Time Synchronisation

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.

5. Synchronisation is vital for any network that conducts time sensitive transactions. Computers use time as the only point of reference between events and if computers on a network are all running different times then untold problems can occur. The problems increase many-fold if a network has to communicate with another network.

4. UTC (coordinated universal time) is a global timescale used all over the world ensuring that all networks linked to a UTC time source are running identical times. Not having synchronisation to UTC can mean that many International Transactions are just not possible.

3. A network time server is a dedicated device which means it receives time directly from an atomic clock source externally. UTC can be obtained from a variety of Internet time sources however this can leave a system open to abuse as the firewall needs to be open to receive the signal. Furthermore, the time protocol NTP has a security measure known as authentication – this does not work over the Internet.

2 A dedicated network time server can be legally audited which means in case of fraud or other legal issues the time provided by the time server is legally accepted as being accurate.

1. A dedicated network time server is a stratum 1 device a stratum 0 device is an actual atomic clock. A device that receives a time signal from a network time server is a stratum 2 device. The higher the stratum number the further away and therefore that less accurate the time signal is. The majority of Internet time servers are all stratum 2 devices and therefore cannot provide anywhere near as accurate timing information

A time server is a common office tool but what is it for?

We are all used to having a different time from the rest of the world. When America is waking up, Honk Kong is going to bed which is why the world is divided into time zones. Even in the same time-zone there can still be differences. In mainland Europe for instance most countries are an hour ahead of the UK because of Britain’s seasonal clock changing.

However, when it comes to global communication, having different times all over the world can cause problem particularly if you have to conduct time sensitive transactions such as buying or selling shares.

For this purpose it was clear by the early 1970’s that a global timescale was required. It was introduced on 1 January 1972 and was called UTC – Coordinated Universal Time. UTC is kept by atomic clock but is based on Greenwich Meantime (GMT – often called UT1) which is itself a timescale based on the rotation of the Earth. Unfortunately the Earth varies in its spin so UTC accounts for this by adding a second once or twice a year (Leap Second).

Whilst controversial to many, leap seconds are needed by astronomers and other institutions to prevent the day from drifting otherwise it would be impossible to work out the position of the stars in the night sky.

UTC is now used all over the world. Not only is it the official global timescale but is used by hundreds of thousands of computer networks all over the world.

Computer networks use a network time server to synchronise all devices on a network to UTC. Most time servers use the protocol NTP (Network Time Protocol) to distribute time.

NTP time servers receive the time from atomic clocks by either long-wave radio transmissions from national physics laboratories or from the GPS network (Global Positioning System). GPS satellites all carry an onboard atomic clock that beams the time back to Earth. Whilst this time signal is not strictly speaking UTC (it is known as GPS time) because of the accuracy of the transmission it is easily converted to UTC by a GPS NTP server.

A network time server is a device that can synchronise a network to a single time source.

Linux comes with a version of NTP installed to configure your Linux system to run as a network time server follow these instructions:

1. Configure /etc/ntp.conf
Edit the ntp.conf file using text editor.
server <example-server-name>

and replace these lines with your servers.
server time-a.nist.gov
server time-b.nist.gov
server time-a.timefreq.bldrdoc.gov
(I am using NIST but other time servers are just as good)

2. Synchronize your clock manually
If your clock is too much behind or ahead then NTP might struggle to synchronise so its est to do it manually:

ntpdate 0. time-a.nist.gov

3. Make your ntp daemon executable:

chmod +x /etc/rc.d/rc.ntpd

4. Start NTP now without rebooting
/etc/rc.d/rc.ntpd start

GPS time servers are network time servers that receive a timing signal from the GPS network and distribute it amongst all devices on a network ensuring that the entire network is synchronised.

GPS is an ideal time source as a GPS signal is available anywhere on the globe. GPS stands for Global Positioning System, the GPS network is owned by the US military and controlled and run by the US air force (space wing). It is however, since the late 1980’s been opened up to the world’s civilian population as tool to aid navigation.

The GPS network is actually a constellation of 32 satellites that orbit the Earth, they do not actually provide positioning information (GPS receivers do that) but transmit from their onboard atomic clocks a timing signal.

This timing signal is what is used to work out a global position by triangulating 3-4 timing signals a receiver can work out how far and therefore the position you are from a satellite. In essence then, a global positioning satellite is just an orbiting clock and it is this information that is broadcast that can be picked up by a GPS time server and distributed amongst a network.

