How do I get the actual Page ID

Hi All,
In my project there is a Business layer through which every classes (including aspx.cs page classes) are inherited. Therefore when I open any page for example PaymentAdvice.aspx, a PaymentAdvice object is loaded and it is stored in a Session["PageObjects"].When I come out from that page the object from the session gets cleared and some other object gets loaded. This is the basic structure. Now I am experiencing a problem. If I try to open a link in a new window for some other object from PaymentAdvice.aspx (Lets say customer.aspx for a customer detail ) I got some wrong information. That is because the Session["PageObjects"] is already holding PaymentAdvice Object. Therefore I have decided to put a collection in the Session["PageObjects"].Now I want to store a page unique ID for every time a browser gets opened in my object's property. Can any body suggest how I will get this actual page unique ID which will be unique for every opened browser? ...