By the end of this lesson you will be able to
- Explain what a computer network is and why devices are connected to one.
- Tell a LAN from a WAN, and say where the internet fits.
- Describe the roles of a client and a server using an everyday example.
- Draw or describe a typical home network from the wall socket to your phone.
- Name three network layouts (topologies) and say which one a home uses.
Your laptop, your phone and perhaps a printer or television all talk to each other and to the wider world. They can only do that because they are joined in a network. Understanding the basic shape of a network turns “the internet is not working” from a mystery into a question you can start to answer: which part of the chain has broken?
A network is devices that can talk
A Network is two or more devices joined together so that they can send data to each other. The devices can be laptops, phones, printers, televisions, cameras or the big computers that hold websites. The join can be a cable or a radio signal.
Think of a village post office system. Each house has an address. A letter written in one house can reach another house because there are roads, sorting offices and agreed rules about how to write the address. A network is the same idea for data: devices have addresses, there are roads (cables and radio), sorting offices (routers and switches) and agreed rules (you will meet them in the next lessons).
Why bother? Three everyday reasons. You can share things, such as one printer or one internet connection for the whole house. You can reach things that are elsewhere, such as a website or a photo stored in the cloud. And you can communicate, through messages, calls and video.
Small networks and big networks
A local area network (LAN) covers a small area: one house, one office, one school lab. Everything in it is usually owned and set up by the same person or organisation. Your home Wi-Fi and the devices on it make a LAN.
A wide area network (WAN) joins networks across long distances, such as between towns or countries. Nobody owns all of it. Companies called internet service providers lay the cables and run the equipment that carries your data from your home LAN out to the world.
The Internet is not one single network. It is a huge collection of networks, large and small, joined together so that any device on one can reach any device on another. Your home LAN is one small piece of it.
- One home, office or school
- Owned and set up by you or your organisation
- Devices are metres apart
- Example: your home Wi-Fi
Your own small patch.
- Towns, countries, the world
- Carried by internet providers and many companies
- Devices can be thousands of kilometres apart
- Example: the link from your home to the internet
The long roads between patches.
Read this figure as text
Two columns comparing a local area network with a wide area network.
Column 1, LAN (local area network): covers one home, office or school; owned and managed by you or your organisation; devices are usually metres apart; fast and cheap; example, your home Wi-Fi. Column 2, WAN (wide area network): covers towns, countries or the world; carried by internet service providers and many companies; devices can be thousands of kilometres apart; you rent access to it through a subscription; example, the connection from your home out to the internet.
Clients and servers
Most network conversations have two roles. A Client asks for something. A Server holds it and answers. Your browser is a client when it asks for a web page. The computer that stores the page is a server. A server is not a special kind of machine; it is any computer running software whose job is to answer requests, though real servers are often powerful machines in a data centre.
A restaurant is a good picture. You (the client) read the menu and place an order. The kitchen (the server) prepares it and sends it back. You never go into the kitchen, and the kitchen serves many tables at once. Sometimes devices talk as equals, with no fixed client or server, for example two phones sharing a photo directly. That is called Peer-to-peer.
Read this figure as text
A sequence diagram with a client and a server exchanging a request and a response.
Two actors: your laptop (the client) and a website's computer (the server). Message 1, from the client to the server: “Please send the page example.org/home”, which is the request, like placing an order. Message 2, from the server back to the client: “Here is the page”, which is the response, like the meal arriving. The client always starts the conversation; the server waits to be asked.
A typical home network
Follow the connection from outside to inside. A cable or radio link brings the internet into your home from your ISP. A Modem (sometimes built into the next box) turns that signal into something your devices understand. A Router connects your home LAN to the internet and decides where data goes. Devices join the router by Wi-Fi (radio) or Ethernet (cable). The next lesson looks at each box in detail; here we just see the shape.
Read this figure as text
A network diagram with the internet on the left, a modem, a router, and a laptop, phone and printer connected to the router.
From left to right. The internet (a cloud) connects by a data link to the modem. The modem connects by a cable to the router. These three boxes sit outside your home LAN. The router, inside the home LAN zone, connects by Wi-Fi to a phone and to a laptop, and by an Ethernet cable to a desktop computer and a printer. Step 1 on the links is the data leaving the home; every device reaches the internet only through the router.
