O-LevelComputer ScienceData Representation2210/11 · May/June 2023 · Q210 Marks

A student has a sound file that is too large to be stored on their external secondary storage device. The student compresses the sound file to make the file size smaller. The compression method used reduces the sample rate and the sample resolution of the sound file.

(a)State what is meant by the sample rate and sample resolution. Sample rate Sample resolution[2]
(b)Identify which type of compression has been used to compress the sound file.[1]
(c)(i)The student sends the sound file to a friend. The file is transmitted across a network that uses packet switching. (i) Identify two pieces of data that would be included in the header of each packet. 1 2[2]
(c)(ii)Explain how the file is transmitted using packet switching.[5]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[2] One mark for each correct definition: • The sample rate is the number of samples taken in a second/per time unit • The sample resolution is the number of bits per sample
[1] Lossy compression
[2] Any two from: e.g. Destination/receivers (IP) address • Packet number • Originator's/senders (IP) address
[5] Any five from: • Data is broken/split/divided into packets • Each packet (could) take a different route • A router controls the route/path a packet takes • selecting the shortest/fastest available route/path • Packets may arrive out of order • Once the last packet has arrived, packets are reordered • If a packet is missing/corrupted, it is requested again

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