Understanding GPS Time in Relation to UTC
Accurate time is so important for modern computer systems that it is now unimaginable for any network administer to configure a computer system without any regard to synchronisation.
Ensuring all machines are running an accurate and precise time, and that the entire network is synchronised together, will prevent problems arising such as data loss, failure of time sensitive transactions and enable debugging and error management which can be near impossible on networks that lack synchronicity.
There are many sources of accurate time for use with NTP time servers (Network Time Protocol). NTP servers tend to use time that is controlled by atomic clocks to ensure accuracy, and there are advantages and disadvantages to each system.
Ideally as a source of time you want it to be a source of UTC (Coordinated Universal Time) as this is the international time standard as used by computer systems worldwide. But UTC is not always accessible but there is an alternative.
GPS time
GPS time is the time as relayed by the atomic clocks on board GPS satellites. These clocks form the basic technology for the Global Positioning System and their signals are what are used to work out positing information.
But GPS time signals can also provide an accurate source of time for computer networks – although strictly speaking GPS time does differ to UTC.
No Leap Seconds
GPS time is broadcast as an integer. The signal contains the number of seconds from when the GPS clocks were first turned on (January 1980).
Originally GPS time was set to UTC but since GPS satellite have been in space the last thirty years, unlike UTC, there has been no increase to account for leap seconds – so currently GPS is running exactly 17 seconds behind UTC.
Conversion
Whilst GPS time and UTC are not strictly the same as they were originally based on the same time and only the lack of leap seconds not added to GPS makes the difference, and as this is exact in seconds, conversion of GPS time is simple.
Many GPS NTP servers will convert GPS time to UTC time (and local time if you so wish) ensuring you can always have an accurate, stable, secure and reliable source of atomic clock based time.
