Chapter 2 Data Transmission: Unit 2.2: Methods of error correction

Question 1

How can errors occur?

Answer 1

Interference
Problems during packet switching
Skewing of data

Question 2

Describe the method of parity checking.

Answer 2

A method used to check if data has been transferred correctly; it makes use of even parity or odd parity

Question 3

Define parity bit

Answer 3

A bit (0/1) added to a byte of data in the most significant position; this ensures that the byte follows the correct even parity or odd parity protocol

Question 4

Define parity block

Answer 4

A horizontal and vertical parity check on a block of data being transmitted

Question 5

Describe the method of checksum

Answer 5

Verification method used to check if data transferred has been altered or corrupted; calculated from the block of data being sent; the checksum value is sent after each data block

Question 6

Describe the method of echo check

Answer 6

Method used to check if data has been transferred correctly; data is sent to a receiver and then immediately sent back to the sender; the sender then checks if the received data matches the sent data

Question 7

Describe the process of check digit

Answer 7

An additional digit appended to a number to check if the entered number is error-free; check digit is a data entry check and not a data transmission check

Question 8

Describe the process of ARQ

Answer 8

ARQ (Automatic Repeat Request) is a method of checking transmitted data for errors; it makes use of acknowledgement and timeout to automatically request re-sending of data if the time interval before positive acknowledgement is too long