A single computer is useful; computers that can talk to each other are far more useful. This lesson sets out why we network computers, how a LAN differs from a WAN, and the two models that decide which computer does what.
A network lets devices share resources, data and communication. A LAN covers a small area (one site) and its infrastructure is owned by the organisation; a WAN covers a large geographical area and uses infrastructure such as telephone lines and satellites leased from others. In the client-server model, clients send requests to a central server that provides a service and holds the data. In the peer-to-peer model there is no central server: every peer is both a client and a server. A thin client depends on the server for processing and storage; a thick client does most of its own processing.
Every networking question starts here: what does connecting the devices actually give you? Be specific about the resource being shared.
| LAN (local area network) | WAN (wide area network) | |
|---|---|---|
| Area | a single building or site | a large geographical area: cities, countries, the world |
| Infrastructure | owned and managed by the organisation | leased from telecoms providers (PSTN, dedicated lines, satellites) |
| Media | copper cable, fibre-optic cable, WiFi | fibre-optic cable, telephone lines, microwave, satellite links |
| Speed and errors | high bit rate, few errors | usually lower bit rate, more transmission errors |
| Example | a school network | a bank linking its branches; the internet |
"A WAN is a big LAN" earns nothing. Give the defining differences: geographical area covered, and who owns the infrastructure (a LAN's is owned by the organisation; a WAN uses leased or public communication links).
The two models differ in where the data and the services live. Exam questions usually ask you to justify one model for a given situation, so learn the benefits and drawbacks as pairs.
| Client-server | Peer-to-peer | |
|---|---|---|
| Roles | server provides services (files, printing, email, web pages, authentication); clients request them | no central server; each peer stores its own files and can request from and serve to other peers |
| Benefits | central backups and security; files in one place; users can log on from any client; scales well to many users | cheap: no server to buy; easy to set up; no single point of failure; load spread across peers |
| Drawbacks | server and network manager are expensive; if the server fails, clients lose its services; server can become a bottleneck | no central backup or security; each user manages their own files; a file is unavailable when its peer is switched off; slows down as it grows |
| Suits | a school, a business, a web site with many users | a small office or home with a few computers; file sharing such as BitTorrent |
Always tie a justification to the scenario. "Client-server is more secure" is weak; "the patient records are on one server, so access rights and backups are managed centrally" earns the mark.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Which feature best distinguishes a LAN from a WAN?
In a peer-to-peer network, which statement is true?
Which is a drawback of the client-server model?
Which describes a thin client?
Within the client-server model, clients differ in how much work they do themselves.
| Thin client | Thick (fat) client | |
|---|---|---|
| Processing | almost all done on the server | most done on the client itself |
| Storage | little or none locally; data and software on the server | its own storage and installed software |
| Depends on the network? | yes: cannot work if the server or connection fails | can carry on working offline |
| Hardware | cheap, low-specification, easy to manage and update centrally | more powerful and expensive; each one must be updated |
| Server load | high: needs a powerful server and a fast network | lower: less traffic and less server work |
| Example | a browser-based terminal, a library catalogue point | a desktop PC running a video editor, an online game client |
Thin and thick describe the client, not the server, and both still exist inside a client-server network. A thin client is not "a client with a slow connection".
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
A bank links the computer systems in its branches in 40 different countries. What type of network is this?
A school wants students to log on from any computer and see their own files. Which model should it use?
Which is a benefit of a thick client over a thin client?
Which is NOT a benefit of networking computers?
This skill is now recorded on your profile. Keep the chain going.