Understand errors after data transmission
Explain how interference can cause data loss, gain or change and why a receiver checks transmitted data.
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 can interference do to transmitted data?
What you will learn
- Describe how interference can affect transmitted data
- Distinguish loss, gain and change errors
- Explain why error checks are needed after transmission
A transmitted message may be altered
Electrical or radio interference can affect data while it travels. Data can be lost, extra data can be gained, or existing data can change.
Apply and check the rule
The receiver should check whether the data is consistent with an error-detection value or rule sent with it. Detection identifies a possible problem; it does not always identify the exact error or repair the data. A resend mechanism such as ARQ may be needed.
Pause and explain
The receiver gets more bits than the sender transmitted. Which error type is this?
Worked example
A sender transmits 101101. The receiver gets 101001. What kind of error occurred?
Show the worked solution
- Compare the sent and received patterns.
- One bit has changed from 1 to 0.
- This is a data-change error.
Answer Data changed during transmission: one bit differs.
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.
A transmitted value 1001 arrives as 1011. Classify the error.
Give me a hint
Compare each bit position.
Compare my reasoning
- The lengths match.
- The third bit changed from 0 to 1.
- This is a data-change error.
Data change
Look for these in your work
- Positions compared
- Change identified
- Error named
A receiver gets only 8 of the 10 bits sent. Classify the problem and state why a check is useful.
Give me a hint
Compare the amount sent with the amount received.
Compare my reasoning
- Two bits are missing, so this is data loss.
- A check can reveal that the received data is incomplete.
- A retransmission request may then be needed.
Data loss; an error check can detect incomplete data and lead to a resend.
Look for these in your work
- Loss classified
- Check purpose
- Recovery noted
An engineer says a parity check repairs corrupted data. Explain the difference between detection and correction.
Give me a hint
Ask whether the check identifies the changed bit and restores its value.
Compare my reasoning
- A parity mismatch can signal that the data may be wrong.
- A single parity value usually does not identify which bit changed.
- A resend or a separate correction method is needed to restore reliable data.
Parity can detect some errors but does not usually locate and correct them. The sender may need to resend the data.
Look for these in your work
- Detection explained
- Correction distinguished
- Recovery method identified
Common mistakes
- Claiming an error-detection check always corrects the data
- Calling additional bits data loss
What can you explain now?
What is the purpose of an error-detection method?
Compare with the explanation
Identify whether transmitted data may contain an error
Detection can trigger a resend, but does not itself guarantee correction.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What are the three broad ways interference can affect transmitted data?
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.