O-LevelComputer ScienceData Transmission2210/11 · May/June 2017 · Q57 Marks
Parity checks are often used to detect errors that may occur during data transmission. The received bytes in the table below were transmitted using odd parity. Tick (✔) to show whether each byte has been corrupted during transmission or not corrupted during transmission.
- (a)Received byte corrupted during transmission (✔) not corrupted during transmission (√) 10110100 01101101 10000001[3]
- (b)Another method of error detection is Automatic Repeat reQuest (ARQ). Explain how ARQ is used in error detection.[4]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [3] 1 mark per correct tick Received byte corrupted during transmission (✔) not corrupted during transmission (√) 10110100 ✔ 01101101 ✔ 10000001 ✔
- [4] Four from: ∞ Uses acknowledgement and time out ∞ Check performed on received data // error is detected by e.g. parity check, check sum ∞ If error detected, request sent to resend data // negative acknowledgment is used ∞ If no acknowledgement is sent that data is received // positive acknowledgement is used ∞ Data is resent / Resend request repeated, till data is resent correctly ... or request times out // limit is reached
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