Computers can transmit data using different methods. Describe the three data transmission methods given.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

1. [2] Two from:
2. ∞ Data is transmitted one bit at a time
3. ∞ Data is transmitted using a single wire
4. ∞ Bits arrive in order/sequence
5. [2] Two from:
6. ∞ Data is transmitted multiple bits at a time/simultaneously
7. ∞ Data is transmitted using multiple wires
8. ∞ Bits may arrive out of sequence/skewed (and are reordered)
9. [2] 1 mark for each:
10. ∞ Data is transmitted in both directions
11. ∞ at the same time/simultaneously
12. [9] Maximum of three marks per error detection method. 1 mark for naming the method, 2 marks for describing it.
13. Parity (check)
14. ∞ Odd or even parity can be used
15. ∞ Bits are added together // 1 bits are counted
16. ∞ Parity bit added (depending on parity set)
17. ∞ Parity checked on receipt
18. ∞ If parity bit is incorrect an error is detected
19. Checksum
20. ∞ Calculation performed on data (to get the checksum)
21. ∞ Checksum sent with data
22. ∞ Checksum recalculated after transmission
23. ∞ Comparison made between checksum before and checksum after transmission
24. ∞ Error detected if checksums are different
25. Automatic repeat request (ARQ)
26. ∞ Uses acknowledgement and timeout
27. ∞ Request is sent (with data) requiring acknowledgement
28. ∞ If no response/acknowledgment within certain time frame data package is resent
29. ∞ When data received contains an error a request is sent (automatically) to resend the data
30. ∞ The resend request is repeatedly sent until packet is received error free/limit is reached/acknowledgement received