Power over Ethernet is ideal for powering and controlling wall clocks and other time devices. The accuracy of a network’s NTP time server can be used to maintain an accurate time on the PoE clock. This means the clock will never drift and will always be accurate to the second – ideal for ensuring punctuality in organisations that runs to a tight time schedule. No matter how many clocks are running on the PoE system, they will all maintain the exact same time, eliminating time inconsistencies in large organisations.
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
Accurate and precise time is increasingly becoming a necessity for computer systems. From corporate networks to public service technologies such as ATMs, traffic lights or CCTV cameras – precise time is what keeps them ticking.
Inaccurate or unsynchronised time is the root cause for many technology breakdowns and failures. For instance, failing to synchronize a traffic lights system can lead to all sorts of confusion of the lights change at the wrong time – and the consequences for systems belonging to industries such as air traffic control could be even worse.
And even a standard computer network such as those used in most offices requires accurate synchronisation to prevent errors, enable debugging and to ensure the system is secure.
Most system administrators are now aware of the importance of accurate and precise time synchronisation but getting a source of accurate time is often where many people make mistakes.
Many network administrators are aware of the time protocol NTP (Network Time Protocol) which is used to ensure accurate synchronisation between computers.
However, many administrators make the mistake of using a source of time from across the internet to distribute with NTP – a common pitfall that can have disastrous consequences.
The internet is not the best source of tine. While it is true, many online NTP servers are available as a source of atomic time or UTC (Coordinated Universal Time) but are they accurate. The truth is it is almost impossible to know. Internet time sources can be affected by the distance of the client (the network) from the time source – it also can’t be authenticated by NTP.
Even more important, internet time sources operate through the firewall which can allow the time signal to be hijacked by malicious programs.
The only secure and accurate method of synchronising a computer network or other technology system is to use an NTP server. These devices receive an external atomic clock time signal often by GPS or even by radio transmissions.
These signals are come direct from atomic clocks so are highly accurate they also can’t be hijacked as they are not connected to the internet.
“Time is what prevents everything from happening at once,’ said eminent physicist John Wheeler. And when it comes to computers his words couldn’t be any more relevant.
Timestamps are the only method that a computer has to establish if an event has occurred, is meant to occur or shouldn’t be occurring just yet. For a home PC, the computer relies on the inbuilt clock that displays the time on the corner of your operating system, and for most home uses this is satisfactory enough.
However for computer networks that have to communicate with each other, relying in individual system clocks can cause untold problems:
All clocks drift, and computer clocks are no different and problems occur when two machines are drifting at different rates as the time does not match up. This poses a conundrum for a computer as it is unsure of which time to believe and time critical events can fail to occur and even simple tasks like sending an email can cause time confusion on a network.
For these reasons, time servers are commonly used to receive the time from an external source and distribute it around the network. Most of these devices use the protocol NTP (Network Time Protocol) which is designed to provide a method of synchronising time on a network.
However, time servers are only as good as the time source that they rely on and when there is a problem with that source, synchronisation will fail and the problems mentioned above can occur.
The most common cause for time server failure or inaccuracy is the reliance on internet based sources of time. These can neither be authenticated by NTP nor guaranteed to be accurate and they can also lead to security issues with firewall intrusion and other malicious attacks.
Ensuring the NTP time server continues to get a source of highly accurate time is fairly straight forward and is all a matter of choosing an accurate, reliable and secure time source.
In most parts of the world there are two methods that can provide a secure and reliable source of time:
- GPS time signals
- Radio referenced time signals
GPS signals are available anywhere on the planet and are based on GPS time which is generated by atomic clocks onboard the satellites.
The atomic clock is not a recent invention. Developed in the 1950’s, the traditional caesium based atomic clock has been providing us with accurate time for half a century.
The caesium atomic clock has become the foundation of our time – literally. The International System of Units (SI) define a second as a certain number of oscillations of the atom caesium and atomic clocks govern many of the technologies that we live with an use on a daily basis: The internet, satellite navigation, air traffic control and traffic lights to name but a few.
