nication of binary data SO that erroneous data reception may be minimised. These result in class of mathematical processes which facilitate detection or correction of reception errors, known as error control coding. The field is divided into two main sub-fields of error detection coding and error correction coding. Error detection coding takes at its input a block of data bits and through a mathematical process calculates an extra sequence of bits (called parity bits) which are then appended to the original block. These bits do not carry any information, and are sometime called redundant bits. The resulting bit sequence, the information and parity bits, is referred to as a 'coded word' or a 'codeword'. The receiver applies the same mathematical process to the received data block and calculates its own set of parity bits. If no error has occurred, then the same set of parity bits is obtained. However if there are errors, it is very unlikely that the same set of parity bits are obtained and therefore the receiver can detect error occurrence. Note that the error detection decoding process does not yield information on where and how many errors have occurred. The decoding process is in effect the logical equivalent of conversational 'what I just heard does not make sense - something is wrong'. Broadband Telecommunications Technologies and Management Example 6.1 An example of error detection coding is single parity bit coding. In this method a parity bit is added to the transmitted bit sequence in order to make the number of bits odd. For example a data block '0011011' is encoded to become '00110111' to have an odd number of 1's. Similarly '0011001' is encoded to become '00110010'. Since the receiver expects a bit sequence with an odd number of 1's it can flag that an error has occurred should a sequence with an even number of 1's be detected. This method is also known as odd parity bit coding. Similarly an even parity bit coding may be designed, where the number of 1's in a bit sequence is set to be even. Parity bit 