Error Detection in Data Link Layer
The network should ensure complete and accurate delivery of data from the source node to destination node. The Error detection is a technique that is used to check if any error occurred in the during the transmission.
Some popular techniques for error detection are:
- Simple parity check
- Cyclic redundancy check
- Checksum
Simple parity check
The most common method used for detecting error when the number of bit in the data is small is the use of the parity bit.
A parity bit is an extra binary digit added to the group of data bit so that the total number of 1’s in one group is even or odd
- 1 is added to the block if it contains odd number of 1’s, and
- 0 is added if it contains even number of 1’s
Example of simple parity check:
Cyclic redundancy check
→Cyclic redundancy check is an error detection method it is based on binary division
→CRC generator is an algebraic polynomial as a bit pattern
Rule of Cyclic redundancy check
→It should be division by x+1 not be x.
→This condition guarantees that all the burst errors affecting an odd number of bits are detection.
→this condition guarantees that all the burst errors of length
Example of cyclic redundancy check:
Checksum:
- In checksum error detection scheme, the data is divided into k segments each of m bits.
- In the sender’s end the segments are added using 1’s complement arithmetic to get the sum. The sum is complemented to get the checksum.
- The checksum segment is sent along with the data segments.
- At the receiver’s end, all received segments are added using 1’s complement arithmetic to get the sum. The sum is complemented.
- If the result is zero, the received data is accepted; otherwise discarded.
Let’s Example of checksum:
