The NTP server is a tool for keeping computer networks synchronised. Without adequate synchronisation networks can be left vulnerable to security threats, data loss, fraud and may find it impossible to interact with other networks across the globe.
Computer networks are normally synchronised to the global timescale UTC (Coordinated Universal Time) enabling them to communicate effectively with other networks also running UTC.
In Europe there are several methods of receiving UTC time. The Internet is an obvious choice but as these time signals are external to the network firewall they can prove a security risk. Internet time sources can also be unreliable in their precision or too far away to make any useful synchronisation.
The GPS network is available everywhere on the planet as long as there is a good clear view of the sky and many NTP server devices are designed to receive such a signal.
In Europe there is another alternative, however, to provide accurate and reliable time. The National Physics Laboratory near Frankfurt, Germany broadcast a long wave frequency time signal based on a constellation of atomic clocks. This time signal is known as the DCF-77 signal and is available across much of Europe (as far as Portugal during the evening).
DCF 77 is an reliable and secure method of receiving UTC and as it is derived from a constellation for atomic clocks is highly accurate. A NTP server received a DCF time signal can provide accuracy to within a few milliseconds of UTC.