The Network Time Protocol (NTP)

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. NTP is most widely used on LINUX as many of the algorithms needed to provide precise time are embedded into its kernel.

NTP is based upon the User Data-gram Protocol (UDP) which is in-turn reliant on the TCP/IP protocol. 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 hardware reference clocks synchronise to precise external timing resources such as GPS, WWVB, MSF and DCF-77 timing standards. 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.