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Last Updated: Tuesday, 5 February 2008, 17:19 GMT
Work begins to repair severed net
Bespoke graphic showing location of the cables

Work has begun to repair two damaged internet cables in the Mediterranean Sea that were severed last week.

Flag Telecom, one of the firms responsible for the cables, says it will take about a week to be fixed.

The break in cables has caused disruption to net services in the Middle East and India. The cause is still not known.

Repairs will involve a team of about 50 people, including navigation experts and cable engineers, said Flag Telecom.

The ship that will repair the first severed cable is already in place, with repairs underway, while the second vessel is expected to begin work on Tuesday.

Bespoke ships

"It will be a highly technical job and should take a week to complete," a spokesperson for Flag Telecom told the BBC News website.

The cause of the damage has not been officially confirmed but there have been reports that the breaks were related to a tanker dragging its anchor along the sea bed.

INSIDE A SUBMARINE CABLE
cable infographic
1 Polyethylene cover
2,4 Stranded steel armour wires
3,5 Tar-soaked nylon yarn
6 Polycarbonate insulator
7 Copper sheath
8 Protective core
9 Optical fibres
Not to scale

However, the Egyptian communications ministry has denied any ships were in the area at the time of the break.

The first job in such a situation was to find the exact location of the damaged cable, said Mark Harper, manager of cable system support at Cable and Wireless.

The firm is not involved in the repair operation, but has carried out similar work in the past.

Often the location of a break can be found by cable engineers back on shore. The areas affected by the outage will give key clues as to what part of the cable is broken.

To get a more precise location, cable engineers can send light pulses along the fibres in the cable using a device known as a Optical Time Domain Reflectometer.

When the pulses hit the broken part of the cable they will bounce back and by measuring the time it takes for them to return, engineers can ascertain the location of the damage to within tens of metres.

The next stage is to employ a specially fitted cable ship, which will have onboard remotely operated vehicles (ROVs).

Fishing

If the ROV is able to locate the cable it can cut out the non-working sections and pull the cable back onto the ship.

Alternatively a device onboard known as a grapnel can hook the cable from the sea floor and drag it on to the ship.

"The first option is preferable because it means you can recover the cable very close to the end whereas a grapnel is less precise," said Mr Harper.

Grapnels have been in use for hundreds of years, and so were part of the equipment employed when the first telegraph cables were laid.

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