Common Issues in Time Synchronisation

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Time synchronization is essential in modern computer networking especially with the amount of time sensitive transactions conducted over the internet these days. Without adequate synchronization computer systems will:

  • Be vulnerable to malicious attacks
  • Susceptible to data loss
  • Unable to conduct time sensitive transactions
  • Difficult to debug

Fortunately ensuring a computer network is accurately synchronized is relatively straight forward. There different methods of synchronizing a network to the global timescale UTC (Coordinated Universal Time) but occasionally some common issues do arise.

My dedicated time server is unable to receive a signal

Dedicated NTP time servers receive the time from either long wave transmissions or GPS networks. If using a GPS NTP server then a GPS antenna needs to be situated on a roof to obtain a clear view of the sky. However, a NTP radio receiver does not need a roof mounted aerial although the signal can be vulnerable to interference and the correct angle toward the transmitter should be attained.

I am using a public time server across the Internet but my devices are not synchronised.

As public time servers can be used by anyone they can receive high levels of traffic. This can cause problems with bandwidth and mean that your time requests can’t get through. Public NTP servers can also fall victim to DDoS attacks and some high profile incidents of NTP vandalism have occurred.

Internet time servers are also stratum 2 devices, in other words they themselves have to connect to a time server to receive the correct time and because of this some online time references are wildly inaccurate.

*NB – internet time servers are also incapable of being authenticated to allow NTP to establish if the time source is coming from where it claims to be, combined with the problem of ensuring the firewall is open to receive the time requests, can mean that internet time servers present a clear risk to security.

The time on my computer seems to be off by a second to standard UTC time

You need to check if a recent leap second has been added to UTC. Leap seconds are added once or twice a year to ensure UTC and the Earth’s rotation match. Some time servers experience difficulties in making the leap second adjustment.

Atomic Clock Synchronization made easy with a NTP Time Server

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Atomic clocks are the ultimate in timekeeping devices. Their accuracy is incredible as an atomic clock will not drift by as much as a second within a million years, and when this is compared to the next best chronometers, such as electronic clock that can drift by a second in a week, an atomic clock is incredibly more precise.

Atomic clocks are used the world over and are the heart of many modern technologies making capable a multitude of applications that we take for granted. Internet trading, satellite navigation, air traffic control and international banking are all industries that rely heavily on

They also govern the world’s timescale, UTC (Coordinated Universal Time) which is kept true by a constellation of these clocks (although UTC has to be adjusted to accommodate the slowing of the Earth’s spin by adding leap seconds).

Computer networks are often required to run synchronized to UTC. This synchronisation is vital in networks that conduct time sensitive transactions or require high levels of security.

A computer network without adequate time synchronization can cause many issues including:

Loss of data

  • Difficulties in identifying and logging errors
  • Increased risk of security breaches.
  • Unable to conduct time sensitive transactions

For these reasons many computer networks have to be synchronized to a source of UTC and kept as accurate as possible. And although atomic clocks are large bulky devices kept in the confines of physics laboratories, using them as a source of time is incredibly simple.

Network Time Protocol (NTP) is a software protocol designed solely for the synchronisation of networks and computer systems and by using a dedicated NTP server the time from an atomic clock can be received by the time server and distributed around the network using NTP.

NTP servers use radio frequencies and more commonly the GPS satellite signals to receive the atomic clock timing signals which is then spread throughout the network with NTP regularly adjusting each device to ensure it is as accurate as possible.

Five Reasons why your Network needs a NTP Server

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Accurate timekeeping if quite often overlooked as a priority for network administrators yet many are risking both security and data loss by not ensuring their networks are synchronised as precisely as possible.

Computers do have their own hardware clocks but these are often just simple electronic oscillators such as exist in digital watches and unfortunately these system clocks are prone to drift, often by as much as several seconds in a week.

