function _send($data)
    {
        switch ($this->mode) {
            case self::MODE_SSH2:
                $this->ssh->_send_channel_packet(SSH2::CHANNEL_EXEC, $data);
                break;
            case self::MODE_SSH1:
                $data = pack('CNa*', NET_SSH1_CMSG_STDIN_DATA, strlen($data), $data);
                $this->ssh->_send_binary_packet($data);
        }
    }