IGCSE Computer Science - Error Detection & Correction

An extra bit added to a string of binary code to ensure the number of 1-bits are either even or odd, depending upon the system used.

• ARQ

• Parity Check

• Checksum

• Check Digit

A block of data is sent alongside a calculated value.

The receiving computer also calculates what it believes should be the value.

The values are then compared to see if an error has occurred during transmission.

• ARQ

• Parity Check

• Checksum

• Check Digit

The final number in a code of numbers. It is calculated from all the other numbers in the code.

It’s purpose is to spot errors on data entry.

• ARQ

• Parity Check

• Checksum

• Check Digit

A form of error detection that uses a system of acknowledgements and timeouts.

• ARQ

• Parity Check

• Checksum

• Check Digit

Using even parity what is the parity bit for this sequence of binary:

0 1 0 1 1 0 0

Using even parity what is the parity bit for this sequence of binary:

1 0 0 1 0 1 1

Using even parity which of the following three 8 bit binary numbers has been transmitted incorrectly?

• 0 1 0 1 1 0 0 1

• 1 0 0 1 0 0 0 1

• 0 0 1 0 1 1 0 1

Using odd parity which of the following three 8 bit binary numbers has been transmitted incorrectly?

• 0 1 0 0 1 1 1 1

• 1 0 0 1 0 0 0 1

• 0 1 0 1 1 0 0 1

What is the significance of TIMEOUT in Automatic Repeat Request?

• The transmission must be completed successfully within TIMEOUT.

• The sender prompts the receiver for ACKNOWLEDGEMENT if the sender does not receive the ACKNOWLEDGMENT within the time specified in TIMEOUT.

• The sender re-sends the data if the sender does not receive the ACKNOWLEDGMENT within the time specified in TIMEOUT.

• None of the above

A checksum function works as follows:

1) Adds all the numbers together

2) Divides the total by 2

3) Discards any remainder

What is the checksum of 256?