Time is essential for modern computer networks, as the majority of applications and processes conducted by a PC are reliant on a timestamp, from sending an email, debugging a server to preventing fraud, therefore, accurate time and synchronisation is vital.
NTP (Network Time Protocol) is an Internet protocol designed for the synchronisation of computer networks. NTP servers are used by millions of system administrators to ensure their networks are keeping accurate time.
However, just as a computer is only as a good as the software it is running, a NTP server is only as good as the timing source it receives.
Despite the hundreds and probably thousands of possible timing references on the Internet, administrators should be aware of some of the possible pitfalls in selecting a timing reference.
A survey conducted by the Massachusetts Institute of Technology (MIT) discovered that not only were half of Internet timing sources inaccurate by over a ten seconds (a lifetime if we are attempting millisecond accuracy) but many were too far away to be provide any useful accuracy.
If an Internet timing source is to be used then not only should the accuracy of the server be checked but also the closest host should be selected to ensure the best accuracy.
Another consideration in using an Internet timing source is to be aware that they cannot be authenticated which means that your system could be vulnerable to malicious attacks and it is recommended by Microsoft and Novell that an external hardware source should be used.
The most secure and accurate method of receiving a timing source is to use a dedicated NTP server that can receive either a national time and frequency transmission (such as WWVB in the US or MSF in the UK). Alternatively a timing source can be received from the GPS network (Global Positioning System), both methods are authenticated and can provide millisecond accuracy.