Explainer: How Subsea Telecommunication Cables Power the Global Internet

How Undersea Cable Systems Operate

When we send an encrypted message from London to Tokyo or stream a video hosted on a server in California, it is easy to imagine our data beaming through the upper atmosphere via communication satellites.

In reality, satellite networks carry less than one percent of transcontinental data traffic. The true backbone of global human civilization consists of roughly 550 fiber optic cables resting on the pitch-black ocean floor.

Despite measuring no thicker than an ordinary garden hose, a single modern subsea cable can transmit over 250 terabits of data per second using dense wavelength division multiplexing.

At depths of several thousand meters, the cable consists primarily of a waterproof polyethylene sheath, steel strength members, a copper power conductor, and hair-thin glass fiber cores.

Every 70 to 100 kilometers, specialized optical amplifiers (repeaters) powered by high-voltage direct current boost the laser signals, ensuring packets cross oceans without degradation.