Emacs: Prevent TRAMP connection closing

I'm using emacs with TRAMP ( C-x C-f /ftp:user@site.com:/ ), and randomly, sometimes ten minutes, sometimes, ~12 seconds (no exaggerating) my connection will close (I think). I'll try to type, or list a dir, and it will say "Opening FTP connection to site.com...". Is there a way to tell it to just keep the connection open until I exit? Or is it the webserver killing the connection? I'm just using standard FTP.

Thanks.