O-LevelComputer ScienceData Transmission2210/12 · May/June 2016 · Q47 Marks
Nigel wants to send a large text file electronically to Mashuda.
- (a)Describe how the size of the text file can be reduced.[3]
- (b)This file will be transmitted to Mashuda as an email attachment. Mashuda then stores it on her computer. Explain how checksums can be used to verify that the file has not been corrupted during transmission or data storage.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.
- [3] 4 (a) 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
- [4] (b) 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
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