The big idea: A bit has to travel as something physical.
Twisted pair sends it as electricity down copper. Fibre optic sends it as light down glass. Wireless sends it as radio through the air.
Two words worth knowing first: Attenuation — the signal getting weaker with distance.
Interference — something else corrupting the signal. Electrical noise affects copper; walls and other radios affect wireless. Light in glass suffers from neither.
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Twisted pair (copper)
- Bandwidth moderate — fine for an office desk
- Cost lowest, and the sockets are everywhere
- Installation easy — flexible, cut and plug on site
- Interference susceptible — nearby electrical noise corrupts it
- Attenuation high — roughly 100 m before it needs help
Fibre optic (glass)
- Bandwidth by far the highest
- Cost highest, in cable and in the equipment at each end
- Installation hard — bends and joins need specialist tools
- Interference immune — light carries no electrical signal
- Attenuation very low — kilometres without help
Wireless (radio)
- Bandwidth shared with everyone nearby, so it varies
- Cost low once the access point is installed
- Installation easiest — no cabling to devices at all
- Interference highest — walls, other networks, appliances
- Security weakest — the signal leaves the building
Security is a physical question: To tap copper or fibre you must reach the cable, which means getting inside.
Wireless sprays the signal past the walls, so anyone in the car park can receive it. That is why wireless must be encrypted and cable need not be.
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Between buildings — fibre
Long distance and high traffic, both of which copper handles badly.
Very low attenuation means it crosses a campus without repeaters, and immunity to interference matters outdoors and alongside power cables.
To a desk — twisted pair
Short runs, one device each, and cost multiplied by hundreds of sockets.
At 20 metres attenuation is irrelevant and the bandwidth is ample, so the cheapest option is the right one.
For people who move — wireless
Laptops, phones and tablets cannot be cabled, so there is no alternative.
Accept the shared bandwidth and the interference, and encrypt everything, because the signal leaves the building.
Bandwidth and range are not the whole answer: Exam questions name the factors they want. If the scenario mentions a factory floor full of machinery, interference is the deciding factor, not speed.
Read the scenario for the constraint, then choose.
Linking a LAN to a WAN: The link out of a building to the provider's network is usually fibre (a leased line), DSL over the telephone line, mobile data (4G or 5G), or a satellite link where nothing else reaches, such as a remote farm.
How this is tested — you must pick the medium from the SCENARIO'S constraint — distance, interference, mobility or cost. It comes up two ways:
Paper 1 Section A
- Compare two media, 3-5 marks
- Recommend a medium for a described link
- Explain attenuation or interference
Paper 1 Section B — case study
- Choose media for the case study's sites
- Justify each from their layout and budget
The classic trap: Recommending fibre everywhere because it is fastest. Fibre to every desk costs many times more for bandwidth nobody uses — the right answer is usually fibre between buildings and copper inside them.
A factory has an office block and a production hall 300 m apart, full of heavy electrical machinery. Staff on the floor use handheld scanners. Recommend transmission media.
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