The Secret Life of the 500+ Cables That Run the Internet

The concert is in London. You’re watching it live from your home in Atlanta. What makes that possible is a network of subsea cables draped across the cold, dark contours of the ocean floor, transmitting sights and sounds at the speed of light through strands of glass fiber as thin as your hair but thousands of miles long.

These cables, only about as thick as a garden hose, are high-tech marvels. The fastest, the newly completed transatlantic cable called Amitié and funded by Microsoft, Meta and others, can carry 400 terabits of data per second. That’s 400,000 times faster than your home broadband if you’re lucky enough to have high-end gigabit service.

And yet subsea cables are low-tech, too, coated in tar and unspooled by ships employing basically the same process used in the 1850s to lay the first transatlantic telegraph cable. SubCom, a subsea-cable maker based in New Jersey, evolved from a rope manufacturer with a factory next to a deep-water port for easy loading onto ships.

Though satellite links are becoming more important with orbiting systems like SpaceX’s Starlink, subsea cables are the workhorses of global commerce and communications, carrying more than 99% of traffic between continents. TeleGeography, an analyst firm that tracks the business, knows of 552 existing and planned subsea cables, and more are on the way as the internet spreads to every part of the globe and every corner of our lives.

You probably know that tech giants like Meta, Microsoft, Amazon and Google run the brains of the internet. They’re called “hyperscalers” for operating hundreds of data centers packed with millions of servers. You might not know that they also increasingly run the internet’s nervous system, too.

“The whole network of undersea cables is the lifeblood of the economy,” said Alan Mauldin, an analyst with TeleGeography. “It’s how we’re sending emails and phone calls and YouTube videos and financial transactions.”

Two thirds of traffic comes from the hyperscalers, according to Telegeography. And the data demands of hyperscalers’ subsea cable is surging 45% to 60% per year, said SubCom Chief Executive David Coughlan. “Their underlying growth is fairly spectacular,” he said.

Hyperscalers’ data demands are driven not just by their own content needs, like Instagram photos and YouTube videos viewed around the world. These companies also often operate the cloud computing businesses, like Amazon Web Services and Microsoft Azure, that underlie millions of businesses’ global operations.

“As the world’s hunger for content continues to increase, you need to have the infrastructure in place to be able to serve that,” said Brian Quigley, who oversees Google’s subsea and terrestrial networks.

The first subsea cables spanned major communication routes like London to New York. Those remain critical, but newer routes are bringing bandwidth far off the beaten track: the west coast of Greenland, the volcanic island of St. Helena west of Africa, the southern tip of Chile, Pacific island nations, the 8,000-person town of Sitka, Alaska.

It’s all part of a gradual transformation of subsea communications. Where once cables were the exception, linking a few high-priority urban centers, now they’re becoming a world-spanning mesh. In other words, despite high costs and exotic technology, subsea cables are coming to resemble the rest of the internet.

But as more internet traffic traverses subsea cables, there’s also reason to worry about them. The explosive sabotage last year of the Nordstream 1 and 2 natural gas pipelines connecting Russia and Europe was much more logistically difficult than cutting an internet cable the thickness of your thumb. An ally of Russian leader Vladimir Putin said subsea cables are fair game for attack. Taiwan has 27 subsea cable connections that the Chinese military could see as tempting targets in an attack.

“There’s a lot of talk these days about how space is the next contested domain. But I think undersea is going to be very much a contested domain,” said Steve Bowsher, president of In-Q-Tel, a CIA-backed nonprofit that invests in startups on behalf of the CIA, FBI, NSA and other US government agencies. “Those are going to be targets in any sort of kinetic conflict.”

The risks are vivid: Vietnam’s internet performance suffered thanks to outages on all five of its cables for months earlier this year, and the volcanic explosion on the island of Tonga severed it from most communications for weeks.

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But those risks are dwarfed by the very real benefits, from the macroeconomic to the purely personal. The network is growing more reliable and capable with faster speeds and a surge in new cables extending the network beyond today’s 870,000 miles of routes, and that’ll coax more and more countries to join.

That makes the internet richer and more resilient for all of us — including you getting work done and finding entertainment after the workday’s over.

Why subsea cables are reaching everywhere

The economic advantages are considerable. Subsea cable links mean faster internet speeds, lower prices, a 3% to 4% boost in employment and a 5% to 7% boost to economic activity, McKinsey estimates.

At the same time that hyperscalers’ traffic demands were surging, the telecommunications companies that traditionally installed subsea cables pulled back from the market.

