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Intro

The Internet is a network of computers connected to each other. But what does each physical connection look like? It depends on the needs of the connection and the size of the network.

Copper cables

Since the landline telephone system originally used copper wires, the first Internet connections reused that technology and many still use it today.

If you’re in a computer lab or near a modem, you can probably find a cable similar to this one:

Photo of the end of a CAT5 cable.

That’s a CAT5 cable, a type of twisted pair cable that’s designed for use in computer networks.

If you were to look inside the cable, you would find four twisted pairs of copper wires:

Photo of a twisted pair cable that's been partially stripped so that four pairs of twisted wires are sticking out of the end.

Twisted pair cables send data through a network by transmitting pulses of electricity that represent binary data:

Illustration of an internet connection between two computers. A wire goes between the two computers, and has little lightning bolts going through it. The wire is labeled with the binary data "100110110110".

To make sure cables are transmitting information in a way that can be understood by the recipient, they follow the Ethernet standards. That’s why twisted pair cables are commonly known as Ethernet cables.

They are used both in networks as small as a company office (a LAN) or as large as an entire country (a WAN).

Fiber-optic cables

A fiber-optic cable contains an optical fiber that can carry light (instead of electricity). The fiber is coated with plastic layers and sheathed in a protective tube to protect it from the environment.

Photo of a fiber optic cable, with light coming out of both ends.

Fiber-optic cables communicate by sending pulses of light that represent binary data:

Illustration of a fiber optic internet connection between two computers. A wire goes between the two computers, and has zig zagging lines going through it. The wire is labeled with the binary data "100110110110".

They typically also follow the Ethernet standards to make sure they’re sending data in a way that can be commonly understood by any recipient in the network.

Fiber-optic cables are capable of transmitting much more data per second than copper cables. They’re often used to connect networks across oceans so that data can travel quickly around the world.

A photo of a coral reef with a fiber optic cable laid over it and a fish swimming by.

A fiber-optic cable laid on the ocean floor.

As fiber-optic cables become less expensive, they’re becoming increasingly common in city-wide networks as well.

Photo of four workers handling a giant roll of fiber-optic cable on a sidewalk, while another worker awaits in a hole in the sidewalk.

A fiber-optic cable being laid along a street in New South Wales, Australia. Image source: Bidgee, Wikipedia

Wireless

Wireless connections don’t involve any wiring at all—at least at first. A wireless card inside the computer turns binary data into radio waves and transmits them through the air:

Illustration of a wireless transmission of binary data. 7 radio waves are shown radiating from the computer are labeled with the binary data "100110110110".

Those radio waves can’t travel very far: 75-100 feet in a place like an office building that’s filled with all sorts of obstacles, or up to 1000 feet in a wide open field.

The waves are hopefully picked up by a wireless access point which converts them from radio waves back into binary data. Wireless access points are connected to the rest of the network using physical wiring, like copper or fiber-optic cables.

Photo of a wireless router with copper and power cables plugged into it.

A wireless router with twisted pair cables.

Wireless connections are limited in how much area they can cover, but they are increasingly commonplace due to the prevalent use of portable computing devices.

All together now

At any given time, our Internet connection might be using a combination of those technologies. Maybe we’re using WiFi to connect to our home router, our home router is using twisted pair copper cables to connect to the metropolitan network, and those cables are hopping over fiber to communicate with overseas data centers.

Each technology has both advantages and disadvantages, so we use whatever is best for the job.

Type Sends Distance Bandwidth Issues
Wireless Radio 100 ft 1.3 Gbps Slower in reality
Twisted pair copper cables Electricity 330 ft 1 Gbps Susceptible to interference
Fiber-optic cable Light 50 miles 26 Tbps Expensive

The data in that table is current as of early 2020. Engineers are constantly discovering new ways to improve network connections, especially when it comes to increasing the bandwidth. We’ll learn more about bandwidth in the next article on bit rate, bandwidth, and latency.

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致谢：Khan Academy - AP® Computer Science Principles