A2.3.2 · Data transmissions
Transmission media
By the end you can
Compare fibre, twisted pair and wireless for bandwidth, cost, range, interference, installation and security.
A is what the signal actually travels through. The three you need are two kinds of cable (fibre optic and twisted pair) and wireless. To compare them, use the same six measures every time.
- Bandwidth: how much data per second it can carry.
- Range and attenuation: how far the signal goes before it fades () and needs boosting.
- Interference: how easily noise from motors, other cables or other radios corrupts it.
- Cost: of the cable and the equipment.
- Installation: how hard it is to fit.
- Security: how easy it is to tap or eavesdrop.
Fibre optic#
Glass or plastic strands carry pulses of light. It has the highest bandwidth (tens of gigabits per second and up to terabits in practice), loses very little signal over tens or hundreds of kilometres, which is why it crosses oceans on the sea bed, and is immune to electromagnetic interference and hard to tap without detection. It is the most expensive to buy and install, and joining it needs specialist skills. Used for backbones, data centres, long links and increasingly to homes.
Twisted pair#
Pairs of insulated copper wires twisted together carry electrical signals; the twisting cancels some interference. UTP (unshielded) is the everyday network cable; STP (shielded) adds screening for noisy places. It is cheap, flexible and easy for a technician to install, and gives gigabit speeds for offices and homes. Its limits are range (about 100 metres per run before the signal needs a repeater), more vulnerability to interference than fibre, and it is easier to tap.
Wireless#
Radio waves through the air (Wi-Fi at 2.4 or 5 GHz, Bluetooth, mobile networks). No cabling, so it is quick to set up and lets devices move, but the bandwidth is lower and shared between everyone on the access point, the signal weakens with distance and walls, other radios and even a microwave oven can interfere, and, because the signal goes in all directions, anyone in range can try to intercept it, so strong encryption such as WPA2 or WPA3 matters.
| Medium | Typical speed | Time for the file | Reach per run |
|---|---|---|---|
| Fibre optic | 10 Gb/s | 400 ms | 40 kmreaches 80 m in one go |
| Twisted pair (Cat 6) | 1 Gb/s | 4.0 s | 100 mreaches 80 m in one go |
| Wi-Fi | 300 Mb/s | 13.3 s | 90 mreaches 80 m in one go |
Rounded typical values for comparing the media. Real speeds depend on the exact cable, equipment, interference and how many devices share the link.
A cable under the ocean that must carry huge volumes of data for thousands of kilometres.
Cabling a new office floor cheaply, with each desk within 80 m of the cupboard.
Visitors in a café want to connect phones with no cables.
A school links its main building to a sports hall 300 m away with the least interference and room to grow.
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Check yourself
Transmission media
Quick questions, made fresh every time and marked here. Do a few until they feel easy.
Exam practice
Paper 1-style questions
4 questions · 14 marks
Write your answer as you would in the exam, then show the mark points and tick each one your answer made. These are our own questions in the style of the exam, not past-paper questions.
1.Outline two types of medium used to transmit data in a network.
[4]Outline: A brief account: the main points, without much detail.
2.Describe one advantage and one disadvantage of fibre-optic cable.
[2]Describe: A detailed account: say what happens, step by step if it is a process.
3.A factory with large electric motors needs a reliable link between two buildings 400 m apart. Justify a suitable choice of medium.
[4]Justify: Give the reasons or evidence that support the answer or decision.
4.Discuss the advantages and disadvantages of wireless networking for a hotel.
[4]Discuss: Look at the question from more than one side, weigh the points against each other, and come to a conclusion.
Past papers
Old exam questions on this topic
From HL Paper 1, May 2014 to November 2025. These papers were set on the previous syllabus, so the wording may differ from today's exam, but the topic is the same. Find the questions and markschemes in your school's past-paper pack.
| Paper | Question | Marks | About |
|---|---|---|---|
| May 2025 TZ2 | 10(b)(i) | 2 | Choosing a communication link (same in TZ3) |
| November 2025 | 3 | 2 | Characteristics of fibre-optic lines |
| November 2025 | 11(b) | 4 | Advantages of a wireless LAN |
| May 2024 TZ1 | 12(a)(i) | 2 | A benefit of fibre cabling (same in TZ2) |
| May 2024 TZ1 | 12(a)(ii) | 2 | A benefit of wireless links (same in TZ2) |
| November 2024 | 11(c) | 4 | Benefits of wired Ethernet |
| May 2023 TZ1 | 11(b) | 2 | What limits a channel's data rate (same in TZ2) |
| November 2023 | 10(e) | 3 | Why a mobile signal gets weaker |
| November 2022 | 10(b) | 4 | Reliability of wired against wireless |
| May 2021 | 6 | 2 | Fibre optic cable against wireless |
| May 2021 | 12(b) | 2 | A benefit of campus Wi-Fi |
| May 2019 | 14(f) | 4 | Why wireless speed changes in a room |
| May 2018 | 12(d) | 4 | Two benefits of a wireless LAN |
| November 2017 | 11(b) | 4 | Two drawbacks of a wireless LAN |
| May 2016 | 12(a) | 4 | How reliable wireless transmission is |
| November 2016 | 3(a) | 4 | Advantages of wireless networks |
| November 2014 | 13(c) | 2 | Choosing media for different links |
In a nutshell
- Fibre optic carries light: highest bandwidth, longest range, immune to electrical interference and hard to tap, but costly to install.
- Twisted pair carries electrical signals in copper (UTP unshielded, STP shielded): cheap and easy to install, moderate speed, about 100 m per run, affected by interference.
- Wireless carries radio waves: no cables and easy mobility, but lower and shared bandwidth, limited range, interference and a bigger interception risk.
- Compare media on bandwidth, range and attenuation, interference, cost, installation and security.
- Choose by the situation: fibre for backbones and long runs, twisted pair for offices, wireless for homes, campuses and mobile devices.