Time Synchronisation With NTP

Network Time Protocol (NTP) is an Internet standard protocol designed over 25 years ago and still under constant development. NTP synchronises devises on a network to a single timing source. If time on a network is not synchronised when applications are conducted over the Internet unintended results can occur such as email being received before it was sent or time sensitive applications failing.

NTP uses a single reference clock to synchronise all clocks on a network to that time. UTC time (Coordinated Universal Time) is the world's official time standard and most NTP servers are synchronized to receive UTC time. UTC time is kept accurate by a constellation of atomic clocks which ensure that all UTC timing references tell the same time.

NTP is organized into a hierarchy. At the top of the hierarchy are the atomic reference clocks, these are known as stratum 0. Below this strata are servers that receive a timing reference directly from a stratum 0 source. Stratum 2 servers receive time from a stratum 1 server and so on.

NTP is highly scalable meaning a synchronisation network may consist of several reference clocks and NTP will select the best candidates to build its estimate of the current time. This makes NTP highly accurate, with precision of a few hundred nano-seconds not unheard of (nano = 1 second every billion years!)

To synchronise a computer clock to timing reference using NTP extremely simple to do with modern operating systems. Most operating system manufacturers install a version of NTP into their systems (albeit a scaled down version, known as SNTP in some).

This means to connect to an Internet stratum 1 time server a user merely has to insert the domain address in the NTP program. This can be done quite simply in windows by double clicking the system clock and opening up the Internet Time tab. On UNIX the ntp.conf file contains the DNS details.

It should be mentioned that Microsoft, amongst others, recommend using an external hardware source as a timing reference as Internet sources cannot be authenticated leaving a network open to malicious attacks.

An external NTP server can receive a UTC timing signal either through a specialist national radio broadcast (so long as the receiver is within range of a suitable transmission) or from the GPS network (via a GPS antenna).

NTP servers are relatively low cost and easy to install and setup, providing accuracy and precision whilst also offering security.