Time Servers and the Importance of Synchronisation.

By: Richard N Williams

Timeservers are like other computer servers in the sense they are usually locatedon a network. A time server gathers timing information, usually from anexternal hardware source and then synchronises the network to that time.

Often timeservers are synchronised to a UTC (Coordinated Universal time) source which isthe global standard time scale and allows computers all over the world tosynchronised to exactly the same time. This has obvious importance inindustries where exact timing is crucial such as the stock exchange or airlineindustry.

There arevarious sources that a time server can use as a timing reference. The Internetis an obvious source, however, internet timing references from the Internetsuch as nist.gov and windows.time can not be authenticated, leaving the timeserver and therefore the network vulnerable to security threats.

There areauthenticated alternatives to the Internet, the most common being to use theGPS network. As the Global Positioning System is reliant on knowing exactlywhat time it is to ensure reliable location information, this information canbe utilised by a time server.

A simpleGPS antenna connected to the time server will allow the GPS timing reference tobe regularly checked by the time server. A GPS time server will be accurate towithin a few hundrednanoseconds (a nanosecond = a billionth of a second).

Thereare also a number of national radio broadcasts such as the WWVB signal fromColorado in the USArticle Search, the MSF signal from Cumbria in the UK and the DCF-77 signalfrom Frankfurt in Germany.

Theseradio signals are limited in their range though and even in major cities suchas London it can be difficult to receive a decent enough signal.

Mosttiming servers use NTP (Network Time protocol) there are other protocolsavailable but NTP is predominately used and is thought of as the standard fortiming protocols. NTP has been around for over 25 years and is currently onversion 4 but is always being updated which is probably why it is by fat themost common timing protocol.

NTP time servers work within the TCP/IP suite and rely onUDP (User Datagram Protocol). A less complex form of NTP - Simple Network TimeProtocol (SNTP) is used in some devices and applications where high accuracytiming is not as important and is also included as standard in Windows software(although more recent versions of Microsoft Windows have the full NTP installedand the source code is free and readily available on the Internet from ntp.org).

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