The Undersea Highways of the Internet
When you send an email to someone on the other side of the world, the data almost certainly travels through a cable buried beneath the ocean. Satellite connections exist, but they are slow and expensive by comparison. Today, a network of more than 400 submarine cables — stretching roughly 1.3 million kilometres in total — carries around 95 percent of all international internet and telephone traffic. These cables are the invisible backbone of the global internet.
A modern submarine cable is surprisingly thin. The core of the cable contains several pairs of optical fibres, each thinner than a human hair. Data travels along these fibres as pulses of light, moving at close to the speed of light itself. A single cable can carry tens of terabits of data per second — enough to transmit millions of high-definition videos simultaneously. To protect the fragile fibres, engineers wrap them in layers of steel wire and waterproof insulation. Near coastlines, where anchors and fishing trawlers pose a risk, the cable is buried beneath the seabed. In deep water, it simply rests on the ocean floor.
Laying a submarine cable is a large and costly engineering project. Specialised cable-laying ships unspool the cable slowly as they sail along a planned route. The route is chosen carefully to avoid underwater volcanoes, earthquake zones, and areas of heavy shipping traffic. Once the cable reaches shore, it connects to a landing station — a building on the coast that links the undersea line to the land-based internet network. The entire process, from planning to completion, typically takes two to three years and can cost hundreds of millions of dollars.
Because so much of the world's communication depends on these cables, their reliability is critical. Cables do break — usually due to undersea earthquakes, ship anchors dragging across the seabed, or equipment failure. Dedicated repair ships are kept on standby in various parts of the world, ready to locate a fault using sonar and send down robotic equipment to splice the cable back together. Repairs in deep water can take several weeks. Governments and internet companies treat major submarine cable routes as strategic infrastructure, and any disruption to a key cable can slow internet speeds across an entire region.
The demand for bandwidth keeps growing, and so does the number of cables being planned and built. Technology companies such as Google and Meta now fund and own submarine cables alongside traditional telecommunications firms. The ocean floor, though invisible to most of us, is where the modern internet truly lives.
Vocabulary
- submarine
- existing or operating under the surface of the sea — The submarine pipeline was inspected by a remote-controlled vehicle.
- backbone
- the most important part of a system that supports everything else — Rail freight forms the backbone of the country's supply chain.
- optical fibres
- very thin threads of glass or plastic that carry information as pulses of light — The hospital's network was upgraded with optical fibres to handle large medical image files.
- terabits
- units of digital information equal to one trillion bits, used to measure very large amounts of data — The new data centre can process several terabits of information every second.
- insulation
- a layer of material used to prevent heat, electricity, or water from passing through something — The wires were covered in thick insulation to protect them from moisture.
- trawlers
- fishing boats that pull large nets along the bottom of the sea — The harbour was busy with trawlers unloading their catch each morning.
- unspool
- to unwind something from a roll or spool in a controlled way — The crew began to unspool the cable from the large drum at the back of the ship.
- landing station
- a building on a coast where an undersea cable comes ashore and connects to a land-based network — The landing station was built in a secure location away from the public beach.
- sonar
- a system that uses sound waves to find objects underwater or measure ocean depth — The research vessel used sonar to map the seafloor along the survey route.
- splice
- to join two ends of a cable or rope firmly together — Technicians had to splice the broken wire before the signal could be restored.
- bandwidth
- the amount of data that can be sent through an internet connection in a given time — Streaming live video requires a large amount of bandwidth.
- strategic infrastructure
- systems or facilities that are essential to a country's safety, economy, or communications — Power grids and water systems are considered strategic infrastructure in most countries.