Computer Networks: Definition, Types, Devices and How They Work

Computer Networks

A computer network allows two or more devices to connect and exchange information. Networks make it possible to browse websites, send emails, share files, use printers, make video calls and access online services.

Devices can connect through:

• Ethernet cables
• Fibre-optic cables
• Wi-Fi
• Mobile networks
• Bluetooth
• Satellite connections

This pillar page provides a simple overview of the most important computer networking concepts. Each topic can be studied in detail on its separate page.

What Is a Computer Network?

A computer network is a group of connected devices that communicate and share data or resources.

Connected devices may include:

• Computers
• Smartphones
• Servers
• Printers
• Routers
• Security cameras
• Smart televisions
• Gaming consoles
• Internet of Things devices

Real-life example: When your phone, laptop and smart television connect to the same home Wi-Fi router, they become part of a home network.

Why Are Computer Networks Used?

Computer networks are used to:

• Share files and information
• Share printers and storage
• Access the internet
• Send emails and messages
• Make voice and video calls
• Use websites and online applications
• Manage devices centrally
• Create backups
• Support remote working
• Play online games

Real-life example: In a school computer lab, many computers can use the same internet connection and network printer.

How Does a Computer Network Work?

A network works by dividing data into small units, sending them through a connection and delivering them to the correct device.

For example, when you open a website:

1. Your device connects to a router through Wi-Fi or Ethernet.
2. DNS finds the IP address of the website’s server.
3. Your request is divided into packets.
4. Routers move the packets across different networks.
5. The website’s server receives the request.
6. The server sends the required data back.
7. Your device reassembles the packets.
8. The browser displays the website.

Real-life example: This process is similar to ordering a product online. Your request reaches the seller, the seller prepares the product and the delivery network brings it to your address.

Basic Components of a Network

Component	Simple Meaning	Real-Life Example
Sender	Device that sends data	Your phone sending a message
Receiver	Device that receives data	Your friend’s phone
Data	Information being shared	Text, image or video
Transmission Medium	Path used by data	Wi-Fi or Ethernet cable
Network Device	Directs or controls data	Router or switch
Protocol	Communication rules	TCP/IP or HTTPS

All these components work together to make communication possible.

What Is a Network Node?

A node is any device or connection point that participates in a network.

Examples include:

• Computer
• Smartphone
• Router
• Switch
• Printer
• Server

Real-life example: Every person in a group conversation is like a node because each person can send or receive information.

What Is a Client?

A client is a device or application that requests a service.

Real-life example: Your web browser acts as a client when it requests a page from a website.

What Is a Server?

A server is a computer or software system that provides services, files or information to clients.

Servers may provide:

• Websites
• Email
• Files
• Databases
• Applications
• User authentication

Real-life example: A restaurant customer requests food like a client, while the kitchen prepares and provides it like a server.

Types of Computer Networks

Networks can be classified according to their size, purpose and geographical coverage.

Personal Area Network

A Personal Area Network, or PAN, connects personal devices over a short distance.

It may use:

• Bluetooth
• USB
• Wi-Fi Direct

Real-life example: Connecting wireless earbuds or a smartwatch to your smartphone creates a PAN.

Local Area Network

A Local Area Network, or LAN, connects devices within a small area.

A LAN may cover:

• A home
• An office
• A school
• A shop
• A single building

Real-life example: Computers connected to the same router in an office form a LAN.

Wireless Local Area Network

A Wireless Local Area Network, or WLAN, is a LAN that uses wireless communication such as Wi-Fi.

Real-life example: Your home Wi-Fi network is a WLAN because devices connect without Ethernet cables.

Campus Area Network

A Campus Area Network, or CAN, connects multiple LANs within a campus or organisation.

Real-life example: A university may connect its library, classrooms, laboratories and offices through one campus network.

Metropolitan Area Network

A Metropolitan Area Network, or MAN, covers a city or large urban area.

Real-life example: A local authority may connect government buildings across a city through a MAN.

