FTP is the grand daddy of file transfer methods. It’s the easiest way to move files over the internet. Normal unsecured FTP uses ports 20 and 21 to transfer data, and it just zips along almost without effort.
Secure FTP is an on one hand / on the other hand proposition. Secure FTP uses a range of ports and almost randomizes which ones to use within the range. There’s probably a method to it, but the only way to make sure you don’t accidentally block one with your firewall is to open them all up for the FTP server. This is called a DMZ and is a little more dangerous than Russian Roulette if you set one up for this purpose. On one hand, the files are transferred securely using SSL. On the other hand, all ports aimed at your FTP server are open, which is like leaving your front door unlocked and wide open when you leave for vacation.
Since WebDAV is available and it can be made quite secure, I would recommend you use it for secure file transfers over the internet. SSH is also available, but it can only be used by the administrator unless you make some complicated modifications to a control file.
Regardless, FTP is still quite useful. You can use a standard browser to access files both anonymously and under the control of user id / password security. It’s a great way to dispense files to the public from your web site.
You need a URL. One can be had for free or at low cost from a Dynamic DNS (DDNS) service. Once you acquire a web address, you’re ready to set up an FTP server.
The QNAP Way
Sign into QNAP and start the FTP service.
Open port 21 on your router and point it toward QNAP.
Go to your browser and fire up your new FTP server.