Whilst strictly speaking GPS time is not the same as the global timescale UTC (coordinated universal time), a GPS time server will automatically convert the time format into UTC.

A GPS time server can provide unbridled accuracy with networks able to maintain accuracy to within a few milliseconds of UTC.

The NTP server or network time server as it is often called is the culmination of centuries of horology and chronology. The history of keeping track of time has not been as smooth as you may think.

What month was the Russian October revolution? I’m sure you have guessed that it is a trick question, in fact if you trace the days back to the October revolution that changed the shape of Russia in 1917 you will find it didn’t start until November!

One of the first decisions the Bolsheviks, who had won the revolution, chose to make was to join the rest of eh world by taking up the Gregorian calendar. Russia was last to do adopt the calendar, which is still in use throughout the world today.

This new calendar was more sophisticated that the Julian calendar which most of Europe had been using since the Roman Empire. Unfortunately the Julian calendar did not allow for enough leap years and by the turn of the century this had meant that the seasons had drifted, so-much-so, that when Russia finally adopted the calendar on after Wednesday, 31 January 1918 the following day became Thursday, 14 February 1918.

So whilst the October revolution occurred in October in the old system, to the new Gregorian calendar it meant it had taken place in November.

Whilst the rest of Europe adopted this more accurate calendar earlier than the Russians they still also had to correct the seasonal drift, so in 1752 when Britain changed systems they lost eleven days which according to the populist painter of the time, Hogarth, caused rioters to demand the return of their lost eleven days.

This problem of inaccuracy in keeping track of time was thought to be solved in the 1950’s when the first atomic clocks were developed. These devices were so accurate that they could keep time for a million years without losing a second.

However, it was soon discovered that these new chronometers were in fact too accurate – compared with the Earth’s rotation anyway. The problem was that while atomic clocks could measure the length of a day to the nearest millisecond, a day is never the same length.

The reason being is that the Moon’s gravity affects the Earth’s rotation causing a wobble. This wobble has the effect of slowing down and speeding up the Earth’s spin. If nothing was done to compensate for this then eventually the time told by atomic clocks (International Atomic Time- TAI) and the time based on the Earth’s rotation used by farmers, astronomers and you and I (Greenwich Meantime- GMT) would drift that eventually noon would become midnight (albeit in many millennia).

The solution has been to devise a timescale that is based on atomic time but also accounts for this wobble of the Earth’s rotation. The solution was called UTC (Coordinated Universal Time) and accounts for the Earth’s variable rotation by having ‘leap seconds’ occasionally added. There have been over thirty leap seconds added to UTC since its inception in the 1970’s.

UTC is now a global timescale used throughout the world by computer networks to synchronise too. Most computer networks use a NTP server to receive and distribute UTC time.

A network time server will synchronise all machines and devices on a network to UTC time (coordinated universal time). They are essential pieces of hardware in modern computer networks, without which, time sensitive transactions would be impossible.

Most network time servers will use NTP (Network Time Protocol) to distribute a single UTC time source (Coordinated Universal Time) around a network. The way a network time sever synchronises devices is by allowing them to ask it the time (poll) if the device is slow or fast compared to UTC then NTP will advance or retreat the system clock.

You would think that on larger networks with hundreds of machines all requesting timing information from a single network time server will cause congestion of the network and the time server. However, NTP is hierarchical, the distance from the time source is split into strata, the closer to the time source the lower the stratum level. So for example a stratum 0 device is an atomic clock while a dedicated network time server that receives the time from an atomic clock is a stratum 1 device while a computer that receives the time from a network time server is a stratum 2 device.

Fortunately stratum 2 devices can also be used to distribute time. Devices that receive time from a stratum 2 device become stratum 3 stratum device. These devices too can be used to distribute time to lower stratum levels, although the accuracy of the devices will lessen the further away from the original time source.

Arranging a network into stratum levels means that all devices can be synchronised using just the one network time server.

There are hundreds of internet based timing sources that allow computers running NTP to synchronise to a UTC time – however, there are several drawbacks in relying on the Internet for a timing reference.

Security is paramount for most computer networks and NTP, one of the Internet’s oldest protocols, is equipped with its own security measures in the form of authentication. Authentication verifies that each timestamp has come from the intended time reference by analysing a set of agreed encryption keys that are sent along with the timing information.

Unfortunately, internet time sources can not be authenticated and Microsoft, Novell and others “strongly recommend” that internet sources are not used for a timing reference as it could leave a network vulnerable and open to malicious hackers, viruses or even a DDoS attack (Distributed Denial of Service – where a server is inundated with traffic rendering it useless).

