Time Synchronisation

Linux operating systems are becoming increasingly popular partly due to the many advantages they have over commercial systems like Windows or OS X. Linux offers increased security (as there are only a handful of viruses that can infect a Linux based system), better stability and in most cases it is free.

It is no wonder more and more home and business users alike are opting to switch to a Linux based operating systems and whether it is Redhat, Mandrake, Ubuntu or the myriad of other UNIX and LINUX based systems, keeping accurate time is relatively straight forward.

Time synchronisation is vital in many time-sensitive applications and most business users find it would be impossible to conduct any online transactions without a synchronized network. Even home-users find an advantage in ensuring their system is running accurate time, emails no longer arrive before they are sent and security is increased.

Most Linux based operating systems contain a version of Network Time Protocol (NTP) an Internet protocol designed to synchronise time on a network. For those that do not contain a pre-packed version, NTP is open source and freely available at ‘NTP.org’.

While NTP is available for most versions of Windows; Linux users have the advantage in that it has traditionally been the primary development platform for NTP. It works by using a timing source either from the Internet or via a dedicated network time server.
These reference clocks run UTC time (coordinated universal time) a global timescale which is relayed to them from atomic clocks that are accurate to a few nanoseconds (a nanosecond is a billionth of a second).

Put simply, the NTP daemon (a service program that runs in the background) compares the time on the computer with the timing source at regular intervals and adjusts it depending on any drift.

The NTP daemon is configured using the ‘NTP.conf’ file. The configuration file is where the location of the NTP timing servers are stored. If attempting to use a public internet timing source it is advised to visit http://www.pool.ntp.org which has a collection of over 200 servers.

However Microsoft and Novell, strongly advise that internet based timing sources are not used as they are unauthenticated and can leave a gateway open for malicious attacks.

Alternatively and most preferably, dedicated NTP time servers are available which provide better accuracy and are far more secure. These time servers receive a timing source from either a national radio broadcast (such as WWVB in the US or MSF in the UK) or via the GPS system.

Once installed these systems continually check the time on all the network computers’ clocks and adjusts them for any drift. A typical GPS receiver can provide timing information to within a few nanoseconds of UTC while national time and frequency transmissions are accurate to 1 – 20 milliseconds (a millisecond is 1/1000 of a second).

Keeping track of the time is essential in the day-to-day running of our lives. We need to know when to start work, when to leave and even when to get up in the morning.

There are of course a myriad of devices that help us keep track of the time of day from wrist-watches and mobile phones to the display on our DVD player and in our cars, clocks, of one sort or another are everywhere.

Computers are no different. Time is essential for the functioning of computer applications, everything from sending and email to debugging a system is reliant on a time stamp.

Computers have their own clocks, real time chips, but unfortunately these on-board clocks are not very accurate timepieces and are prone to drift and the subsequent differences in time on a network can lead to all sorts of problems.

A network time server gets around this problem by using an absolute time source, that is a time source that is so accurate that it would barely lose a second in millions of years.

The only clocks capable of supplying such accurate time are atomic clocks but unfortunately these are highly expensive and delicate machines only to be found in large scale physics laboratories. Thankfully a network time server can receive the time told by these devices by using either the Internet (although that can be inaccurate and cause security problems, the GPS network or specialist radio transmissions.

These time signals broadcast UTC – coordinated universal time, which is a global timescale developed to ensure networks around the world are keeping the same time.

The network time server will synchronise the entire network of computers to this time, continually checking for drift and ensuring millisecond accuracy.

By using a network time server, security is increased and time-sensitive applications will run without error.

What is NTP?

NTP is a protocol developed over 25 years ago to deal with the problems of time synchronisation across the Internet. Network Time Protocol distributes a single time source to all computers and devices by using an algorithm to inspect the drift of each device and then correcting the time.

While NTP can distribute any time reference it was designed in particular to synchronise computer networks to UTC (Coordinated Universal Time). UTC is a global time scale used by computer networks around the world. It is based on the time told by atomic clocks and is therefore highly accurate.

What is GPS?

The Global Positioning System (GPS) is currently the world’s only global navigational satellite system (GNSS) and is controlled by the American military. GPS is most commonly thought of as a navigational tool but as the principles of GPS navigation involve an atomic clock onboard each GPS satellite transmitting its time, this information can be used by NTP as a highly accurate source of UTC.

What does a NTP GPS server do?

A NTP GPS server is a dedicated computer server that receives a GPS timing signal via a GPS antenna and then distributes it amongst the network.  NTP GPS servers can provide accuracy to within a few milliseconds of UTC time.