How the Internet Travels Under the Sea: The Hidden Cables That Connect India
Your WhatsApp video call to a cousin abroad doesn’t go through space — it travels through cables on the ocean floor. How undersea cables work, why they get cut, and India’s place in this network.
In early September 2025, many people in India noticed websites loading slowly and video calls breaking up. The reason was not a problem with their Wi-Fi or mobile tower. It was thousands of kilometres away, at the bottom of the Red Sea, where undersea cables near Jeddah in Saudi Arabia had been damaged.
That incident reminded me of something most of us never think about: the internet is not “in the cloud”. It runs through physical wires — and many of the most important ones lie on the ocean floor.
🌊 Satellites or Cables? Mostly Cables
Many people assume international internet traffic goes through satellites. In reality, close to 99% of the world’s international data traffic travels through submarine (undersea) fibre-optic cables. Satellites help in remote areas, but cables carry far more data, far faster and more cheaply.
There are roughly 600 such cables around the world, together running around 1.5 million kilometres — enough to wrap around the Earth dozens of times.
💡 What Is Inside a Cable?
At the centre are hair-thin strands of glass called optical fibres. Data is sent as pulses of laser light that travel through the glass at enormous speed. A single modern cable can carry many terabits of data every second.
Around the fibres are layers of protection: a metal tube, copper, plastic insulation and, near the coast, steel armour wires. Surprisingly, in the deep ocean, a cable can be about as thick as a garden hose. Near the shore, where risks are higher, it is thicker and often buried under the seabed.
Light weakens over long distances, so repeaters are placed along the cable at regular intervals to boost the signal. They get power through the copper layer from the shore.
🚢 How Are They Laid — and Why Do They Break?
Special cable ships carry thousands of kilometres of cable coiled in giant tanks. They move slowly across the ocean, laying the cable on a pre-surveyed route on the seabed.
Cables get damaged more often than you might think. Most faults are caused by ship anchors and fishing trawlers near coasts. Earthquakes and underwater landslides can also break them. Repair ships then locate the fault, lift the cable to the surface, splice in a new section and lower it back — a job that can take days or weeks.
In the September 2025 Red Sea incident, cables including SMW4 and IMEWE were damaged, and connectivity slowed in parts of the Middle East and South Asia, including India. Internet companies rerouted traffic through other paths, which is why the internet slowed down instead of stopping completely.
“Every message we send makes a journey across the ocean floor — in a blink.”
🇮🇳 India’s Place in the Network
India’s international internet connects to the world mainly at cable landing stations on the coast. According to a 2026 Carnegie India study, India had around 18 international subsea cables by 2025, landing in cities such as Mumbai, Chennai, Kochi, Thoothukudi and Thiruvananthapuram. Mumbai is by far the largest hub, handling the bulk of India’s international bandwidth.
Chennai is our gateway on the eastern side, connecting India towards Singapore and South-East Asia. New cables landing on the east coast help reduce dependence on a single city — an important step for a country with hundreds of millions of internet users.
The same study notes that repair ships serving Indian waters are based in places like Singapore and Dubai, so responding to a fault near India can take days. Building more routes and local repair capacity is part of making our internet resilient.
📱 Your Video Call’s Journey
When you video-call a relative in the USA from Chennai, roughly this happens:
- Your phone sends data to the mobile tower or Wi-Fi router.
- Your telecom operator carries it through fibre lines across India.
- It reaches a cable landing station and enters an undersea cable.
- It may hop through several cables and countries on the way.
- It lands on the other side and travels to your relative’s phone.
All of this happens in a fraction of a second. Much of what we call “the cloud” is actually large data centres connected by these cables — I wrote more about it in cloud computing explained simply.
✨ Takeaway
- The internet is physical: about 99% of international data flows through undersea cables.
- Cables carry light through glass fibres and are mostly damaged by anchors and fishing.
- India connects mainly through Mumbai and Chennai, with more landing points coming up.
- Multiple routes keep the internet running even when one cable breaks.
The next time a website loads instantly, spare a thought for the quiet cables lying on the dark ocean floor, carrying our conversations across the world.
Sources: Carnegie India, “India’s Stake in the Global Subsea Cable Race” (2026); news reports on the Red Sea cable cuts of 7 September 2025.
Software engineer by skill, storyteller by soul. I write about life, health, money and technology from my own experience — and build free tools you can use every day.
