Posts by: Stuart

The Effects of No Time Signal

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NTP servers (Network Time Protocol) are an essential tool in the modern computer network. They control the time, ensuring every device on the network is synchronised.

Because of the importance of time in controlling nearly every aspect of computer networking accurate and synchronised time is essential which is why so many system administrators deploy a NTP time server.

These time servers use a single time source as a base to set all the clocks on a network to; the time is often got from the GPS network or radio signals broadcast from physics laboratories such as NPL in the UK (whose signal is broadcast from Cumbria).

Once this signal is received by the time server, the time protocol NTP then distributes it around the network – comparing the system clock of every device to the time reference and adjusting each device. By regularly assessing the drift of these devices and correcting for them NTP keeps clocks accurate to within milliseconds of the time signal and when this signal emanates from an atomic clock – it ensures the network is as accurate as physically possible, but what happens if you lose the time signal?

Damaged GPS antennas, maintenance of time signal transmitters or technical faults can lead to a NTP time sever failing to receive a time signal. Often, this is only temporary and normal service is resumed within a few hours but what happens if it doesn’t, and what is the effect of having a failed time signal?

Fortunately, NTP has back-up systems for just such an eventuality. If a time signal fails and there is no other source of time, NTP cleverly uses the average time from all the clocks on its network. So if some clocks have drifted a few milliseconds faster, and others a few milliseconds slower – then NTP takes the average of this drift ensuring that the time remains accurate for as long as possible.

Even if a signal has failed for several days – or even weeks – without knowledge of the system users, this does not mean the network will drift apart. NTP will still keep the entire network synchronised together, using the average drift, and while the longer the time signal remains off the les accurate the network will be it can still provide millisecond accuracy even after a few days of no time reference.

Time Synchronisation Getting it Right

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Time is essential for computers, networks and technology. It is the only reference technology has to ascertain if a task has happened or is due to take place. As time, in the from of timestamps, is so important for technology, when there is uncertainty over time, due to different devices on a network having different times, it can cause untold errors.

The problem with time in computing is that all devices, from routers to desktop PCs, have their own onboard timepiece that governs the system clocks. These system clocks are just normal electronic oscillators, they type commonly found in battery powered watches, and while these are adequate for humans to tell the time, the drifting of these clocks can see devices on a network, seconds and even minutes out of sync.

There are two rules for time synchronisation:

  • All devices on a network should be synchronised together
  • The network should be synchronised to UTC (Coordinated Universal Time)

 

NTP

To synchronise a network you need to make use of Network Time Protocol (NTP). NTP is designed for accurate network time synchronisation.  IT works by using a single source of time which it then distributes it to all devices on the NTP network.

NTP continually checks the devices for any drift and then adjusts to ensure the entire network is within a few milliseconds of the reference time.

UTC

Coordinated Universal Time is a global timescale that is kept true by atomic clocks. By synchronising a network to UTC you are in effect ensuring your network is synchronised to every other UTC network on the planet.

Using UTC as a reference source is a simple affair too. NTP time servers are the best way to find a secure source of UTC time. They use either GPS (Global Positioning System) as a source of this atomic clock time or specialist radio signals keeping the UTC time source external to the network for security reasons.

A single NTP server can synchronise a network of hundreds and even thousands of devices ensuring the entire network is to within a few milliseconds of UTC.

The Time According to UTC (Coordinated Universal Time)

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The modern world is a small one. These days, in business you are just as likely to be communicating across the Atlantic as you are trading with you neighbour but this can cause difficulties – as anybody trying to get hold of somebody across the other-side of the world will know.

The problem, of course, is time. There are 24 time zones on Earth which means that people you may wish to talk to across the other side of the world, are in bed when you are awake – and vice versa.

Communication is not jus a problem for us humans either; much of our communication is conducted through computers and other technologies that can cause even more problems. Not just because time-zones are different but clocks, whether they are those that power a computer, or an office wall clock, can drift.

Time synchronisation is therefore important to ensure that the device you are communicating with has the same time otherwise whatever transaction you are conducting may result in errors such as the application failing, data getting lost or the machines believing an action has taken place  when it has not.

Coordinated Universal Time

Coordinated Universal Time (UTC) is an international timescale. It pays no heed to time-zones and is kept true by a constellation of atomic clocks – accurate timepieces that do not suffer from drift.

