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The Network Time Protocol (NTP) was developed more than 25 years ago to synchronise Internet servers to the correct time. NTP is now one of the oldest protocols still in operation today. The protocol is widely used to synchronise Internet and intranet infrastructure and processes. This article briefly outlines the operation of NTP and some of the terminology associated with the protocol.
NTP was originally developed to solve the requirement of synchronisation of critical time processes across the Internet. The NTP protocol is primarily intended for operation on LINUX servers; however, it has recently been ported to other operating systems such as Microsoft Windows. LINUX is still however the primary platform associated with the Network Time Protocol.
NTP utilises the UDP (User Data-gram Protocol) over TCP/IP. It communicates using UDP port 123, which is reserved solely for use by NTP. The protocol basically consists of a number of fields, which specify: clock-offset, round-trip delay and dispersion relative to a precise time source. The information stored in each NTP packet allow a network time client to accurately synchronise time with a NTP server.
NTP is a structured protocol that operates in a hierarchical manner. At the top of the tree, a primary time reference is known as a stratum 1 time server. Servers that synchronise to a stratum 1 server are known as stratum 2 servers and so on down each level of the hierarchy. As the stratum increases, so generally precision decreases.
Over a number of years NTP has been enhanced to operate with a plethora of precision hardware clock devices, or reference clocks. NTP reference clocks are available for GPS hardware and also many of the National Radio Time and Frequency standards such as MSF, DCF-77 and WWVB. Many hardware reference clocks also provide backup precision timing outputs such as TCXO, OCXO and rubidium references to maintain accurate time in the event of signal loss.
A spin-off of the NTP protocol is SNTP or Simple Network Time Protocol, which is basically as the name implies, a simplified version of NTP. SNTP is generally used in small low-powered computing devices such as micro-controllers. It allows low-powered devices the ability to synchronise time to NTP servers over a network.
To summarise, NTP is a long-standing and widely used protocol for synchronising time between time critical processes. It has a straightforward hierarchical structure that allows synchronisation of large numbers of network time clients. For applications that require critical timing, NTP provides a de-facto standard solution.
Dave Evans is an experienced technical author that specialises in computer network timing applications. Dave has written a number of articles to help computer professionals with network time synchronisation solutions. Click here, if you would like more information on NTP servers.
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