Error checking is vital in a communications system because they make sure that the right information is going through the system.
Parity check
A parity bit, or check bit is a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value one is even or odd. Parity bits are used as the simplest form of error detecting code. There are two variants of parity bits: even paritybit and odd parity bit. An even Parity bit is where there are an even number of 1s and 0s in the binary e.g. 11111111 or 00000000. An odd is one where there is more of one then the other 1110000. It has around a 66% success rate but it varies on how many different codes there are.
Checksum
Relies on multiplication or division of a ‘divisor’. A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, it’s assumed that the complete transmission was received. It is more accurate then parity checks because it does more checks however this also makes it take longer.
Cyclic Redundancy Check
Cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents. It is more accurate then checksum because it gathers a remainder. CRC is extremely slow which is why it is not the only error check used.
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