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NTP servers or Network Time Protocol are devices that connect to a computer network and synchronise all machines to a single time source. Of course most operating systems have an inbuilt NTP program called Windows Time that can synchronise to an Internet time source; however, these can not be authenticated and can leave a computer network open to abuse.
NTP servers are normally rack mountable and take up 1U of space but some are built smaller for networks without a dedicated server room. NTP is based on UDP and requires TCP/IP.
The timing source for an NTP server can either be taken from a specialist radio transmission that are broadcast from national physics laboratories or from the GPS network.
Radio time references are only broadcast by a few countries, in particular the US (WWVB), the UK (MSF), Germany (DCF), Japan (JJY), France (TDF), Switzerland (HBG) and China (BPM). However, depending on the distance from these transmissions it is possible to receive the signals in neighbouring countries although being mainly long wave these signals are easily blocked by mountains, buildings and bad weather.
If a NTP Server is in a location with a clear radio signal it is possible to receive the transmission indoors which has an advantage over the GPS system which requires and antenna with a clear view of the sky (although it is possible to receive a transmission near a window).
GPS is however more accurate than radio transmission and can provide accuracy to within a hundred nanoseconds (a nanosecond is 1 billionth of a second). They can also receive a signal from literally anywhere in the world (as long as the antenna can get a clear view of the sky).
NTP servers are extremely easy to install and just need to be provided with a static IP address and have its internal time synchronized with the external timing reference. Once synchronised (which can take up to an hour) the NTP server will continually ensure all the clocks on the network are running the correct time.
Heightened security options such as authentication can also be used to ensure the NTP Server and network is secure from abuse.
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