The method used to check errors is checksum. In this method data is treated as a sequence of integers and their arithmetic sum is calculated and the carry bits are added to the final sum. Then checksum is calculated by transmission then it is sent along the data and the receiver and the same camputation is done and then compared with the original checksum transferred. In this way errors are checked if the received checksum is different from the sender.

The figure explained the example.

The integers may be 8,32 or 16 bits. Checksum is easy to check. It needs only addition but it has also limitations and can not check all errors. As given below.