ASP.Net How to kill unused session

[jim3481]

we can write code by which we can kill session when user click on log out button or click on close button of browser but some time user may go to another site from my site or suddenly browser crash and close and some time power cut so machine close. how to handle this kind of situation and kill session for that particular user. what would be the best strategy for session management for big portal.i will be glad if any experience developer gude me how to kill unused session and also guide me for best strategy & session management for big portal. thanks