Data can travel as electrical pulses in copper, as light in glass fibre, or as radio waves, microwaves and satellite signals. Each medium trades speed, distance, cost and security. Then see how Ethernet stops devices talking over each other.
Copper cable (twisted pair or coaxial) carries electrical signals: cheap and easy to install, but it suffers from interference and attenuation. Fibre-optic cable carries pulses of light: very high bandwidth over long distances, immune to electrical interference, but more expensive. Wireless media (radio waves including WiFi, microwaves, satellites) give mobility without cables but are slower, less secure and more affected by interference. Ethernet is the standard protocol for wired LANs; on a shared cable it uses CSMA/CD: listen before transmitting, detect any collision, send a jam signal, then wait a random time before trying again.
Compare media using the same four headings every time: bandwidth (bit rate), distance, interference and cost.
| Copper cable (twisted pair, coaxial) | Fibre-optic cable | |
|---|---|---|
| Signal | electrical pulses | pulses of light, reflected along a glass or plastic core |
| Bandwidth | lower | much higher, so a higher bit rate |
| Distance | signal weakens (attenuates) quickly; repeaters needed every hundred metres or so | low attenuation; travels many kilometres before regeneration |
| Interference | affected by electromagnetic interference and crosstalk (twisting reduces it) | immune to electromagnetic interference |
| Security | easier to tap | very hard to tap without being detected |
| Cost and handling | cheap, flexible, easy to install and join | more expensive, needs specialist installation; fragile if bent too far |
| Typical use | LAN cabling to desks, telephone lines | backbones between buildings, undersea cables, internet core |
Wireless media are all electromagnetic waves; they differ in frequency, range and whether they need line of sight.
| Medium | Characteristics |
|---|---|
| Radio waves (WiFi, Bluetooth) | lower frequency; pass through walls; short range for WiFi (tens of metres); bandwidth shared by all devices on the channel; signal reduced by walls and interference from other networks |
| Microwaves | higher frequency, more bandwidth; travel in straight lines so need line of sight between dishes or masts; used for point-to-point links and the mobile phone network; affected by heavy rain |
| Satellites | microwave signals relayed by a satellite, covering huge areas including oceans and remote regions; a geostationary satellite is about 36 000 km up, so the signal travels about 72 000 km up and down, causing a noticeable delay (latency) of roughly a quarter of a second |
| Wired networks | Wireless networks |
|---|---|
| faster and more reliable; consistent bit rate | slower; bit rate falls with distance, obstacles and number of users |
| more secure: an intruder needs physical access to a cable | signals can be intercepted by anyone in range, so encryption (e.g. WPA2/WPA3) is essential |
| less interference | interference from walls, other networks and devices |
| devices are tied to a socket; cabling is costly and disruptive to install | mobility: users move around; easy to add devices; no cables to lay |
Wireless is not insecure by nature, but its signals spread beyond the building. The mark is for saying that signals can be intercepted, so data must be encrypted.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Which is an advantage of fibre-optic cable over copper cable?
Why do microwave links between masts need line of sight?
In the lab, what happens straight after two frames collide?
Which is a disadvantage of a wireless network compared with a wired one?
In the lab, choose CSMA/CD, then make two PCs send at almost the same moment. Watch the collision, the jam signal and the random wait.
CSMA/CD does not prevent every collision: it detects them and recovers. Make sure the answer includes the jam signal and the random wait, which are the commonly missed marks.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Why is there a noticeable delay on a telephone call relayed by a geostationary satellite?
In CSMA/CD, what is meant by carrier sense?
Why are collisions very rare on a modern switched Ethernet LAN?
A company needs to link two buildings 2 km apart with a high bit rate and no interference from nearby machinery. Which medium is best?
This skill is now recorded on your profile. Keep the chain going.