We can set timeout value in web.config file using Forms Authentication as mentioned below, Default value is 20 minutes.
This value gets reset or slide if there are calls between client and server and session expiration occurs if idle or no postbacks for specified time.
<sessionState mode="InProc" cookieless="false" timeout="12">
This will cause session to expire if user is inactive for 12 minutes, there are scenarios where you would like to prevent timeout to keep session alive if user goes idle beyond set value in web.config.
We can use XMLHttpRequest to interact with server.
We can use timer control with update panel to send requests to server.
<asp:ScriptManager ID="ScriptManager1" runat="server"/>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<asp:Timer ID="Timer1" runat="server" Interval="600000"/>