Disconnection without any reason after exactly 2 hours

Last day I have installed ServerU 6.1 on my pc as server and Smart FTP 1.5 as client on my friend's pc using ADSL connection 640/256. Why Pc with Smart FTP after exactly two hours of download from my server disconnected? We have resumed and after exactly two hours it was happened again. Why does it break? Another question: Is it possible download and upload from ServU at the same time because when my friend used SmartFTP for downloading that broke after 2 hours couldn't up anything to my server. Is it normal this or I haven't good setup of Smart FTP? Thank you for the answer and help.