Running different machines on a network that have different times – even by only a few seconds – can cause havoc as so many computer tasks rely on time. Time, in the form of timestamps, is the only reference computers use to distinguish between different events and failure to accurately synchronize a network can lead to all sorts of untold problems.

Here are some of the major reasons why your network should be synchronised using Network Time Protocol, prefasbly with a NTP time server.

Data Backups – vital to safeguard data in any business or organization, a lack of synchronisation can lead to not only back ups failing but older versions of files replacing more modern versions.

Malicious Attacks – no matter how secure a network, somebody, somewhere will eventually gain access to your network but without accurate synchronisation it may become impossible to discover what compromises have taken place and it will also give any unauthorised users extra time inside a network to wreak havoc.

Error logging – when faults occur, and they inevitably do, the system logs contain all the information to identify and correct problems. However, if the system logs are not synchronised it can sometimes be impossible to figure out what went wrong and when.

Online Trading – Buying and selling on the internet is now commonplace and in some businesses thousands of online transactions are conducted every second from seat reservation to buying of shares and a lack of accurate synchronisation can result in all sorts of errors in online trading such as items being bought or sold more than once.

Compliance and legality – Many industrial regulations systems require an auditable and accurate method of timing. A unsynchronised network will also be vulnerable to legal issues as the exact time an event is alleged to have taken place can not be proved.

Did you Remember the Leap Second this Year?

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When you counted down on New Year’s Eve to mark the beginning of the next year did you start at 10 or 11? Most revelers would have counted down from ten but they would have been premature this year as there was an extra second added to last year – the leap second.

Leap seconds are normally inserted once or twice a year (normally on New Year’s Eve and in June) to ensure the global timescale UTC (Coordinated Universal Time) coincides with the astronomical day.

Leap seconds have been used since UTC was first implemented and they are a direct result of our accuracy in timekeeping. The problem is that modern atomic clocks are far more accurate timekeeping devices than the earth itself. It was noticed when atomic clocks were first developed that the length of a day, once thought to be exactly 24 hours, varied.

The variations are caused by the Earth’s rotation which is affected by the moons gravity and tidal forces of the Earth, all of which minutely slow down the earth’s rotation.

This rotational slowing, while only minuscule, if it is not checked then the UTC day would soon drift into the astronomical night (albeit in several thousands of years).

The decision on whether a Leap Second is needed is the remit of the International Earth Rotation Service (IERS), however, Leap Seconds are not popular with everybody and they can cause potential problems when they are introduced.

UTC is used by NTP time servers (Network Time Protocol) as a time reference to synchronise computer networks and other technology and the disruption Leap seconds can cause is seen as not worth the hassle.

However, others, such as astronomers, say that failing to keep UTC in line with the astronomical day would make studying of the heavens nearly impossible.

The last leap second inserted before this one was in 2005 but there have been a total of 23 seconds added to UTC since 1972.

Network Time Protocol Time Synchronisation Made Easy

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One of the most important aspects of networking is keeping all devices synchronised to the correct time. Incorrect network time and lack of synchronisation can play havoc with system processes and can lead to untold errors and problems debugging.

And failing to ensure devices are continually checked to prevent drift can also lead to a synchronised network slowly becoming unsynchronised and leading to the kinds of problems aforementioned.

However, ensuring a network not only has the correct time but that that time is not drifting is achieved using the time protocol NTP.

Network Time Protocol (NTP) is not the only time synchronisation protocol but it is by far the most widely used. It is an open source protocol but is continually updated by a large community of Internet time keepers.

NTP is based around an algorithm that can work out the correct and most accurate time from a range of sources. NTP allows a single time source to be used by a network of hundreds and thousands of machines and it can keep each one accurate to that time source to within a few milliseconds.

The easiest way of synchronising a network with NTP is to use a NTP time server, also known as a network time server.

NTP servers use an external source of time, either from the GPS network (Global Positioning System), or from broadcasts from national physics laboratories such as NIST in the US or NPL in the UK.

