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AS · Practice questions · Wired and wireless media, Ethernet and CSMA/CD

Listen before you speak.

Six original Cambridge-style questions on transmission media and CSMA/CD, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Four headings.

01
Explain
[4 marks]

Describe two differences between copper cable and fibre-optic cable.

  • Copper carries electrical signals; fibre carries pulses of light. ✓
  • Fibre has a higher bandwidth / bit rate than copper. ✓
  • Fibre suffers less attenuation, so it can carry data further without a repeater. ✓
  • Fibre is immune to electromagnetic interference / harder to tap; copper is cheaper and easier to install (any two differences, both sides). ✓
02
Recall
[3 marks]

Describe the characteristics of satellite communication.

  • Microwave signals are sent up to a satellite and relayed back down to another location. ✓
  • Covers very large areas, including oceans and remote regions without cables. ✓
  • Long distance (about 36 000 km to a geostationary satellite) causes a noticeable delay / latency; signals can be affected by weather. ✓
03
Explain
[5 marks]

Explain how CSMA/CD is used to manage the transmission of frames on a shared Ethernet cable.

  • A device listens to the cable to check whether it is idle before transmitting (carrier sense). ✓
  • If the cable is busy, it waits until it is idle; then it transmits. ✓
  • While transmitting, it monitors the cable to detect a collision. ✓
  • If a collision is detected, it stops transmitting and sends a jam signal to all devices. ✓
  • Each device waits a random time before trying to transmit again. ✓
04
Apply
[4 marks]

A café wants to provide internet access to its customers. Discuss whether it should use a wired or a wireless network.

  • Wireless: customers can use their own phones and laptops anywhere in the café without cables. ✓
  • Easy and cheap to install, and any number of customers can join. ✓
  • But signals can be intercepted, so the network should be encrypted / separated from the café's own systems. ✓
  • Wireless is the better choice because mobility for customers matters more than the higher speed of cables. ✓
05
Explain
[2 marks]

Explain why a device waits a random amount of time after a collision.

  • If both devices waited the same time, they would transmit again at the same moment ... ✓
  • ... and collide again; a random wait makes it likely one starts first and the other senses the cable is busy. ✓
06
Analysis
[3 marks]

A rural farm 15 km from the nearest town needs an internet connection. There are no cables to the farm. Evaluate the use of a microwave link and a satellite link.

  • Microwave link: higher bandwidth and less delay than satellite, but needs line of sight between masts/dishes, which hills or trees may block. ✓
  • Satellite link: works anywhere with a view of the sky, but has high latency (delay) because of the distance to the satellite and can be affected by weather. ✓
  • Conclusion: microwave if a line-of-sight path to the town is available, otherwise satellite. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.