2.2 - Error Detection Methods Flashcards
What is parity checking? [1]
One method used to check whether data has been changed or corrupted following data transmission
How does parity check work? [2]
An extra bit called parity bit is added to the message
Extra bit is based on which parity system is being used
What are the two parity systems? [2]
Odd Parity or Even Parity
What is checksum? [1]
A method used to check if data has been changed or corrupted following data transmission
What are the steps of checksum? [4]
- Checksum calculated by the sending computer using an agreed algorithm
- data sent as a block with the checksum
- checksum is recalculated by receiving computer using the same algorithm
- any differences in checksum = error occurred
How does echo check work? [4]
When data is sent to another device which is then again sent back to the sender and then the sender compares the two sets of data to see if any errors occurred during transmission
What are checkdigits used for? [1]
Identify errors in date entry caused by mistyping or mis-scanning a barcode
What type of errors do checkdigits identify? [4]
An incorrect digit entered
Transposition errors
Omitted or extra digits
Phonetic errors
What does ARQ stand for? [1]
Automatic Repeat Request
What are acknowledgments? [1]
Messages sent to the receiver that data has arrived at its destination unchanged
What is timeout? [1]
Time interval allowed to elapse before an acknowledgment is received
How does ARQ work? [8]
It uses acknowledgements and timeout
Receiver gets an error detection code (CRC)
If no error = positive acknowledgment sent back, else negative acknowledgment
If negative = requests re-transmission of the data
There is a timeout time and if there’s no acknowledgment till that time then automatic re-sending of data till positive acknowledgment reached
What does an error detection code do? [1]
Checks whether received date contains any transmission errors
