Error detection is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver.
Error correction is the detection of errors and reconstruction of the original error free data.
Error detection and correction are implemented at the data link layer or the transport layer of the open system interconnection model (OSI)
1. single bit error.
2. multiple bit error or burst error.
1. single bit error
As it name signifies- The term single bit error means that only one bit of the given data unit (such as byte, character or packet) is changed from 0 to 1 or from 1 to 0.
single bit error are the least likely type of error in serial data communication.
this is because for a single bit error to occur the noise must have duration of 1micro second which is very rare. Noise normally last for much Longer than this.
2. Burst error (multiple bit error)
The term burst error means that two or more bit of the given date unit have changed from 0 to 1 or from 1 to 0.
A burst error does not means that error occur in consecutive bits.
The central concept in detecting and correcting error is redundancy.
To be able to detect or correct error we need to send some extra bits with our data. These extra bits are called redundant bits.
Basically, Redundancy is a technique for detection and correction of error in which redundant bits itself do not have any information or data but they act as data bits.
redundant bits are added by the sender and are removed by the receiver.
METHODS OF ERROR DETECTION
1. VRC (vertical redundancy check )
In VRC a parity bit is added to every data unit so that the total number of 1s become even.It can detect all single bit error. It can detect burst error only if total number of errors in the data unit is odd.
2. LRC ( Longitudinal redundancy check )
In LRC, block of bits are divided into rows and a redundant rows of bits is then added to the whole block.
It detects all errors involving an odd number of bits as well as most errors involving an even number of bits.
Basically the error detection method used by the higher layer protocols is called checksum.
4. The fourth and most efficient method of error detection is CRC that is cyclic redundancy check.
A CRC i.e. cyclic redundancy check is a non secure hash function designed to detect accidental changes to raw computer data and is commnly used in digital networks and storage devices such as hard disk.
Two methods of error correction are-
1. reverse error correction (REC).
2. Forward error correction( FEC)
In the first approach the receiver requests for the retransmission of the code word whenever it detects an error after that the receiver locates the error by analyzing the received code and revers the erroneous bits.
In the second approach the code set is so designed that it is possible for the receiver to detect and correct error as well by itself.