29. Apparatus to receive a data packet comprising: said data packet comprising a header and payload data; said header comprising a data length word, and a received error management code; a parity generator for deriving a calculated error management code, said parity generator generating a set of at least four parity bits from said data length word, each parity bit having a parity bit position in said parity bit set, each data bit in said data length word having a data bit position in said data length word; said parity generator associating each data bit position with a different syndrome, each syndrome comprising a sub-set of at least three parity bit positions, such that each said sub-set has at least one parity bit position shared with at least one other said sub-set and wherein said associating is such that a syndrome associated with a lower order data bit position defines a base 2 number with a lower numerical value than does a syndrome associated with a next higher order data bit position; and said parity generator calculating a parity bit value for each parity bit position from all data bit positions associated with said each parity bit position.
29. Apparatus to receive a data packet comprising: said data packet comprising a header and payload data; said header comprising a data length word, and a received error management code; a parity generator for deriving a calculated error management code, said parity generator generating a set of at least four parity bits from said data length word, each parity bit having a parity bit position in said parity bit set, each data bit in said data length word having a data bit position in said data length word; said parity generator associating each data bit position with a different syndrome, each syndrome comprising a sub-set of at least three parity bit positions, such that each said sub-set has at least one parity bit position shared with at least one other said sub-set and wherein said associating is such that a syndrome associated with a lower order data bit position defines a base 2 number with a lower numerical value than does a syndrome associated with a next higher order data bit position; and said parity generator calculating a parity bit value for each parity bit position from all data bit positions associated with said each parity bit position. 30. The apparatus of claim 29 further comprising a comparator for comparing said received error management code with said calculated error management code and, based on said comparison, selectively correcting said data length word.