The race to repair Tonga’s fibre optic lifeline

“Throughout the ship the pent-up enthusiasm overflowed, the roaring bravos of our guns drowned the huzzahs of the crew, and the whiz of rockets was heard rushing high into the clear morning sky to greet our consort-ships with the glad intelligence.”

This extract from the diary of John C. Deane, Secretary of Anglo-American Telegraph Company, describes the euphoria aboard engineer I.K. Brunel’s massive cable-laying steamship, the Great Eastern, on September 2, 1866, after the successful salvage and repair of the trans-Atlantic cable.

A hydrographic survey and dive team from HMNZS Wellington inspect the coastal waters off Tonga after a volcano eruption. The single undersea fibre optic cable which connects the Pacific nation to the outside world was severed after the eruption and tsunami. Credit:AP

They had ample reason to be chuffed. Having been mocked for attempting the impossible, they had dragged the ocean floor, thousands of kilometres from land, grabbed the wire from “19,000 fathoms down”, or almost four kilometres, and successfully spliced it to another, re-establishing the link from Valentia, Ireland, to Heart’s Content, Newfoundland (and thus London to New York).

Undersea cables have come a long way since 1866. Not so much in distance, as much of the world was connected by telegraph with the laying of the Pacific cable in 1902, but in capacity and affordability. The first trans-Atlantic cable could carry eight words per minute. Sending a 25-word Christmas telegram to London in 1880 would have cost a Sydney telegraph operator (female, who were paid less than their male counterparts) about six months’ wages.

Even in 1970, a five-minute international phone call from Melbourne to New York would have set you back more than $150 in today’s terms.

Unlike the 1866 Atlantic copper wire, the cable which linked Tonga with the world until last month sent and received data using optic fibres, a technology developed in the 1980s and steadily improved upon since. The Tonga cable alone could carry every telegram sent across the Atlantic between 1886 and 1914 in under two seconds.

But no matter how sophisticated, how carefully deployed, constructed and protected, submarine cables share one quality with every other technology from sewer pipes to radio telescopes – every now and again, they break.

Tonga’s crucial single undersea fibre optic cable was severed on January 15 after a volcanic eruption and subsequent tsunami. Preliminary estimates indicated the break in the cable, which was laid in 2013, was located about 37 kilometres offshore from the main island of Tongatapu. Another cut in the domestic cable was about 47 kilometres offshore.

The severed main Tonga cable runs to Fiji, where it intersects with the trans-Pacific Southern Cross Cable, connecting Tonga to Australia, the US and the rest of the world. It sits on the seabed, running 827 kilometres at depths of up to 3.5 kilometres.

Satellite connections have been used to restore international call services to some areas. Some people have been able to send emails or get limited internet connectivity.

“There are parts of town where we just don’t know exactly what has happened,” said Australian minister for the Pacific, Zed Seselja.Credit:

But like many small Pacific countries, Tonga relies on this single cable to stay connected and has little in the way of a back-up plan. Three years ago, a cable break believed to have been caused by a ship dragging its anchor led to two weeks of disruption. It was described then by local authorities and businesses as “a catastrophe”.

While the capacity of undersea cables has increased from the glacial dots and dashes of Morse code to a torrent of terabytes, one thing hasn’t changed since 1866. If a cable breaks at the bottom of the ocean, you have two choices: either lay another one, or trawl for the original and haul it out of the murk to be fixed.

While the cost of sending data has plummeted over time in inverse proportion to the explosion of available bandwidth, cables themselves have always been expensive pieces of hardware, so the 19th and 21st centuries share at least one specialised piece of marine equipment – the cable repair ship.

For the 1.3 million kilometres of cable strung around the bottom of the world’s seas, there are 59 operational cable-laying and maintenance vessels that are on call to either lay cables or fix faults, according to the International Cable Protection Committee.

“People are calm. Coming out of a total blackout, just being able to call outside and send an email has settled them a bit.”

The ship entrusted with reconnecting Tonga with the world is the CS Reliance, which is sailing more than 4000 kilometres from Papua New Guinea via Samoa, and is expected to arrive in Tonga on Sunday.

The Reliance, registered in the Marshall Islands, spends much of its time in the Pacific and south-east Asia. Despite being hundreds or even thousands of metres underwater, cable breaks are common (up to 200 per year). The Reliance, one of the largest vessels of its kind, has no shortage of work thanks to the Pacific Ring of Fire, which is prone to earthquakes and volcanic eruptions.

Tonga’s cable breaks were, of course, caused by a volcano, and when you consider the seismic instability of places as far-flung as New Zealand, Indonesia and the Philippines, there will always be a need for these ships.

For the Tongan cable, a volcano is a mightier adversary than any anchor, and the Reliance may find that part of the cable has been buried in an underwater avalanche, a possible cause of the consequent tsunami.

“If the volcano blast or tsunami shifted or collapsed a seamount on top of the cable, it could be very difficult to locate or retrieve,” said Jonathan Brewer, a telecommunications engineer at consulting company Telco2.

Repair ships carry spare cable with them – the Reliance has a capacity to carry 5466 metric tonnes of cable – so that they can replace sections that may be lost in such an event, and are greatly helped in the optical era when it comes to locating the breaks by virtue of the nature of the fibre itself.

When laser light is sent down the cable from the shore, it reflects back to its source when it hits the break. By measuring the time between transmission and reception of the reflection, an engineer can locate the break.

A deep sea hook is lowered which cuts the cable into two. One end of the cable is held by a buoy and the other is brought onto the deck. The cable is spliced and repaired onboard with a new joint assembly.

The fibre optic cable isn’t easy to fix. A technician splices the glass fibres and uses glue to attach the new section of the cable. This fibre optic splicing can take up to 16 hours and is the most crucial aspect of the repair work, with each fibre not much thicker than a human hair.

Clean-up on Tonga’s main island. Smaller islands took the brunt of the January 15 volcanic eruption and tsunami.Credit:AP

After the splicing is completed, the cables are attached to each other and are wrapped in multiple protective layers. The cables are then joined onboard the vessel and gently lowered back down to the seafloor.

The cable-laying vessel may tow a sea plough across the ocean floor to bury the cable, and a remotely operated vehicle (ROV) may descend to the seabed to inspect and help bury the cable.

The Tongan cable will be working again in possibly 10 days, the critical lifeline returned to 105,000 Tongans who are still reeling from the devastating effects of the eruption.

At first the volcanic ash was so heavy that it knocked out satellite communication links with the outside world. Satellites carry only around 1 per cent of all phone and data traffic worldwide. The remainder is from underwater cables, but with the ash cloud cleared and damage to ground stations repaired, at least some emails, calls and texts are now getting through.

Samieula Fonua, who chairs the board at Tonga Cable Ltd., the state-owned company which owns the fibre optic cable, said Tongans had been somewhat understanding of the communication disruptions caused by the disaster.

“People are calm. Coming out of a total blackout, just being able to call outside and send an email has settled them a bit,” Fonua said.

Reuters, AP

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