Networks - Lesson 1
Free Theory Networks Lesson 1
Networks - Lesson 1 of 6

What is a Network?

Before protocols, topologies or the internet, you need to understand what a network actually is, why we build them, and how to tell a LAN from a WAN. These distinctions appear in almost every exam question on this topic.

45 - 60 min LAN, WAN, hardware, client-server
Opening question

Right now, as you read this, your device is talking to at least a dozen others simultaneously. Servers, routers, DNS resolvers. None of them are in the same room as you. Some are in different countries.

Think about it: Without lifting a finger, how many separate computer systems did your device contact in the last 60 seconds? What makes that possible?
The answer is computer networks. A network is what makes every connected device in the modern world function. Understanding how networks are built, classified, and managed is one of the highest-weighted topics in GCSE Computer Science.
Why this matters in the exam

Questions about networks appear in every paper. The most commonly tested areas are: LAN vs WAN characteristics, naming and describing hardware devices, and client-server vs peer-to-peer. Students who lose marks here typically confuse routers with switches, or mix up the definitions of LAN and WAN. This lesson fixes that.

Section 1

What is a computer network?

A computer network is two or more devices connected together so they can communicate and share resources. Those devices could be computers, phones, printers, servers, or anything with a network interface.

Networks exist because sharing is more efficient than duplicating. Instead of every computer needing its own printer, its own copy of every file, and its own internet connection, a network lets all of them share.

Network
Two or more devices connected together to share data and resources.
Node
Any device connected to a network (computer, printer, server, phone).
Network Interface Card (NIC)
Hardware inside a device that allows it to connect to a network (wired or wireless).
Bandwidth
The maximum amount of data that can be transmitted over a connection per second (measured in Mbps or Gbps).

Why build a network?

The benefits of networking are heavily examined. Make sure you can give specific, developed reasons:

Resource sharing
Printers, scanners, storage and software licences can be shared across all devices rather than buying one per computer.
Communication
Email, instant messaging and video calls all depend on network infrastructure. Networks enable real-time collaboration.
Centralised data
Files stored on a central server mean everyone accesses the same up-to-date version. Backups happen in one place.
Centralised security
Administrators can apply updates, run antivirus software and manage user access from a single location.
Internet access
A single internet connection can be shared across many devices on the network through a router.
Cost efficiency
Sharing resources reduces duplication. One network printer for 30 computers costs far less than 30 individual printers.
Section 2

LAN vs WAN: the most examined distinction

Networks are classified by their geographical size. The two you must know for GCSE are LAN and WAN. This distinction comes up in almost every networks exam question.

LAN
Local Area Network
Covers a small geographical area - one building or site
Typically owned and managed by one organisation
Uses private infrastructure (cables, switches, WAPs)
Generally faster and more secure than a WAN
Examples: school network, home network, office floor
WAN
Wide Area Network
Covers a large geographical area - cities, countries, continents
Often uses infrastructure owned by third parties (ISPs, telecoms)
Uses public or leased lines to connect distant LANs
Generally slower and more vulnerable than a LAN
The internet is the world's largest WAN
Exam technique: LAN or WAN?

When asked to identify whether a network is a LAN or WAN, justify your answer with two reasons. The most reliable justifications are: (1) the size of the geographical area covered, and (2) whether the organisation owns the infrastructure. A school with 20 computers in one building → small area + organisation owns it = LAN.

Think about it

1. A company has its headquarters in London, a branch office in Manchester, and a data centre in Dublin. They connect all three sites together. Is this a LAN or WAN? Justify your answer with two reasons.

This is a WAN. Reason 1: the sites span multiple cities and countries - London, Manchester and Dublin are geographically far apart, not a small area. Reason 2: connecting sites across these distances requires using infrastructure owned by third-party ISPs and telecoms companies, not infrastructure the company owns itself.
Section 3

Network Hardware Explorer

Students consistently lose marks by confusing network devices. Click each device to see exactly what it does, a real-world analogy, and the exam traps to avoid.

