Error Detection and Correction In Data Transfer
Networks must be able to transfer data from one device to another
with complete accuracy.
But data can be corrupted (altered) during the transit due to noise.
Therefore error must be detected and corrected for good
communication and transmission of data between devices.
Types of error:
1. Single-bit error
2. 2.Burst error
Single-bit error:
In a single bit error, only one bit in the data has changed.
1 is changed to 0 and 0 is changed to 1.
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| single-bit error |
There is more chance of single bit errors in parallel transmission, as
one or more of the wires could become noisy. This will affect the
data bits.
Burst error:
Two or more bits in the data unit have changed from 1 to 0 or 0 from 1.
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| Burst error |
The length of the burst error is measured from the first bit
Corrupted (altered) bit to the last corrupted bit.
Some bits in between may not have been corrupted.
Error Detection
The simplest method is to send the data twice to cross check the sent
and received data.
But there is a chance of the data sent second time getting corrupted.
Moreover, it is slow.
Another method is to add a small group of bits to the end of each
data unit.
… ==>
The extra bits are redundant (unnecessary for the information sent)
to the information.
These extra bits are used to detect error in the received data unit.
These extra bits are removed as soon as the correctness of the data is
determined.
This method is called redundancy method.
Types of redundancy:
1. Vertical Redundancy Check (VRC)
( It is also called as Parity Check. )
2. Longitudinal Redundancy Check (LRC)
3. Cyclic Redundancy Check (CRC)
4. Checksum
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