Monitoring PPP/Dialup usage

[Jamie Carl <jamie p-c-s com au>]

I'm hoping there's someone out there that has had some experience with
this.  I'm running RH6.0 on two machines for a small ISP.  At the moment
we charge a flat rate but are thinking of changing that.  So i would
like to know how i can monitor the usage of our users and write stats
out to a file or something, so that we know how much to bill.  Just
things like logon/logoff times, bytes sent/received all that stuff.

Any ideas on where to start looking?

Thanx.

Jamie