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A time server is a computer server that obtains precise timing information from an external hardware clock and provides this information to clients across a computer network. A time server may be located on a local network, or intranet, or may be located on the internet.
A time server utilises an external hardware clock to obtain precise timing information. There are a number of hardware clocks that a time server may utilise to obtain accurate time. One of the most common external hardware clock references is the Global Positioning System, or GPS. GPS satellites provide highly accurate timing and positioning information. The timing component of GPS transmissions is accurate to within a couple of hundred nanoseconds of the correct time. There is also a number of National time and frequency radio broadcasts available. The WWVB signal is transmitted from Colorado and is available throughout the USA. The DCF-77 radio time signal is broadcast from Frankfurt, Germany, and is available throughout much of Central and Western Europe. While, the MSF-60 radio time signal is transmitted from Anthorn in Cumbria, UK, and can be received throughout much of North-Western Europe. Alternatively, a time server may just obtain time from another time server in a hierarchy of time servers.
A time server may be an existing file server that also provides timing information in addition to it's primary function as a file server. Alternatively, it may be a dedicated device whose only function is to provide time to client computers on the network. The advantage of dedicated devices is that additional hardware may be incorporated to maintain accurate time in the event of external reference clock signal loss. Typically, many dedicated time servers have back-up TCXO, OCXO or Rubidium crystals that are much more accurate than standard quartz crystals. A Rubidium crystal may typically lose only a few milliseconds per year.
There are a number of protocols that can be used for precise time transfer between computers. Many of these protocols have become obsolete. By far the most widely used is the Network Time Protocol, or NTP. NTP has been used for the transfer of time around the Internet and local networks for over two decades. The protocol basically defines a set of algorithms and specifies data-structures for the transfer of time between computers. NTP operates in a hierarchical manner, with a level 1, or stratum 1, time server sitting at the top of the tree and filtering time information to lower stratum time servers. The lower the stratum of the time server, the further away it is from the reference server and hence less accurate.
For a number of years David Evans has written technical articles and white papers on computer timing technology. David has also been involved in the maintenance and installation of NTP server systems for a number of organisations. Please click here to visit our web-site if you would like more information on Time Servers.
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