Freeradius + ldap

Hi, I installed freeradius and configured it with LDAP and installed pptp also in debian lenny. I can login to radius server from windows and I have VPN connection and internet. Now I want to restrict my VPN users' bandwidth and internet charge(for example 4G charge for each user), but I don't know how to do it with freeradius+LDAP. I would be grateful if you can answer me as soon as possible. Regards, Raoufnezhad