NTP (Network Time Protocol) is perhaps the oldest and most commonly used protocol employed by computers and yet it is probably the least understood.
NTP is used by nearly all computers, networks and other devices that are involved in communicating across the internet or internal networks. It was developed in the very earliest stages of the internet when it became evident that some method of ensuring accuracy over distance was required.
The protocol works by selecting a single time source, of which NTP has the ability to establish the accuracy and reliability of, which it then distributes around every device on the NTP network.
Each device is regularly checked against this reference clock and adjusted if any drift is noticed. A version of NTP is now deployed with virtually every operating system allowing any machine to be synchronized to a single time source.
Obviously if every network in the world selected a different time source as its reference, the reason for of all this synchronization would be lost.
Fortunately, a global timescale based on an international consortium of atomic clocks has been developed to provide a single time source for the purposes of global synchronisation.
UTC (Coordinated Universal Time) is used by computer networks worldwide as a time reference which means any device that is synchronised to UTC with NTP will in effect be synchronised with every network that uses UTC as its base time.
There are many different methods that NTP can access UTC time. The internet is a common location although this does provide security and firewall issues. A more secure (and accurate) method is to use a dedicated NTP time server that takes the time from external sources such as the GPS network (GPS works by broadcasting an atomic clock timestamp that is easily converted to UTC by a NTP server).
With NTP, a dedicated time server and access to UTC an entire network can be synchronised to within a few milliseconds of the universal time providing a secure and accurate network that can operate in complete synchronicity with other networks across the globe.