Error checking methods

Question 1

describe parity checking

Answer 1

this is used to check whether data has been changed or corrupted following transmission from one device to another
even parity - even number of 1s
odd parity - odd number of 1s

Question 2

method of parity checking

Answer 2

both parties agree on protocol
sender adds parity bit to data
sends the data
receiver checks that it is the parity bit agreed
it is incorrect, the receiver requests for the data to be resent

Question 3

describe automatic repeat requests

Answer 3

Uses acknowledgement and time out
Check performed on received data
If error detected, request sent to resend data
if acknowledgement sent data is correct
If no acknowledgement is sent that data is received
Data is resent / Resend request repeated, till data is resent correctly
or request times out // limit is reached

Question 4

describe checksum

Answer 4

Sending device creates value from calculation on data
Value is transmitted with the data
Receiving device performs same calculation
Values are compared after transmission
If values do not match an error is detected

Question 5

describe echocheck

Answer 5

receiver sends a copy of data immediately back to the sender for comparison - you cant tell when error occurred