How the Internet connects continents: from the seabed to the starry sky

The Internet is designed to allow data to flow quickly and reliably between billions of devices worldwide. Within countries, this is done by terrestrial fiber-optic cables that stretch along roads, and through towns and villages. But how does your video call from Kyiv to Los Angeles go almost without delay? The answer is a fiber-optic communications system that connects continents at speeds that would make even a cheetah uncomfortable.

And no, it's not about satellites, as half of internet users think. Nearly 99% of international traffic runs through undersea fiber-optic lines, the digital arteries stretching across the oceans.

• There are more than 500 such cables/
• Their total length — 1.4 million kilometers.
• This is enough to wrap the Earth around the equator as many as 32 times!"

A bit of history: how it all began

The idea to link continents by undersea cable was considered a brilliant idea back in the 19th century. In those days, however, it was all about the telegraph. In 1858 the United States and Great Britain laid the first cable across the Atlantic Ocean. But the joy was short-lived: the cable lasted only a couple of weeks: an epic fiasco worth millions of dollars (by today's standards)!

Messages were transmitted at 1 bit per second — "Hello!" reached in a couple of minutes. By 1866 it was already possible to speed up to 8 words per minute.

Today, of course, technology is a head cooler. Almost all of the world's internet traffic passes through fiber-optic cables laid on the bottom of the oceans. And only a small fraction of data is transmitted via satellites, mostly for remote regions or special tasks.

How submarine cables are laid

First, scientists explore the seabed. They don't just lay the cable anywhere - they must avoid underwater mountains, faults, and volcanoes. Everything is considered - underwater currents, geology and even the migration of whales. Sometimes the planning takes longer than the actual laying process

The cost of laying a single cable — millions of dollars. For example, the MAREA project (6,600 kilometers long) connecting the U.S. and Spain cost $250 million.

By the way, the cable itself is not just a "wire", but an engineering masterpiece. It is protected by several layers: steel, plastic, bitumen, more steel. It's only 7 centimeters in diameter, but it's strong enough to withstand corrosion, pressure, and the teeth of curious sharks.

Fiber is laid on the ocean floor using special ships and underwater robotic units. The ship moves slowly along a pre-planned route, lowering the cable to the ocean floor and skirting all the underwater mountains and hollows. Sometimes this happens at depths of up to 8,000 meters, where the pressure is such that it would squeeze a tank. Although the process is cumbersome, the cable is laid with jewel-like precision. Even a slight deviation from the route can cause damage if, for example, it is stretched too tightly on an underwater slope.

An average of 10-12 kilometers of fiber is laid per day. This is done by using underwater plows as well as robots that remove debris or rocks from the cable's path. Deeper waters are left uncovered, while closer to shore the cable is protected — it is a favorite of sharks and fishing trawlers.

There are also devices installed every 50-100 kilometers to amplify the signal. Otherwise, the data won't reach its destination. By the way, every submarine cable is regularly monitored from space by satellites. After all, they are incredibly reliable but still invulnerable. Repair is not easy and costly. For example, lifting a cable from a depth of 4000 meters and repairing it costs $1-2 million. Repairing 100-200 damages every year is a common thing.

Who funds internet networks between continents

IT giants like Google, Meta (Facebook), Microsoft and Amazon are the main players. These guys don't just own data centers, they're also investing in laying subsea backbones. The cost of the issue? In 2022, the submarine cable systems market size was $12.58 billion, projected to reach $30.50 billion by 2030 (according to The Insight Partners).

For example, about $250 million has been spent on a 6600-kilometer-long cable connecting the U.S. and Spain (the MAREA project is an example).

One kilometer of such a fiber-optic backbone costs up to $50,000.

Causes of damage to submarine lines

The reasons can be both the expected and the exotic:

• Loving dolphins. These clever marine mammals often play in the marine jungle - using cables as toys, and often breaking them. In 2014, several undersea cables near Taiwan were damaged at once, and it was… dolphins who were the culprits! They are certainly cute, but 10% of the internet in the region was "lost" for a couple of days.
• Ship Anchors. It's not just marine animals that can cause accidents. Sometimes the causes are more down-to-earth — such as anchors. These types of accidents happen more often than not. For example, in 2008, the anchor of a cargo ship broke through an undersea cable that connected Malta to the rest of Europe. As a result, an entire island was left without stable internet for several days.
• Earthquakes. In 2004, a powerful tremor in the Indian Ocean disrupted several backbones, cutting off connectivity for 70% of  Asia users.

Submarine cable map

What about the satellites?

Yes, everyone has heard of Starlink Elon Musk. This network of thousands of low-orbit satellites allows you to "distribute" the Internet in remote regions — on islands, in mountains, or in deserts. True, there is a nuance: the speed is lower, delays are higher, and it costs more than the usual cables. But satellites work where other technologies fail.

At the moment (2024) Starlink covers more than 95% of the Earth's surface, where people live, thanks to the deployment of tens of thousands of satellites. However, due to some technical peculiarities, there are still dead zones. These are less than 5% and include:

• polar regions;
• oceanic areas away from shipping lanes;
• some mountainous or inaccessible areas.

It is the Starlink system that provides our invincible defenders - the soldiers of the Armed Forces of Ukraine - with the ability to enjoy reliable communications in the most remote and inaccessible points in the current war with the horde.

