Topology Tour
How networks are put together and why the shape matters. LAN against WAN, client-server against peer-to-peer, and the two topologies OCR actually examines, compared on what they cost and what happens when something breaks.
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Two questions about every network
A network is just computers that can talk to each other. Everything in this topic answers one of two questions about a given network. **How big is it?** That is LAN against WAN. **How is it arranged?** That covers who holds the files (client-server or peer-to-peer) and how the cables run (the topology). Keep those two questions apart and the topic stops being a pile of terms.
The words this topic runs on
Four pairs of terms, and the exam expects you to use them precisely rather than loosely.
Match each network to what it is
- The computers in one school building, wired to its own switches
- A company's offices in four cities, joined by leased connections
- A router, two laptops and a printer in one house
- The internet
- A LAN: one site, hardware owned by the organisation
- A WAN: several sites far apart, connections leased between them
- A LAN, and the smallest kind most people ever use
- The largest WAN in existence, owned by nobody in particular
One company, four cities
A company has an office in each of four cities. Each office has its own wired network, and the four are joined by leased connections. What has it got?
- Four LANs joined together into a WAN
- One WAN and nothing else
- One very large LAN
- Neither, because leased lines are not a network
Who holds the files?
This is a choice about management, not about speed. It matters most as a network gets bigger.
What a server actually buys you
A school with 400 computers uses client-server rather than peer-to-peer. Select the TWO reasons that best justify it.
- Files and backups are held centrally, so work is not lost when one machine fails
- User accounts, permissions and updates are managed from one place instead of 400
- It is cheaper than peer-to-peer
- It removes any single point of failure
Which diagram is which?
Two network topologies. Choose the right name for each.
- Star topology: every device connects to one central switch
- Mesh topology: devices connect directly to each other, with no central device
Star and mesh on three measures
The exam wants these compared on **cost, reliability and scalability**, with a reason attached to each. Here is what that sounds like. **Cost.** Star needs one cable per device plus a switch, so it is cheaper to install than a wired mesh, where the number of connections grows far faster than the number of devices. **Reliability.** In a star, one broken cable disconnects one device, but the switch failing takes the whole network down. A mesh has several routes between any two devices, so traffic can go round a break, and there is no one component that ends it. **Scalability.** Adding a machine to a star is one cable, until the switch runs out of ports. Adding one to a full mesh means connecting it to everything already there.
What breaks everything?
This is the star network from Diagram A. Tap the ONE component whose failure would cut off every device on it.
The topic in a paragraph
A network confined to one site with hardware the organisation owns is a _____, while one spanning several sites over leased connections is a _____. A school of 400 machines would use a _____ arrangement so that backups and accounts are handled centrally. In a _____ topology every device runs a single cable to a central switch, which is cheap but leaves that switch as a single point of failure. A _____ topology avoids that by giving several routes between devices.
Revising from the wrong material
A revision video covers star, mesh and bus topologies in detail. Which of these should you take into a J277 exam?
- Star and mesh only, because those are the two this specification examines
- All three, since more knowledge is always safer
- Bus and star, since mesh is too complex for GCSE
- Mesh only, since star is too simple to be examined
Wiring a new building
A firm is fitting out one floor of an office for 30 staff. Work through the decisions.
- All 30 machines are on one floor, in one building the firm occupies. What kind of network is this?
- Staff share documents constantly and the firm must be able to back everything up nightly. Which arrangement?
- For the cabling, the budget is tight and the building is a single open floor. Star or mesh, and why?
Your turn: recommend a network
A small library is replacing its network. It has 25 machines in one building, needs nightly backups, and has limited money. Recommend a network and justify it.
- Say whether this is a LAN or a WAN, and why
- Recommend client-server or peer-to-peer, with a reason tied to the backups
- Recommend star or mesh, comparing them on cost AND reliability
- State one weakness of what you have recommended, and how the library could reduce it