UTC also compensates for the slowing of the Earth’s spin by adding leap seconds to ensure there is no drift that would eventually cause noon to drift towards night (albeit in many millennia; so slow is the slowing of the Earth).

Most technologies and computer networks across the globe use UTC as their source of time, making global communication more feasible.

Network Time Protocol and NTP Time Servers

Receiving UTC time for a computer network is the job of the NTP time server. These devices use Network Time Protocol to distribute the time to all technologies on the NTP network. NTP time servers receive the source of time from a number of different sources.

  • The internet – although  internet time sources can be insecure and unreliable
  • The GPS (Global Positioning System) – using the onboard atomic clocks from navigation satellites.
  • Radio signals – broadcast by national physics laboratories like NPL and NIST.

The Hierarchy of a NTP Time Server Stratum Levels Explained

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When it comes to time synchronisation and using Network Time Protocol (NTP) to ensure accuracy on a computer network, it is important to understand the hierarchy of NTP and how it affects distance and accuracy.

NTP has a hierarchical structure known as stratum levels. In principle the lower the stratum number the closer the device is (in accuracy terms) to an original time source.

NTP time servers work by receiving a single time source and using this as a basis for all time on the network, however, a synchronised network will be only as accurate as the original time source and this is where stratum levels come in.

And atomic clock, either one sat in a large scale physics laboratory, or those aboard GPS satellites, are stratum 0 devices. In other words these are the devices that actually generate the time.

Stratum 1 devices are NTP time servers that get their source of time directly from these stratum 0 atomic clocks. Either by using a GPS receiver or a radio referenced NTP server, a stratum 1 device is as accurate as you can get without having your own multi-million dollar atomic clock in the server room. A stratum 1 NTP time server will typically be accurate to within a millisecond of the atomic clock time.

Stratum 2 devices are the next step down on stratum level chain. These are time servers that receive their time from a stratum 1 device. Most online time servers, for instance, are stratum 2 devices, getting their time from another NTP time server. Stratum 2 devices are obviously further away from the original time source and therefore are not quite as accurate.

The stratum levels on an NTP network continue on, with devices connecting to devices going all the way down to stratum 10, 11, 12 and so on – obviously the more links in the chain the less accurate the device will be.

Dedicated stratum 1 NTP time servers are by far the most accurate, reliable and secure method of synchronising a computer network and no business network should really be without one.

NTP Servers Which Signal is Best Radio or GPS?

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NTP time servers (Network Time Protocol) are an essential aspect of any computer or technology network. So many applications require accurate timing information that failing to synchronize a network adequately and precisely can lead to all sorts of errors and problems – especially when communicating with other networks.

Accuracy, when it comes to time synchronization, means only one thing – atomic clocks. No other method of keeping time is as accurate or reliable as an atomic clock. In comparison to an electronic clock, such as a digital watch, which will lose up to a second a day – an atomic clock will remain accurate to a second over 100,000 years.

Atomic clocks are not something that can be housed in an average server room though; atomic clocks are very expensive, fragile and require full time technicians to control so are usually only found in large scale physics laboratories such as the ones run by NIST (National Institute of Standards and Time – USA) and NPL (National Physical Laboratory – UK).

Getting a source of accurate time from an atomic clock is relatively easy. For a secure and reliable source of atomic clock time there are only two options (the internet can neither be described as secure nor reliable as a source of time):

  • GPS time
  • UTC time broadcast on long-wave

GPS time, from the USA’s Global Positioning System, is a time stamp generated onboard the atomic clocks on the satellites. There is one distinct advantage about using GPS as a source of time: it is available anywhere on the planet.

All that is required to receive and utilise GPS time is a GPS time sever and antenna; a good clear view of the sky is also needed for an assured signal. Whilst not strictly UTC time (Coordinated Universal Time) being broadcast by GPS (UTC has had 17 leap seconds added to it since the satellites were launched) the timestamp included the information needed for NTP to convert it to the universal time standard.

UTC, however, is broadcast directly from physics laboratories and is available by using a radio referenced NTP server. These signals are not available everywhere but in the USA (the signal is known as WWVB) and most of Europe (MSF and DCF) are covered. These too are highly accurate atomic clock generated time sources and as both methods come from a secure source the computer network will remain secure.

The Time According to Cumbria Using the UKs MSF Time and Frequency Signal

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Getting an accurate source of time for computer networks and other technologies is increasingly becoming more important. As technologies advance and global communications mean that we are just as liable to communicate with technology across the other side of the planet as we are at home.

