Tech Original explainer
Your video call crosses oceans on glass threads thinner than a hair. This is the hidden journey of your data.
Open a video on your phone and it starts in a second. It feels instant, and wireless, and somehow everywhere at once. Almost none of that is true. Most of your data does not travel through the air at all. It travels through glass threads lying on the ocean floor, then through cables under roads, and only in the last few hundred metres does it jump through the air to your phone. The internet is, above all, a physical thing — and most of it is underwater.
The numbers are startling. About 99 per cent of international data traffic travels through undersea fibre-optic cables, according to the International Telecommunication Union. Satellites, which most people picture when they think of global communication, carry only a tiny remainder. There are more than 600 cable systems in service, stretching over 1.5 million kilometres across the ocean floor. Every video call home, every UPI payment that touches a foreign server, every episode you stream from abroad rides on this hidden network.
A submarine cable is, at its heart, a bundle of glass fibres thinner than a human hair. Data travels through them as pulses of laser light, flickering on and off billions of times a second. The cable itself is about as thick as a garden hose in deep water, wrapped in steel and plastic to protect it. The glass is so clear that light can travel for dozens of kilometres before it needs a boost. Every 50 to 80 kilometres, a small sealed unit amplifies the signal and sends it on its way. A single fibre can now carry more than 20 terabits per second — enough for millions of video streams at once.
Laying a cable is slow, expensive work. A specialised ship unspools it across the seabed at walking pace, and near the shore it is buried under the sand to protect it from anchors and fishing trawlers. In deep water it simply rests on the bottom, because at those depths there is almost nothing to disturb it. The network is owned not by governments but by consortia of telecom companies and tech giants, who share the cost and the capacity. When a new cable is planned, it is a business decision as much as an engineering one.
A cable comes ashore at a landing station, a heavily guarded building on the coast where the undersea fibre meets the land network. From there, the signal travels through fibre-optic cables buried along highways and railway lines to data centres in big cities. These data centres are the internet's warehouses: rows of servers that store videos, run apps, and answer requests. When you open an app, your request usually goes to one of these buildings, or to a smaller cache server kept closer to your city so the answer comes back faster.
The last leg of the journey is the only wireless part. Your home Wi-Fi router or the mobile tower near your house picks up the signal from the fibre network and broadcasts it over radio waves. A mobile tower covers a few kilometres at most. That is why your signal weakens indoors or in a crowded place: the radio link is the fragile part. Everything before it — ocean cable, buried fibre, data centre — is wired, shielded and fast.
Cables break more often than you might think. The industry records roughly 150 to 200 faults a year, and about two-thirds are caused by fishing boats dragging anchors or trawls across them. Earthquakes and undersea landslides cause the rest. A repair ship has to sail to the spot, haul the cable up from the seabed, splice in a new section, and lay it back down — work that can take days or even weeks in bad weather. Your internet usually survives a break because traffic is automatically rerouted through other cables. But when a key route is cut, whole regions feel it: pages load slowly, video calls freeze, and offices switch to backup links.
India's own connection to this network matters more every year. As more Indians come online and more businesses run on the cloud, the cables landing on Indian shores carry a bigger share of the country's economy. New cables are being planned all the time, and old ones are retired after twenty or twenty-five years. Each new generation carries far more data than the last, which is one reason your connection keeps getting faster even as the number of users grows.
Knowing the journey changes how you think about the internet. It is not a cloud. It is glass and steel and ships, built and repaired by people, and it can be damaged by a trawler or a tremor. When your video buffers, the problem is often the last hop — your Wi-Fi or your tower — not the ocean. And when someone says the internet is free and borderless, remember the map: the cables follow trade routes and politics, landing where it is profitable and safe, and skipping places it is not. The next time a page loads in a blink, spare a thought for the thread of glass on the seabed doing the heavy lifting.
This explainer was written by The Daily Short's desk from the sources listed above. It is general information, not professional advice. Spot an error? See our Corrections Policy or tell us via the Contact page and we will correct it. Follow our official Instagram @thedaily.short.