def _parse_protocol_psutil(self, conn):
        """
        Returns a string describing the protocol for the given connection
        in the form `tcp4`, 'udp4` as in `self.cx_state_gauge`
        """
        protocol = self.PSUTIL_TYPE_MAPPING.get(conn.type, '')
        family = self.PSUTIL_FAMILY_MAPPING.get(conn.family, '')
        return '{}{}'.format(protocol, family)