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Using Gps For Stratum 1 Ntp Servers
By David Evans
GPS is a US military system designed for navigation and precise positioning. It consists of 24 earth-orbiting satellites, each with an on-board atomic clock. Accurate time combined with triangulation from a number of satellites can provide precise positioning anywhere on the globe. However, the precise timing information supplied by can also be used for time and frequency applications such as computer network time synchronisation. This article discusses how the Global Positioning System can be utilised by NTP server systems to provide precise network synchronisation. Additionally, it describes the equipment required in order to receive accurate time from the system and to synchronise computer time.
Time is referenced to Universal Coordinated Time (UTC), which is the same worldwide and does not vary with time zones. The satellites continuously transmit precise time information. time is not affected by leap seconds and is currently 14 seconds ahead of UTC time. UTC time can easily be calculated from time and used for accurate timing purposes. The satellites broadcast a very weak low-power radio signal. The signal has two frequencies, L1 and L2. L1 is intended as a civilian band broadcast at 1575.42 MHz. L2 should provide stronger signal transmissions in the future. The signal travels in a straight line and can pass through clouds, glass and plastics but is blocked by objects such as metal and brickwork. Therefore, ideally, a antenna requires a good view of the sky. The ideal location for a antenna is on rooftop with a good view of the sky. If it is impractical to locate a roof-mounted
antenna, installation on the side of a building can be adequate.
GPS provides a free-to-air precision time and frequency service. Many computer networks utilise the clock as an accurate timing reference for computer synchronisation. Precise NTP server systems utilise reference clocks as an external synchronisation source. The system can supply highly precise time and frequency information accurate to a couple of nanoseconds. This accuracy is generally more than enough for most computer network timing applications.
Most receivers transmit time and positioning information in a serial format using the standard NMEA protocol. Information is transmitted as sentences of character strings. Additionally, a highly accurate timing pulse is generated which marks the beginning of each second. This timing pulse can be converted to a RS232 signal level and fed into a RS232 control line interrupt to provide a precise timing reference. When the timing pulse is combined with the NMEA output sentences, a very accurate timing reference becomes available for use by NTP servers or computer timing equipment. Article Source: Article Beam - a service of A1 Web Server Web Hosting D. Evans is a technical author with many years experience in the field of computer network time synchronisation. Click here to find out more about GPS NTP Server systems.
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