Limit Bandwith

Sorry if this topic already posted or on wrong forum How can we set speed if the user already over quota ie first day of month they get 1Mbps bandwith after spent 1Gig the speed will decrease to 512Kbps until end of month without turning off modem and re-authenticate. is that possible? Lebih Bersih, Lebih Baik, Lebih Cepat - Rasakan Yahoo! Mail baru yang Lebih Cepat hari ini! http://id.mail.yahoo.com