Fair usage package implementation

[Ming-Ching Tiew]

I wonder if how such a "package" can be implemented,


       1. Unlimited rate normally
       2. But when downloaded packets exceed certain defined 
          figure, download rate is trottled.

Assumption
==========
1. Assuming the radius client is sending accounting information
   to the server, and so the downloaded octets can be obtained
   from the database through some sql query.

2. Assuming the radius client has some radius attributes which
   can set the download rate, WISPr-Bandwidth-Max-Down for example.

One way I could think of is to run a batch job which work out
per user octet usage and then set the attribute WISPr-Bandwidth-Max-Down
accordingly. But this will have to be per day basis, it might be too late ( after the subscriber have over abused it ).

Is there way such a thing can be implemented inside radiusd so that
everything happens on the fly ?

Regards.