Question : how to keep the session variable alive until the user close the browser?

Hai,
  I had developed a web application in C#ASP.net 1.1.I have set application session time out as 45 min. in web.config.
I had used windows authentication mode in web config.
  In my application its has several pages and the user can login from any page of my application.I had passed the username between the pages using session variable.
  My problem is, when a user working in my apllication in different tabs of same browser and the user works continously in one tab and another tabs are keep remain and the session variables are expired in another tabs.and the user clicks the login page it shows that "YOU ARE ALREADY SIGNED IN"?
   how to prevent this type of problem?
  And I also needed that, can we use different session between the browser tabs.Is it possible?

Plz give me a solution to solve this kind of problem
       

Answer : how to keep the session variable alive until the user close the browser?

Hai,
   Thanks for your reply

   to prevent this type of problem while given it checks the session expired time and it check the session is available or not.
  If it is yes and extended the session time and it is not and it expired