Tag: Parity Check Error Detection

Error Detection in Computer Networks | Parity Check

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-

 

 

  1. Single Parity Check
  2. Cyclic Redundancy Check (CRC)
  3. 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-

 

Step-01:

 

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.

 

Step-02:

 

  • The newly formed code word (Original data + parity bit) is transmitted to the receiver.

 

Step-03:

 

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,┬átotal 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

 

  • Consider the data unit to be transmitted is 10010001 and even parity is used.
  • Then, code word transmitted to the receiver = 100100011
  • Consider during transmission, code word modifies as 101100111. (2 bits flip)
  • On receiving the modified code word, receiver finds the number of 1’s is even and even parity is used.
  • So, receiver assumes that no error occurred in the data during transmission though the data is corrupted.

 

To gain better understanding about single parity check,

Watch this Video Lecture

 

Next Article- Cyclic Redundancy Check

 

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