Compare simplex, half-duplex and full-duplex
Classify the direction and timing of communication between two devices.
Exam scope and assessment notes
This sequence follows Cambridge IGCSE Computer Science 0984, 2026–2028 syllabus Version 4. It covers subject content sections 2.1–2.3 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding. Cambridge states that 0984 has the same 2026–2028 subject content as 0478, with 9–1 grading. In June and November, Cambridge lists 0984 in Administrative zone 3 and for centres in Oman and the UAE. Confirm availability for your centre and exam series with Cambridge International. The separately published 2029–2031 syllabus changes to Python 3 only and removes pseudocode; this 2026–2028 route does not cover those changes.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does simplex mean?
What you will learn
- Describe simplex communication
- Distinguish half-duplex from full-duplex
- Apply each direction mode to a communication example
Direction describes who can send
Simplex sends data in one direction only. A one-way broadcast is a useful model: the receiver does not send information back over that same communication path.
Apply and check the rule
Half-duplex allows data in both directions, but not at the same time. Full-duplex allows both devices to send and receive simultaneously. These describe direction and timing, not whether bits are sent serially or in parallel.
Pause and explain
Which mode allows both devices to send at the same time?
Worked example
Two people can talk and hear each other at the same time during a call. Which direction mode is this?
Show the worked solution
- Communication travels in both directions.
- Both people can send at once.
- That is full-duplex communication.
Answer Full duplex
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify a sensor that sends readings to a controller but does not receive data back over that link.
Give me a hint
Check whether communication goes in one direction or two.
Compare my reasoning
- The sensor sends to the controller.
- No reverse transmission is available.
- This is simplex.
Simplex
Look for these in your work
- One-way direction identified
- Mode named
A radio system allows both endpoints to send, but each must wait for the other to finish. Classify it.
Give me a hint
Two-way but not simultaneous is the key clue.
Compare my reasoning
- Both directions are supported.
- Only one device transmits at a time.
- This is half-duplex.
Half-duplex
Look for these in your work
- Two-way communication identified
- No simultaneous sending
- Mode named
A live support service needs the agent and student to speak while both can hear the other. Recommend a direction mode and distinguish it from the transmission method.
Give me a hint
Consider simultaneous two-way communication; direction is a different property from serial or parallel.
Compare my reasoning
- Both endpoints need to send and receive at the same time.
- Full-duplex supports simultaneous two-way communication.
- The physical link can still use serial or parallel bit transmission.
Use full-duplex communication. This specifies simultaneous direction; serial or parallel separately describes how bits travel over the link.
Look for these in your work
- Requirement interpreted
- Full duplex selected
- Two classification axes distinguished
Common mistakes
- Treating half-duplex as one-way
- Confusing duplex direction with serial/parallel transmission
What can you explain now?
A walkie-talkie lets either user speak, but only one at a time. Which mode is it?
Compare with the explanation
Half duplex
It supports two-way communication, but not simultaneously.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How does half-duplex differ from full-duplex?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.