Determining an 'active' user count of an ASP.NET site

Question

On an ASP.NET site, what are some techniques that could be used to track how many users are logged in to the site at any given point in time?

So for example, I could

Answer 1

First set Session timeout for 1 minute.

Create a simple heartbeat.aspx page with no HTML content just the following javascript code:

This will re-request itself every 30 seconds and keep session alive.

Put heatbeat.aspx page in a hidden frame.

To get user count just get session count by using static counter in Session_Start and Session_End events in Global.asax.