2.2. Methods of error detection
A subsection of Computer Science, 0478, through 2. Data transmission
Listing 10 of 40 questions
Check digits are used to ensure the accuracy of input data. A 7-digit code number has an extra digit on the right, called the check digit. Digit position Digit – – – – – – – – The check digit is calculated as follows: • each digit in the number is multiplied by its digit position • the seven results are then added together • this total is divided by 11 • the remainder gives the check digit (if the remainder = 10, the check digit is Calculate the check digit for the following code number. Show all your working. … Check digit An operator has just keyed in the following code number: X Has the operator correctly keyed in the code number? Give a reason for your answer. When data are transmitted from one device to another, a parity check is often carried out on each byte of data. The parity bit is often the leftmost bit in the byte. If a system uses even parity, give the parity bit for each of the following bytes: parity bit parity bit A parity check can often detect corruption of a byte. Describe a situation in which it cannot detect corruption of a byte.
0478_w15_qp_12
THEORY
2015
Paper 1, Variant 2
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Five computer terms and seven descriptions are shown below. Draw a line to connect each computer term to its correct description. An error detection method that uses response and time out when transmitting data; if a response is not sent back to the sender in an agreed amount of time, then the data is re-sent Several bits of data sent down several wires, in both directions, but not at the same time Serial, simplex data transmission Description Computer term Several bits of data sent down several wires, in both directions, at the same time An even or odd number of bits set to 1 in a byte, used to check if the byte has been transmitted correctly One bit sent at a time, over a single wire in one direction only An additional digit placed at the end of a number to check if the number has been entered correctly A value transmitted at the end of a block of data; it is calculated using the other elements in the data stream and is used to check for transmission errors Parallel, half-duplex data transmission Parity check Automatic repeat request (ARQ) Checksum
0478_w16_qp_11
THEORY
2016
Paper 1, Variant 1
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Nine bytes of data are transmitted from one computer to another. Even parity is used. An additional parity byte is also sent. The ten bytes arrive at the destination computer as follows: parity bit bit 2 bit 3 bit 4 bit 5 bit 6 bit 7 bit 8 byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 byte 7 byte 8 byte 9 parity byte One of the bits was corrupted during the data transmission. Circle the corrupt bit in the corrupt byte in the table above. Explain how the corrupted bit was found.
0478_w16_qp_12
THEORY
2016
Paper 1, Variant 2
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Five computer terms and seven descriptions are shown below. Draw a line to connect each computer term to its correct description. An error detection method that uses response and time out when transmitting data; if a response is not sent back to the sender in an agreed amount of time, then the data is re-sent Several bits of data sent down several wires, in both directions, but not at the same time Serial, simplex data transmission Description Computer term Several bits of data sent down several wires, in both directions, at the same time An even or odd number of bits set to 1 in a byte, used to check if the byte has been transmitted correctly One bit sent at a time, over a single wire in one direction only An additional digit placed at the end of a number to check if the number has been entered correctly A value transmitted at the end of a block of data; it is calculated using the other elements in the data stream and is used to check for transmission errors Parallel, half-duplex data transmission Parity check Automatic repeat request (ARQ) Checksum
0478_w16_qp_13
THEORY
2016
Paper 1, Variant 3
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A file server is used as a central data store for a network of computers. Rory sends data from his computer to a file server that is approximately 100 metres away. It is important that the data is transmitted accurately. Rory needs to be able to read data from and write data to the file server at the same time. Use ticks (3) to identify the most suitable data transmission methods for this application. Method 1 Tick (3) Method 2 Tick (3) Serial Simplex Parallel Half-duplex Duplex Explain why your answer to part is the most suitable data transmission. Identify and describe two methods of error checking that can be used to make sure that the data stored after transmission is accurate. Method 1 Method 2
0478_w17_qp_12
THEORY
2017
Paper 1, Variant 2
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Computers can transmit data using different methods. Describe the three data transmission methods given. Serial data transmission Parallel data transmission Duplex data transmission Data can sometimes be corrupted when it is transmitted from one computer to another, causing errors to be present in the data. Identify and describe three methods of error detection that could be used to see if an error has occurred. Error detection method 1 Description Error detection method 2 Description Error detection method 3 Description
0478_w18_qp_12
THEORY
2018
Paper 1, Variant 2
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Data is valuable to a company. Companies use error detection methods to make sure that data is accurate. One error detection method is the use of a check digit. Explain what is meant by a check digit and how it is used to detect errors. Companies can use a range of security methods to keep their data secure. Identify two security methods that a company can use to keep their data secure and explain how each method can keep the data secure. Security method 1 Security method 2
0478_w19_qp_12
THEORY
2019
Paper 1, Variant 2
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Questions Discovered
40