When it comes to time synchronisation and using Network Time Protocol (NTP) to ensure accuracy on a computer network, it is important to understand the hierarchy of NTP and how it affects distance and accuracy.
NTP has a hierarchical structure known as stratum levels. In principle the lower the stratum number the closer the device is (in accuracy terms) to an original time source.
NTP time servers work by receiving a single time source and using this as a basis for all time on the network, however, a synchronised network will be only as accurate as the original time source and this is where stratum levels come in.
And atomic clock, either one sat in a large scale physics laboratory, or those aboard GPS satellites, are stratum 0 devices. In other words these are the devices that actually generate the time.
Stratum 1 devices are NTP time servers that get their source of time directly from these stratum 0 atomic clocks. Either by using a GPS receiver or a radio referenced NTP server, a stratum 1 device is as accurate as you can get without having your own multi-million dollar atomic clock in the server room. A stratum 1 NTP time server will typically be accurate to within a millisecond of the atomic clock time.
Stratum 2 devices are the next step down on stratum level chain. These are time servers that receive their time from a stratum 1 device. Most online time servers, for instance, are stratum 2 devices, getting their time from another NTP time server. Stratum 2 devices are obviously further away from the original time source and therefore are not quite as accurate.
The stratum levels on an NTP network continue on, with devices connecting to devices going all the way down to stratum 10, 11, 12 and so on – obviously the more links in the chain the less accurate the device will be.
Dedicated stratum 1 NTP time servers are by far the most accurate, reliable and secure method of synchronising a computer network and no business network should really be without one.