Introduction to computer networks: purpose, benefits and risks

Networks are everywhere

Think about an ordinary day: a phone call, a video stream, a message to a friend abroad, an online game, a card payment in a shop. Each of these depends on a network working quietly in the background. Some networks carry voice, some carry video, and most now carry all kinds of data together.

What exactly is a computer network?

A computer network is a collection of independent computing devices that are linked together so they can exchange information. To understand each other, the devices follow shared rules called protocols, and they send their data over a shared communication medium such as copper cable, fibre or radio waves.

Note: one computer with its own printer and scanner attached is not a network. A network needs at least two independent devices that communicate.

Words you will hear all the time

• Node: any device connected to the network, such as a PC, printer, switch or phone.
• Host: a node that sends or receives data for users or applications, usually a computer or server.
• Data transfer rate: how fast data moves from one place on the network to another, measured in bits per second. It is one of the most important qualities of any network.

Why build a network? The benefits

The risks of network computing

Connecting devices also connects their problems. Every network faces threats such as:

• Equipment faults and system failures, sometimes caused by power cuts, fire, flood or storms.
• Attackers trying to break in, steal data or stop services.
• Malware such as viruses and ransomware spreading from one machine to many.

This is why networking and security always go together: every design decision should ask "what happens if this fails or is attacked?"

How do we judge a network? Three key factors

1. Performance

• Transit time: how long a message takes to travel from one device to another.
• Response time: the time between sending a request and getting the reply.
• Performance also depends on the number of users, the efficiency of the software and the capability of the connected hardware.

2. Reliability

How often the network fails and how quickly it recovers. The fewer the failures, the more reliable the network.

3. Security

Protecting data from unauthorised access or change. Data crosses many devices on its way to the destination, and anything in the path could try to read it, so security must be designed in from the start.

Real-world example: a small dental practice gets networked

A dental practice with four treatment rooms used to keep patient records on one reception PC and carry X-ray images between rooms on USB sticks. A local IT contractor installed a switch, a small file server and a business router. Now every room opens the same patient record, the X-ray machine saves images straight to the server, and all staff print to one shared printer. That is the benefit side: shared data, shared hardware and less wasted time.

The risk side arrived quickly too. Within a month a receptionist opened a fake invoice email, and the same network that shared the records could have spread malware to every room. The contractor added nightly backups to an offline disk, separate user accounts, automatic updates and a firewall rule blocking unneeded inbound traffic. The practice kept the benefits while managing the new risks, which is exactly the balance every network design has to strike.