An optic fibre cable that carries Australia's burgeoning Internet traffic across the Pacific Ocean failed for the first time last month - five kilometres below the surface of the sea and 2,000 kilometres north of New Zealand.

But the system was switched within minutes through a communications satellite, used as a backup for just such emergencies. Most academics in the two countries would have been unaware of the electronic hiccup.

A specially equipped ship was sent to the area to replace the damaged section of cable and investigate the cause of the failure. Normal Internet and telephone traffic over the cable link took 10 days to restore.

A spokesman for Telecom Australia said it was the first time since the cable was laid more than two years ago that such a serious fault had occurred, although ocean cables were often being broken by ships' anchors or underwater disturbances such as earthquakes. It was still not known what had caused the latest failure. It could have been due to undersea subsidence or a short circuit resulting from a power surge.

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Peter Saalmans, general manager of the Australian Academic Research Network, AARNet, said that other cables connected Australia through Asia to the rest of the world but that AARNet preferred the optic fibre cable connection.

This was because it was a digital and not an analogue cable and therefore offered better quality of transmission as well as being more economical.

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The cable connects AARNet to the Internet via the US government-owned NSF Network, which it joins at the Ames Research Centre in California's Silicon Valley.

But from May 1, NSFNet will be shut down and this has forced AARNet to negotiate a new deal with one of America's biggest commercial providers, MCI.

"Since AARNet was established in 1989 we have been connected to the Internet through NSFNet," Mr Saalmans said. "As that era is coming to an end, we will begin testing the new connections with MCI this month ready for the changeover on April 30."

Mr Saalmans said America acted like a giant hub in accepting Internet traffic from Australia and Asia and re-routing it as required around the rest of the globe. The switch to MCI would not result in any additional cost for AARNet customers as it had been budgeted for a year ago when the American government announced that the NSF network would be shut down.

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