2.2 Methods of error detection

• Why - error check?

  computers require data to be arranged in a specific order
• results of errors - data loss, data gain, data change
• Parity check - each byte of data allocates a single bit at the start of the byte to the parity bit, if odd parity is used then the byte should be odd when received, vice-versa.
• Checksum - data is divided by a divisor, the sum of all data is divided by divisor to get the 'checksum' checksum is compared between the sender and receiver.
• check digit - a calculation is done on the data sent, when tis he data received check digit is subtracted by (MOD) of total
• AQR - (Automatic Repeat Request)
• AQR - If there's an error when sending data, the receiver will send a negative acknowledgement transmission to the sender, vice-versa.
• AQR - If the reciever doesn't receive all the data before a set time period (time-out), the data will be automatically resent, this will repeat until all data is received correctly.