SharePoint - how to know how many users are currently looged in accross site collection in sharepoint

hi all,

how to know how many users are  currently looged in accross site collection in SharePoint 2010 .

i am already tried to
SPUser sUser = web.CurrentUser;

but it is showing only 1 user , i want all user who currently logged in.

regards
Sushant Kumar Kesari

Yes, This will give you current logged in username. Try this link-

http://sharepoint.stackexchange.com/questions/33042/how-to-find-the-number-of-active-logged-in-users-across-all-site-collections