These time signals are generated by atomic clocks which are many times more accurate than the clocks on computers and servers. NTP will distribute this atomic clock time to all devices on a network it will then keep checking each device to ensure there is no drift and correcting the device if there is.

Configuring a Network to use a NTP Server Part two: Distributing the Time

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NTP (Network Time Protocol) is the protocol designed for time distribution amongst a network. NTP is hierarchical. It organises a network into strata, which are the distance from a clock source and the device.

A dedicated NTP server that receives the time from a UTC source such as GPS or the national time and frequency signals is regarded as a stratum 1 device. Any device that is connected to a NTP server becomes a stratum 2 device and devices farther down the chain become stratum 2, 3 and so on.

Stratum layers exist to prevent cyclical dependencies in the hierarchy. But the stratum level is not an indication of quality or reliability.

NTP checks the time on all devices on the network it then adjusts the time according to how much drift it discovers. Yet NTP goes further than just checking the time on a the reference clock, the NTP program exchanges time information by packets (blocks of data) but refuses to believe the time it is told until several exchanges have taken place, each passing a set of tests known asprotocol specifications. It often takes about five good samples until a NTP server is accepted as a timing source.

NTP uses timestamps to represent the current time the day. As time is linear, each timestamp is always greater than the previous one. NTP timestamps are in two formats but they relay the seconds from a set point in time (known as the prime epoch, set at 00:00 1 January 1900 for UTC) The NTP algorithm then uses this timestamp to determine the amount to advance or retreat the system or network clock.

NTP analyses the timestamp values including the frequency of errors and the stability. A NTP server will maintain an estimate of the quality of both its reference clocks and itself.

Time Server Basic Questions Answered

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What is a time server?

A time server is a device that receives and distributes a single time source across a computer network for the purposes of time synchronization. These devices are often referred to as a NTP server, NTP time server, network time server or dedicated time server.

And NTP?

NTP – Network Time Protocol is a set of software instructions designed to transfer and synchronize time across LANs (Local Area Network) or WANS (Wider Area Network). NTP is one of the oldest known protocols in use today and is by far the most commonly used time synchronization application.

What timescale should I use?

Coordinated Universal Time (UTC) is a global timescale based on the time told by atomic clocks. UTC doesn’t take into account time zones and is therefore ideal for network applications as in principle by synchronizing a network to UTC you are in effect synchronizing it to every other network that utilises UTC.

Where does a time server receive the time from?

A time server can utilise the time from anywhere such as a wrist watch or wall clock. However, any sensible network administrator would opt to use a source of UTC time to ensure the network is as accurate as possible. UTC is available from several ready sources. The most used is perhaps the internet. There are many ‘time servers’ on the internet that distribute UTC time. Unfortunately, many are not at all accurate an in using an internet time source you could be leaving the network vulnerable as malicious users can take advantage of the open port in the firewall where the timing information flows.

It is far better to use a dedicated NTP time server that receives the UTC time signal external to the network and firewall. The best methods for doing this is to either use the GPS signals transmitted from space or the national time and frequency transmissions broadcast by several countries in long wave.

Using NTP Networks

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Network Time Protocol is by far the most widely used application for synchronizing computer time across local area networks and wider areas networks (LANs and WANs). The principles behind NTP are fairly simple. It checks the time on a system clock and compares it with an authoritative, single source of time, making corrections to the devices to ensure they are all synchronized to the time source.

Selecting the time source to use is perhaps the fundamentally most important thing in setting up a NTP network. Most network administrators opt, quite rightly to use a source of UTC time (Coordinated Universal Time). This is a global timescale and means that a computer network synchronized to UTC is not only using the same timescale as every other UTC synchronized network but also there is no need to worry about different time zones around the globe.

