How to prevent avoid Session Timeouts in an Asp.Net C# vb.net Page

As we knew that its a very big problem specially when developers provide a very large entry page to users. It will be Irritating for users after entering all data & then session timeout occur. To prevent or avoid session timeout problem, there is no fixed or specific or direct way to handle. But one can handle this problem using javascript asynchronous call. But one thing keep in mind that time