Networks and types
A computer network is a collection of computers (and other devices) connected to share data and resources. AQA expects you to distinguish LAN from WAN, and client-server from peer-to-peer architectures, with the trade-offs of each.
Why use a network?
- Share resources — printers, files, internet access.
- Communicate — email, messaging, video calls.
- Centralised management — one server hosts files; updates and backups in one place.
- Collaboration — multiple users edit shared documents.
Drawbacks: cost (hardware, maintenance), security risk (more entry points), single point of failure (server outage).
LAN vs WAN
LAN (Local Area Network)
- Geographically small — single building or campus.
- High speed (1 Gbps+).
- Owned and managed by one organisation.
- Examples: school computer room, home Wi-Fi network, office LAN.
WAN (Wide Area Network)
- Geographically large — across cities, countries or globally.
- Slower (typically) than LAN.
- Often relies on infrastructure owned by telecoms (BT, AT&T) — leased lines, fibre, microwave links.
- The Internet is the largest WAN.
A LAN can connect to a WAN through a router/firewall.
Client-server architecture
In a client-server network, one or more powerful servers provide services; many clients request and use those services.
- Server — always on; stores files, hosts a website, runs a database, authenticates users.
- Client — a user's device that connects to the server when needed.
Advantages:
- Centralised security and backups.
- Easy to add/remove clients.
- Powerful server can handle many clients.
Disadvantages:
- Server is a single point of failure — if it goes down, all clients lose service.
- Server hardware and licensing is expensive.
- Requires expert administration.
Examples: school file server, web servers (apache/nginx), email server.
Peer-to-peer (P2P) architecture
In a P2P network, every device is equal — no central server. Each peer can act as both client and server.
Advantages:
- No need for an expensive server.
- No single point of failure — if one peer goes down, others continue.
- Cheap to set up for small networks (e.g. home).
Disadvantages:
- Performance suffers if peers are turned off.
- Difficult to back up centrally.
- Hard to enforce security and updates.
- Doesn't scale to thousands of peers easily.
Examples: BitTorrent file sharing, small home network with shared printer, blockchain.
When to choose which?
| Scenario | Best fit |
|---|---|
| 500-pupil school | Client-server (centralised file storage, logins) |
| 4-person home network | P2P (cheap, simple) |
| Global file sharing | P2P (BitTorrent style) |
| Bank with branches | Client-server (security, control) |
| Multiplayer indie game | Could be either |
✦Worked example
A small business with five employees wants to share files. Recommend an architecture and justify.
- P2P suitable — small scale, low cost B1.
- Each computer can share files directly B1.
- No server required B1.
- Trade-off: no central backup, security must be set per machine B1.
If the business grows to 50 employees, a client-server model with a dedicated file server becomes more appropriate.
Bringing it together
LAN and WAN describe geographic scope; client-server and P2P describe architecture. They are independent: a LAN can be P2P (small office) or client-server (school); the Internet is a WAN that mostly runs client-server (websites) but supports P2P (torrents) on top.
⚠Common mistakes— Pitfalls
- Mixing scope with architecture. WAN ≠ client-server.
- Saying "the Internet is a network". True but reductive — it's a WAN, specifically a network of networks.
- Calling a server "always remote". A server is defined by its role, not its location — it can sit in the next room.
- Treating P2P as inherently illegal. P2P is a topology; legality depends on what's shared.
- Forgetting the cost trade-off. Client-server costs more upfront but scales better.
➜Try this— Quick check
For each scenario, identify (a) LAN/WAN and (b) client-server/P2P:
- A school network with central logins: LAN, client-server.
- The internet: WAN, mostly client-server.
- BitTorrent download: WAN, P2P.
- Home Wi-Fi with three laptops sharing: LAN, P2P.
AI-generated · claude-opus-4-7 · v3-deep-computer-science