How engineers will reconnect Tonga’s broken internet cable

Race to reunite Tonga

How engineers will repair an undersea communication cable cut by a recent volcanic eruption

Global map of undersea communication cables running across the Pacific Ocean with China to the west and the United States to the east. The map shows the eruption of the Tonga volcano and several cables passing near the island nation.

The South Pacific country of Tonga has been completely cut off from the world after the massive eruption of the Hunga Tonga-Hunga Ha’apai volcano on January 15th, when an undersea communication cable was cut. .

Limited satellite connectivity has provided some relief, but connectivity remains elusive as some outlying islands are still cut off.

Tonga signed a 15-year contract to provide the satellite link in 2019 after the cable was cut before the ship anchored. However, the use of satellite phones has been affected by volcanic ash covering the country. Some people reported that they could only make calls and not receive calls.

A specialist vessel is heading to the area to recover the cable. The ship departed Port Moresby, Papua New Guinea, about 4,700 km (2,900 miles) away on January 20 and is expected to arrive there on January 30. The operation is expected to take several weeks.

The 827 km (514 mi) cable from Fiji to Tonga is one of 436 active submarine cables connecting the world.

According to network monitoring company Kentik, five days after the eruption, the country’s main telecommunications operators were able to connect to the global Internet via satellite.

However, the capacity of satellite-based Internet is very limited, says Doug Madory, a network analyst at Kentuck. “Satellite service in the Pacific is expensive because of the wide coverage and relatively small population,” he said.

Tonga’s cable was built in 2013 at a cost of $15 million. The World Bank and the Asian Development Bank have provided grants to help end dependence on expensive satellite communications.

Subsea communication cables can vary in size and construction, but are roughly the diameter of a garden hose. Although relatively thin, these cables have multiple layers that protect the fiber optic cable in the center. Despite layers of protection and avoiding crash-prone areas, an average of 100 cable failures are reported each year, according to telecoms research firm Telegeograph.

Structure of submarine cable

Most cable damage is caused by environmental factors such as ship anchors or fishing trawlers and sometimes earthquakes.

Outages are common and usually most traffic is diverted to another cable. However, Tonga has only one cable connecting the country. It also sits on the Pacific Ring of Fire, prone to earthquakes and volcanic eruptions, adding an additional risk.

According to Jonathan Brewer, telecommunications engineer at Telco2 Limited, it is better to have multiple cables or multiple cable landing stations to manage the risk of disruption. However, this can be expensive. Pacific islands such as Guam and French Polynesia have significant support from the US and French governments that allow them to have such extensive infrastructure.

The repair vessel, CS Reliance, is one of six identical vessels owned by submarine cable-laying company SubCom. She is based in New Caledonia, a French overseas territory west of Tonga, and is one of the largest ships of her kind.

As of June 2021, there are 59 operational cable-laying and maintenance vessels designated from time to time to either lay cables or repair faults under the International Cable Protection Committee.

A pulse of light sent through a fiber optic cable would normally travel to the other end. However, in the broken fiber, the pulse bounces back, and engineers can measure the time it takes to bounce back to find the break.

“If a cable is buried or moved away from its original route, it can be difficult to locate. If a volcanic eruption or tsunami has shifted or collapsed the seabed above the cable, it can be very difficult to locate or remove it,” Brewer said.

A deep sea hook is lowered, cutting the cable in two. One end of the cable is held by a buoy, and the other is brought to the deck. The cable is connected with a new joint and repaired on board.

Fixing a fiber optic cable is not easy. The technician joins the glass fibers together and uses glue to attach the new section of cable. This fiber optic splicing can take up to 16 hours and is the most important aspect of the repair job.

After the connection is completed, the cables are glued together and wrapped in several protective layers to prevent pressure and environmental damage.

The cables are then joined on board the ship and gently lowered back to the seabed in a hairpin fashion.

Also, depending on seabed conditions, a cable hauling vessel may drag a sea plow across the ocean floor to bury the cable.

A remotely operated vehicle (ROV) can descend to the seabed to inspect and help bury the cable, although they can only operate at a certain depth. In the case of Reliance, the car can descend up to 2500 meters.

Most of these cables have an estimated lifespan of 25 years and are usually retired and replaced with newer ones. Some are salvaged for their reusable raw materials.

Although telephone connections between Tonga and the wider world have begun to be reconnected, it could take a month or more to restore full internet connectivity, according to the owner of the archipelago’s only undersea communications cable.


Telegeography; Kentish; Global Volcanism Program, Smithsonian Institution; United States Geological Survey; SubCom; Refinitive Eikon; International Cable Protection Committee; Natural Earth

Data for CS Reliance road updated as of 28 January 2022 6:35 AM GMT

Edited by

Philippa Fletcher

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