O-LevelComputer ScienceData Representation2210/13 · Oct/Nov 2024 · Q224 Marks

An employee has a report that they need to email to their employer. The employee compresses the report file before emailing it.

(a)State the effect the compression has on the report file.[1]
(b)Give two benefits of compressing the report file before emailing it. 1 2[2]
(c)The employee decides to use lossless compression to compress the file. Explain why lossy compression is not suitable.[3]
(d)(i)When the employee enters the email address, the computer uses Unicode to convert the email address to binary. State what Unicode is an example of.[1]
(d)(ii)Give two advantages of the computer using Unicode instead of American standard code for information interchange (ASCII). 1 2[2]
(d)(iii)Give one disadvantage of the computer using Unicode instead of ASCII.[1]
(e)(i)The report is broken down into packets to be emailed. Circle three items of data that can be found in the packet header. trailer originator's address payload interrupt input operating system destination address antivirus packet number[3]
(e)(ii)Each packet is sent along a different path from the employee's device to the employer's device. Tick (✔) one box to show the name of this method of sending packets. A packet networking B packet circuiting C packet switching D packet transferring[1]
(e)(iii)A hardware device is used to control the path that each packet takes. Give the name of this hardware device.[1]
(f)(i)The email data is checked for errors after it has been transmitted, using an echo check and a checksum. Explain how the echo check is used to check for errors in the email data.[3]
(f)(ii)In the checksum error detection method, two values are compared after transmission. If the values do not match, an error is detected. Explain why the values not matching would show an error has occurred.[2]
(g)(i)The email data is encrypted using asymmetric encryption before it is sent. Give one reason why the email data is encrypted.[1]
(g)(ii)Give one similarity between symmetric encryption and asymmetric encryption.[1]
(g)(iii)Give two differences between symmetric encryption and asymmetric encryption. 1 2[2]

Mark scheme

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

[1] The file size will be reduced
[2] It will be under the file size limit for the email; It will be uploaded/transmitted/downloaded faster; It will take less storage space (on computer); It will use less data allowance (if mobile data used); Requires less bandwidth
[3] Data will be permanently removed; and that could be important/necessary data; (The report will have text in it and) lossy is not suitable for text files; as it will damage/corrupt the file; The report may have images in it and the quality of these will be reduced
[1] Character set
[2] It can represent more characters; It can represent emojis/symbols; It can represent more languages
[1] Each character requires more storage space
[3] originator's address; destination address; packet number
[1] C
[1] Router
[3] A copy of the data is sent back to the employee's device/sender; The employee's device/sender compares the data sent to the data received back; If the original and the copy do not match, an error has occurred
[2] The checksum is calculated from/using the data; using the same algorithm; so, if the values are different the data must be different
[1] To keep it secure; The data is sensitive/confidential; To make it meaningless
[1] They both use a key; They both scramble the data // both make the data meaningless; They both turn plain text into cypher text
[2] Symmetric uses one/public key whereas asymmetric uses two/public and private keys; Symmetric can send the key with the data whereas asymmetric does not; Symmetric decrypts the data using the same key whereas asymmetric decrypts the data using a different key; Symmetric is less secure than asymmetric