Wide Area Network

A Wide Area Network, or WAN, connects devices and smaller networks across large geographical areas.

It may cover:

• Multiple cities
• Different countries
• Entire continents

Real-life example: A bank connecting its branches across the United Kingdom uses a WAN.

The internet is the world’s largest collection of interconnected networks.

Storage Area Network

A Storage Area Network, or SAN, is a specialised high-speed network that connects servers to shared storage systems.

Real-life example: A data centre may use a SAN so that multiple servers can access a central storage system.

Virtual Private Network

A Virtual Private Network, or VPN, creates an encrypted connection across another network, usually the internet.

A VPN is a logical private connection rather than a physical network based only on distance.

Real-life example: An employee working from home can use a VPN to access their company’s internal systems securely.

Wired and Wireless Networks

Wired Network

A wired network uses physical cables such as:

• Ethernet cable
• Fibre-optic cable
• Coaxial cable

Wired networks generally provide stable connections, high speed and low delay.

Real-life example: A gaming computer connected directly to a router using an Ethernet cable is using a wired network.

Wireless Network

A wireless network sends data using radio waves or other wireless signals.

Examples include:

• Wi-Fi
• Bluetooth
• Mobile networks
• Satellite communication

Wireless networks provide mobility and reduce the need for cables.

Real-life example: Using Wi-Fi on a smartphone while moving around the house is wireless networking.

Wired vs Wireless Network

Feature	Wired Network	Wireless Network
Connection	Physical cable	Radio signals
Mobility	Limited	High
Stability	Usually more stable	Can be affected by interference
Installation	Requires cables	Easier for mobile devices
Common Example	Ethernet	Wi-Fi

Network Architecture

Network architecture describes how devices share responsibilities and resources.

Peer-to-Peer Network

In a peer-to-peer network, devices can share resources directly without depending on one central server.

Real-life example: Two computers directly sharing files with each other are using a simple peer-to-peer arrangement.

Peer-to-peer networks are easy to create but can become difficult to manage as the number of devices increases.

Client-Server Network

In a client-server network, clients request services from a central server.

Real-life example: When you log in to a website, your browser sends a request to the website’s server.

Client-server networks provide central management, security and backup, but they require dedicated server resources.

Important Network Devices

Network Interface Card

A Network Interface Card, or NIC, allows a device to connect to a network.

A NIC may support:

• Ethernet
• Wi-Fi
• Fibre connection

Real-life example: The Wi-Fi adapter inside your laptop is a wireless NIC.

Hub

A hub connects multiple devices but sends incoming data to every connected port.

Real-life example: A hub behaves like someone announcing a message to everyone in a room, even when the message is intended for only one person.

Hubs are now rarely used because switches manage traffic more efficiently.

Switch

A switch connects devices within a LAN and forwards data towards the intended device using network information such as MAC addresses.

Real-life example: A switch is like a receptionist who sends a letter to the correct employee instead of giving copies to everyone.

Router

A router connects different networks and chooses a path for data.

At home, a router commonly connects the local network to the internet.

Real-life example: A router is like a road junction that directs vehicles towards different destinations.

Modem

A modem connects a home or business network to the communication service provided by an Internet Service Provider.

The exact equipment varies between DSL, cable and fibre connections.

Real-life example: The modem acts like an entrance between your home network and your internet provider’s network.

Wireless Access Point

A wireless access point allows Wi-Fi devices to connect to a wired network.

Real-life example: An office may install access points on different floors so employees can connect through Wi-Fi.

Repeater

A repeater receives and regenerates a weakened signal so it can travel farther.

Real-life example: A Wi-Fi extender can help provide coverage in a room where the original signal is weak.

Bridge

A bridge connects two sections of a network and helps control traffic between them.

Many modern switches perform functions that were traditionally provided by bridges.

Real-life example: A bridge is like a connection between two sections of the same building.

Gateway

A gateway connects networks that may use different systems or communication methods.

A device’s default gateway is commonly the router used to reach destinations outside the local network.

