Radius Attribute "acct-interim-interval"

[Computer Network Man]

Dear All;
I found FreeBSD powerful and started using it. But I'm new in it and have
some questions? where is the best place for asking?
For example I have installed poptop on freebsd 8.2 and it's a pptp (vpn)
server(My NAS Server). But it uses an external Radius server for auth and
acct.
I have set the radius attribute "acct-interim-interval=60sec" in radius but
the NAS doesn't send interim updates. Can anyone help me?

Thanks in advance

comnetboy