Problem

What is controlled by the "timer" parameter of the FT_FTP entity?

This value defines the timer (in seconds) of network inactivity before disconnection in server mode. (The same is true for the "timer" parameter for other protocols.)

Note that because FTP uses separate ports for control and data, this timer value may be reached while a file transfer is going on, in which case the control connection will be closed and the transfer will fail. You will need to have the client send NOOP commands at intervals, to keep the control connection open.