how can we implement "IsOnline" for CustomMembershipProvider....

 Hi,
I have a custom MembershipProvider developed and working with no issues except "IsOnline".
I followed this post to do this: http://www.asp.net/learn/videos/video-189.aspx
When the user logs in & out the "IsOnline" values is not changing.
How can we bind the DB field to the membership.IsOnline property so it will update each time when the user logs in & out of the website?
I am fetchiing all the users using membership.GetAllUsers() in which it is always showing "IsOnline" as false for all the users,even though there are any users logged in also.
Any suggessions on how to do this?
 
Thanks,
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