Networks and Topologies

A network is two or more computers connected so they can share data and resources. Networks are classified by their geographic scale.

Type	Full name	Coverage	Ownership
LAN	Local Area Network	Single site — one building, school, office	Usually owned by the organisation
WAN	Wide Area Network	Multiple sites — across cities, countries, or globally	Uses infrastructure owned by third-party providers (telecoms companies)

LAN examples: A school network; a home Wi-Fi network; computers in an office building.

WAN examples: The internet (the world's largest WAN); a bank connecting its branches across the country; a company linking offices in different cities.

Key distinction: A LAN is contained within one location; a WAN connects multiple locations across a wider geographical area.

Several factors influence how fast and reliably data moves across a network:

Factor	Effect
Number of devices connected	More devices sharing the same connection increases congestion and reduces available bandwidth per device
Bandwidth	Higher bandwidth (capacity of the connection) allows more data to be transmitted per second
Interference	Wireless signals degrade in the presence of other wireless devices, walls, or interference from microwaves/other electronics
Transmission medium	Wired connections (Ethernet/fibre) are faster and more reliable than wireless

Computers in a network can take different roles:

Client-server network:

• A powerful server computer provides centralised services (file storage, web pages, email, printing)
• Client computers request and use those services
• The server manages authentication, security, and backups centrally
• Used in schools, businesses, and most internet services

Peer-to-peer (P2P) network:

• All computers have equal status — each can act as both a client and a server
• Files and resources are shared directly between devices without a central server
• No central point of control: each device manages its own security
• Used in home networks, some file-sharing applications

Feature	Client-server	Peer-to-peer
Central server	Yes	No
Security management	Centralised	Each device
Scalability	Good (add more servers)	Limited
Cost	Higher (server hardware)	Lower
Typical use	Schools, businesses	Small home networks

The following hardware components are needed to build a LAN:

Component	Function
Wireless Access Point (WAP)	Allows wireless devices to connect to a wired network; transmits and receives Wi-Fi signals
Router	Connects a LAN to the internet (or another network); routes data packets between networks
Switch	Connects multiple devices within a LAN; directs data only to the intended recipient device (unlike a hub which broadcasts to all)
NIC (Network Interface Controller/Card)	Hardware component inside each device that physically connects it to a network — wired (Ethernet port) or wireless (Wi-Fi chip)
Transmission media	The physical or wireless medium that carries data — e.g. copper cable (Ethernet), fibre optic cable, or radio waves (Wi-Fi)

The Internet is a worldwide network of networks — it is not a single network but a vast collection of interconnected networks (LANs and WANs) communicating using common protocols.

Key services and concepts:

Domain Name System (DNS):

• The internet uses numerical IP addresses to identify devices, but humans use names (e.g. www.bbc.co.uk)
• A DNS (Domain Name System) translates domain names into IP addresses
• A DNS is made up of many Domain Name Servers distributed worldwide
• When you type a URL, your browser asks a DNS server to resolve it to the correct IP address

Web servers and clients:

• A web server stores website files and responds to HTTP requests by sending web pages to clients
• A client (web browser) requests and displays those pages
• The web operates on a client-server model

Hosting:

• Web hosting is a service where a company stores website files on their servers, making those sites accessible on the internet
• Businesses can host their own servers or pay hosting providers

The Cloud:

• Cloud computing provides IT resources — storage, software, processing power — over the internet rather than on local hardware
• Advantages: Access from anywhere; no need to maintain hardware; scales easily; automatic backups
• Disadvantages: Requires internet access; dependent on third-party provider; data privacy concerns; ongoing subscription costs

A topology describes how devices are physically or logically arranged and connected in a network.

Star topology

All devices connect to a central switch or hub. Data travels from a device → switch → destination device.

Advantages:

• If one cable/device fails, the rest of the network continues working (failure is isolated)
• Easy to add new devices — just connect to the switch
• Performance: data is directed specifically to the target device (if using a switch)

Disadvantages:

• If the central switch fails, the entire network goes down
• Requires more cabling than some other topologies (every device needs its own cable to the switch)
• More expensive due to the central switch requirement

Mesh topology

Every device connects directly to every other device (full mesh) or to multiple other devices (partial mesh). There is no single central point.

Advantages:

• Highly reliable — if one connection fails, data can be rerouted via another path
• No single point of failure
• Can handle high traffic as multiple paths are available simultaneously

Disadvantages:

• Expensive and complex to set up — large amounts of cabling/connections needed
• Difficult to manage and maintain (especially full mesh)
• Adding new devices requires connecting them to all existing devices

The diagrams below contrast the two layouts: a star routes everything through one central switch, while a full mesh gives every device a direct link to every other.

1. Confusing LAN and WAN by size alone

A LAN is a single site network. A WAN connects multiple sites across a wider geographical area. Size matters, but the key distinction is single-location vs. multiple locations connected.

2. Saying a router "connects devices within a network"

A switch connects devices within a LAN. A router connects a LAN to another network or the internet. They do different jobs.

3. Saying "the Internet is a single network"

The Internet is a worldwide network of networks — millions of LANs and WANs connected together. It is not one network.

4. Confusing client-server and peer-to-peer

In client-server, a dedicated server provides services to clients. In peer-to-peer, all devices have equal roles. The difference is whether there is a central, dedicated server.

Mistake	Correction
"A router connects devices within a LAN"	A switch connects devices within a LAN; a router connects the LAN to other networks
"Star topology is best because it has no single point of failure"	The central switch IS a single point of failure in a star topology — if it fails, the whole network fails
"Mesh topology is cheaper than star"	Mesh requires many more cables and connections; it is more expensive than star