Time Synchronisation

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.

Accurate time on a network is essential for all businesses and institutions. Without an accurately synchronised system a computer network can be vulnerable to all sorts of problems, from malicious hackers and other security threats to fraud and data loss.

Network Time Protocol is the key to keeping accurate time it is a software algorithm that has been constantly developed for over two decades. NTP takes a single time source that is received by the NTP server and distributes it across a network ensuring all machines in that network are running to exact same time.

Whilst NTP can maintain synchronisation of a network to within a few milliseconds it is only as good as the time source it receives. A dedicated NTP server will use a time signal from an external source and so keep the network secure as the firewall will not have to be disturbed.

The two preferred methods for most users of NTP servers is the GPS network (Global Positioning System) or specialist time and frequency transmissions put out be several national physics labs such as the UK’s NPL.

These time signals are UTC (Coordinated Universal Time) which is the world’s civil timescale. An NTP server receiving time source from either a frequency transmission or the GPS network can realistically provide accuracy to within a few milliseconds of UTC

Network time servers are preferred as a synchronisation tool rather than the much simpler internet time servers because they are far more secure. Using the internet as a basis for time information would mean using a source outside the firewall which could allow malicious users to take advantage.

Network time servers on the other hand work inside the firewall, both of these type of signals are incredibly accurate and secure with each method providing millisecond accuracy to UTC. However, there are downsides to both systems. The radio signals broadcast by nation time and frequency laboratories are susceptible to interference and locality, while the GPS signal, although available literally everywhere on the globe can occasional be lost too (often due to bad weather interfering with the line-of-sight GPS signals.

For computer networks where high levels of accuracy are imperative, dual systems are often incorporated. These dual network time servers receive the time signal from both the GPS network and the radio transmissions and select an average for even more accuracy. However, the real advantage of using a dual system is that if one signal fails, for what ever the reason, the network will not have to rely on the inaccurate system clocks as the other method of receiving UTC time should still be operational.

UTC – Coordinated Universal Time (from the French: Universel Temps Coordonné) is a global timescale based on Greenwich Meantime (GMT – from the Greenwich Meridian line where the sun is above at 12 noon). But accounts for the natural slowing of the Earth’s rotation. It is used globally in commerce, computer networks via a NTP server, air-traffic control and the World’s stock exchanges to name but a few of its applications.

UTC is really the only solution for time synchronisation needs. While it is just as possible to synchronise a computer network with an NTP server to a time other than UTC it is pointless. As UTC is utilised by computer networks all across the globe by using a UTC time source that means your network can synchronise with every other network in the world that is synchronised to UTC.

UTC is most commonly received from across the Internet, however, this can only be recommended for small network users where either accuracy or security is an issue. An Internet based UTC source is external to the firewall so will leave a potential hole for malicious users to exploit.

Two secure methods of receiving UTC are commonly available. These are either the GPS network (Global Positioning System) or specialist radio transmission broadcast on long wave from several of the world’s national physics laboratories. The two methods have both advantages and disadvantages which need to be ascertained before a method is selected.

A radio transmission such as the UK’s MSF, the German DCF-77 or the USA’s WWVB signal are vulnerable to local topography although many of these signals can be picked up indoors. Whilst not every country transmits a UTC radio signal around the neighbouring countries that do it is possible to still receive it.

GPS on the other hand is available literally anywhere on the globe. The signal comes directly from above and as long as the antenna has a good clear view of the sky it can be received anywhere. However, as the antenna has to be on a roof looking up this can have logistical problems (particularly for very tall buildings).

Specialist dedicated network time servers are available that can actually receive both methods of UTC but whether using GPS or a radio transmissions synchronisation of a network to within a few milliseconds is possible.

1. The business world is now more global than ever with as much likelihood of  your customer’s being from the other side of the planet as from around the corner. Any transactions conducted virtually across the Internet require adequate time synchronisation otherwise your company can be open to abuse or fraud, customers may claim they paid you at a certain time but how do you ascertain if they have without adequate synchronisation?

2. Does your system conduct time sensitive transactions? Computers have only one reference between events and that is time. If a network is not synchronised then many events and transactions may fail to happen. This can have a knock-on effect as one transaction or event fails so do others and without adequate synchronisation it may be quite a while before anyone realises the errors.

3. Do you have valuable or sensitive data? A lack of synchronisation can often lead to data loss. Storage and retrieval is also time reliant so if a computer believes the time data should have been saved has past then it may assume the data is already saved. The problem can be exaggerated if the data is continually updated as the inaccurate timestamps may mean that certain updates are not completed.