The need for accurate time is therefore essential if you wish to prevent time sensitive applications on your network failing or to avoid debugging problems – not too mention keeping your system secure.

NTP time servers (Network Time Protocol) are common devices that many computer networks use to provide a source of accurate time as NTP is able to ensure entire networks are synchronised to just a few milliseconds to the time reference.

The time reference that NTP servers use can come from several locations:

  • The internet
  • GPS satellite
  • And National Physical Laboratories

In the UK, the National Physical Laboratory (NPL) produce a time signal that can be received by radio referenced NTP time servers. This used to be broadcast from rugby in central England but in recent years the transmission has been moved to Cumbria.

The Cumbrian signal, known as MSF, is broadcast from Anthorn with a signal strength of 100 microvolts per metre at a distance of 1000 km. This should mean that the signal is available everywhere in the UK; however, this is not strictly the case as many MSF clocks and time servers can run into trouble when first trying to receive this atomic clock generated signal.

However, a simple checklist should ensure that no matter what your location you should be able to receive a signal to your MSF clock or NTP time server:

  • Check the power. Perhaps the most common problem ensure the battery is inserted and if the clock uses both mains power and a battery, remember to switch the mains power on. It can take quite a few minutes for the clock to pick up the MSF signal, so be patient.
  • Try rotating the clock or time server. As the MSF signal is long wave the antenna needs to be perpendicular to the signal for best reception.
  • If all else fails move the clock or time server to a different location. The signal can be blocked by local interference from electrical and mechanical devices.

* Note the MSF signal is down for scheduled maintenence on Tuesday 9 September 2010 from 10:00 BST to 14:00 BST

 

GPS Time Servers Precise Time all the Time

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Keeping computer networks accurate and synchronised can’t be emphasised highly enough. Accurate time is essential in the modern global economy as computer networks across the globe are required to constantly talk to each other.

Failing to ensure a network is accurate and precise can lead to headache after headache: transactions can fail, data can get lost, and error logging and debugging can be virtually impossible.

Atomic Clocks

Atomic clocks form the basis of the global timescale – UTC (Coordinated Universal Time). UTC is used across the globe by technology and computer networks enabling the entire commercial and technological world to communicate in synchronicity together.

But as atomic clocks are highly technical (and expensive) pieces of hardware that require a team of technicians to control – where do people get a source of such accurate time?

The answer is quite simple; atomic clock timestamps are transmitted by physics laboratories and are avlaible from a whole host of sources – kept accurate by the time software NTP (Network Time Protocol).

NTP Time Servers

The most common location for sources of atomic clock generated UTC is the internet. A whole host of online time servers are avlaible for synchronisation but these can vary in their accuracy and precision. Furthermore, using a source of internet time can create vulnerabilities in the network as the firewall has to allow these timestamps through and therefore can be utilised by viruses and malicious software.

By far the most secure and accurate method of receiving a source of atomic clock generated time is to utilise the GPS network (Global Positioning System).

GPS time servers are unique in that as long as there is a clear view of the sky they can receive a source of time – anywhere on the globe, 24 hours-a-day, 365 days a year.

They are also highly accurate with a single GPS NTP time server able to synchronise entire networks to just a few milliseconds of UTC.

How accurate does NTP Synchronisation need to be?

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Computers advance at a remarkable rate; in effect computers double in power, speed and memory every five years, and with such advances in technology many people assume that the clocks that control the time of a computer are just as powerful.

However, nothing could be further from the truth; most system clocks are crude crystal oscillators that are prone to drift, which is why computer time synchronisation is so important.

In modern computing, nearly every aspect of managing a network is reliant on time. Timestamps are the only frame of reference a computer has to ascertain if an event has occurred, is due to, or shouldn’t occur.

From debugging, to conducting time sensitive transactions over the internet, accurate time is essential. But how accurate does it have to be?

Coordinated Universal Time

Coordinated Universal Time (UTC) is a global timescale derived from atomic clocks. UTC was developed to allow technological devices, such as computer networks, to communicate with a single time.

Most computer networks use time servers governed by NTP (Network Time Protocol) to distribute UTC across the network. For most applications, accuracy to within a few hundred milliseconds is sufficient – but achieving this accuracy is where the difficulty lies.

