http://weblogs.asp.net/stevewellens/archive/2009/06/09/ah-ah-ah-ah-staying-alive-staying-alive.aspx
Sometimes you want your web page to ‘stay alive’. That is,if a user is filling out a complicated form,you do not want the session to time out before they are finished. The user could get very angry and rightfully so: You might even get yelled at!
It’s not simply a matter of increasing the session timeout to a very large value. If you do that,the sessions would be left active in the server memory for hours—long after the visitors have left the site. Increasing the session timeout IS a solution… but not necessarily a good solution.
The goal is that the session should stay active as long as the web page is open on the client machine …even if there are no post backs to reset the session timer. When the web page is closed,the session should time out normally.
I implemented a solution for this: The client will “ping” the server at intervals of less than the session timeout which will reset the session timer. This is known as the Heartbeat design pattern (I couldn’t find a decent site/page to link to)…
