What is a Computer Network?
You used a network today before you even got to school. A message on your phone, a video you watched, a payment at a shop — each one travelled from one device to another. This lesson is about what joins them.
1The definition
Two parts of that sentence matter. The devices must be connected, and the reason for connecting them is to share. Six computers standing in the same room are not a network. Put a cable between them and they are.
Try it. The lab below has no cables yet.
Send a file first with the cables out, then plug them in and send it again.
Nothing about the computers changed between your two tries. The only difference was the connection — and that is the whole definition.
2Every device is a node
Each device on a network is called a node. A node does not have to be a computer. Anything that can send or receive data over the network counts.
A computer that stores files or runs a service for the others is called a server. The computers that use it are called clients. In the lab, the tall box is a file server and the six computers are its clients.
3Every connection is a link
The connection between two nodes is called a link. A link can be:
A cable — like the ones in the lab above. Fast and steady, but the device has to stay where the cable reaches.
Signals through the air, like Wi-Fi or Bluetooth. You can move around, but walls and distance weaken the signal.
The kinds of cable and signal have names and a lesson of their own, Transmission Media. For now, “cable or air” is enough.
In the lab, every cable ran to one small box in the middle called a switch. It is the meeting point that passes data from one cable to the right other cable. You will open it up in Network Devices.
Think of a road map
4From two phones to the whole world
The smallest network is two devices — your phone and your earbuds. A computer lab is a bigger one. The largest is the Internet, which joins networks all over the planet.
They all obey the same definition. What changes is how far they reach, and that is exactly how networks are sorted into types in the Types of Networks chapter.
5Recap
Two or more devices connected to share data and resources.
Any device on the network — computer, phone, printer, server.
The connection between nodes — a cable, or a wireless signal.
Which of these is a computer network?
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