“Roughly 10 years ago, a lot of the traditional telco providers started to really focus on wireless and what was happening within their last-mile networks,” said Frank Rey, who leads hyperscale network connectivity for Microsoft’s Azure cloud computing business. The wait for new cables grew longer, with the planning phase alone stretching to three to five years. The hyperscalers needed to take control.

Hyperscalers initially began with investments in others’ projects, a natural move given that subsea cables are often operated by consortia of many allies. Increasingly, hyperscalers now build their own.

The result: a massive cable buildout. TeleGeography, which tracks subsea cables closely, projects $10 billion will be spent on new subsea cables from 2023 to 2025 around the world. Google-owned cables already built include Curie, Dunant, Equiano, Firmina and Grace Hopper, and two transpacific cables are coming, too: Topaz this year and, with AT&T and other partners, TPU in 2025. 

Such cables don’t come cheap: A transatlantic cable costs about $250 million to $300 million to install, Mauldin said.

The cables are critical. If one Azure region fails, data centers in another region come online to ensure customers’ data and services keep humming. In the US and Europe, terrestrial cables shoulder most of the load, but in Southeast Asia, subsea cables dominate, Rey said.

With the hyperscalers in charge, pushing data instead of voice calls, subsea networks had to become much more reliable. It might be a minor irritation to get a busy signal or dropped call, but interruptions to computer services are much more disruptive. “If that drops, you lose your mind,” Coughlan said. “The networks we make today are dramatically better than what we made 10 years ago.”

The origin story of subsea communications

Today’s cables send up to 250 terabits per second of data, but their technology dates back to the 1800s when scientists and engineers like Werner Siemens figured out how to lay telegraph cables under rivers, the English Channel and the Mediterranean Sea. Many of the early cables failed, in part because the weight of a cable being laid on the bottom of the ocean would rip the cable in two. The first transatlantic cable project that succeeded operated for only three months in 1858 before failing and could only send just over one word per minute.

But investors eager to cash in on rapid communications underwrote the development of better technology. Higher copper purity improved signal transmission, stronger sheathing reduced cable breaks, repeaters installed periodically along the cable boosted signal strength and polyethylene insulation replaced the earlier rubberlike material harvested from gutta-percha trees.

Telephone calls eventually replaced telegraph messages, pushing technology further. A transatlantic cable installed in 1973 could handle 1,800 simultaneous conversations. In 1988, AT&T installed the first transatlantic cable to use glass fiber optic strands instead of copper wires, an innovation that boosted capacity to 40,000 simultaneous phone calls.

SubCom’s subsea cable factory dates back to its rope-making roots in the 1800s. “Most rope in that time was used on ships or needed to be transported by ships,” CEO Coughlan said. “A factory on a deep port, with quick access to the ocean and with winding capabilities, is what was needed to transform into the telephone cable business.”

The tech inside subsea cables

Fiber optic lines transmit data as pulses of laser light. As with terrestrial fiber optic lines, using multiple frequencies of light — colors, to you and me — means more data can be sent at once. Network equipment ashore at either end of a cable encodes data into the light for transmission and decodes it after it’s received.

Fiber optics are great for fast broadband and long-haul data transmission, but the technology has its limits. That’s why there’s a big bulge in the cable every 30 to 60 miles called a repeater, to boost the signal strength.

Repeaters require power, though, and that’s where another part of the cable construction comes into play. Outside the fiber optic strands, a copper layer carries electricity at up to 18,000 volts. That’s enough to power repeaters all the way across the Pacific Ocean just from one end of the cable, though power typically is available from both ends for greater reliability. 

Why not keep raising the laser power, so you don’t need repeaters as often? Because boosting it too high would eventually melt the fibers, said Brian Lavallée, a senior director at networking technology giant Ciena.

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His company makes the network equipment at either end of the subsea cables, employing different data encoding methods — manipulating light waves’ frequency, phase and amplitude — to squeeze as much data as possible onto each fiber.

“We’ve been able to get very, very close to the Shannon limit, which is the maximum amount of information you can send down a communication medium,” Lavallée said.

How ships install subsea cables

Companies installing a cable start by picking a route, surveying the route to dodge marine problems like nature preserves, rough seafloor and other cables. When multiple countries, telecommunications firms and businesses are involved, finding an agreeable route and obtaining permits can be very complex.

The cables themselves are gradually paid out from specialized ships. That isn’t as simple as unspooling your string when you’re flying a kite on a windy day.

