How does the Internet work? Part 2: Cables
Hey Reader, Happy Wednesday!
Let’s look at the second part of the 4-part internet series this week. I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for food, etc. Let’s jump in!
How it works: 15-second answer
The internet is physical and fragile. The YouTube video is stored on a computer in a building (aka data center) somewhere in the world, like Ashburn, Virginia. When you click a video on your phone to watch, the video travels from this computer in a building through a cable that is inches in diameter and miles long across oceans and continents, close to the speed of light in the form of 0s and 1s to your home router. This is how the internet works!
There are four parts to the Internet. Last week, we looked at Maps. This week, we’ll look at the second section, which is the cables through which data travels!
Maps - Part 1 of the series discussed last week.
Cables, data, and their speed - which we’ll explore this week.
Data centers where information is stored - Part 3 of the Internet series.
Internet network - Part 4 of the Internet series.
Quick recap from last week
Read the first part of the series about internet maps for a better understanding here: Read
The internet map showed us the world’s undersea communications cables - the physical connections between continents through which internet data travels in the form of 0s and 1s.
Each line drawn on the map represented a single cable, inches in diameter but thousands of miles in length. It looks huge on the map, but it would be the size of a garden hose on the ocean floor. Your YouTube video, blog post, and other information travel through this cable as 1s and 0s across the world to someone’s desktop at the speed of light.
What's inside the cable?
Figure 1: Inside an undersea cable carrying internet data
At the center are multiple optical fibers, basically thin glass (silica) about the diameter of a human hair.
This carries data as pulses of light through it from one end to another. There are hundreds to thousands of data lines within a single undersea cable.
99% of the remaining cable is layers protecting these optical fibers from damage and corrosion.
Figure 2: Different parts of an undersea cable. Source: Wikipedia
And every 50 miles, the cable contains devices that boost the light signal to compensate for signal loss over long distances.
How does light carry internet data?
Cables are containers for light, as a subway tunnel is for trains.
A laser blinks on and off ten billion times per second, sending data as light pulses through an optical fiber.
Figure 3: Module called SFP+ that converts data into light signals (simplified)
If the light turns off, it’s a 0. If it turns on, then it’s a 1.
Let’s say 0 represents the letter H and 1 represents the letter I. Then, one can send HI by sending a light off and light on signal. Images, videos, and files are converted into 1s and 0s this way and sent across.
Won’t it take a long time to transfer these files then? No. Each cable has data speeds of up to hundreds of terabits per second.
How is the cable laid under the ocean?
These cables go underwater, over the mountains, and on terrains you least expect. So, how are they laid then?
Figure 4: Ship laying internet cables in the ocean using specialized systems after planning the route.
Specialized ships conduct surveys of the ocean bottom, carefully plotting routes. The paths carefully avoid major shipping lanes to limit the risk of damage from dragging anchors.
If the cable does fail, a repair ship is dispatched to lift both ends to the surface using grappling hooks and fuse the ends back together - an expensive, slow process.
After traveling across the ocean, the data hops onto other cables within the land for the final stretch of data delivery to the customers.
Laying these fiber-optic cables in a city like New York is a carefully planned and highly physical process. Workers first map out the route underground. On installation night, crews use trucks and winches to pull the long fiber-optic cable through the manholes, section by section.
Who owns these cables?
Figure 5: Giants like Google, Meta, Amazon, etc. own most of the cables. Google owns 33 subsea cables as of 2025.
Only about 1% of submarine cables are owned, in whole or in part, by government entities.
Approximately 99% of undersea cables are owned by private organizations like AT&T, Verizon, Tata, Google, Amazon, Meta, content providers (such as tech giants), and investor groups. Yes, you read that right!
Historically, telecom companies formed consortia to share the enormous costs and risks of building and maintaining these cables.
In 2004, Tata paid $130 million for the Tyco Global Network, which included almost forty thousand miles of fiber-optic cable spanning three continents, including major undersea links across both the Atlantic and Pacific Oceans. Geography matters so much with regard to the Internet.
How do companies owning these cables make money?
To simplify this, let’s say AT&T owns all the undersea cables between London and New York. And if there are many Google users trying to send information between these two cities, then Google would approach AT&T and pay them to use some of their cables or a portion of them for sending over data through multi-year contracts.
This is everything about internet cables. Let’s look at where the internet data is stored and how they are managed next week - the most exciting of the 4 parts about the internet.
Thank you for reading!
Have an amazing rest of the week, and take care!
Until next to next Wednesday,
Chendur
