public function cancelReservation($rno)
    {
        $this->_checkRNO($rno);

        $digestSecret = self::digest(
            $this->colon($this->_eid, $rno, $this->_secret)
        );
        $paramList = array(
            $rno,
            $this->_eid,
            $digestSecret
        );

        self::printDebug('cancel_reservation', $paramList);

        $result = $this->xmlrpc_call('cancel_reservation', $paramList);

        return ($result == 'ok');
    }