How do subsea cables work?

Texting a friend who lives overseas. Researching travel plans for your next vacation. Joining a Zoom call with an international colleague. It’s easy to take these everyday internet uses for granted when the exchange of information across continents happens so quickly.

But the hidden infrastructure that enables all of this might surprise you: subsea cables that crisscross the ocean’s floor, transporting hundreds of terabytes of data per second. The industry is the “best-kept secret ever” because it's “fairly invisible,” Nigel Bayliff, senior director of global submarine networks at Google, told Tech Brew.

These underwater pipes don’t look impressive at first glance—some are no bigger than a household garden hose—but they hold the global internet together.

“In some ways, the factories of today’s era are data centers, and fiber-optic subsea cables are the railroads that connect them together,” Brian Quigley, Google’s VP of global network infrastructure, said at a Jan. 17 event announcing a project to run such cables linking Guam with the islands of Fiji and French Polynesia.

At the very heart of the cable, there are typically 16 slim fiber-optic strands that actually transmit the data, surrounded by a layer of copper armoring to protect and stabilize the strands. This core is then encased in a polyethylene jacket.

This lightweight cable—about the circumference of your thumb—runs through the deepest parts of the ocean, where it’s unlikely to be disturbed by activities like boat anchoring and fishing operations. As the cable travels into shallower water that sees more traffic, it’s armored with additional casings that can reach about two inches in diameter. Even as the cable grows in size, its precious cargo—data, and the fiber optics that carry it—remains the same.

Data’s submarine journey

A subsea cable starts its journey at an information and communications technology center, and continues to a landing station, where the cable physically leaves the shore and tunnels into the sea.

When laying a new cable, a ship with thousands of miles of cable coiled in its bowels begins a slow journey, feeding the cable off the back of the ship much like unfurling a coil of rope. The ship is outfitted with a plow that creates a trough in the bed of the ocean for the cable, and the underwater currents eventually bury it in the sand. The cable periodically runs through housings made out of alloy that can survive on the seabed for roughly 25 years, amplifying the data on its journey.

Amazingly, the method for laying subsea cables hasn’t changed since the advent of the telegraph: It’s just the amount of data the cables can carry and the speed of transmission that have evolved.

The results

With a network of roughly 500 subsea cables that traverse the globe, everyone from data centers down to everyday web users can enjoy more stable and reliable internet access.

“We have those multiple routes to connect people. Our goal…is to organize the world’s information and make it universally accessible,” Bayliff said.