Router
Connects networks together
What it does
A router connects two or more different networks together. Most importantly, it connects your LAN to the internet (a WAN). It reads the IP address on each data packet and decides the best route to send it. It also assigns IP addresses to devices on the local network using DHCP.
Real-world analogy
A router is like a postal sorting office. It reads the destination address on each parcel (packet) and decides which road to send it down to reach the correct network.
Exam tip: Routers route data between different networks. They are the device that connects your home LAN to the internet. Routers work at the network level using IP addresses.
Common mistake: Students say "a router connects computers together" - that is what a switch does. A router connects networks, not individual computers.
Router vs Gateway
A router connects networks that use the same protocol (typically TCP/IP). A gateway connects networks that use different protocols or architectures, translating between them. Think of a router as a postman who knows which road to use; a gateway is an interpreter who converts the message into a different language entirely. In home networking, the router is often loosely called the "default gateway" - this is simply the IP address of the router that traffic must pass through to leave the local network. The terms blur in everyday use, but the distinction matters at A-Level.
Switch
Connects devices within a LAN
What it does
A switch connects multiple devices within the same network (the LAN). It uses MAC addresses to send data only to the specific device it is intended for, not to every device on the network. This makes it more efficient and secure than a hub.
Real-world analogy
A switch is like an internal telephone exchange in an office building. When you call extension 204, your call goes only to that desk - not to everyone in the building.
Exam tip: Switches send data only to the intended recipient using MAC addresses. This is more efficient than a hub, which broadcasts to everyone. Switches operate within a single LAN.
Common mistake: Confusing a switch with a hub. A hub broadcasts to all devices; a switch sends data only to the destination device. In modern networks, hubs are almost never used.
Hub
Broadcasts to all devices (legacy)
What it does
A hub connects multiple devices on a LAN, but unlike a switch it has no intelligence. When it receives data, it broadcasts that data to every device connected to it, regardless of the intended recipient. Each device must then check whether the data was meant for them.
Real-world analogy
A hub is like shouting a message in a crowded room. Everyone hears it, but only the intended person acts on it. Inefficient, and everyone can hear everyone else's conversations.
Exam tip: Hubs are inefficient (wasted bandwidth) and insecure (all devices can see all data). This is why switches replaced them. You may be asked to compare them - always say a switch sends data only to the target device.
Common mistake: Thinking hubs and switches are the same thing. They are not. A hub broadcasts; a switch directs. This distinction is examined directly.
Wireless Access Point (WAP)
Allows wireless devices to join the LAN
What it does
A Wireless Access Point (WAP) allows Wi-Fi enabled devices to connect to a wired LAN wirelessly. It acts as a bridge between the wireless signal and the wired network infrastructure. Devices connect to the WAP via radio waves; the WAP connects to the network via an Ethernet cable.
Real-world analogy
A WAP is like a translator at a conference. Delegates speaking English (wireless) communicate through the translator to delegates speaking French (wired network). The conversation happens in two different forms, but they can all communicate.
Exam tip: A WAP does not provide internet access on its own - it connects wireless devices to the existing wired LAN. The router provides the internet connection. In a home router, these are often combined in one device.
Common mistake: Saying "you need a WAP to get internet access". A WAP provides wireless access to the LAN. It is the router that connects the LAN to the internet.
Network Interface Card (NIC)
The hardware that lets a device connect
What it does
A NIC is a hardware component inside a device (computer, phone, printer) that allows it to connect to a network. Every NIC has a unique hardware identifier called a MAC address. Modern NICs typically support both wired (Ethernet) and wireless (Wi-Fi) connections.
Real-world analogy
A NIC is like a passport. Without it, you cannot enter the network. Its MAC address is like the passport number - unique to that specific device, issued at manufacture.
Exam tip: Every device that connects to a network needs a NIC. The MAC address burned into the NIC is used by switches to direct traffic to the correct device. MAC addresses are 48 bits, written as 6 pairs of hexadecimal digits.
Common mistake: Confusing MAC address (hardware identifier, fixed, set by manufacturer) with IP address (software identifier, can change, assigned by the network). Both identify devices but at different levels.
Modem
Converts signals for transmission
What it does
A modem (modulator-demodulator) converts digital signals from your network into analogue signals suitable for transmission over telephone lines or cable, and back again at the other end. It is what physically connects your home or office to the ISP's network.
Real-world analogy
A modem is like a bilingual translator between your digital world and the analogue telephone network. Your network speaks binary; the telephone line speaks analogue waves. The modem translates in both directions.
Exam tip: Modem = signal conversion. Router = routing data between networks. In most home devices these are combined ("router" or "broadband hub"), but in the exam they may be asked about separately.
Common mistake: Saying "a modem provides internet access". The modem converts the signal; the router routes the traffic. Both are needed. Confusing their roles loses marks.
The three-way confusion: Router vs Switch vs Hub

