VPN Server - one connection from each user only

Hi,

I just managed to set-up a VPN Server on Windows Server 2003 using Routing
and Remote Access. However, by default, the VPN server allows multiple
connections from the same username. I need some help from the experts over
here on how to ensure that one username is only able to make a one VPN
connection to the server.

I tried Googling but most of the results turn out to be guides on setting up
the VPN server. Perhaps it was the keywords I used for the search.

Thanks in advance.