def get_meta_data(self, request_adu):
try:<EOL><INDENT>transaction_id, protocol_id, length, unit_id =unpack_mbap(request_adu[:<NUM_LIT:7>])<EOL><DEDENT>except struct.error:<EOL><INDENT>raise ServerDeviceFailureError()<EOL><DEDENT>return {<EOL>'<STR_LIT>': transaction_id,<EOL>'<STR_LIT>': protocol_id,<EOL>'<STR_LIT>': length,<EOL>'<STR_LIT>': unit_id,<EOL>}<EOL>
Extract MBAP header from request adu and return it. The dict has
        4 keys: transaction_id, protocol_id, length and unit_id.

        :param request_adu: A bytearray containing request ADU.
        :return: Dict with meta data of request.