Abstract: A monitoring OAM cell assisted method enables continuous intrasystem determination of bit errors which have occurred in ATM useful cells with a useful information field and a cell head on an ATM transmission link. First control bits are generated by evaluating bits of ATM useful cells with selected target addresses in the cell head prior to feeding the ATM useful cells into the transmission link, and the control bits are additionally encoded to generate second control bits. The first and second control bits and OAM cells are then transmitted along with the ATM useful bits. The second control bits of the monitoring OAM cells are received at the far end of the ATM transmission link and examined for errors to determine if the monitoring OAM cells were received without error. The first control bits are used to determine if the useful ATM cells were received error-free.