The big idea: A networking model is about where the data and the work live.
Client-server — one machine holds everything and serves the rest. Peer-to-peer — every machine holds a share and serves the others directly.
One question separates them: Is there a machine in charge?
If yes, it is client-server. If every machine is both a client and a server to the others, it is peer-to-peer.
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One machine serves the rest: Clients send requests; the server holds the data and answers them.
Your browser is a client. The website is on a server. The same pattern runs email, online banking and school file storage.
What it gives you
- One copy of the data, so everyone sees the same thing
- Security and access controlled in one place
- Backing up means backing up the server
- Easy to manage, update and audit
What it costs
- The server is a single point of failure
- It must be powerful enough for everyone at once
- It can become a bottleneck when demand rises
- Buying and running it is expensive
Why a bank must use it: A balance has to have one correct value that the bank controls.
That rules out any model where copies live on customers' own machines — so online banking is client-server, whatever it costs.
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Every machine serves the others: There is no central server. Each machine holds part of the data and supplies it directly to whoever asks.
The more machines join, the more capacity there is — which is the opposite of a server bottleneck.
What it gives you
- No single point of failure — losing one peer loses nothing
- Capacity grows as more peers join
- No expensive server to buy or run
- Used for file sharing, some VoIP, and blockchains
What it costs
- No central control over who sees what
- Data may be inconsistent between peers
- Harder to secure — every peer is a way in
- Availability depends on enough peers being online
A blockchain is peer-to-peer on purpose: Every participant holds a copy of the ledger and they agree among themselves what it says.
That is the whole design goal: no single organisation decides what is true.
How this is tested — you must compare in one sentence, not define each model separately. It comes up two ways:
Paper 1 Section A
- Compare and contrast the two models, 4-6 marks
- Give a benefit and drawback of one
- Say which suits a stated application
Paper 1 Section B — case study
- Identify the model the case study uses
- Evaluate whether it is the right choice for them
The classic trap: Two separate paragraphs. "Compare and contrast" needs sentences holding both: "a client-server system has one authoritative copy, whereas in peer-to-peer each peer holds its own and they may disagree".
A company is choosing between a client-server system and a peer-to-peer one for sharing large design files between forty staff. Compare the two models for this purpose.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.