Hub → broadcasts to all devices (old, inefficient, insecure). Switch → sends data only to the target device using MAC addresses (within LAN). Router → connects different networks together using IP addresses (LAN to WAN). These are directly compared in exam questions.

Network Traffic Visualiser
Built for this lesson
Watch data packets travel in real time through a hub, a switch, and a router. See exactly why switches replaced hubs and why a router is needed to cross between networks.
Open Visualiser
Networking Toolkit
A-Level depth
Explore the TCP/IP layer stack, build topologies, simulate packets, trace DNS lookups and more. Broader tool for deeper study beyond this lesson.
Open Toolkit
Section 4

Client-Server vs Peer-to-Peer

Networks are not just about the physical hardware. The relationship between devices on a network is equally important. There are two main models you need to know.

Client-Server Most common
One powerful central machine (the server) stores data and provides services
Other devices (the clients) request data or services from the server
The server controls access, security and resources centrally
If the server fails, clients cannot access resources
Used in: schools, businesses, websites (your browser is a client; Google is a server)
Easier to manage, back up and secure at scale
Peer-to-Peer (P2P) Decentralised
Every device on the network is an equal peer - both client and server simultaneously
Devices share resources directly with each other with no central server
No single point of failure - if one device goes offline, others continue
Harder to manage security and access control
Used in: home networks, file sharing (BitTorrent), some VoIP systems
Better for small networks; does not scale well to large organisations
Discussion

2. An artist uploads images to be displayed on a website. In this client-server relationship, which computer is the client and which is the server? Justify each answer.

Client: The artist's computer. Justification: it is making a request to send data to another computer (the web server) - it is initiating the service request.

Server: The web server hosting the website. Justification: it receives the uploaded images, stores them, and serves them to users who request to view the website. It provides the service; the client requests it.
Interactive Tool

Network Builder

Drag devices from the palette onto the workspace to build a network. When you're done, hit Check My Network to get feedback on whether it's valid and what type of network you've built.

Add devices:
Click a device above to add it
Interactive Tool

Transfer Time Calculator

Bandwidth and file size appear in every networks paper. Use this calculator to see exactly how the maths works and build your number sense for typical values.

Try:
Section 5

Check your understanding

LAN or WAN?
Drag each characteristic into the correct category. Some may surprise you.
Covers a single building
Spans multiple countries
Owned by one organisation
Uses infrastructure from an ISP
School or home network
The internet is an example
Typically higher speed connections
Connects multiple LANs together
Uses private cables and switches
Leased lines or telephone infrastructure
LAN
WAN
Lesson Quiz - 5 questions
Based on real exam question styles. Choose your answer to reveal instant feedback.
Question 1 of 5
A youth centre has 20 computers in a single building connected together. Which TWO of the following correctly identify why this is a LAN and not a WAN?
Question 2 of 5
What is the key difference between a switch and a hub?
Question 3 of 5
In a client-server network, which device acts as the server when a user views a webpage on the internet?
Question 4 of 5
Which device is required to connect a LAN to the internet?
Question 5 of 5
Which of the following is an advantage of a peer-to-peer network over a client-server network?
0
/5
Extended thinking

3. A school is deciding whether to upgrade from a peer-to-peer network to a client-server network. Give three reasons why the client-server model would be more suitable for a school.

