite will run for over a million years before it will drift by as much as a second (compared to the average electronic watch which will drift by a second in a week or two)

Because of this high level of accuracy the atomic clocks on board GPS satellites can be used as a source of accurate time for the synchronization of computer networks and other devices that require synchronization.

Receiving this time signal requires the use of a NTP GPS server that will synchronize with the satellite and distribute the time to all devices on a network.

Why Bother Using a NTP Time Server?

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Keeping computers synchronized on a network is vitally important, especially if the network in question deals with time sensitive transactions. And failing to keep a network synchronized can cause havoc leading to errors, vulnerabilities and endless problems with debugging.

However with the amount of online time servers available from reputable places such as NIST or Microsoft it is often queried as to why computer networks need to be synchronised to an external NTP time server.

These dedicated NTP devices are often seen as an unnecessary expense and many network administrators simply forgo them and connect to an online time server, after-all, it does the same job doesn’t it?

Actually there are two major reasons why NTP time servers are not only important but essential for most computer networks and to overlook them could be costly in many ways.

Let me explain. The first reason why an external NTP server is important is accuracy. It’s not that internet time sources are generally inaccurate (although many are) but there is the question of distance the time reference has to travel. Furthermore, in times when the connection is lost -whether it’s because of a local connection fault or the time server itself goes down – the network will start to drift until the connection is restored.

Secondly and perhaps most important is the security issues involved in using an Internet time source. The main problem is that if your connection to a time server through the then a open port (UDP 123 fro NTP requests) has to be left open, And as with any open port that can used as a gateway for malicious software and users.

The reason dedicated NTP time servers are essential for computer networks is that they work completely independently and external to the network’s firewall. Instead of accessing a time source across the Internet they use either GPS or radio transmissions to get the time. And in doing so they can provide accurate time all the time without fear of losing a connection or allowing a nasty Trojan through the firewall.