Real-life example: A gateway is like an international airport that connects travellers from different transport systems.

Firewall

A firewall monitors and controls network traffic according to security rules.

It can block unauthorised or suspicious connections.

Real-life example: A firewall is like a security guard who checks people before allowing them to enter a building.

What Is Network Topology?

Network topology describes how devices and connections are arranged.

It can describe the physical cable layout or the logical movement of data.

Bus Topology

In a bus topology, devices share one main communication cable.

Real-life example: It is similar to houses built along one main road.

Bus topology is simple but a problem with the main cable can affect the entire network.

Star Topology

In a star topology, every device connects to one central switch or hub.

Real-life example: It is like several roads meeting at one central roundabout.

Star topology is widely used in modern LANs. If one device cable fails, other devices can continue working. However, failure of the central device can affect the whole network.

Ring Topology

In a ring topology, devices form a circular connection.

Data travels through the ring to reach its destination.

Real-life example: It is similar to people standing in a circle and passing a message from one person to the next.

Mesh Topology

In a mesh topology, devices have multiple connections to other devices.

Real-life example: A city with several alternative roads between locations works like a mesh network.

Mesh networks provide alternative paths, but they can be more expensive and complex.

Tree Topology

A tree topology arranges devices in connected levels or branches.

Real-life example: A company may have a main network connected to separate networks for each department.

Hybrid Topology

A hybrid topology combines two or more topology types.

Real-life example: A university may use star networks inside buildings and connect those buildings using another network design.

Important Network Terms

Packet

A packet is a small unit of data sent across a network.

Large files are divided into multiple packets and reassembled at the destination.

Real-life example: Sending a large item in several numbered boxes is similar to dividing data into packets.

Bandwidth

Bandwidth is the maximum amount of data a connection can carry within a period.

It is commonly measured in:

• Mbps
• Gbps

Real-life example: Bandwidth is like the width of a road. A wider road can carry more vehicles at the same time.

Latency

Latency is the time taken for data to travel from one point to another.

It is commonly measured in milliseconds.

Real-life example: During an online game, high latency can cause a delay between pressing a button and seeing the action.

Throughput

Throughput is the amount of useful data actually transferred during a period.

Real-life example: A road may support 1,000 vehicles, but traffic problems may allow only 600 to pass. The actual number is similar to throughput.

Upload

Uploading means sending data from your device to another system.

Real-life example: Adding a video to a website is an upload.

Download

Downloading means receiving data from another system.

Real-life example: Saving a PDF from a website to your phone is a download.

IP Address

An IP address identifies a device or network interface for communication using the Internet Protocol.

Real-life example: An IP address works like a postal address that helps data reach the correct destination.

Two commonly used versions are:

• IPv4
• IPv6

MAC Address

A MAC address is a hardware-related address used mainly for communication within a local network.

Real-life example: An IP address is similar to a building address, while a MAC address is similar to the identity label of a particular device inside that building.

Public and Private IP Addresses

A public IP address is used for communication across the internet.

A private IP address is used inside a local network.

Real-life example: Your house has one public street address, while each room has its own internal location.

Port Number

A port number helps the operating system send network data to the correct application or service.

Real-life example: If an IP address identifies a building, a port number is like a room number inside that building.

Domain Name

A domain name is a readable name used to access an internet resource.

Real-life example: People remember a website name more easily than a long numerical IP address.

Important Network Protocols

A protocol is a set of rules that devices follow when communicating.

Real-life example: People need a common language and conversation rules to understand one another. Devices need protocols for the same reason.

TCP

TCP stands for Transmission Control Protocol.

TCP provides reliable and ordered delivery of data.

Real-life example: TCP is like sending numbered boxes and checking that every box arrives in the correct order.

It is commonly used for web pages, emails and file transfers where missing data can cause problems.

UDP

UDP stands for User Datagram Protocol.

UDP sends data with less delivery checking, which can reduce delay.