1. Centralised security: An administrator can manage user accounts, access permissions and security policies from one server, rather than configuring each computer individually.

2. Centralised backup: All student files stored on the server can be backed up automatically and regularly from one location, reducing data loss risk.

3. Scalability: A client-server network handles many users efficiently. A peer-to-peer network becomes unmanageable as the number of users grows - a school with hundreds of students needs central management.

Also accept: centralised software installation/updates; easier to monitor network usage; consistent user experience across all machines.
Revision
Networks Flashcards
All key terms across all 6 lessons. Filter by topic, flip to reveal, mark as known.
Open flashcards
Lesson 2: Network Topologies
Networks Lesson 1 - Teacher Resources
What is a Network?
Teacher mode (all pages)
Shows examiner notes on exam practice pages
Suggested starter (5 min)
Write on the board: "You want to share one printer between 30 computers. Go." Give students 60 seconds to sketch a solution. Almost all will draw something resembling a network without naming it. Then ask: "What did you just design?" They have already built the concept before you've defined it. Now define a network and they already own the idea. This is far more memorable than beginning with a textbook definition.
Lesson objectives
1Define a computer network and state at least three specific benefits of networking with developed justifications.
2Distinguish between a LAN and a WAN using geographical size and ownership of infrastructure as the two key criteria.
3Identify and describe the function of each key network hardware device: NIC, router, switch, hub, WAP and modem - including the critical differences between router/switch and switch/hub.
4Compare client-server and peer-to-peer network models, giving advantages and disadvantages of each in context.
Key vocabulary (board-ready)
Network
Two or more devices connected together for the purpose of sharing data and resources.
LAN (Local Area Network)
A network covering a small geographical area (single building/site), owned and managed by one organisation using private infrastructure.
WAN (Wide Area Network)
A network spanning a large geographical area, typically using infrastructure owned by third-party ISPs or telecoms companies. The internet is the largest WAN.
Router
A device that routes data packets between different networks (e.g. LAN to WAN) using IP addresses.
Switch
A device that connects multiple devices within a LAN and sends data only to the intended recipient using MAC addresses.
Hub
An older, less intelligent device that connects devices within a LAN by broadcasting all received data to every connected device.
WAP (Wireless Access Point)
A device that allows wireless devices to connect to a wired LAN via Wi-Fi radio signals.
NIC (Network Interface Card)
Hardware inside a device that enables network connectivity. Contains a unique MAC address assigned at manufacture.
Client-server
A network model where a central server provides services and resources to client devices that make requests.
Peer-to-peer
A network model where all devices are equal and share resources directly without a central server.
Suggested lesson plan (60 min)
0-5 min: Starter: "Share one printer between 30 computers - sketch a solution." Reveal they've designed a network. Define network formally.
5-15 min: Benefits of networking: work through the 6 benefit cards on screen as a class. Students copy a developed version of each into notes - "sharing resources means..." not just "sharing resources".
15-25 min: LAN vs WAN: use the comparison cards. Key drill: always justify with (1) geographical size and (2) ownership of infrastructure. Practice with 3 quick scenarios (school, multinational company, home).
25-40 min: Network Hardware Explorer: go through each device as a class using the interactive cards. Focus heavily on Router vs Switch vs Hub (the three-way confusion is the most commonly dropped mark on this topic).
40-50 min: Client-server vs P2P: use the comparison panel. Ask students: "Why would a school not use P2P?" and "Why might a home network be P2P?" Bring out the management vs flexibility trade-off.
50-60 min: Drag activity and quiz in pairs. Exit ticket on mini-whiteboards. Address the most common wrong answer as a class.
Discussion prompts
Your school network is a LAN. But the school also sends emails to parents outside school. At what point does the LAN end and the WAN begin in that process? What device sits at the boundary?