Also a survey by MIT (Massachusetts Institute of Technology) of over 900 internet time references, discovered nearly half were offset by over ten seconds (one by a staggering six years – but there were fortunately not many peers) and less that a third where described as being at all “useful”.

The report also discovered that many internet time reference hosts were too far away from their peers to allow any accurate time synchronisation to take place.

Fortunately a dedicated NTP network time server can receive other sources of UTC time which do offer complete security, authentication and are far more accurate and reliable. The first is the national time and frequency broadcasts transmitted by several countries. In the US the signal is referred to as WWVB and is broadcast by NIST (National Institute for Standards and Technology) in Colorado. In the UK the National Physical Laboratory (NPL) broadcasts the MSF signal from Cumbria and similar systems are broadcast in Germany (DCF-77), Japan (JJY) and France (TDF).

Another, equally accurate and secure method is to use the timing signals broadcast by the American GPS (Global Positioning System).
The GPS is currently the world’s only Global Navigation Satellite System, although Europe’s Galileo and the Russian GLONASS system are expected to be up and running over the next five years.

It is a consequence of needing accurate timing information to be able to pin-point positioning  that GPS satellites all contain an atomic clocks and the signal that is broadcast can be received and used by a network time server.

A network time server is just a name given to any device that controls time on a network. This does not necessarily need to be a dedicated server as any workstation, equipped with a time protocol such as NTP (Network Time Protocol). However, for most network administrators, for reasons of security and accuracy, opt to use a dedicated network time server. For the purposes of this article it is these dedicated devices that we will discuss.

The types of dedicated network time servers really come down to how the time severe receives its timing source. While it is possible for a workstation to receive an Internet timing source that relays UTC (coordinated universal time) that is neither, accurate or secure for any serious time synchronisation needs.

There are two secure and accurate methods that a network time server can receive a UTC timing source. The first is from the GPS network. This is possibly the most reliable and accurate method or receiving UTC time. As long as a GPS antenna is connected and has a good clear view of the sky accuracy to within a few milliseconds of UTC should be expected.

The other method is to use the national time and frequency transmissions that are broadcast by several national physics laboratories. These are only available in certain countries (USA, UK, Germany, France, Switzerland and Japan) and the long-wave transmissions are vulnerable to local topography.

The two types of dedicated network time server are therefore radio clock/receivers and GPS clock/receivers.  For those really serious about time synchronisation there are dedicated network time servers that can receive both radio and GPS signal ensuring higher levels of accuracy and reliability.

What is a network time server?

A network time server is a hardware device that utilises a single time source and distributes it amongst a network to ensure all computers and devices are telling the same time.

What is NTP?

Network Time Protocol is a protocol designed to distribute time across computers. NTP uses an algorithm to work out drift and inaccuracies and compensates for them ensuring all devices on a network are synchronised.

What is UTC?
Coordinated Universal Time (UTC) is a global timescale used by computer networks throughout the world. It is based on the time told by atomic clocks but compensates for the slowing of the Earth’s rotation by adding Leap Seconds, this also keeps it inline with GMT (Greenwich Meantime).

How does a network time server receive UTC?

UTC is broadcast by several national time and frequency transmissions on long-wave. Not every country has one and the signals are finite and vulnerable to interference. Alternatively as GPS satellites (Global Positioning System) all transmit timing information from their onboard atomic clocks this can be used also as a timing source for network time servers.

Can’t I use the Internet as a timing source?
There are many sources of UTC time on the Internet but many are not very accurate and for those that are the distance away can cause a drop-off in precision. More importantly, Internet time sources can’t be authenticated. Authentication is a security measure that ensures that a timing reference is what it says it is.

Which method is best for me a radio referenced time server or one that utilises the GPS network?

This depends primarily on where the network time server is to be situated. If a national radio signal is available and local topography doesn’t cause interference then a radio referenced network time server is probably the best option. However, if a radio signal is unavailable then the GPS network would be an obvious solution. While GPS signals are available everywhere on the planet they do have a downside in that their antennas have to have a clear view of the sky to receive the signal, this can be problematic  if a server room is on the ground floor of a skyscraper – although it is possible to receive a GPS signal via window.

How accurate are time servers?

A radio referenced network time server can provide UTC time to an accuracy of 100 microseconds, while the GPS network can fare even better with accuracies of a few milliseconds reasonably possible.