NTP (Network Time Protocol) has been around for a long time now. First conceived in the early eighties it has been providing synchronisation for over 25 years.
Many people assume that because they are running NTP then their networks are perfectly synchronised and running accurate UTC time (UTC – Coordinated Universal Time – the world’s standard timescale).
However, NTP is a protocol designed for synchronisation and does just that it synchronises. NTP can synchronise time from an atomic clock that doesn’t lose more than a second every million years or so or to a cheap plastic wrist watch that runs a minutes slow each week. A time server is therefore only as good as the timing reference that it uses to synchronise to.
Many administrators select a timing source from the Internet and automatically assume that their server is running accurate UTC time. However, many Internet timing sources are wholly inaccurate and those that are not can often be too far away from a client to provide any hope of an accurate time source, not to mention the fact that Internet timing references can’t be authenticated and can leave a system open to a malicious attack.
Fortunately there are two methods that can provide both accurate and secure timing information to a time server. The first method is to use a radio referenced time server. These simple pieces of kit receive the national time and frequency transmission that many countries broadcast. This signal can be picked up usually within a 1000km of the transmitter and provides accuracy to within a few milliseconds. unfortunately places outside the transmission’s country of origin or areas with topographical features such as mountains may struggle to receive a signal.
Fortunately a GPS time server can receive a signal anywhere on Earth as long as the antenna can see a patch of blue sky. Also a GPS time server provides slightly better accuracy than a radio referenced one. They are also relatively inexpensive, however, the antenna does normally have to go to the roof which can bring with it its own costs.
