What is Vertical Redundancy Check - VRC Error Detection

There are number of error detection techniques in computer networking. People get confused what is VRC and vertical redundancy check, both are same they are just acronym. In academic career you will be asked Difference between Vertical and Longitudinal Redundancy Check.

Vertical Redundancy Check

Vertical redundancy check is maintenance of parity bit. An additional bit is added with original block to ensure that data transmitted correctly. It is also known as parity check technique.

In VRC there are two types of parity bit "Even parity bit" and "Odd parity bit".

Example Even Parity Bit:

vertical redundancy check even parity

Consider data " 1 1 0 0 0 0 1 " if we passed this data to Even parity generator.

  1. Count the number of  1's which are 3 so ODD ( 1 1 0 0 0 0 1 ).
  2. Now add bit 1 as parity bit  so numbers will become ( 1 1 0 0 0 0 1 1).
  3. Again count the number we alter the data now number of 1's are 4 so even.

Problems with VRC:


  • Consider a sender sends a data 1 0 0 0 0 0 1 and we count the number of 1's in data.  They are even so we add 0 in the end. The data becomes 1 0 0 0 0 0 1 0. 
  • In case sender sends a data 1 0 0 0 0 0 1 if it has error and data becomes 1 0 0 0 1 0 1 , the parity bit will be added and data become 1 0 0 0 1 0 1 1.
  •  Error detection method in this case is failed because we get an unknown bit in middle

Whenever even number of bits found in the data during transmission, either there is an error or not VRC will accept the data and will not detect the error. So this is the major problem with vertical redundancy check. Video Example

To over come the problem of vertical redundancy (vrc) there is another solution called Longitudinal redundancy check (lrc).

What is VRC - VRC Definition?

Vertical redundancy check  is an error detecting technique used to detect errors on an eight-bit ASCII character. To determine either the transmission is correct, a parity bit is linked to every byte of data.

Vertical redundancy check only works if an even number of bits is distorted hence it is not considered as reliable technique for error detection.

Traverse Redundancy Check

When vertical redundancy check is used with other error-detection/controlling method like longitudinal redundancy check then this technique is called transverse redundancy check.

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