Patent ID: 7738461

Claim:
A communication apparatus comprising: a terminal operating unit that performs a process of receiving a frame; and a switching unit that outputs a received frame to the terminal operating unit, and forwards the received frame by a cut-through method, wherein the frame includes a destination address (DA) field in which a destination address is stored; a source address (SA) field in which a source address is stored; a type field in which a frame length is stored; a user data field in which user data subjected to be transmitted is stored; and a frame check sequence (FCS) field in which an FCS code as a check code used for an error detection of data stored in the DA field, the SA field, the Type field, and the user data field is stored, the user data field includes a DATA field in which the user data is stored, the DA field, the SA field, the type field, and a data check sequence (DCS) field in which a DCS code as a check code used for an error detection of data stored in the DATA field is stored, the switching unit includes a code calculating unit that performs a predetermined calculation from a head of the received frame, and calculates a DCS code based on data stored in the DA field, the SA field, the Type field, and the DATA field and an FCS code based on data stored in the DA field, the SA field, the Type field, the DATA field, and the DCS field; a DCS checking unit that compares the DCS code calculated by the code calculating unit with the DCS code stored in the DCS field of the received frame, and outputs a result of a comparison as a result of a DCS check to the terminal operating unit; an FCS checking unit that compares the FCS code calculated by the code calculating unit with the FCS code stored in the FCS field of the received frame, and outputs a result of a comparison as a result of an FCS check; an FCS converting unit that forwards the received frame without any change if the result of the FCS check is matching, and forwards a frame that the calculated FCS code is stored in the FCS field of the received frame if the result of the FCS check is mismatching; and an error frame counter that increments if the result of the FCS check is mismatching, and the terminal operating unit executes normal processing based on a frame input from the switching unit if the result of the DCS check is matching, and executes error processing if the result of the DCS check is mismatching.