By the way, Iran, China, and North Korea prohibit Starlink usage on their territory. Even if the satellites can technically provide coverage, availability is still restricted by local laws. They're not allowed to use Starlink in their territories.

Now Starlink is actively working to expand coverage, including launching next-generation satellites with laser inter-satellite links that reduce reliance on ground stations. This should reduce even dead zones, especially in oceans and remote regions. 

Causes of communication damage in space

• Solar storms. Powerful solar flares can cause serious disruptions in satellite communications. For example, in 2003, one such storm shut down all communications satellites worldwide.
• Cosmic interference. In 2008, a Chinese satellite with the latest communications technology accidentally collided with a Russian one. This caused major disruptions and it took years, not weeks, to restore communications.
• Meteorites and space trash. In 2016, space debris damaged a satellite providing communications in Africa. Space — is not a void, but a «graveyard» of old satellites and debris that can cause malfunctions or disable a satellite.

The Future of the Internet: What's in store for us?

• Scale satellite networks. Projects like Starlink, OneWeb, and Amazon Kuiper promise to make the internet available even in the most remote corners of the world.
• Development of the quantum internet. This is a new technology that will make communications virtually invulnerable to hacking.
• Next Generation Underwater Cables. Engineers are already developing cables that can withstand decades of use without breaking.

Why is this important? The reason is the modern internet is not just memes and YouTube. It's medicine, education, emergency services, and billions of important processes. When disaster strikes, it's the internet that becomes the lifeline.

So the next time you send a friend a photo of a kitty across the ocean, remember: somewhere at the bottom of the sea, a tiny ray of light travels miles of fiber optic, skirting mountains and troughs. 

Data rate comparison

Speeds continue to rise. In the coming years, we expect to see cables with bandwidths of 500 Tbps or more, making the internet even faster and more accessible. Maybe soon we'll be able to download a movie in the blink of an eye — as soon as you blink, it's on your device

Top accidents with submarine cables

1. Shark attack. It turns out that sharks like to bite underwater cables. In 2008 one of the cables in the Atlantic suffered from the teeth of the marine predator. Scientists believe that sharks are attracted to the cables' weak electromagnetic field. As a result, communication in several countries disappeared. It took several weeks to repair because the cable had to be lifted from a depth of 3000 meters. Since then, they have been wrapped in special armor.

2. Anchor vs. cable. In 2006, a tanker accidentally dropped anchor on an undersea cable in Hong Kong. The fiber optic was shredded like butter with a knife. As a result, about 10 million users in Asia were left without Internet access. And financial losses for ISPs and banks amounted to $40 million per day of downtime, it took 10 days to repair.

3. Taiwan earthquake. In December 2006, a strong earthquake of magnitude 7.1 damaged several submarine cables off the coast of Taiwan. Almost all communication between China, Japan, and the US was disrupted. Internet commerce in these regions was suspended for several days and the speed of traffic restoration was slow due to the huge load on backup lines. Repairs took almost 2 months to complete! The waters were too deep, which slowed down the work.

A few facts for last

• The longest cable already laid: SEA-ME-WE 3 (South East Asia – Middle East – Western Europe)— 39,000 km! It connects Asia, Europe, and Africa and is so long that it could almost circle the Earth at the equator (if you try a little harder and add a spare). The cable connects 33 countries from Germany to Australia.
• The shortest: the Cross-Harbour Tunnel Cable (Hong Kong) — only 3 kilometers. This “ little thing” is laid across the harbor and connects the two shores of the city.
• Project 2Africa — is one of the most ambitious submarine cable projects in the history of mankind, its construction is underway. It will encircle almost all of Africa, with a total length of – 45,000 km (more than the length of the equator!). The cable will connect 33 countries on 3 continents: Africa, Europe, the Middle East, and Asia. The estimated cost of the project is — 1 billion US dollars.

2Africa Project Map

• There are no direct cables between South America and Australia due to their vast distances, high costs, and low traffic. Instead, the data goes through North America or Asia.
• The largest concentration of submarine cables is found: in the Atlantic Ocean (between Europe and the US), where there are over 400 cables, and around Europe. Europe — the most "fiber-optic" continent.
• In 1999 Japan's Midori communications satellite died due to a software error. The problem was an undercounted comma in the code!
• There are now about 8,000 satellites in orbit, of which about 5,500 are actively used, the average satellite life span is 10-15 years, but accidents are much more frequent.
• On average, undersea cables break about 200 times per year! The cable off the coast of Vietnam (APG) is damaged every 2-3 months due to fishing nets and accidental anchor strikes. 40% of all damage — fishing trawls, 20% — ship anchors, 8-10% — natural disasters (tsunamis, earthquakes), the rest – humans and animals.
• It is said that APCN 2 (Asia Pacific Cable Network 2), which is 19,000 km long, —is the most expensive project, costing about 5 billion USD. This cable connects 9 countries in the Asia-Pacific region. But why is it so expensive? It passes through areas of high volcanic activity, which requires enhanced protection.
• The fastest construction is the "FASTER" backbone (from Google). This 11,629 km cable (launched in 2016) from the US to Japan was built in 18 months. Somebody's home repairs are taking longer than that!