Why submarine/subsea cables rather than satellite? This started as a story between a friend of mine from a finance background and myself.
One of my friends, who is totally foreign to our industry, visited me at home. It was a family dinner, and as I said, he is not a network engineer but just a curious person.
I was talking about telecom companies with him. I said that 99% of our Internet data (not only data, but voice and video traffic too) is carried through undersea cables (often we call them submarine or subsea cables), and he asked a clever set of questions. I was not expecting that, to be honest—not because he is not smart, but because he is a finance guy, so he is not supposed to ask those. You will see.
First he said that it is really old-fashioned that we still have physical cables, and asked why we still see cables going through the air.
My response was that we are actually talking about subsea cables; we don't see them. Even at the shore, cables are buried, so we don't see them. Even aerial fiber is generally not seen in public places, but maybe in datacenters, which you don't have access to. What you see is probably electric cables.
Then he said: why subsea cables, then—wouldn't it be too costly? Why not just a satellite? Wouldn't it be faster to install and use than a subsea cable?
I suspected that he was studying network engineering with these questions. He has some points here, actually.
Yes, subsea cables are really costly, depending on distance, transmission equipment, fiber types, physical subsea routes, and the number of repeaters (it might be a repeaterless submarine cable, though).
Building a communication satellite, launching it, operating it, and having a frequency license is not cheap either. If you are leasing capacity from a satellite provider, that is a different case and would surely be much cheaper.
But as you might know, there are two main problems with communication satellites. The first is latency (delay) and the second is available bandwidth.
Of course, while I was explaining these terms to him, I did not use technical jargon. For latency, I just said: the first problem is how long you wait for a website like YouTube to load. For bandwidth, I said: if you and your wife try to watch an HD video at the same time, with satellite it will be a problem, but with subsea fiber you will watch without buffering.
Those who have experience with satellite networking know that I am talking about GEO (36,000 km above the earth) satellites; that is why we have this latency. Other satellites orbiting in LEO and MEO spaces have less latency due to their lower altitude. But let's not turn this into a deep-dive satellite post.
Wouldn't it be faster to install satellite than a submarine cable?
If we are not talking about building a satellite, launching it, waiting in orbit for tests, and taking it into operation, then yes. As with other wireless deployments, setting up a satellite communication link is much faster than deploying submarine cables (which in some cases take years).
Although I did not talk about the reliability and security aspects with my friend from the finance background, submarine cables—in fact, almost all wired (copper, fiber, coaxial) connections—are more reliable than wireless (satellite is a wireless technology that uses RF spectrum). In summary, fiber provides effectively unlimited bandwidth (governed by Shannon's capacity limit) and very low latency compared to satellite communication. Day by day, more bandwidth is demanded from networks, and even with very low latency satellite systems, submarine cable will remain the primary method to carry data between countries and continents for a long time.
Submarine Cable Basics
To understand why submarine cables dominate international connectivity, it helps to know the basics. A submarine cable is also known as a subsea or undersea cable, and it uses fiber-optic infrastructure. There are approximately 430 submarine cables in service around the world. Cables are typically as wide as a garden hose, but the actual component that carries the light is only about the diameter of a human hair. The first submarine cables were deployed for telegraph communication—purely voice communication—but some cable systems now carry more than 200 Tbps of combined data, voice, and video traffic.
Submarine cables are still not a well-known topic among network engineers, especially those who do not work in a service provider, carrier, or telco. That is why so many people ask how country X communicates with country Y, and what the methods are. In one customer meeting, someone even asked what would happen if one country cut the fiber and left a neighboring country without Internet. In practice, a single cut does not take a country offline, but the question shows why it is important to understand how these systems are built.
How Long Are Submarine Cables?
- Cables are laid in deep sea directly on the ocean floor, but nearer to the shore they are buried under the seabed for protection.
- More than 1.1 million kilometers of submarine cables have been laid around the world.
- Some submarine cables are quite short, like the 131-kilometer CeltixConnect cable, while others are very long, such as the 20,000-kilometer Asia America Gateway cable.
Who Builds Submarine Cables?
- Cables were traditionally owned by telecom carriers, who would form a consortium of all parties interested in using the cable. Later, an influx of entrepreneurial companies built private cables and sold off the capacity to users.
- Both the consortium and private cable models still exist, but one of the biggest changes has been the type of companies involved in building cables.
- Content providers such as Google, Facebook, Microsoft, and Amazon are now major investors in new cable. The amount of capacity deployed by these private network operators has outpaced internet backbone operators, because owning new submarine cables makes sense given ongoing massive bandwidth growth.
Who Uses Submarine Cables?
Users of submarine cable capacity include a wide range of types: telecom carriers, mobile operators, multinational corporations, governments, content providers, and research institutions all rely on submarine cables to send data around the world. Ultimately, anyone accessing the internet, regardless of the device they are using, has the potential to use submarine cables. When you call a friend on another continent from your mobile phone, that call almost certainly crosses at least one submarine cable system (for example, at least one cable system across the Transatlantic).
Submarine Cable System Architecture
An end-to-end submarine cable system consists of two parts: wet and dry plants. Dry plants start from the beach manhole. There are many parts to know if you want to learn more about submarine cable systems, such as repeaters, PFE (Power Feed Equipment), SLTE, landing points, and repeatered versus repeaterless design choices. When you learn more about international transport systems—submarine cables, satellites, and cross-border terrestrial systems—you realize how much they broaden your networking knowledge. For a deeper understanding of service provider networks, you can also check the Service Provider Networks Design and Perspective book.
