Computer Science · May / June 2016 · Paper 12 · Question 4
2210
As printed in the paper
The question as text
Nigel wants to send a large text file electronically to Mashuda.
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4(a)[3]
Any three from:
– The file can be compressed – The compression that is used is lossless (not lossy) – use of a compression algorithm – repeated words can be indexed – repeated word sections (e.g. “OU”) can be replaced by a numerical value – reference to zip files – save file as a pdf/convert to pdf [3]
4(b)[4]
Any four from:
– the checksum for the bytes is calculated – this value is then transmitted with the block of data – at the receiving end, the checksum is re-calculated from the block of data received – the calculated value is then compared to the checksum transmitted – if they are the same value, then the data was transmitted without any error – if the values are different, then an error has been found – if the values are different, then a request is sent for the data to be re-transmitted [4]
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