This clause contains the detailed specification of the logic of the Communications Operation Procedure-1 (COP-1) in the transfer sublayer. COP-1 consists of a pair of synchronized procedures which execute within one virtual channel at the sending and receiving ends of the transfer sublayer. At the sending end, the Frame Operation Procedure-1 (FOP-1) is executed. At the receiving end, a corresponding Frame Acceptance and Reporting Mechanism-1 (FARM-1) is executed. COP-1 is just one of the procedures performed within the transfer sublayer. It is the first procedure performed when a frame data unit (FDU) is received by the transfer sublayer at the sending end and the last one performed before the FDU is delivered to the next higher sublayer at the receiving end.