public function setDisconnectTime($milliseconds = null)
    {
        if (is_integer($milliseconds)
             && $milliseconds >= self::DEF_DISCONNECT_TIME
        ) {
            $this->_disconnecttime = $milliseconds;
        } else {
            $this->_disconnecttime = self::DEF_DISCONNECT_TIME;
        }
        return $this->_disconnecttime;
    }