NTP uses different layers, known as strata, to determine the closeness and therefore accuracy, to a time source. As UTC is governed by atomic clocks, any atomic clock giving out a time signal is referred to as stratum 0 and any device that receives the time directly from an atomic clock is stratum 1. Stratum 2 devices are devices that receive the time from stratum 1 and so on. NTP supports over 16 different stratum levels although accuracy and reliable decrease with each stratum layer further away you get.

Man network administrators opt to use an internet source of UTC time. Apart from the security risks of using a time source from the internet and allowing it access through your firewall. Internet time servers are also stratum 2 devices in that they are normally servers that receive the time from single stratum 1 device.

A dedicated NTP time server on the other had are stratum 1 devices in themselves. They receive the time directly from atomic clocks, either via GPS or long wave radio transmissions. This makes them far more secure than internet providers as the time source is external to the network (and firewall) but also it makes them more accurate.

With a stratum 1 time server a network can be synchronized to within a few milliseconds of UTC without risk of compromising your security.

Using a NTP Server in your Network

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The Network Time Protocol server is used in computer networks all over the world. It keeps an entire network’s systems and devices synchronised to the same time, normally a source of UTC (Coordinated Universal Time).

But is a NTP time server a necessary requirement and can your computer network survive without one?  The short answer is perhaps yes, a computer network can survive without a NTP server but the consequences can be dramatic.

Computers are meant to make our lives easier but any network administrator will tell you they can cause an awful amount of difficulty when they inevitably go wrong and without adequate time synchronisation, identifying an error and putting it right can be nearly impossible.

Computers use the time in the form of a timestamp as the only reference they have to distinguish between two events. Whilst computers and networks will still function without adequate synchronisation they are extremely vulnerable. Not only is locating and correcting errors extremely difficult if machines are not synchronised the network will be vulnerable to malicious users and viral software that can take advantage of it.

Furthermore, failing to synchronise to UTC can cause problems if the network is to communicate with other networks that are synchronised. Any time sensitive transactions could fail and the system could be open to potential fraud or other legal implications as proving the time of a transaction could be near impossible.

NTP servers are easy to install and receive the UTC time signal from either long wave transmissions or the GPS satellite network which they then distribute amongst the network’s machines. As a dedicated NTP time server operates externally to the network firewall it does so without compromising security.

Bringing Atomic Clock Precision to your Desktop

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Atomic clocks have been a huge influence on our modern lives with many of the technologies that have revolutionised the way we live our lives relying on their ultra precise time keeping abilities.

Atomic clocks are far different to other chronometers; a normal watch or clock will keep time fairly accurately but will lose second or two each day. An atomic clock on the other hand will not lose a second in millions of years.

In fact it is fair to say that an atomic clock doesn’t measure time but is the foundations we base our perceptions of time on. Let me explain, time, as Einstein demonstrated, is relative and the only constant in the universe is the speed of light (though a vacuum).

Measuring time with any real precision is therefore difficult as even the gravity on Earth skews time, slowing it down. It is also almost impossible to base time on any point of reference. Historically we have always used the revolution of the earth and reference to the celestial bodies as a basis for our time telling (24 hours in a day = one revolution of the Earth, 365 days = one revolution of the earth around the Sun etc).

Unfortunately the Earth’s rotation is not an accurate frame of reference to base our time keeping on. The earth slows down and speeds up in its revolution meaning some days are longer than others.

Atomic clocks however, used the resonance of atoms (normally caesium) at particular energy states. As these atoms vibrate at exact frequencies (or an exact number of times) this can be used as a basis for telling time. So after the development of the atomic clock the second has been defined as over 9 billion resonance ’ticks’ of the caesium atom.

The ultra precise nature of atomic clocks is the basis for technologies such as satellite navigation (GPS), air traffic control and internet trading. It is possible to use the precise nature of atomic clocks to synchronise computer networks too. All that is needed is a NTP time server (Network Time Protocol).
NTP servers receive the time from atomic clocks via a broadcast signal or the GPS network they then distribute it amongst a network ensuring all devices have the exact same, ultra precise time.