Network Time Protocol (NTP) is one of the oldest protocols on the Internet is still in use. Invented by Dr. David Mills from the University of Delaware has in use since 1985. NTP is a protocol to synchronize clocks on computers and networks over the Internet or Local Area Networks (LANs).
NTP (version 4) may take some time over the Internet within 10 milliseconds (1/100th of a second) and still can do more over LANs with accuracies of 200 microseconds(1/5000th of a second) under ideal conditions.
NTP works within the TCP/IP suite and relies on UDP, a less complex form of NTP exists called Simple Network Time Protocol (SNTP) that does not require the storing of information about previous communications, needed by NTP. It is used in some devices and applications where high accuracy timing is not as important.
Time synchronization with NTP is relatively simple, it synchronizes time with reference to a reliable clock source. This source could be relative (a computer's internal clock or the watch-time on a wrist) or absolute (A UTC - Universal Coordinated Time - clock source that is accurate as humanly possible).
Atomic clocks are the absolute time-keeping devices. They operate on the principle that has the atom, cesium-133, exact number of cycles of radiation every second (9,192,631,770). This has been so precisely, the International System of Units (SI) has now theSeconds, the duration of 9192631770 cycles of radiation of cesium-133 atom.
However, atomic clocks are extremely expensive and are usually found only in large physics laboratories. However, NTP can synchronize networks to an atomic clock by using either the Global Positioning System (GPS) or a specialist radio transmission.
The most widely used is the GPS system, which consists of a series of satellites for accurate positioning and isLocation information. Each GPS satellite can do this which are in turn used as a timing reference only by the use of an atomic clock.
A typical GPS receivers on timing information, is located within a few nanoseconds of UTC as long as there is an antenna with a good view of the sky.
There are also a number of national time and frequency radio transmissions that are used that can synchronize to an NTP server. Will be broadcast in Britain called the signal (MSF)by the National Physics Laboratory in Cumbria which serves as the United Kingdom's national time reference, there are similar systems in Colorado, USA (WWVB) and in Frankfurt, Germany (DCF-77). These signals provides UTC time to an accuracy of 100 microseconds, but the radio signal has a finite range and is vulnerable to disruption.
The distance from the reference clock is known as the stratum level, and they exist to prevent cycles in the NTP. Stratum 0, unitssuch as atomic clocks is directly connected to a computer. Stratum 1, computers are connected to 0-layer devices, while Stratum 2 computers that are located by mail to stratum 1 NTP servers. NTP can be up to 256 layers.
All Microsoft Windows versions since 2000, the Windows Time service (W32Time.exe), the ability to synchronize the computer clock to an NTP server (or an SNTP server - a simplified version of NTP), many Linux and UNIX has-based operating systemsalso a version of NTP, but the source code is free (to download current version 4.2.4) on the NTP website (ntp.org).
We strongly by Microsoft and others that should be used for external timing, rather than Internet-based recommended because this can not be authenticated. Specialist NTP servers are available that can synchronize the time on networks using either the MSF (or equivalent) or GPS signal.
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