Try it: build a network
Use the simulation below to place the boxes yourself. Nothing here touches your real network. Try leaving out the router and see what stops working.
Place a modem, a router and some devices, join them, then test whether each device can reach the internet.
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Shapes of networks
The way devices are joined together is called the Topology of the network. Three shapes are worth knowing. In a star, every device connects to one central box; if one cable fails, only that device is cut off. In a bus, all devices share one long cable; it is cheap but one break can cut everyone off, and it is now rare. In a mesh, devices connect to several others, so data can take another route if one link fails.
- Every device joins one router or switch
- One cable fails: only that device is lost
- Easy to add a device
What your home uses.
- All devices share a single cable
- A break can cut everyone off
- Cheap but rarely built now
Mostly history.
- Devices link to several others
- Data goes round a failure
- Used by the internet and Wi-Fi mesh kits
Most resilient.
Read this figure as text
Three columns describing star, bus and mesh network layouts with their strengths and weaknesses.
Star: every device connects to one central box such as a router or switch. Strength: one broken cable affects only one device; easy to add devices. Weakness: if the central box fails, everyone is cut off. Used in almost all homes and offices. Bus: all devices attach to one shared cable. Strength: cheap. Weakness: a break in the main cable can stop everyone; rare today. Mesh: devices link to several neighbours. Strength: data can go round a failure. Weakness: more cabling or radios. Used by the internet itself and by Wi-Fi mesh kits that cover a large house.
Common mistakes
✖ Instead of: Saying “the internet” when you mean “the Wi-Fi”.
✔ Do this: Wi-Fi is only the local radio link between your device and the router. You can be joined to the Wi-Fi and still have no internet if the router cannot reach the provider.
✖ Instead of: Thinking a server must be a huge special machine.
✔ Do this: A server is any computer running software that answers requests. A small laptop can act as a server, though websites usually use powerful machines in data centres.
✖ Instead of: Believing the modem and router are always the same thing.
✔ Do this: They do different jobs. They are often combined in one case, but the jobs stay separate.
If something goes wrong
- I cannot tell which box in my home is the router.
- Look for the box your provider supplied, with an Ethernet socket labelled LAN and Wi-Fi lights. Its sticker usually names the model and Wi-Fi name. If unsure, ask the provider's support using the account details on your bill.
- The network builder lab does not show my changes.
- Make sure you joined each device with a link, not just placed it. Use the reset button in the lab and start again. The lab runs inside this page only.
Key terms
- Internet service provider (ISP)
- A company you pay to connect your home or office to the internet.
- Peer-to-peer
- A way of connecting in which two devices talk as equals instead of one being a client and one a server.
- Topology
- The shape formed by the devices and links of a network.
- LAN
- A network covering a small area such as a home or school.
- Client
- A device or program that asks another computer, called a server, for something.
- Server
- A computer that holds information or services and sends them to other devices that ask.
Practise it for real
Reading is not the same as being able to do it. Complete these on your own computer, then tick only what you have actually done. These ticks are your own honest record: nothing checks them for you.
Draw your own home network
On paper, draw a box for every device in your home that connects to the internet (phones, laptop, television, printer, anything smart). Draw the router in the middle and join each device to it with a line. Mark each line as Wi-Fi (wavy) or cable (straight). Look at the back or underside of the router and write down what the labels say. You do not need to log in to anything.
Challenge: find clients and servers
Pick three things you did on a device today, such as opening a website, sending a message or playing a video. For each, write which device was the client, which was the server, and what the request and response were. Then decide whether each happened inside your LAN, across the WAN, or both.
Knowledge check
6 questions. You need 80% to pass. Mistakes here are part of learning, and you can retry as often as you like.
Summary
- A network is devices joined so they can send data to each other.
- A LAN is small and local; WANs join networks over long distances; the internet is a collection of networks.
- A client asks and a server answers.
- A home network is a star: devices connect to the router, and the router connects to the internet.
Checklist: can you do these?
Marking a lesson as read does not prove you can do it. Skills count as demonstrated when you pass the quiz (not yet) and complete the practical tasks (not yet).
Related lessons
References and further reading
Official sources for details that can change between versions.
- Networking, web, email and chat (Ubuntu Desktop Guide) (Ubuntu)
- What is a computer network? (Amazon Web Services)