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  • Writer's pictureSarah Whiteford

How do undersea data cables work?

Have you ever wondered how a YouTube video can be sent across the world in milliseconds? Or how can you video chat with a friend in Australia from the United States in real-time? This is all possible due to undersea cables stretching thousands of miles along the seafloor to connect continents, countries, and cities all over the world. Laying cable under the sea floor takes very special cable, a lot of preparation, and some really cool equipment.

Why is undersea cable so important?

With a lot of old telecommunication running through satellites, many people would think that data travelling thousands of miles could just be beamed to a satellite and over to the next country. As it turns out, satellites can’t handle that much flow of information. It’s too expensive, and loss of signal and data during transfer is a problem. Sending terabytes of data through space could cost billions of dollars per line. In fact, “Ninety-nine percent of international data is transmitted by wires at the bottom of the ocean called submarine communications cables”, according to Mental Floss. So the vast majority of the information in the world travels through the ocean on over a million kilometers of cable. From point to point, each cable can be as short as 131 kilometers all the way up to 20,000 kilometers for the Asia America Gateway cable. The screenshot below shows the world map of submarine cables built from 1989 to current and planned through 2023.

Image Credit: Visual Capitalist

Submarine cable is old business

Laying cable along the bottom of the ocean may seem like it requires advanced technology - and the equipment used today definitely is - but we’ve actually been doing it over 160 years! The first Transatlantic cable was laid in 1858 for telegraph communications. Connecting Newfoundland, Canada to Ireland, once finished, it only took minutes to communicate between the two countries. Unfortunately, the connection started to degrade, and the voltage was turned up in an effort to make the signal stronger, frying the cable. Over the next couple of years, two more cables were fried before a new type of cable was laid in 1865, fixing the issue.

Now, repeaters sit along the cable every 40-80 kilometers, amplifying the signal to ensure it can travel thousands of miles. New cables can handle over 200 Tbps of data, and with speeds like that, imagine a few strands of cable about the size of - a human hair. Fiber optic cables about the width of a hair carry data across the ocean. A typical cable might have 4-12 of these strands inside, and if laid in deeper ocean where it doesn’t need much protection, will only be a little larger than the width of your thumb, and if in shallower water or extremely deep ocean where it needs to be tougher, a little smaller than your wrist. Even with these sizes, the actual data is being carried across flawless glass the size of a needle.

Image Credit: Quora

How are the cables made?

This process is pretty simple, the cable is layered until it is tough enough to survive the environment where it will live for the next 25 plus years. If cable is being buried in the ocean, it is generally smaller. The fiber optic cable is gel-coated and stays inside copper tubing that carries electricity. A plastic tube surrounds the copper, followed by an aluminum water barrier and stranded steel wires. After that, they can be braided with more steel wire if additional protection is needed, followed by nylon rope, then tar. Last is a plastic coating to seal the whole package. As you can see in the photo above, the difference between a low protection cable and one that needs significant protection is quite a bit. If you’re wondering why the fiber optics are encased in copper tubing, the copper is powered to run the repeaters mentioned earlier to amplify the light to make sure the signal is strong enough to reach its destination. You can see a repeater in the photo below, some weighing in at over 250 kilograms, or 550 pounds.

Image Credit:

So how are these cables installed?

First, the cables have to be loaded onto a cable-lay vessel that will take them out to sea. Some of these vessels can hold up to 2,000 kilometers of cable on board. It can take 3 to 4 weeks just to load the cable, which can then be laid at a rate of around 200 kilometers per day with the right equipment. Once the cable is on board, starting from shore, the cable is laid out to the edge of the water. The cable laying ship gets as close to shore as possible without grounding, and starts digging. Ships pull a type of plough that digs a trench and lays the cable at the same time. Sometimes, cables have to be picked up if run over another cable, or if the cable can’t be buried. There is a lot of planning that goes into the route the ship will take - undersea mountains, valleys, coral reefs, rocks, and fault lines are all taken into consideration. Preferably, the cables will also be located in areas that minimize the risk of damage from boat anchors and fishing trawlers. To save time in the process, ships can even start from two separate points and lay cable until they meet, then attach the two cables together.

Image Credit: Quora

Sharks and spies!

What are the dangers to undersea cables? Well, as it turns out sharks find them to be quite tasty. On multiple occasions, sharks have been caught gnawing on the cables, and no one is really sure why. Mental Floss put it best: “Maybe it has something to do with electromagnetic fields. Maybe they’re just curious. Maybe they’re trying to disrupt our communications infrastructure before mounting a land-based assault. (My theory.) The point remains that sharks are chewing on the Internet, and sometimes damage it. In response, companies such as Google are shielding their cables in shark-proof wire wrappers.”

Another danger of undersea cables is they lay on or under the sea floor unprotected from spying. The USSR transmitted weakly encoded messages during the Cold War through a cable that the Soviets thought was too well guarded to be of any concern. The United States developed a special submarine called the U.S.S. Halibut to wiretap the cable and pick up the transmissions at regular intervals. Ever since, it has been a common occurrence to tap underwater transmission cables for information.

Image Credit: Mental Floss

What happens when the cables are outdated?

There are multiple options for cables that are no longer in use. The typical lifespan of cables is thought to be about 25 years, but they don’t really ever expire. Usually, before the 25 years is up, new technology means the cables have become obsolete, and new cables are run for more data capacity. When that happens, they can be repositioned and laid along a new path, which is good for areas that don’t need as much capacity and want to save on costs, since running these types of cables usually costs hundreds of millions of dollars. Some companies gain rights to pull the cables up and salvage them for the raw materials. They can also be left in place, in which case, they are called dark fiber. Even without signals running through the cables, they make a great seismic network for scientists to study geologic structures and earthquakes.

There is a great video from Earth Titan on subsea cables you check out below:


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