NTP is the standard protocol for distributing accurate time around the Internet to time clients. There are many public stratum 1 NTP servers that reside on the Internet. However, often it may be necessary for an organisation to install a private local stratum 1 NTP server. This article describes a number of reference clock solutions available for synchronizing a stratum 1 NTP server.
Probably the most widely used NTP reference clock resource is currently the Global Positioning System (GPS). The GPS system consists of a number of orbiting satellites providing accurate positioning and location information. However, each GPS satellite also has an integral highly accurate atomic clock that can be used as a timing reference. Utilising the GPS system for time synchronisation has a number of advantages. The Global Positioning System is ideal to provide an accurate timing reference utilising low-cost components. A typical GPS receiver can provide timing information to within a few nanoseconds of UTC. Also, provided the antenna is shown a good view of the sky, the GPS timing signal can be received world-wide. The disadvantage of using the GPS system is the very fact that the antenna requires a view of the sky. In many installations, locating an antenna on a rooftop can be impractical or expensive.
There are also a number of national time and frequency radio transmissions that can be used to synchronise a stratum 1 NTP server. The advantage of using a radio time reference is that generally a good signal can be obtained indoors close to the host computer. This can greatly reduce potential installation costs. However, radio time references are generally less accurate than GPS systems. Typically, national time and frequency transmissions are accurate to 1 - 20 milliseconds. The radio transmission is regional and has a finite range dependant on transmitter power. Additionally, local interference or environmental issues can cause problems with reception. Placing a radio antenna too close to electrically noisy equipment can result in signal loss. Also, locating an antenna inside a metal enclosure or underground in a basement can also be a problem.
There are numerous radio national time and frequency resources each broadcasting to a regional audience.
The WWVB time and frequency signal is a 60kHz radio broadcast transmitted from Fort Collins, Colorado, USA. The WWVB signal continuously transmits time and frequency signals throughout the US and much of Northern America. The signal provides UTC time to an accuracy of 100 microseconds.
The DCF-77 time and frequency signal is transmitted from Frankfurt, Germany. DCF-77 broadcasts timing information continously at 77.5kHz. The transmission covers Germany and much of Central and North Western Europe. Time and frequency information is broadcast to an accuracy of <20msec.
The MSF radio time and frequency broadcast is transmitted at 60kHz from Anthorn, Cumbria, UK. The broadcast covers the British Isles and much of North Western Europe. Time and frequency information is broadcast to an accuracy of <1msec.
The TDF time signal is broadcast from Allouis, France. It continuously broadcasts time and frequency information at 162kHz. The transmitter has a power output of 2000kW, with coverage of France and much of Central and Western Europe.
The JJY long-wave time and frequency broadcast is transmitted from Tokyo, Japan. The broadcast is continuously transmitted at 60kHz and covers much of Japan and Far Eastern Asia.
To conclude, there are many sources of time and frequency reference broadcasts available. When choosing a reference to utilise for a stratum 1 NTP server, regional availability must be taken into account along with ease of installation and required accuracy.
The Network Time Protocol (NTP) was developed to provide a way of synchronising Internet clients to an accurate network time reference. NTP allows the time on client computers to be set to within a fraction of the correct time. The NTP protocol is a suite of programs designed specifically for time synchronisation purposes. The application source code is freely downloadable from the NTP website. Originally developed for the Linux operating system, NTP has since been ported to Microsoft Windows platforms.
By interfacing an accurate reference clock to the NTP software distribution, you can provide a stratum 1 NTP server. 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 downloadable NTP tar file extracts to a directory where scripts are available to make compilation and configuration very straight-forward. Many Linux distributions provide pre-installed versions of the software. 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. Dedicated hardware timing devices can be prohibitively expensive. 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. Many low-cost GPS devices use the NMEA protocol, which is a standard GPS protocol for providing location and timing information. 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.
David Evans has sinced written about articles on various topics from Computers and The Internet, Personal Desktop and Computers and The Internet. For a number of years, David Evans has been involved in the telecommunications and computer timing industry. David is a technical author with a long history of involvement in installing and configuring timing systems. David has also provided a technical a. David Evans's top article generates over 18100 views. to your Favourites.