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NTP was developed over 25 years ago as a means of synchronising time on client machines across the Internet. The Network Time Protocol is one of the oldest Internet protocols still in use today. NTP was originally developed for Linux but has been ported to the Microsoft Windows operating systems. NTP provides a suite of programs that allow a client to synchronise to within fractions of a second of an accurate timing reference.
Combining an accurate external timing reference with the NTP application provides a highly accurate network timing device. This article describes how to utilise a low-cost GPS receiver in combination with the NTP software distribution to provide an accurate stratum 1 NTP server timing reference.
The NTP source code can be obtained from the NTP website and must be compiled on the local machine. The distribution extracts to a working directory where simple configuration and compilation scripts are available to install the software. Linux distributions such as Redhat and Debian install the NTP distribution by default. In order to configure a stratum 1 NTP server an accurate reference clock is required. The NTP software provides a large number of reference clock drivers that can be utilised to interface with a range of hardware timing references. Hardware timing references can generally be fairly expensive pieces of equipment. However, the popularity of GPS navigation devices has reduced the cost of GPS technology. Low-cost GPS receivers are now readily available from around $100. Many GPS receivers have a RS232 serial communications port, which can easily be connected to a PC. Most GPS receivers utilise the NMEA communications protocol which provides time and location information each second. The timing information can be utilised by the NTP software as an accurate timing reference to provide a stratum 1 NTP server.
The NTP software needs to be compiled with the NMEA reference clock driver to interface with the GPS receiver. Once compiled the application must be configured to utilise the correct serial port. When correctly installed and configured, the NTP application will provide your network with an accurate, stable timing reference.
A NTP server can be utilised to synchronise time on most computer operating systems and network infrastructure. Any device that has a NTP or SNTP client can be configured to obtain accurate time from a server. Generally, clients only need the IP address of the NTP server for synchronisation. With a NTP server, you can synchronise almost any device on your network.
