Time Synchronisation

Network Time Protocol (NTP) has been around for nearly 25 years. It is one of the Internet’s oldest protocols and is still widely used and under constant development.

NTP was developed and designed in 1985 by Professor David Mills from the University of Delaware in the United States. Its success owes much to the fact that it was one of the first ever protocols on the Internet and was first used when the World Wide Web was in its infancy.

The importance of NTP on modern computer networks cannot be stressed highly enough, without NTP and NTP servers many of the applications and processes that we conduct over the Internet and now take for granted

Internet auction sites, email and global trading all require accurate time synchronisation. Just imagine booking an airline ticket only to discover your seat was resold after you had purchased it because the buyer had a slower clock on their computer?

Confusion and problems such as these would be commonplace without NTP and NTP servers, just think of the hysteria around the millennium bug!

NTP servers allow not only computers on a particular network to be perfectly synchronised but as most NTP servers are set to receive time from a UTC time source, computers around the entire globe can be synchronised together. UTC or Coordinated Universal Time is a global time scale based on the time told by atomic clocks.

NTP servers can receive a timing reference from the Internet, although this is fairly inaccurate, or from dedicated time and frequency radio signals or the GPS network.

Currently an NTP server receiving an authoritative timing source can provide accuracy over the Internet to within a few hundred nanoseconds (a nanosecond is 1 second every billion years.)

NTP or Network Time Protocol is, like other protocols, merely a set of instructions. However, NTP is one of the Internet’s most successful and oldest of protocols. NTP was developed by Professor David Mills in the mid 1980’s when the Internet was in its earliest stages.

NTP is based on Marzullo’s Algorithm. Algorithms are mathematical equations and Marzullo’s algorithm is designed to set an optimal value from a set of estimates which is ideal for time synchronisation as the best estimate taken from several sources will provide far greater accuracy than relying on just one or two sources.

NTP has been an astronomical success and is now used in nearly 99 per cent of time synchronisation devices and a version of it is included in most operating system packages.

NTP owes much of its success to the development and support it continues to receives nearly three decades after its inception and is now used throughout the world in NTP time servers.

Network Time Protocol – is just that a protocol designed to deal with delivering time across a network. Even when the Internet was in its infancy with just a few hundred machines connected together it was clear that some way of keeping machines miles apart synchronised was essential.

Many of the tasks we now employ the Internet to do all of which would be impossible without synchronisation. Trading in stocks and shares, airline reservation, Internet auctions and even sending and receiving email are all reliant on time being synchronised. If computers were not synchronised then emails would arrive before they were sent or airline seats could be double booked.

NTP was developed by Professor David Mills of the University of Delaware and has been in continuous use and constant development for the last twenty years. There are other time synchronisation protocols around but NTP is by far the most widely used in time server applications and is installed in most versions of Windows and Linux.

The time server’s job is to receive a timing signal. Normally this time reference comes direct from an atomic clock from either the GPS network or via specialist radio transmissions. NTP then distributes the time received by the time server around the network. Checking each client and advancing or retreating the system clock to ensure synchronisation with the time server.

A time server is a computer server that reads the time from an accurate clock and distributes this information to its clients across a computer network.

The reference used by a time server is normally a UTC (coordinated universal time) time source. UTC is a global time scale adopted all over the world and based on the time told by atomic clocks The most common source for UTC time is now the GPS system (global positioning system).

The most widely-used protocol for distributing and synchronising time is Network Time Protocol (NTP) which has been around almost as long as the Internet itself, having been developed in 1985 by Professor David Mills.

NTP receives the time from the time server and then checks or clocks on its networks to see if they need advancing or retreat.

To prevent overload of networks requesting timing information, NTP is hierarchical.  The term “stratum” is used to label the nearness to a stratum 0 server – that atomic clock. The higher the stratum number the further away the server is. A GPS time server is normally a stratum 1 device as it receives time from a stratum 0 device. However, stratum 2 and stratum 3 devices can still synchronise with each other.