However, recent developments in optical quantum clocks that use single atoms of metals like aluminium or strontium are thousands of times more accurate than traditional atomic clocks. To put this in perspective, the best caesium atomic clock as used by institutes like NIST (National Institute for Standards and Time) or NPL (National Physical Laboratory) to govern the world’s global timescale UTC (Coordinated Universal Time), is accurate to within a second every 100 million years. However, these new quantum optical clocks are accurate to a second every 3.4 billion years – almost as long as the earth is old.
For most people, their only encounter with an atomic clock is receiving its time signal is a network time server or NTP device (Network Time Protocol) for the purposes of synchronising devices and networks and these atomic clock signals are generated using caesium clocks.
And until the world’s scientists can agreed on a single atom to replace caesium and a single clock design for keeping UTC, none of us will be able to take advantage of this incredible accuracy.
As with the advance of computer technology that seems to exponentially increase in capability every year, atomic clocks too seem to increase dramatically in their accuracy year on year.
Now, those pioneers of atomic clock technology, the US National Institute of Standards Time (NIST), have announced they have managed to produce an atomic clock with accuracy twice that of any clocks that have gone before.
The clock is based in a single aluminium atom and NIST claim it can remain accurate without losing a second in over 3.7 billion years (about the same length of time that life has existed Earth).
The previous most accurate clock was devised by the German Physikalisch-Technische Bundesanstalt (PTB) and was an optical clock based on a strontium atom and was accurate to a second in over a billion years. This new atomic clock by NIST is also an optical clock but is based on aluminium atoms, which according to NIST’s research with this clock, is far more accurate.
Optical clocks use lasers to hold atoms still and differ to the traditional atomic clocks used by computer networks using NTP servers (Network Time Protocol) and other technologies which are based on fountain clocks. Not only do these traditional fountain clocks use Caesium as their time keeping atom but instead of lasers they use super-cooled liquids and vacuums to control the atoms.
Thanks to work by NIST, PTB and the UK’s NPL (National Physical Laboratory) atomic clocks continue to advance exponentially, however, these new optical atomic clocks based on atoms like aluminium, mercury and strontium are a long way from being used as a basis for UTC (Coordinated Universal Time).
UTC is governed by a constellation of caesium fountain clocks that while still accurate to a second in 100,000 years are by far less precise than these optical clocks and are based on technology over fifty years old. And unfortunately until the world’s science community can agree on an atom and clock design to be used internationally, these precise atomic clocks will remain a play thing of the scientific community only.
Synchronization of computer networks is something that many administrators take for granted. Dedicated network time servers can receive a time source and distribute it amongst a network, accurately, securely and precisely.
However, accurate time synchronization is only made possible thanks the time protocol NTP – Network Time Protocol.
NTP was developed when the internet was still in its infancy and Professor David Mills and his team from Delaware University were trying to synchronise the time on a network of a few machines. They developed the very earliest rendition of NTP which has continued to be developed to this very day, nearly thirty years after its first inception.
NTP was not then, and is not now, the only time synchronisation software, there are other applications and protocol that do a similar task but NTP is the most widely used (by far with over 98% of time synchronisation applications using it). It is also packaged with most modern operating systems with a version of NTP (usually SNTP – a simplified version) installed on the latest Windows 7 operating system.
NTP has played an important part in creating the internet we know and love today. Many online applications and tasks would not be possible without accurate time synchronization and NTP.
Online trading, internet auctions, banking and debugging of networks all rely on accurate time synchronisation. Even sending an email requires time synchronisation with email server – otherwise computers would not be able to handle emails coming from unsynchronised machines as they may arrive before they were sent.
NTP is a free software protocol and is available online from NTP.org However, most computer networks that require secure and accurate time mostly use dedicated NTP servers that operate external to the network and firewall obtaining the time from atomic clock signals ensuring millisecond accuracy with the world’s global timescale UTC (Coordinated Universal Time).
No matter where we are in the world we all need to know the time at some point in the day but while each day lasts for the same amount of time no matter where you are on Earth the same timescale is not used globally.
