Reading: Matching Headings: Question 2

A It is a common assumption that the world's internet traffic (video calls, financial transfers, emails, streamed films) travels mainly through satellites orbiting overhead. In reality, more than ninety-five percent of all data moving between continents passes instead through a global network of cables laid along the ocean floor, an infrastructure most users never see and rarely think about.

B A modern submarine cable is deceptively slender, often no thicker than a garden hose, yet it houses a bundle of optical fibres each about the width of a human hair. Data travels along these fibres as pulses of light rather than electrical signals, allowing enormous volumes of information to move at close to the speed of light. Layers of steel wire, copper and waterproof polyethylene are wound around the fibres to protect them from water pressure, abrasion and corrosion during decades on the seabed.

C Laying a cable begins with months of route surveying: engineers map the seafloor to avoid volcanic fault lines, existing pipelines and busy fishing grounds before a specialised cable ship spools thousands of kilometres of cable out behind it. Near the coast, where the risk of damage is highest, the cable is buried beneath the seabed using an underwater plough; in the deep ocean, far from ships and anchors, it is usually left to rest directly on the seafloor.

D Despite careful planning, cables break with some regularity. The great majority of faults are caused not by dramatic events but by fishing trawlers dragging nets across the seabed or ships' anchors snagging a cable in shallow coastal waters. Less frequently, undersea landslides or earthquakes can sever several cables at once, occasionally cutting off a whole region's international internet connection for days.

E Repairing a break requires a purpose-built cable ship to sail to the fault's location, identify the exact point of damage by sending test signals along the line, and then use a grappling hook to haul the cable up from the seabed. Technicians splice in a new section of fibre inside an onboard workshop kept as clean as an operating theatre, since even a speck of dust can degrade the signal, before lowering the repaired cable back to the ocean floor.

F Because such an enormous share of global communication depends on a relatively small number of these cables, governments and telecommunications companies increasingly treat them as critical national infrastructure. Investment in additional, redundant routes has grown in recent years, alongside rising concern that a deliberate, coordinated attack on a handful of key cables could disrupt the internet access of entire nations.

The passage has six paragraphs, A–F.

List of Headings i. Layers of protection inside a slender cable ii. The hidden scale of data crossing the ocean floor iii. Why satellites carry the bulk of global data traffic iv. Careful planning before a cable is laid v. The everyday causes of accidental cable damage vi. The rising cost of laying a transatlantic cable vii. Restoring a connection after a break viii. Cables as a matter of national security

Choose the correct heading for each paragraph from the list of headings below.

Paragraph A Paragraph B Paragraph C Paragraph D Paragraph E Paragraph F