How do I get clients names using TMG 2010 monitor bandwidth LAN?

Hi!
I am using TMG 2010 monitor bandwidth LAN for my internet service provision. What I do not understand is the fact that all the user computers show as anonymous. I wanted an application that will be able to identify each user with a name so I can know their internet bandwidth usage. What setting do I need to change to activate this functionality? Thanks for your assistance.