Real-life example: During a live conversation, receiving the next word quickly may be more useful than stopping to recover one missed sound.

UDP is commonly used in real-time applications such as streaming, gaming and voice communication, depending on the application design.

IP

IP stands for Internet Protocol.

IP provides addressing and helps move packets between networks.

Real-life example: IP works like the addressing system used by a delivery service.

HTTP

HTTP stands for Hypertext Transfer Protocol.

It is used to transfer web content between browsers and web servers.

Real-life example: Your browser uses HTTP rules when requesting a web page.

HTTPS

HTTPS stands for Hypertext Transfer Protocol Secure.

It uses encryption and authentication mechanisms provided by TLS to protect web communication.

Real-life example: HTTPS is like sending information in a protected package instead of an open postcard.

DNS

DNS stands for Domain Name System.

DNS translates domain names into IP addresses.

Real-life example: DNS works like a phone contact list that connects a person’s name with their number.

DHCP

DHCP stands for Dynamic Host Configuration Protocol.

DHCP automatically gives devices network settings such as an IP address.

Real-life example: When your phone joins home Wi-Fi, the router can automatically assign it an address.

FTP and SFTP

FTP is used to transfer files between systems.

SFTP transfers files through a secure SSH connection.

Real-life example: Website administrators may use a file-transfer service to upload website files to a server.

SMTP

SMTP stands for Simple Mail Transfer Protocol.

It is mainly used to send email.

Real-life example: SMTP acts like the postal service that moves an outgoing letter towards the recipient.

IMAP and POP3

IMAP and POP3 are used by email applications to access messages.

• IMAP normally keeps messages synchronised with the mail server.
• POP3 traditionally downloads messages to a device.

Real-life example: IMAP allows the same mailbox to remain updated on your phone and computer.

SSH

SSH stands for Secure Shell.

SSH allows secure remote access to another computer or server.

Real-life example: A system administrator can use SSH to manage a remote Linux server without being physically present.

Communication Modes

Simplex

In simplex communication, data travels in only one direction.

Real-life example: A traditional television broadcast sends information to viewers, but viewers do not send information back through the same broadcast channel.

Half-Duplex

In half-duplex communication, data can travel in both directions, but not at the same time.

Real-life example: Two people using walkie-talkies take turns speaking.

Full-Duplex

In full-duplex communication, data can travel in both directions at the same time.

Real-life example: During a phone call, both people can speak and listen simultaneously.

What Is the OSI Model?

The OSI model is a seven-layer conceptual framework used to understand network communication.

Layer	Main Purpose	Simple Example
7. Application	Provides network services to applications	Web browser requesting a page
6. Presentation	Translates, compresses or encrypts data	Preparing encrypted web data
5. Session	Manages communication sessions	Maintaining an online meeting
4. Transport	Manages end-to-end delivery	TCP checking packet delivery
3. Network	Handles IP addressing and routing	Router selecting a path
2. Data Link	Handles local frames and MAC addresses	Switch forwarding local traffic
1. Physical	Sends bits as physical signals	Ethernet cable or radio signal

Real-life example: The OSI model is like sending a parcel through different departments. Each department performs a particular task before the parcel reaches its destination.

What Is the TCP/IP Model?

The TCP/IP model is the practical networking model used by the internet.

Its main layers are:

1. Application
2. Transport
3. Internet
4. Network Access

Real-life example: When opening a website, HTTPS works at the application level, TCP manages delivery, IP handles addressing and Wi-Fi or Ethernet carries the signals.

Internet, Intranet and Extranet

Internet

The internet is a global system of interconnected networks available through authorised internet connections.

Real-life example: Public websites and online video platforms operate through the internet.

Intranet

An intranet is a private network or internal web-based system used by an organisation.

Real-life example: A company portal that only employees can access is an intranet.

Extranet

An extranet provides selected external users with controlled access to part of an organisation’s private resources.

Real-life example: A supplier may use a company’s extranet to check orders and delivery information.

Internet vs World Wide Web

The internet is the global network infrastructure connecting devices and networks.

