| On occasion we all need to know the time and | | | | NTP time servers (Network Time Protocol) use a |
| we have a multitude of different devices to tell us | | | | single time reference to synchronise all machines |
| it; from our mobile phones and wrist watches to | | | | on the network to that time. This time reference |
| the office wall clock or the chimes on the radio | | | | can be either relative (a computer’s internal |
| news. | | | | clock or the time on a wrist-watch perhaps) or |
| But how accurate are all these clocks and does it | | | | absolute such as an atomic clock that relays UTC |
| matter if they are all telling different times? For | | | | time (Universal Coordinated Time) and is as |
| our day-to-day business it probably doesn’t | | | | accurate as is humanely possible. |
| matter too much if the office wall clock is faster | | | | Atomic clocks are the most absolute time-keeping |
| than your wrist-watch your boss probably | | | | devices accurate to a second every 1.4 million |
| won’t fire you for being a minute late. But in | | | | years. However, atomic clocks are extremely |
| some environments accuracy and synchronisation | | | | expensive and are generally only to be found in |
| are vital where a minute can make all the | | | | large-scale physics laboratories. However, NTP can |
| difference in something being sold or not or even | | | | synchronise networks to UTC time via an atomic |
| something being stolen! | | | | clock by using either the Global Positioning system |
| Time synchronisation in modern computer | | | | (GPS) network or specialist radio transmissions |
| networks is essential. It not only provides the only | | | | (MTF in the UK). |
| frame of reference between all devices, it is | | | | While some organisations have to synchronise |
| critical in everything from securing, planning and | | | | their networks to UTC such as airlines and the |
| debugging a network to providing a time stamp | | | | stock exchange, a network can be synchronised |
| for applications such as data acquisition or email. | | | | to any time and still function, but there really is no |
| Most PC’s and network devices internal | | | | substitute for UTC time. Not only is it more |
| clocks, called Real Time Clock chips (RTC) | | | | efficient to have network synchronised with the |
| providing time and date information. The chips are | | | | rest of the world, a UTC time source is vital in |
| battery backed so that even during power | | | | providing security against fraud, data loss and legal |
| outages, they can maintain time. However, | | | | exposure and without it, organizations can be |
| personal computers are not designed to be | | | | vulnerable and lose credibility. |
| perfect clocks, their design has been optimized | | | | NTP (version 4) can maintain time over the public |
| for mass production and low-cost rather than | | | | Internet to within 10 milliseconds (1/100th of a |
| maintaining accurate time. | | | | second) and can perform even better over LANs |
| Therefore these internal clocks are prone to drift | | | | with accuracies of 200 microseconds (1/5000th of |
| and although for many application this is can be | | | | a second) under ideal conditions. |
| quite adequate, often machines that work | | | | Note: it is strongly recommended by Microsoft |
| together on a network will become out of sync | | | | and others, that external based timing should be |
| with each other and problems can arise | | | | used rather than Internet based, as these |
| particularly with time sensitive transactions. Can | | | | can’t be authenticated. Specialist NTP servers |
| you imagine buying an airline seat only to be told | | | | are available that can synchronise time on |
| at the airport that the ticket was sold twice | | | | networks using either the MSF (or equivalent) or |
| because it was purchased afterwards on a | | | | GPS time server signal. |
| computer that had a slower clock? | | | | |