O-LevelComputer ScienceData Transmission2210/13 · Oct/Nov 2023 · Q57 Marks
Errors can occur when data is transmitted.
- (a)Give one reason an error may occur when data is transmitted.[1]
- (b)Some error detection methods use a calculated value to check for errors. Tick (✔) one box to show which error detection method does not use a calculated value to check for errors. A Check digit B Checksum C Echo check D Parity check[1]
- (c)An automatic repeat request (ARQ) can be used to make sure that data is received free of errors. It can use a positive or negative acknowledgement method to do this. Explain how an ARQ operates using a positive acknowledgement method.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.
- [1] (a) Interference // crosstalk
- [1] (b) C
- [5] (c) Any five from: Timer is started when sending device transmits a data packet to receiver, Receiving device checks the data packet for errors, Once the receiving device knows the packet is error free it sends an acknowledgement back to the sending device ...and the next packet is sent, If the sending device does not receive an acknowledgement before the timer ends ...a timeout occurs, ... the data packet is resent ...until acknowledgement received // until max number of attempts reached
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