Error Detection in Computer Networks
When sender transmits data to the receiver, the data might get scrambled by noise or data might get corrupted during the transmission.
Error detection is a technique that is used to check if any error occurred in the data during the transmission. 
Error Detection Methods
Some popular error detection methods are
 Single Parity Check
 Cyclic Redundancy Check (CRC)
 Checksum
In this article, we will discuss about Single Parity Check.
Single Parity Check
In this technique,
 One extra bit called as parity bit is sent along with the original data bits.
 Parity bit helps to check if any error occurred in the data during the transmission.
Steps Involved
Error detection using single parity check involves the following steps
Step01:
At sender side,
 Total number of 1’s in the data unit to be transmitted is counted.
 The total number of 1’s in the data unit is made even in case of even parity.
 The total number of 1’s in the data unit is made odd in case of odd parity.
 This is done by adding an extra bit called as parity bit.
Step02:
 The newly formed code word (Original data + parity bit) is transmitted to the receiver.
Step03:
At receiver side,
 Receiver receives the transmitted code word.
 The total number of 1’s in the received code word is counted.
Then, following cases are possible
 If total number of 1’s is even and even parity is used, then receiver assumes that no error occurred.
 If total number of 1’s is even and odd parity is used, then receiver assumes that error occurred.
 If total number of 1’s is odd and odd parity is used, then receiver assumes that no error occurred.
 If total number of 1’s is odd and even parity is used, then receiver assumes that error occurred.
Parity Check Example
Consider the data unit to be transmitted is 1001001 and even parity is used.
Then,
At Sender Side
 Total number of 1’s in the data unit is counted.
 Total number of 1’s in the data unit = 3.
 Clearly, even parity is used and total number of 1’s is odd.
 So, parity bit = 1 is added to the data unit to make total number of 1’s even.
 Then, the code word 10010011 is transmitted to the receiver.
At Receiver Side
 After receiving the code word, total number of 1’s in the code word is counted.
 Consider receiver receives the correct code word = 10010011.
 Even parity is used and total number of 1’s is even.
 So, receiver assumes that no error occurred in the data during the transmission.
Advantage
 This technique is guaranteed to detect an odd number of bit errors (one, three, five and so on).
 If odd number of bits flip during transmission, then receiver can detect by counting the number of 1’s.
Also Read Checksum
Limitation
 This technique can not detect an even number of bit errors (two, four, six and so on).
 If even number of bits flip during transmission, then receiver can not catch the error.
EXAMPLE

To gain better understanding about single parity check,
Next Article Cyclic Redundancy Check
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