Satellite bug could affect some networks

Some Irish businesses could find their computer networks knocked out over the weekend because the satellite time broadcasts that some computer networks use to synchronise themselves may be affected by a date problem similar to the Year 2000 glitch.

Satellites which are part of the Global Positioning System (GPS) - a system of 24 US Department of Defence satellites that enables a receiver on earth to pinpoint its position to within a few metres - also broadcast accurate time readings.

GPS is used widely for navigation. But because computer systems use time to initiate, co-ordinate and identify various activities and functions, some system administrators like to use the precise GPS broadcasts to synchronise their networks.

"It's cheap and incredibly accurate," said Mr Chris Davey, technical director of Dublin new media company Oniva. Receivers that plug into a computer can be bought for around £200 (#254), he said.

But because the satellites measure time in a cycle of 1,024 weeks rather than in days, the computerised timeclocks of the 24 satellites roll over to 00:00:00 at midnight on Saturday. That date indicates the moment when the GPS was initiated - January 6th, 1980. While the satellites are prepared for the rollover, some receivers may not be. Computer systems would thus be told they had reversed 20 years into the past.

As with the Year 2000 problem, which will cause the internal clocks of computers to roll over to 00:00:00, systems may react unpredictably or could simply shut down.

Like many Internet service providers, Ireland On-Line uses GPS to synchronise system timeclocks, but a spokesman said the system was 1999-compliant and would not experience problems.

"It's only one of six independent time sources we use to keep our clocks accurate," he said. "The other sources are atomic clocks and other satellite systems. All six of them would have to fail and several months would have to pass before our internal clocks would drift by more than a couple of seconds."

ISPs are considered such an accurate source for time readings that many other organisations, such as Oniva, synchronise their networks to the ISPs. Using a method called Network Time Protocol, or NTP, computers can use a software programme to request time readings across the Internet from reliable locations. The programme then automatically synchronises the networked computers.

Several other organisations with large networks - Trinity College, Bank of Ireland, Microsoft, AIB Bank, and IBM - said they did not use GPS and would not be affected by the rollover problem.