4. Is security important to your business? A lack of time synchronisation can leave a computer network open to malicious users, hackers and even fraud. If computers on a network are running different times then this can be exploited by malicious users and without time synchronisation you may not even know they have been there. A perfectly synchronised network will also offer legal protection with a NTP server (Network Time Protocol) being auditable and unquestioned in a court of law.

5. Is the credibility of your company important? A lack of synchronisation can be extremely costly not just in time and money but also in the credibility of your company. Without synchronisation a network will be vulnerable to mistakes and while these may be easily rectified once a customer has to complain word will soon get out.

Running a synchronised network adhering to Universal Coordinated Time (UTC) the world’s standard timescale is fairly simple. Dedicated NTP time servers that receive a UTC time source from either a radio transmission or the GPS network (Global Positioning System).are readily available, simple to set up, accurate and secure.

Many network administrators boast that there networks are perfectly synchronised because they have an atomic clock as an NTP server. In actual fact as atomic clocks cost several millions of pounds and are quite vast in size it is doubtful the average server room contains such a timepiece.

What in fact they are referring to is that they have an NTP server that receives a timing source from an atomic clock. However, just because atomic clocks are the most accurate chronometers in the world, accurate to a few nanoseconds (billionth of a second) it doesn’t necessarily mean that a network using one as a timing source is receiving the same sort of accuracy

Atomic clocks work on the principle that certain atoms (in most atomic clocks the caesium -133 atom) oscillates at an exact frequency at certain energy levels. In the case of the caesium atom it resonates at exactly 9,192,631,770 every second.  Because of this exact resonance, atomic clocks lose less than a second in millions of years. In fact, the resonance of the caesium atom is so precise that the International System of Units has defined the second as exactly that number of oscillations of the caesium atom.

NTP servers can receive the time from an atomic clock through several sources. Obviously the Internet contains thousands of timing servers, some of which are hooked up to an atomic clock, others however, can be over ten seconds out of sync.

Furthermore, using an Internet timing source can leave a system open to abuse as the timing references cannot be authenticated. Also, the distance from a host, client and server can make dramatic differences in the accuracy.

The most accurate and effective way of receiving a timing source from an atomic clock is to use the national time and frequency broadcast that several country’s national physics laboratories transmit. Alternatively the American GPS (Global Positioning System) transmits the time from its own satellite’s atomic clocks. both methods can provide perfect synchronisation and accuracy to within a few milliseconds.

Network time servers are essential tools for keeping computer networks synchronised and secure. Lack of synchronisation can have many consequences and can leave a computer network vulnerable to security threats and fraud.

Whilst synchronisation over the Internet is available this is not recommended by Microsoft among others are they can leave a system vulnerable to security threats (being as they are external to the network firewall).

A network time server can receive a time signal from two sources: the GPS network (Global Positioning System) a highly accurate method of receiving UTC (Coordinated Universal Time) and available everywhere on the globe (with a good clear view of the sky).

An alternative to the GPS signal in the UK and northern Europe is the MSF long wave signal transmitted by the British National Physical Laboratory (NPL) from Cumbria in Northern England.

The MSF signal provides and accurate, reliable and secure method of receiving UTC and is available across Britain and many parts of northern Europe. With a dedicated MSF compatible network time server a computer network can be synchronised to within a few milliseconds of UTC.

3. Security Breaches:

When networks are not synchronised log files are not recorded properly or in the right order which means that hackers and malicious users can breach security unnoticed. Many security software programs are also reliant on timestamps with anti-virus updates failing to happen or scheduled tasks falling behind. If your network controls time-sensitive transactions then this can even result in fraud if there is a lack of synchronisation.

4. Legal Vulnerability:

Time is not just used by computers to order events it is used in the legal world too. Contracts, receipts, proof-of-purchase are all reliant on time. If a network is not synchronised then it becomes difficult to prove when transactions actually took place and it will prove difficult to audit them. Furthermore, when it comes to serious matters such as fraud or other criminality a dedicated NTP server or other network time server device synchronised to UTC is legally auditable, its time can not be argued with!

5. Company Credibility:

Succumbing to any of these potential hazards can not just have devastating effects on your own business but also that of your clients and suppliers too. And the business grapevine being what it is any potential failing on your part will soon become common knowledge amongst your competitors, customers and suppliers and be seen as bad business practices.