Fiber optic strands are narrow, but subsea cables are thicker, heavier and bulkier. They’re stored in metal cylinders that wind and unwind the cables as they’re moved from shore to ship or from ship to ship. A single ship’s three “tanks” can hold 5,000 tons of cable, which works out to about 1,800 miles of lightweight cable and 600 miles of cable that’s been armored for busy waters.

SubCom has to figure out the installation order for each cable segment and make sure that when installation begins, the right end of the cable is at the top of the coil. That means before loading onto the ship, while the cable is stored at SubCom’s depot, it must be stored “flipped” the other way up. It reverses direction to the correct configuration as it’s transferred loop by loop onto the ship, SubCom’s Coughlan said.

That’s already complicated, but weather, permits or other concerns can force changes to the installation order. That can require flipping a cable at sea with two ships side by side. In a very digital business it turns out to be a very analog problem trying to account for factors like the ships lurching on the open ocean and the cable’s weight and bending limits.

“We have one guy in particular that’s just a savant at this,” Coughlan said. “He has to be able to solve it with his hand with string first, because we found the computer modeling never works.”

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Near shore, cables are armored with steel cable and buried in the sea floor with a special plow towed behind the ship. The plow pulls up into the water any time the new cable crosses another that’s already installed. In the deeper ocean, where fishing equipment and anchors aren’t a problem, the cable has less protection and is simply laid on the bottom of the sea floor.

Fixing severed subsea cables

Subsea cables are pretty tough, but every three days or so, one gets cut, TeleGeography said. The primary culprits, accounting for about 85% of cuts, are fishing equipment and anchors. Ships often will anchor themselves to ride out storms, but the storms push the ships and they drag their anchors.

Most of the other cuts are from the Earth itself, like earthquakes and mudslides. Tonga, whose single subsea cable connection was severed by a volcanic eruption, is another example.

Human-caused climate change, which is creating more extreme storms, worries Microsoft’s Rey. “What keeps me awake at night is large-scale climate events,” he said. In 2012, Hurricane Sandy cut 11 of the 12 high-capacity cables that connected the US and Europe, he said.

Most cuts occur closer to land, where boat traffic is higher and water is shallower. There, cables are clad in metal armor and buried in the sea floor, but even so, cable cuts are a matter of when, not if. At any given moment, more than 10 cables are typically cut around the world, Google’s Quigley said. The worst season for outages is October to December because of a combination of harsher weather and fishing activity.

Cable operators can pinpoint cable cut locations, but repair ships often must await government permits. Repairs average two weeks, Rey said, but three or four is common, according to.marine cable division chief Takahiro Sumimoto of Japanese telecommunications power NTT. After the Fukushima earthquake of 2011, it took two months.

“It was too deep, and the cable was cut into pieces,” Sumimoto said.

The repair requires a ship to fish up one end of the broken cable, often latching on with the same kind of grappling equipment that’s been used for centuries. The ship floats that end of the cable with a buoy while the other end is retrieved. The ship splices the optical fibers back together, with splices housed in a thicker package.

Faster new subsea cable tech

With cables so expensive to install, there’s a strong incentive to pack in more data. There’s plenty of room for more optical fibers, but that approach is limited by the need for electrical power for the repeaters.

Today’s new cables use 16 pairs of fibers, but a new cable that NTT is building between the US and Japan employs 20 fiber pairs to reach 350Gbps. Another Japanese tech giant, NEC, is using 24 fiber pairs to reach speeds on its transatlantic cable to 500Tbps, or a half petabit per second.

“Especially after the pandemic, we observed a capacity shortage everywhere. We urgently need to construct new cables,” Sumimoto said. “The situation is a bit crazy. If we construct a cable, the capacity is immediately sold out.”

Along with the new cable installations, sometimes older cables can be upgraded with new network hardware. A recent Ciena upgrade quadrupled the capacity of fiber optic lines without changing anything underwater, Lavallée said.

Microsoft also is betting on a fundamental improvement to optical fibers themselves. In December, it acquired a company called Lumenisity developing hollow fibers with a tiny central tube of air. The speed of light in air is 47% faster than in glass, a reduction to the communication delay known as latency that’s a key limit to network performance.

Transpacific cables have a latency of about 80 milliseconds. Cutting latency is important for time-sensitive computer interactions like financial transactions. Microsoft also is interested in hollow fibers for shorter-haul fiber optic lines, since lower latency effectively brings data centers closer together for faster fallback if one fails.