If hubs broadcast every packet to every device, that means any device on the network can theoretically read every other device's data. What security implications does this have? Why did switches replace hubs?
The internet is described as the world's largest WAN. But it is actually made up of millions of LANs connected together. At what point does a collection of LANs become a WAN?
In a P2P network, every device is both a client and a server. What problems does this create when you need to ensure that only certain users can access certain files?
Common misconceptions
X"A router connects computers" - a router connects networks (specifically different networks, e.g. LAN to WAN). Computers within a LAN are connected by a switch. This distinction costs marks on almost every Networks paper.
X"A router and a gateway are the same thing" - a router connects networks using the same protocol (TCP/IP). A gateway connects networks that use different protocols, translating between them. The term "default gateway" in network settings refers to the router's IP address - the exit point from the LAN - which is why the terms are confused. At GCSE the distinction is rarely examined precisely; at A-Level it matters.
X"A WAN is just a bigger LAN" - the key distinction is not only size but ownership of infrastructure. A WAN uses third-party (ISP/telecoms) infrastructure; a LAN uses infrastructure owned by the organisation.
X"A WAP gives you internet access" - a WAP connects wireless devices to the LAN. It is the router that connects the LAN to the internet. In home broadband boxes these are combined, which causes the confusion.
X"A hub and a switch do the same thing" - a hub broadcasts all data to all devices; a switch sends data only to the intended device. A hub is inefficient and insecure; switches replaced them almost entirely.
X"The server is always a large computer in a server room" - in a client-server model, any device providing a service is a server. A Raspberry Pi can be a server. The role matters, not the size of the machine.
Exit ticket questions
Give two reasons why a school network is a LAN and not a WAN.
[2 marks - small geographical area (single building/site); owned and managed by the school / organisation owns the infrastructure]
Describe the difference between a switch and a hub.
[2 marks - switch sends data only to the intended device using MAC addresses; hub broadcasts data to all connected devices]
State one advantage and one disadvantage of a client-server network compared to a peer-to-peer network.
[2 marks - advantage: centralised management/security/backup; disadvantage: single point of failure if server goes down / higher cost of server hardware]
Which device connects a LAN to the internet, and how does it decide where to send data packets?
[2 marks - router; reads the IP address on each data packet and routes it to the correct network]
Homework idea
Students draw and annotate a network diagram for their home. They must: (1) identify and label every device (phone, laptop, TV, smart speaker, games console), (2) label which device is the router and which device is the WAP (or note if they are combined), (3) classify the home network as LAN or WAN with two justifications, (4) identify whether it is client-server or peer-to-peer and justify. Bring in the diagram next lesson for peer review.
Classroom tips
The Hardware Explorer works best projected to the class and worked through together before students explore individually. The "Common mistake" sections are worth pausing on - read them aloud and ask students to explain in their own words why the mistake is wrong.
The LAN/WAN drag activity generates good discussion when done in pairs. Students often disagree on borderline items - use that disagreement productively by asking them to justify their choice using the two key criteria.
For the router/switch/hub confusion: draw three columns on the board, one for each device, and have students contribute one characteristic to each column. Students are far more likely to remember information they generated themselves.
The client-server vs P2P distinction is best taught through examples. "When you visit YouTube, which device is the client and which is the server?" Then: "When you AirDrop a photo to a friend, is that client-server or P2P?" Real examples stick.
Resources
Worksheet 1 - Recall: key terms and hardware Worksheet 2 - Apply: network scenarios Worksheet 3 - Exam-style questions Networks series overview Networks flashcards Set as class homework (coming soon)