A company owner has installed a new network. Data is correct before it is transmitted across the network. The company owner is concerned that data might have errors after transmission.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [3] 9(a) Any three from: Data could be lost; Data could be gained/added; Data could be changed; Bits could be reassembled in the wrong order; Interference could occur; Crosstalk could occur; Data collisions occur; Data packets could time out/reach their hop count; Network could be infected with malware
2. [8] 9(b)(i) Any eight from: The 1s are counted (in each byte); Each byte has a parity bit; If the number of 1s are odd the parity bit is 0 (otherwise it is 1); (The first packet of) data is sent and a timer is started; The receiving device counts the number of 1s (in each byte); If the number of 1s are odd/data meets odd parity an acknowledgement is sent to say the data is error free ... the sender then sends the next packet of data ... and the timer is restarted; If the number of 1s is even an acknowledgement is not sent; If no acknowledgement is received within a set timeframe/before timeout ... the data packet is resent
3. [2] 9(b)(ii) Any two from: Echo check; Checksum; Even parity check; Negative ARQ
4. [5] 9(c)(i) Any five from: Criteria can be set (for traffic); ...such as a blacklist/whitelist (of IP addresses); It will examine traffic coming into the network; It will check that the traffic meets the set criteria; ...and will reject it if it does not meet criteria; Certain ports used by hackers can be blocked/closed
5. [2] 9(c)(ii) Any two from: Example: Virus; Worm; Trojan horse; Spyware; Adware; Ransomware