How to check user online, offline by runtime process in silverlight

Hi all,

I have a problem when check user online, offline in silverlight. I update user status to offline when they close my app or redirect to another page in onbeforeunload event of body tag. But if I open the app in many tabs and close one of them, this make user to offline status although the app is running in other tabs.

So I think about runtime process to check user online or offline, it will check the will be close all of tab and window or not. If any one has experience in this, please help me.