Ever wondered how data is checked when it is transferred from A to B? When you download a file online, wondered how the downloaded file is checked to see if it was downloaded properly? Here’s how.
Parity
One way data is checked is by checking the bits in a byte, if you have a fair knowledge of this stuff you’ll know a byte is something like this: 11010101, made up of only 1s and 0s. There are two types of parity, odd and even, if even parity is used, the bytes would be checked to have an even number of 1s, if odd parity is used the byte would be checked to have an odd number of 1s, also bytes consist of only 7 bits (1s and 0s), the last bit is used to make the number of 1s odd or even based on the parity method used to check the bytes. In case there is an error during transfer it is detected, of course like all error checking methods this method is not completely foolproof, if two bits are changed during transmission the error won’ be detected.
Echoing back
This is a wasteful yet very accurate process; here the receiver sends the data back to the transmitter for the data to be checked, if there is an error the data is resent by the source. That data is again sent for checking and so on. As you can see, this method is very foolproof, but is time consuming and costly as data has to be transferred twice.
Check Sum
Generally, data is sent as a block of bytes, here the number of bytes sent can be calculated and sent along with the bytes, at the receiving end the sum is recalculated and compared with the original sum, in case the sum is different an error has occurred and the data will have to be resent.
This method is quite accurate as well but cannot detect errors within the bytes.
Therefore as all methods have inaccuracies, data is usually tested by more than one method to ensure the correctness of the data being transferred. These checks all happen in a matter of a few seconds and is usually not noticed by the users involved.
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