Running a synchronised network adhering to UTC is not difficult. Many network administrators think that synchronisation just means an occasional time request to an online NTP time source; however, doing so will leave a system just as vulnerable to fraud and malicious users as having no synchronisation. This is because to use an Internet time source would require leaving a permanent port open in the firewall.

The solution is to use a dedicated NTP time server that receives a UTC time source from either a radio transmission (broadcast by national physics laboratories) or the GPS network (Global Positioning System). These are secure and can keep a network running to within a few milliseconds of UTC.

Most businesses these days rely on a computer network. Computers in most organisations conduct thousands of tasks a second, from controlling production lines; ordering stock; preparing financial records and communicating with computers on other networks – often from the other side of the world.

Computers use just one thing to keep track of all these tasks: time. Timestamps are the computers only reference for when an event or task occurs in relation to other events. They receive time in the form of timestamps and they measure time in periods of milliseconds (thousandth of a second) as they may conduct hundreds of processes each second.

A global timescale known as UTC (Coordinated Universal Time) has been developed to ensure computers from different organisations all over the world can synchronise together. So what happens if the clocks on computers don’t coincide with each other or with UTC?

The consequences of running a network with computers that are not synchronised can be disastrous. Here are five reasons why all businesses need adequate network synchronisation using a NTP server (Network Time Protocol) or other network time server device.

1. Tasks fail to happen:

When computers are running at different times, events on different machines can fail to happen as often a PC may assume an event on another machines has already happened if the time for that event has passed according to its own clock. And what is worse, when one task fails it has a knock-on effect with other tasks failing to happen and in turn causing further tasks to fail.

2. Loss of Data:

When tasks fail to happen it soon gets noticed but when networks are not synchronised data that is meant to be kept can quite easily be lost and it can go unnoticed for quite a while. Data can be lost because storage as and retrieval is also reliant on time stamps.

Synchronising a network is often considered a headache by network administrators who fear that getting it wrong can lead to disastrous results and while there is no deny that a lack of synchronisation can cause unforeseen problems particularly with time sensitive transactions and security, perfect synchronisation is simple if these steps are followed:

1. Use a dedicated NTP server. The NTP server is a device that receives a single time source then distributes it amongst a network of computers using the protocol NTP (Network Time Protocol) one of the oldest Internet based protocols and by far the most widely used time synchronisation software. NTP is often packaged with modern operating systems such as Windows or Linux although there is no substitute for a dedicated NTP device.

2. Always use a UTC time source (Coordinated Universal Time). UTC is based on GMT (Greenwich Meantime) and International Atomic Time (TAI) and is highly accurate. UTC is used by computer networks all over the world ensuring that commerce and trade are all using the same timescale.

3. Use a secure an accurate time signal. Whilst time signals are available all over the Internet they are unpredictable in their accuracy and while some may offer decent enough precision an Internet time server is outside a networks firewall which if left open to receive a timecode will cause vulnerabilities in the security of the network. Either GPS (global positioning system) or a dedicated radio signal such as those transmitted by national physics laboratories (such as MSF – UK, WWVB – USA, DCF –Germany) offer secure and reliable methods of receiving a secure and accurate time signal.

4. Organise a network into stratum, levels. Strata ensure that the NTP server is not inundated with time requests and that the network bandwidth doesn’t become congested. A stratum tree is organised by a few select machines being stratum 2 devices in that they receive a time signal from the NTP server (stratum 1 device) these in turn distribute the time to other devices (stratum 3) and so on.

5. Ensure all machines are utilising UTC and the NTP server tree. A common error in time synchronisation is to not ensure all machines are properly synchronised, just one machine running inaccurate time can have unforeseen consequences.

The NTP Pool of time servers has announced that they now have a collection of over 1,000 time servers in Europe alone. The NTP pool was set up to prevent NTP server abuse and to insure there is not too much strain on the stratum 1 time servers.

The pool is now so popular over one million users choose top get their timing sources from there as most of the stratum 2 NTP servers on the NTP pool website are free to use and access over the Internet.

The NTP Pool is an ideal location for those running single machines or smaller networks were security and accuracy is not really an issue, however, for those charged with running a secure network or where accuracy is really important then internet time servers should not be seriously considered.

Unfortunately Internet time services cannot be authenticated (NTP’s security measure) which can leave a machine vulnerable, furthermore, Internet time sources are outside of a network’s firewall so a port needs to be left open to allow the time server can network to communicate.

For those serious about synchronisation there is no alternative other than to invest in a dedicated NTP server that receives its time securely from either radio signals or the GPS network.

Network Time Protocol is an Internet protocol used to synchronise 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 NTP  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.