A method, system and computer program product is provided which automatically detects multiprotocol encapsulation in a protocol data unit (PDU) to determine whether a Frame Relay/ATM service interworking function should operate in translation or transparent mode. A multiprotocol encapsulation detection module first reads a control field value in a received PDU. The control field value is then compared to a predetermined value representative of the presence of multiprotocol encapsulation in the PDU. An indication of the detected presence of multiprotocol encapsulation in the PDU is then provided when the control field value equals the predetermined value. An FR/ATM service interworking function module is then operated in translation mode when multiprotocol encapsulation has been detected and indicated. Otherwise, the FR/ATM service interworking function module is operated in transparent mode when multiprotocol encapsulation has not been detected.