Getting an accurate source of time

There are several options for synchronizing a network to UTC. Firstly, there is the internet. The internet is awash with time servers that proclaim to supply an accurate source of UTC. However, surveys of these online sources of time indicate that many of them are wholly inaccurate being seconds, minutes and even days out.

And even the most accurate and respected sources from NIST (National Institute of Standards and Time) and Microsoft, can vary depending on the distance your network is away.

Dedicated Time servers

Dedicated NTP time servers use a more direct approach to achieve accurate synchronisation. Using atomic clocks, either from the GPS satellite network or from physics laboratories (like NIST and the UKs NPL); the time is beamed directly to the NTP time server that is connected to the network.

Because dedicated devices like this receive the time directly from atomic clocks they are incredibly accurate, enabling the entire network to be synchronised to within just a few milliseconds of NTP.

Solar Flares and the Vulnerability of GPS

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Whilst GPS is commonly associated with satellite navigation and wayfinding, many technologies and computer networks rely on the GPS satellite system for a source of accurate time.

GPS time servers utilise the onboard atomic clocks of the global positing satellites and use this stable and accurate time source as a basis for their NTP synchronisation (Network Time Protocol)

GPS has become the preferred source of atomic clock time for many network operators. There are other methods where UTC (Coordinated Universal Time) can be used; radio signals and across the internet to name but two sources, but none is as secure or readily available as GPS.

Unlike radio signals, GPS is available everywhere on the planet, is never down for scheduled maintenance and is not commonly vulnerable to interference. It also doesn’t have any security implications like connecting across an internet firewall to an online time server can.

However, this doesn’t mean GPS is completely invulnerable as recent news reports have suggested.
It has been recently reported that a sunspot (sunspot 1092) the size of the Earth has flared up and a massive coronal ejection (solar flare), described in the press as a “solar tsunami” which was suggested to be large enough to satellites and wreck power and communications grids.

Solar activity, such as sunspots and solar flares (ejected hot plumes of plasma and radiation from the sun), have long been known to be able to damage and even disable satellites.

GPS is particularly vulnerable because of the high orbits of geostationary satellites (some 22,000 miles up) this leaves them unprotected by the earth’s magnetic field.

However, following the recent solar activity there has been no reported damage to the GPS system but as so many people rely on satellite navigation and GPS time for NTP servers could a future solar storm lead to havoc on Earth?

Well the short answer is yes; GPS satellites have been in orbit for several decades and while redundant satellites were introduced into the system many have been used up due to previous failures and it would only take a couple of disabled satellite to cause real problems for the network.

Fortunately, help is at hand as the Europeans, Russians and Chinese are all working on their own GPS equivalents which should work hand-in-hand with the American GPS network allowing GPS receivers to pick and choose from all four GNSS networks (Global Navigational Satellite Systems) ensuring that even if a really violent solar storm hits in the future there will be more than enough geo stationary satellites to ensure no loss of signal.

Using Windows 7 and Reasons Your Network Still Needs an NTP Server

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Time synchronisation becomes more and more relevant as we become more dependent on the internet. With so many time sensitive transactions conducted across the globe, from banking and commerce to sending emails, the correct and accurate time is vital in preventing errors and ensuring security.

Increasingly, more and more people are relying on sources of internet time especially with many of the modern flavours of Microsoft’s Windows such as Windows 7 having NTP and time synchronisation abilities already installed.

Windows 7 and Time Synchronisation

Windows 7 will, straight out of the box, attempt to find a source of internet time; however, for a networked machine this does not necessarily mean the computer will be synchronised accurately or securely.

Internet time sources can be wholly unreliable and unsecure for a modern computer network. Internet time has to come through the firewall and as a gap is left for these time codes to come through, malicious software can take advantage of this firewall hole too.

Not only can the accuracy of these devices vary depending on the distance away your network is but also an internet time source very rarely comes direct from an atomic clock.

In fact, most internet time sources are known as stratum 2 devices. This means they connect to another device – a stratum 1 device – namely a NTP time server which gets the time directly from the clock and transmits it to the stratum 2 device.

Stratum 1 NTP time servers

For true accuracy and security, there is no replacement for your network’s own stratum 1 NTP server. Not only are these devices secure, receiving a time source externally to the firewall (often using GPS) but also they receive these signals direct from atomic clocks (The GPS satellite that transmits this signal has an onboard atomic clock that generates the time.