The World Wide Web is one service that uses the internet to deliver websites and web pages.

Real-life example: Email uses the internet, but it is not the same service as the Web.

Basic Network Security

Network security protects devices, services and data from unauthorised access, damage and attacks.

Common protections include:

Strong Passwords

Strong and unique passwords reduce the risk of account access.

Real-life example: A strong Wi-Fi password prevents nearby strangers from easily joining your network.

Encryption

Encryption converts readable data into a protected form.

Real-life example: HTTPS encrypts information exchanged between your browser and a supported website.

Firewall

A firewall allows or blocks traffic according to security rules.

Real-life example: It acts like a guard checking who can enter or leave.

Authentication

Authentication confirms the identity of a user or device.

Real-life example: Entering a password and verification code proves that you are the authorised account owner.

Software Updates

Updates repair known security weaknesses and software errors.

Real-life example: Updating a router can fix a vulnerability that attackers might otherwise use.

Network Segmentation

Segmentation divides a large network into smaller controlled sections.

Real-life example: A company may keep guest Wi-Fi separate from computers containing business data.

VPN

A VPN can protect data travelling across an untrusted network.

Real-life example: An employee may use a company VPN when working through public Wi-Fi.

Advantages of Computer Networks

• Fast communication
• File and resource sharing
• Shared internet access
• Central data management
• Remote access
• Online collaboration
• Easier backups
• Shared printers and storage
• Support for cloud services
• Reduced duplication of resources

Real-life example: Employees in different offices can work on the same online document instead of sending multiple separate copies.

Limitations of Computer Networks

• Security risks
• Privacy concerns
• Installation costs
• Maintenance requirements
• Dependence on network availability
• Possible congestion
• Hardware or service failures
• Malware spreading between connected devices
• Need for technical management

Real-life example: If an office’s main router fails, many employees may lose access to shared systems and the internet.

Topics Covered in This Chapter

The Computer Networks section can include separate detailed pages on:

• Introduction to Computer Networks
• Types of Computer Networks
• Wired and Wireless Networks
• Client-Server and Peer-to-Peer Networks
• Network Topologies
• Network Devices
• OSI Model
• TCP/IP Model
• Network Protocols
• IPv4 and IPv6
• Public and Private IP Addresses
• MAC Addresses
• Ports and Services
• DNS and DHCP
• Ethernet and Wi-Fi
• Switching and Routing
• Internet, Intranet and Extranet
• Network Security Basics
• Common Network Commands
• Basic Network Troubleshooting

Frequently Asked Questions

What is a computer network?

A computer network is a group of connected devices that communicate and share information or resources.

What are the main types of networks?

Common types include PAN, LAN, WLAN, CAN, MAN and WAN.

What is the difference between LAN and WAN?

A LAN covers a small area such as a home or office. A WAN connects networks across much larger geographical areas.

What is a router?

A router connects different networks and directs data towards its destination.

What is the difference between a router and a switch?

A switch mainly connects devices within a local network. A router connects different networks.

Is Wi-Fi the same as the internet?

No. Wi-Fi is a wireless method of connecting to a local network. The internet is a global collection of interconnected networks.

A device can connect to Wi-Fi even when that network has no working internet connection.

What is an IP address?

An IP address identifies a device or network interface for communication using the Internet Protocol.

What is a network protocol?

A network protocol is a set of rules that devices follow to communicate.

What is network topology?

Network topology describes how devices and connections are arranged.

What is the largest network?

The internet is the largest global collection of interconnected computer networks.

Conclusion

A computer network connects devices so they can communicate and share data, services and resources.

Networks can be small, such as a Bluetooth connection between a phone and earbuds, or extremely large, such as the internet.

Important networking concepts include:

• Network types
• Routers and switches
• Wired and wireless connections
• IP and MAC addresses
• Network protocols
• Topologies
• OSI and TCP/IP models
• Network security

In simple words, a computer network allows connected devices to exchange information and work together.