The impracticality of Australians having to wake up at 17.00 or those in the US having to start work at 14.00 would rule out suing a single timescale, although the idea was discussed when the Greenwich was named the official prime meridian (where the dateline officially is) for the world some 125 years ago.
While the idea of a global timescale was rejected for the above reasons, it was later decided that 24 longitudinal lines would split the world up into different timezones. These would emanate from GMT around with those on the opposite side of the planet being +12 hours.
However, by the 1970’s a growth in global communications meant that a universal timescale was finally adopted and is still in much use today despite many people having never heard of it.
UTC, Coordinated Universal Time, is based on GMT (Greenwich Meantime) but is kept by a constellation of atomic clocks. It also accounts for variations in earth’s rotation with additional seconds known as ‘leap seconds’ added once of twice a year to counteract the slowing of the Earth’s spin caused by gravitational and tidal forces.
While most people have never heard of UTC or use it directly its influence on our lives in undeniable with computer networks all synchronised to UTC via NTP time servers (Network Time Protocol).
Without this synchronisation to a single timescale many of the technologies and applications we take for granted today would be impossible. Everything from global trading on stocks and shares to internet shopping, email and social networking are only made possible thanks to UTC and the NTP time server.
Atomic clocks are a marvel compared to other forms of timekeepers. It would take over 100,000 years for an atomic clock to lose a second in time which is staggering especially when you compare it to digital and mechanical clocks that can drift that much in a day.
But atomic clocks are not practical pieces of equipment to have around the office or home. They are bulky, expensive and require laboratory conditions to operate effectively. But making use of an atomic clock is straightforward enough especially as atomic time keepers like NIST (National Institute of Standards and Time) and NPL (National Physical Laboratory) broadcast the time as told by their atomic clocks on short wave radio.
NIST transmits its signal, known as WWVB from Boulder, Colorado and it is broadcast on an extremely low frequency (60,000 Hz). The radio waves from WWVB station can cover all of the continental United States plus much of Canada and Central America.
The NPL signal is broadcast in Cumbria in the UK and it is transmitted along similar frequencies. This signal, known as MSF is available throughout most of the UK and similar systems are available in other countries such as Germany, Japan and Switzerland.
Radio controlled atomic clocks receive these long wave signals and correct themselves according to any drift the clock detects. Computer networks also take advantage of these atomic clocks signals and use the protocol NTP (Network Time Protocol) and dedicated NTP time servers to synchronise hundreds and thousands of different computers.
While there are several protocols available for time synchronisation the majority of network time is synchronised using either NTP or SNTP.
Network Time Protocol (NTP) and Simple Network Time Protocol (SNTP) have been around since the inception of the Internet (and in the case of NTP, several years beforehand) and are by far the most popular and widespread time synchronisation protocols.
However, the difference between the two is slight and deciding which protocol is best for a ntp time server or a particular time synchronisation application can be troublesome.
As its name suggests, SNTP is a simplified version of Network Time Protocol but the question is often asked: ‘what exactly is the difference?’
The main difference between the two versions of the protocol is in the algorithm that is used. NTP’s algorithm can query multiple reference clocks an calculate which is the most accurate.
SNTP use for low processing devices – it is suited to less powerful machines, do not require the high level accuracy of NTP. NTP can also monitor any offset and jitter (small variations in waveform resulting from voltage supply fluctuations, mechanical vibrations or other sources) whilst SNTP does not.
Another major difference is in the way the two protocols adjust for any drift in network devices. NTP will speed up or slow down a system clock to match the time of the reference clock coming into the NTP server (slewing) while SNTP will simply step forward or backward the system clock.
This stepping of the system time can cause potential problems with time sensitive applications especially of the step is quite large.
NTP is used when accuracy is important and when time critical applications are reliant on the network. However, its complex algorithm is not suited to simple machines or those with less powerful processors. SNTP on the other hand is best suited for these simpler devices as it takes up less computer resources, however it is not suited for any device where accuracy is critical or where time critical applications are reliant on the network.