Repairs to the 38,000-kilometre underwater fibre-optic voice and data cable linking Australia, Asia and Europe should be completed by 8 o'clock tonight, Australian time.

Telstra says its ISP's network will be returned to normal capacity by tomorrow.

The 20-hour repair was delayed earlier this week when the repair ship enountered rough seas at the site of the damage, around 70 kilometres off the coast of Singapore. Sea conditions then were deemed too unstable to conduct the operation, which included splicing together the two ends of the cable and replacing a vital data relay component.

Telstra's public affairs manager Stuart Gray said the cable would be dropped back into the ocean at 8 o'clock tonight, but would not be operational until tomorrow.

The cable would be -powered up" and tested overnight, he said.

-We don't just dump fifty percent of our traffic on it as soon as it's back in the ocean."

The ISP's 650,000 Australian customers have been experiencing a slowdown when logging onto all overseas Web sites since the afternoon of November 20, when the cable was sliced in two by unknown forces.

The SEA-ME-WE3 cable connects Australia with Asia, the Middle East and Europe and normally holds around 60 percent of Telstra's international Web traffic.

The mishap immediately slowed the Telstra Bigpond network down to around 30 percent capacity. Alternative re-routing of international Web traffic brought that up to 80 percent while repairs were underway.

Gray said the overall cost of the damage would be minimal for the ISP because the repair is paid for by the consortium of more than 90 international companies, including Telstra, that own the cable.

A similar repair recently cost that consortium around AU$200,000. Gray said Telstra's stake in the consortium was less than five percent.

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