Parity check

Parity check is use to check error of the data send. When data is send from source to receiver , data may lose or having error. The receiver will receive error data. There are 2 types of error:
  1. Single bit error- Only one bit is changed from 1 to 0 or from 0 to 1.
  2. Burst error- 2 or more bits in the data unit have changed.
For the receiver to ensure the data send is correct , error detection is use. Error detection uses the concepts of redundancy, which means adding extra bits detecting error of the destination.

Parity check is the simplest technique in error detection techniques. A redundant bit is appended(added at the end of the data) to every data unit.The parity also have 2 type which are odd parity and even parity.

Even Parity is the total number of 1's in data plus parity bit must be an even number while the Old parity is odd number.

Example of even parity:


Data#1's in dataParity bit(P)# 1's (data + P)
01101104(even)04(even)
00111115(odd)16(even)
10101003(odd)14(even)

Therefore the data send must have 8 bit and the number of 1's must be even number this is call even parity. While the odd parity is another way round which number of 1's in data must be odd number.

In parity check have 2 method which are:
  1. Vertical Redundancy Check (VRC)
  2. Longitudinal Redundancy Check (LRC)
Wait! What you mean 2 method????

The even and odd parity is the concept of parity check, but parity check got 2 method to carry out the even and odd parity.

Vertical Redundancy Check

VRC can detect all single bit errors. It can also detect burst error as long as the total number of bits changed is odd. How about the total number of bit changed is even? yes,this is the problem.

Example of VRC

Data:
1110111 --6 1's
1101111 --6 1's
1110010 --4 1's
1101100 --4 1's
1100100 --3 1's

The parity bit is added at the end of the data like below

11101110 --6 1's
11011110 --6 1's
11100100 --4 1's
11011000 --4 1's
11001001 --4 1's

After the data is send to the destination, if the number 1's is not a even number then the receiver will ask the source to retransmit the data.
PS: I'm using even parity.


Longitudinal Redundancy Check

LRC increases the likehood of detecting burst errors. LRC can easily detect a burst error of n bits.A burst error of more than n bits is also detected by LRC with a very high probability.

Example of LRC
Data:
11100111
11011101
00111001
10101001

then another row is added

11100111
11011101
00111001
10101001
----------------
10101010<-- LRC


This is the parity check, hope it will help you to understand how parity check work. If have any question or correction please leave a comment below. Thank you for reading.

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