def decode(self, pdu):
        """decode the contents of the PDU into the BVLCI."""
        if _debug: BVLCI._debug("decode %s", str(pdu))

        # copy the basics
        PCI.update(self, pdu)

        self.bvlciType = pdu.get()
        if self.bvlciType != 0x81:
            raise DecodingError("invalid BVLCI type")

        self.bvlciFunction = pdu.get()
        self.bvlciLength = pdu.get_short()

        if (self.bvlciLength != len(pdu.pduData) + 4):
            raise DecodingError("invalid BVLCI length")
decode the contents of the PDU into the BVLCI.