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This lesson covers the different types of computer networks, including LAN, WAN, PAN, SAN, the Internet, intranets, and the key models of client-server vs peer-to-peer. These are fundamental concepts for the OCR H446 specification section 1.3.
A computer network is a collection of interconnected devices (computers, servers, printers, phones, etc.) that can communicate and share resources. Networks are classified by their size, geographical coverage, and purpose.
A LAN covers a small geographical area, such as a single building, office, school, or home.
| Feature | Detail |
|---|---|
| Coverage | Small area (single building or site) |
| Ownership | Owned and managed by a single organisation or individual |
| Speed | High speed (typically 100 Mbps to 10 Gbps) |
| Hardware | Switches, routers, access points, cabling |
| Examples | School network, office network, home WiFi |
A WAN spans a large geographical area, connecting multiple LANs across cities, countries, or continents.
| Feature | Detail |
|---|---|
| Coverage | Large area (city, country, global) |
| Ownership | Often uses infrastructure owned by third parties (e.g., telecom companies) |
| Speed | Generally slower than LAN (depends on connection type) |
| Hardware | Routers, leased lines, satellite links, undersea cables |
| Examples | The Internet, a company connecting offices in London and New York |
A PAN is a very small network for personal devices, typically within a range of a few metres.
| Feature | Detail |
|---|---|
| Coverage | A few metres (around one person) |
| Technology | Bluetooth, USB, infrared |
| Examples | Phone connected to wireless earbuds, smartwatch syncing with a phone |
A SAN is a high-speed network dedicated to providing access to consolidated, block-level data storage.
| Feature | Detail |
|---|---|
| Purpose | Provides shared storage that appears as locally attached drives |
| Speed | Very high (fibre channel, typically 8-32 Gbps) |
| Use case | Data centres, enterprise storage, server farms |
| Key benefit | Centralised storage management, high availability, fast data access |
The Internet is a global WAN — a vast network of interconnected networks that uses standardised protocols (TCP/IP) to allow communication between billions of devices worldwide.
| Feature | Detail |
|---|---|
| Structure | Network of networks |
| Protocols | TCP/IP |
| Ownership | No single owner — governed by organisations like ICANN, IETF, W3C |
| Services | World Wide Web, email, file transfer, streaming, cloud computing |
| Access | Via ISPs (Internet Service Providers) |
The Internet is not the same as the World Wide Web. The Internet is the physical infrastructure (cables, routers, servers). The Web is a service that runs on the Internet, using HTTP/HTTPS to deliver web pages.
An intranet is a private network within an organisation that uses Internet technologies (TCP/IP, web browsers) but is only accessible to authorised users.
| Feature | Detail |
|---|---|
| Access | Restricted to organisation members |
| Purpose | Internal communication, document sharing, HR systems |
| Technology | Uses TCP/IP and web technologies |
| Security | Protected by firewalls from external access |
An extranet is an extension of an intranet that allows limited access to authorised external users (e.g., suppliers, partners, clients).
In a client-server network, one or more dedicated servers provide services (files, authentication, email, web pages), and clients request those services.
| Feature | Detail |
|---|---|
| Server | Dedicated machine that manages resources and responds to client requests |
| Client | A device that requests services from the server |
| Centralised | Data and services are managed centrally |
| Security | Easier to manage — access rights controlled by the server |
| Backup | Centralised backup of data on the server |
| Cost | Higher — requires dedicated server hardware and administration |
| Examples | School networks, websites, email systems, company file servers |
In a peer-to-peer network, all devices (peers) are equal — each can act as both a client and a server, sharing resources directly.
| Feature | Detail |
|---|---|
| No dedicated server | All devices share resources equally |
| Decentralised | No central point of control or failure |
| Security | Harder to manage — each device manages its own security |
| Backup | Each device responsible for its own backup |
| Cost | Lower — no dedicated server needed |
| Scalability | Can become slower as more peers join |
| Examples | Home file sharing, BitTorrent, some blockchain networks |
| Feature | Client-Server | Peer-to-Peer |
|---|---|---|
| Central management | Yes | No |
| Security | Easier to enforce | Harder to enforce |
| Reliability | Server is a single point of failure | No single point of failure |
| Performance | Server handles load (can be powerful) | Performance depends on all peers |
| Cost | Higher (server + admin) | Lower (no server needed) |
| Scalability | Good (upgrade server) | Limited (network congestion) |
| Data backup | Centralised | Distributed (per device) |
Exam Tip: Exam questions often describe a scenario and ask you to recommend client-server or peer-to-peer. Always justify your choice by linking the features to the specific requirements of the scenario. For example, a school network needs centralised security and backup -> client-server. A small home office sharing files -> peer-to-peer.
Exam Tip: Be precise with definitions. LAN is defined by small geographical area AND single-site ownership. WAN is defined by covering a wide area, often using third-party infrastructure. Do not confuse the Internet (infrastructure) with the Web (a service).