The NTP server is now an essential part of the modern computer network. Without a dedicated NTP server administrators are forced to rely on unsecure and inaccurate Internet sources to synchronise their network clocks too.
The potential risks involved in this, namely leaving a hole open in the network firewall and the lack of the NTP security measure: authentication, means that networks that use an Internet based timing source are risking their system to attacks from malicious user and hackers.
It should also be noted that a survey of Internet based timing sources found less than a third were accurate to UTC time and those that were could still be too far away from client to make any useful synchronisation.
There are two types of dedicated NTP server, the GPS NTP server and the radio referenced NTP server. The difference between the two is based solely on the method they receive their UTC time source from. A GPS NTP server will use the signals broadcast from the GPS satellites above the Earth’s atmosphere. These signals are very reliable and can be picked up anywhere in the Worlds as long as the GPS antenna has a clear view of the sky.
The alternative is to use a dedicated NTP server that can receive a signal from the national time and frequency transmissions broadcast by several national physics laboratories. While not available in every country and quite vulnerable to interference these long-wave time signals are still an accurate and secure method of receiving UTC time. They are also ideally suited for network administrators who, for reasons of logistics can’t place a GPS antenna on the roof.