» Network Time Synchronisation Using NTP Servers

By Dave Evans

Network Time Protocol, or NTP as it is most commonly known, provides a mechanism to synchronise the time of computer devices and other network infrastructure. The protocol was originally developed for the Linux operating system by Dr D Mills of the University of Delaware. For more than two decades, NTP has provided time synchronisation of critical devices on the Internet making it one of the oldest protocols still in continuous operation. This article provides a brief overview of NTP and some of the technical phrases used in computer timing.

NTP was originally developed to solve the requirement of synchronisation of critical time processes across the Internet. The Network Time Protocols primary platform is the LINUX operating system. NTP is provided under the GNU public licence; however, it has also been sucessfully ported to the Windows operating system. LINUX is still however the primary platform associated with the Network Time Protocol.

NTP utilises the UDP (User Data-gram Protocol) over TCP/IP. NTP messages are communicated using UDP port 23, which is reserved solely for the use of NTP traffic. The protocol basically consists of a number of fields, which specify: time-offset, network delay and jitter relative to an accurate time reference. 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. A number of third-party timing hardware manufacturers have installed precision crystals into their reference clocks to provide an accurate backup timing reference,.

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. NTP has a linear heirarchical structure that can provide a timing resource for large numbers of clients. For applications that require critical timing, NTP provides a de-facto standard solution.

Dave W Evans provides technical authoring services to the time and frequency industries. Dave has published a number of articles and white-papers detailing the operation of NTP. Click here, if you would like more information on NTP server solutions.