Atomic clocks using as external NTP Timing Reference

Atomic clocks have been around for over fifty years or more. They have clocks that use a resonant frequency as the element's atomic timekeeping, rather than conventional crystal oscillating as quartz.

Most atomic clocks use the resonance of cesium-133, which resonates at a frequency of exactly 9,192,631,770 every second. Since 1967, the international system of Units (SI) has defined the oscillators as the number of cycles of cesium atomic clocks, which is -133 (sometimes called cesium seconds) standard for measuring time.

Because the resonance of cesium 133 is so precise, which makes atomic clocks accurate to less than 2 nanoseconds per day, equivalent to about one second in 1.4 million years.

That the atomic clocks are so accurate, a scale capable of maintaining stable and continuous time, universal time, UTC (Coordinated Universal Time or Universal Time Coordinated), was prepared and supports features such as leap seconds - added to compensate for the slowing rotation of the Earth.

However, atomic clocks are extremely expensive and are usually found in the physics laboratory scale. However, the NTP (Network Time Protocol), the standard way to obtain time synchronization networks of computers, you can synchronize with an atomic clock, using the Global Positioning System (GPS) network or specialist radio transmissions .

The most used is the GPS (Global Positioning System), developed by the U.S. Army. Contains at least 24 GPS satellites in orbit to provide high precision positioning and location information. Each GPS satellite can be done using an atomic clock, which in turn can be used as reference.

A GPS time server is the ideal time and frequency source because it is capable of providing highly accurate time anywhere in the world using relatively cheap components. Each GPS satellite transmits two frequencies of level 2 for military use and L1 for use by civilians transmitted at 1575 MHz, the antennas at low cost GPS receivers have become widely available.

There are also a number of national terms and the radio frequency that can be used to synchronize an NTP server. In Britain the signal (called MSF) is broadcast by National Physical Laboratory in Cumbria which serves as the national reference time of the United Kingdom, there are also similar systems in Colorado, USA (WWVB) and Frankfurt, Germany (DCF-77) . These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a limited scope and is vulnerable to interference.

Using a GPS NTP server or a radio based NTP time server, network client in turn can be synchronized within milliseconds of UTC based on network traffic.