Most of the ISP (Internet Service Provide) automatically disconnects internet connection when there is no action on your computer for long time, this may be issue for those users who have tendency to keep their machine scheduled for downloading purpose in nights.
Here is an excellent freeware tool Stay Connected 1.0 which is an application that allows you to maintain your network connection. Stay Connected allows you to send a ping request at a configurable time interval in order to maintain a connection to a network. You can configure it to ping either a DNS name or IP address. It resides in the tray to stay out of your way.
Stay Connected 1.0
Download Stay Connected 1.0 to Keep your Internet Connection Alive.