← IGCSE Computer Science Paper 1

Choosing a transmission method for a scenario

Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 32, WA Computer Science ATAR Year 11 — Network Communications — Module 23

Understanding Choosing a transmission method for a scenario in IGCSE Computer Science Paper 1

What it does: One-way-only data is simplex. A long distance means serial, because parallel suffers from data skew and costs more over distance. The two-way need with taking turns is half-duplex. Serial is a safe choice because it is reliable and needs fewer wires. One-way needs point to simplex. Full-duplex is only needed when both devices must send at the same time. No reply is needed, so one-way simplex is enough.

Common mistakes: Simplex means data travels in one direction only, so the reason must say it flows one way. 'Both ways' would need half-duplex or full-duplex. It should read 'Because: data flows one way'. Half-duplex is two-way but only one device sends at a time, so the users take turns. 'At the same time' describes full-duplex. It should read 'Because: two-way, taking turns'.

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This module's key terms are also in a printable crossword (Modules 131–141) and word search (Modules 121–141).

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Learning
Duo
A temperature sensor sends readings to a display screen. The sensor never needs to receive anything back. Which direction fits?
Simplex, because data only ever flows one wayFull-duplex, because data must flow both ways at once
Matches
A security camera streams video to a monitor in the next office. Method: full-duplex, because it sends data both ways.
↓
The data only goes one way, from the camera to the monitor, so full-duplex is wrong. It should be simplex.
Applying
Meanings
Term
transmission method
Meaning
Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.
Practice
Scenario: video call to a friend abroad
Testing
Gaps
direction =
Check Answer
Spots
3Bits: serial
4Because: data flows both ways

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Quick Questions

1. A temperature sensor sends readings to a display screen. The sensor never needs to receive anything back. Which direction fits?
A. Full-duplex, because data must flow both ways at once
B. Simplex, because data only ever flows one way ✓
One-way needs point to simplex. Full-duplex is only needed when both devices must send at the same time.
2. Two engineers use walkie-talkies on a building site. Only one person speaks at a time. Which direction fits?
A. Half-duplex, because data goes both ways but not at the same time ✓
B. Simplex, because data goes both ways at the same time
Two-way, but taking turns, is half-duplex. Simplex is one direction only.
3. Two friends talk on a video call and both can speak and be heard at the same time. Which direction fits?
A. Full-duplex, because both devices send and receive at the same time ✓
B. Half-duplex, because both devices send and receive at the same time
Sending and receiving at the same time is full-duplex. Half-duplex means taking turns.
4. Data is sent between two computers in different countries over a long distance. Which bit arrangement is the better choice?
A. Serial, because bits sent one after another avoid data skew over long distances ✓
B. Parallel, because several bits at once are never affected by distance
Over long distances, parallel wires suffer data skew, so bits arrive out of sync. Serial is more reliable.
5. A printer sits 1 metre from a computer and needs data sent as fast as possible. Which bit arrangement could be justified?
A. Serial, because it sends many bits at once, so it is faster over short distances
B. Parallel, because the distance is short and sending many bits at once is faster ✓
Parallel sends several bits at once, so it is faster over short distances. Serial sends one bit at a time.

Match the Pairs

Scenario: a computer sends data to a printer 1 m away, and the printer replies only with 'ready' or 'error'. Method: half-duplex, parallel → Two-way data, but only one direction at a time, over a very short distance, so parallel is acceptable
Scenario: a video call between two offices 500 km apart. Method: full-duplex, serial → Both sides send and receive at the same time over a long distance, so serial is used to avoid data skew
A TV station broadcasts a programme to many homes. Nothing comes back, and the distance is long. → Method: simplex, serial. Because data travels one way only and serial avoids skew over a long distance.
Two walkie-talkies on a building site. Only one person speaks at a time over a short distance. → Method: half-duplex, serial. Because data goes both ways but not at the same time.
A security camera streams video to a monitor in the next office. Method: full-duplex, because it sends data both ways. → The data only goes one way, from the camera to the monitor, so full-duplex is wrong. It should be simplex.
Sending a file to a server 3000 km away. Method: parallel, because it sends many bits at once so it is faster. → Parallel over a long distance suffers data skew, so bits arrive out of sync. Serial should be chosen.

Key Term

transmission method
Pick the direction (simplex, half-duplex or full-duplex) and the bit arrangement (serial or parallel), then justify both using the scenario's distance, speed and two-way needs.

Fill in the Blanks

1. scenario = "TV remote to TV" direction = simplex
Hint: Type the direction mode where data only ever travels one way.
2. scenario = "Walkie-talkie chat" direction = half-duplex
Hint: Type the direction mode that allows two-way data, but only one side at a time.
3. scenario = "Phone call between two people" direction = full-duplex
Hint: Type the direction mode where both sides send and receive at the same moment.
4. scenario = "500 m between two buildings" bits = serial
Hint: Type the bit arrangement that sends one bit at a time and suits a long distance.
5. scenario = "500 m between two buildings" answer = "Serial because the distance is long"
Hint: Type the connecting word that starts a justification in an exam answer.

Spot the Error

Question 1
A Scenario: keyboard to PC
B Direction: simplex
C Bits: serial
D Because: data flows both ways
Line D — Simplex means data travels in one direction only, so the reason must say it flows one way. 'Both ways' would need half-duplex or full-duplex. It should read 'Because: data flows one way'.
Question 2
A Scenario: walkie-talkie
B Direction: half-duplex
C Because: two-way, at same time
D Bits: serial
Line C — Half-duplex is two-way but only one device sends at a time, so the users take turns. 'At the same time' describes full-duplex. It should read 'Because: two-way, taking turns'.
Question 3
A Direction: simplex
B Scenario: video call
C Because: both send at once
Line A — In a video call both people send and receive at the same time, so the direction is full-duplex. Simplex is one-way only. Line 1 should be 'Direction: full-duplex'.
Question 4
A Scenario: CCTV to a monitor
B Direction: full-duplex
C Because: video flows one way
Line B — The camera only sends video and the monitor only receives it. This one-way need is simplex. Full-duplex is for two-way data at the same time. It should be 'Direction: simplex'.
Question 5
A Scenario: radio broadcast
B Direction: simplex
C Bits: serial
D Because: listeners can reply
Line D — A radio broadcast is simplex because listeners cannot send data back. Saying they can reply contradicts the simplex choice. It should read 'Because: listeners can't reply'.

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