Computer Science · May / June 2025 · Paper 11 · Question 4
0478
As printed in the paper
The question as text
A restaurant has an electronic ordering system. The system allows customers to select the food they want to order. The data for the order is transmitted across their network to a computer in the restaurant kitchen.
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
4(a)(i)[2]
Two from (one mark for serial, one mark for full-duplex):
serial
Serial is suitable as data may be travelling a long distance (over 5 metres).Serial is suitable to make sure that bits don’t arrive skewed/arrives in order.Serial is suitable as there is less chance of error.Serial has sufficient transmission speed as not much data being sent.full-duplex
Full-duplex is suitable as data needs to go between customer and kitchen computer // data needs to go in both directions // so notification of errors can be sent back to customer.4(a)(ii)[1]
The data may be transmitted faster.
4(b)(i)[5]
Any five from:
The checksum is calculated from/using the data.… using an algorithm // by example.The (checksum) value is transmitted with the data.The (checksum) value is recalculated after transmission/by recipient.If the checksum values do not match, an error is detected // If the checksum values match, no error is detected …… request for data to be resent if there is an error.4(b)(ii)[1]
Any one from:
Parity byte/block checkEcho check4(c)(i)[1]
D
4(c)(ii)[2]
Any Two from:
The packets arrive in the wrong order.Each packet could take a different route.Some packets may take longer than others to be transmitted.Some packets may not arrive/be corrupted and need to be requested again.
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