general howto bandwidth control

[mike]

hi folk,

we have a little network with some cable modems. all modems use 
freeradius for authenticating and all useres use a pppoe session against 
freeradius to connect with the router. this works. now we want a 
bandwidth limitation for each modem.
is this possible with freeradius? or how can we realize this in this 
enviroment (iptable rules are rejected from me...) ?
my /etc/raddb/users looks like:

DEFAULT
    Fall-Through = Yes
#modem-client
000723023233 Auth-Type := Local, Cleartext-Password := "anonymous", 
NAS-Identifier == "000723023114"
        DS2-profile = 1

i searched for some documentation about this but nothing found.
my guess is there is a options that can be inserted here, but where and 
how...

thanks for any hints