Each FTP connection is a permanent TCP/IP connection, it meaning the server may not provides a lot of connections simultaneously for users since it increases server loading by this way. Most FTP server limits max online connections for example 50 to 200 users and disconnect your connection if you are idle at the server within 30 to 60 seconds.
Most users complain about this behavior because of the server kicks them out when they are browsing a remote directory, and they must to connect the server again and again, waste time and patience!
Is there a way to avoiding it? yeap! our FTP client sends random command such as NOOP or LIST or CWD to the server in order to keep the connection alive every several minutes. for example, when you are looking for a file in the server, or just leave away for coffee, it sends "NOOP" or random commands to avoiding timeout from server to let the FTP server thinking you are doing some thing, not a idler!
How to enable Keep alive option?
Starts your FTP client and press F6 key to displays the Option dialog, and click the "Keep Alive" node, make sure you checked the "Enable Keep Alive" checkbox, It demonstrates the way to connect the server again automatically when got kicked.