A lot of people are interested in TimeServer NTP technology and time synchronisation in general. This is a great start point for your personal investigations. Following list is especially helpful to beginners and laymen interested in GPS and NTP.

Q & A - TimeServer NTP

Your timeserver questions answered
What does NTP stand for?

= Network Time Protocol

NTP or Network Time Protocol is an Internet protocol for time synchronisation over computer networks. However other protocols for time synchronisation are available, NTP is by far the most widely used. NTP has been around since the mid 1980's when the Internet was still waiting for its breakthrough.

What is UTC?

UTC - Coordinated Universal Time is a global timescale based on atomic clocks time source. The truth is, atomic clocks are even more accurate than the Earth's rotation, so a leap second has to be added to keep this time equation accurate.

What is a TimeServer for NTP?

NTP TimeServer = NtpServer

An NTP TimeServer also known as a NtpServer. TimeServer is a network device that receives a UTC time signal and then distributes it among the other devices on a network. PPS pulses and other standars were created, so that TimeServers can easily distribute time signals. The time protocol NTP then ensures that all machines are kept synchronised to that time.

Where is UTC time source of TimeServer NTP?

There are several sources where a UTC time reference can be taken. The Internet is the most vast source with hundreds of pretty accurate TimeServers relaying their UTC time signals. However these are known to be inaccurate. Also the Internet is not a secure source and is not suitable for any network where critical accuracy and security of time source issues are a concern.

Other methods exist, that provide a more accurate, secure and reliable source of UTC time is to either use the national time broadcast on long-wave or GPS.

What is the rule of thumb for number of NTP TimeServers to synchronize to?

It is entirely up to your tolerance for outages and inaccurate timings. There is a good place to start, and you can progress to three-groups-of-three if you feel the need. Remember that network outages are at least as likely as TimeServer outages, so if you only have one network path to the outside world then adding a lot more TimeServers doesn't really improve your reliability

How come TimeServer can synchronise my stations?

TimeServers use a special NTP Port for communicating with other network devices. You can synchronise other machines on the same network with UDP port 123.

Can I receive a radio time signal from anywhere?

Unfortunately not. Only certain countries have a time signal broadcast from their national physics laboratories and these signals are finite and vulnerable to interference. In the USA the signal is broadcast from Colorado and is known as WWVB, in the UK it is broadcast from Cumbria and is called MSF. Similar systems exist in Germany, Japan, France and Switzerland.

What about GPS? Can I receive a GPS signal from anywhere?

A satellite navigation system relies on the time signals from the onboard atomic clocks in the GPS satellites. It is this time signal that is used to triangulate positioning and it can also be received by a network time server fitted with a GPS antenna. GPS is available everywhere in the World but an antenna does need to have a clear view of the sky.

Will I need multiple NTP TimeServers, when I have large network?

More TimeServers means better accuracy, doesn't it?

Not necessarily. NTP is hierarchical and divided into 'stratum' an atomic clock is a stratum 0 device, a time server that receives the clocks signal is a stratum 1 device and a network device that receives a signal from a time server is a stratum 2 device.

NTP can support 12 stratum (realistically, although more is possible) and each strata can be used as a device to synchronise to. Therefore a stratum 2 device can synchronise other machine lower down the strata and so on. This means no matter how big a network is, only one network time server would be required.