Also coming are fibers with multiple data transmission cores inside instead of just one. “We can’t get much more improvement in bandwidth over a single fiber,” TeleGeography’s Mauldin said.

A portion of Google’s TPU cable will use two-core fibers, the company confirmed, but that’s only a first step. Fiber optic company OFS announced four-core fiber optics this year and sees a path to subsea cable capacity of 5Pbps. That’s 20 times more data than today’s new cables.

Geopolitical tensions with subsea cables

There’s only one internet, but strains can show when it connects countries that are at odds, for example when the Chinese government blocks Google and Facebook or US companies sever their connections to Russia’s internet. These techno-political tensions have spread to the world of subsea cables.

The US effectively blocked three cables that would have directly linked China and the US, causing them to reroute to other Asian nations. And the US has worked to sideline HMN Tech, a Chinese subsea cable installation and maintenance company that grew out of Huawei, according to a report by The Financial Times.

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But with many other countries in Southeast Asia, there are many indirect connections, with more to come. “There are 17 new intra-Asian cables that are currently in the works, and many more that haven’t been announced yet,” TeleGeography analyst Tim Stronge said in a June blog post. And when it comes to internet routing rules that govern the flow of traffic around the world, there are effectively open borders. In other words, the internet itself doesn’t care much about where exactly the cables go.

The new geopolitics has complicated business for SubCom, which serves the US military as well as private companies like Google.

“A lot of governments exert their power in ways they had in the past,” Coughlan said, and it isn’t just the China-US issue. Several countries, including Canada and Indonesia, are enforcing cabotage laws that require work done in their territorial waters to be done by a sovereign ship of that nation.

“This is leading to a lot of complications around the duration of permits and how to perform the work,” Coughlan said. “Because of these cabotage laws, cables are harder to put in. They take longer. Some of these countries only have one ship, and you have to wait to get it.”

But ultimately the economic incentives to build the cable usually prevail.

“Whatever big dustups there are going to be — trade wars, actual wars — when it gets to the local level, the local countries want these cables,” SubCom’s Coughlan said. “That’s the only reason this gets built.”

Vulnerabilities in subsea cables

Cable vulnerabilities are real. Anchors and fishing equipment are the main risks, particularly in crowded corridors where there are multiple cables. The cables are designed to thwart corrosive salt water, not an attacking human.

“It would not take much to break these cables. And a bad actor could do it,” Coughlan said. A 2017 think tank paper by Rishi Sunak, who’s since become prime minister of the UK, concluded that subsea cables are “indispensible, insecure.”

In a 2021 report, the Center for a New American Security, a bipartisan national security think tank, concluded that subsea cables are vulnerable. It simulated Chinese and Russian military actions using adversarial “red teams.” In these simulations, Chinese attacks cut off Taiwan, Japan, Guam and Hawaii, but Russian attackers had a harder time thanks to the large number of Atlantic subsea cables.

“In CNAS wargames, Chinese and Russian red teams launched aggressive attacks on undersea cables, specifically where they ‘land’ ashore. In nearly every case, these attacks allowed red teams to disrupt and degrade US, allied, and partner communications, and contributed to confusion and distraction at the strategic level as governments were forced to respond to sudden losses of connectivity,” CNAS senior fellow Chris Dougherty said in the report.

Sunak recommended a treaty to protect cables, NATO wargames to better understand their importance, and sensors on the cable to better detect threats. The most practical advice, though, was simple: build more cables for geographic diversity and redundancy.

Making the subsea network more resilient

Given the importance and vulnerability of subsea cables, it’s no surprise there’s a race afoot to make the technology more robust.

That’s why there’s a major push to expand to new landing sites. When Hurricane Sandy struck, all the most powerful transatlantic cables landed in New York and New Jersey. Now more leave from Massachusetts, Virginia, South Carolina and Florida.

“If you run all cables on the same path, you’re an anchor drag away from multiple cables being brought down,” Quigley said.

Often, operators will swap capacity on each others’ cables, access that gives each a fallback data pathway if their cable is cut. Effectively, they’re not putting all their communication eggs in one cable basket.

“People are trying to build resiliency into the system,” In-Q-Tel’s Bowsher said.

Ultimately, the geographic diversity Sunak seeks is becoming a reality, boosted by better branching technology that makes multistop cables economical. The new Sea-Me-We 6 cable stretches from France to Singapore by way of 17 other countries. And new cables are being built to connect Europe, Africa, the Middle East, Asia, the Americas and many island nations.

“They’re all over the world,” Ciena’s Levallée said. “There is truly a mesh of these cables.”

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