What a Network Is and Why It Matters

Monday morning at Bellflower Design

Charlotte Reed starts her new job as IT assistant at Bellflower Design, a small studio that designs labels, packaging and websites for its customers. There are about a dozen people, a busy printer, a server full of design files and a great deal of coffee.

Hannah Fletcher, the office manager, shows her to a desk and hands her a laptop. “You've arrived at an interesting time,” she says. “In a few weeks we move into a bigger office on two floors, and the whole network has to move with us. William looks after our network. He's in on Mondays and Thursdays, and you'll be working with him.”

William Ashby, the studio's network engineer, puts his head round the door. “The first thing to understand,” he says, “is that nothing here works on its own any more. The designers' computers, the printer, the server, the phones, the internet: they are all one network. When the network is unhappy, everybody is unhappy. Our job is to keep it happy.”

What is a network?

A computer network is a group of devices joined together so that they can send messages to each other. The devices might be computers, laptops, phones, printers, cameras or servers. The joins might be cables or radio waves. What makes it a network is that any device on it can, in principle, reach any other.

That sounds simple, and the basic idea is. The hard part, and the reason people make careers from it, is making it work reliably for hundreds or millions of devices at once, keeping it fast, and finding out quickly what has gone wrong when it breaks.

What a network lets people do

Think about an ordinary morning at the studio and count how many things depend on the network:

Without the network, each of those would mean carrying a memory stick, a sheet of paper or a message by hand. Networks let a small team share one printer, one set of files and one internet connection, and let them work with people anywhere in the world.

Small networks and the biggest network

The studio's own network, inside its office, is a local network, often called a LAN (local area network). It belongs to the studio, and the studio decides how it is set up.

The internet is something different. It is not one network but many thousands of separate networks, owned by different organisations, all joined together and all following the same rules for passing messages to each other. Your home network, the studio's network, a university's network and the networks of the internet providers are all part of it. That is why the internet is often called a network of networks. The studio pays an internet provider to connect its local network to the rest of the internet.

Messages travel in small pieces

When James opens a large design file from the server, the file does not travel across the network in one enormous lump. It is cut into many small pieces called packets, each with a label saying where it came from and where it is going, a little like a long letter posted as many numbered postcards. Every device along the way reads the label and passes the packet on, and James's computer puts the pieces back together in the right order.

Sending small pieces has big advantages. Many conversations can share the same cable at the same time, taking turns packet by packet. If one packet is damaged or lost, only that small piece needs to be sent again. And if one route is busy or broken, packets can go another way.

You can see this happen in the practice network below, which is a copy of the studio's network running inside your browser. Type ping news.example and press Enter. Ping sends a few small test packets to a website on the pretend internet and reports each reply and how long it took. The blue line on the map shows the path the packets took: from Charlotte's laptop, through the studio's switch and router, out to the internet and back. Lesson 1.2 explains every part of the map.

Why networking skills matter

Almost every organisation now runs on a network, so people who understand networks are needed everywhere. Some of the jobs where these skills are used every day:

• IT support (help desk) staff, who are often the first to hear “the internet isn't working” and need to work out whether the problem is one laptop, one cable or the whole office.
• Network technicians and engineers, who plan, build and look after networks like the studio's, and much larger ones.
• System administrators, who run servers that everyone reaches over the network.
• Security staff, who need to know what normal network traffic looks like before they can spot anything unusual.
• Software developers, whose programs increasingly talk to other programs across networks.

The ideas in this course are the same whichever brand of equipment an organisation buys. The exact commands differ from one make of router to another, but addresses, subnets, routing, names and the method for finding faults work the same everywhere. Learn the ideas properly and you can pick up any particular piece of equipment quickly. Many entry-level IT and networking certificates cover the same core topics as this course.

How this course works

You will follow Charlotte through her first weeks at Bellflower Design, as the studio runs its current office and then moves into the new one. There are ten modules:

1. Getting started: devices, cables and the layers that divide up the work.
2. Local networks: hardware addresses, switches, cables and link speeds, and splitting one switch into separate networks.
3. IP addresses: binary, masks and prefixes, subnetting step by step, and private and public addresses.
4. Getting between networks: finding neighbours, the default gateway and routing tables.
5. Conversations and ports: TCP, UDP and reading a packet capture.
6. Services every network needs: automatic addresses, names, sharing one public address, and what web, email and file sharing look like on the wire.
7. Wireless networks: radio, channels, coverage and interference.
8. IPv6: the newer, much larger address system.
9. Finding faults: a method that works, ping and traceroute, and slow networks.
10. Design and final project: plan, build and document the studio's new office network.

Every lesson has practice networks like the one above, which you use by clicking devices and typing short commands. Nothing you type can harm a real computer, so try things freely. From lesson 1.2 onwards, every lesson has five exercises that are checked as soon as you press Check my answer, and every lesson ends with a short quiz. You need no programming and no earlier networking knowledge: every new word is explained the first time it appears.

Quick check

Choose an answer to see whether you are right and why.

Found a mistake on this page, or something unclear? Report a problem and mention “Computer Networking Fundamentals Lesson 1.1”.