I've been searching for the same solution and am wondering if either of you (or anyone) found one?
We used IPCOP with TCAR in our internet cafe for years to monitor wireless clients (most of whom were not heavy download / uploaders) and was so sure (at the time) it was counting both ways.
I've now set it up at home and am using it to monitor neighbours I'm providing wireless internet access to.
Have tried a host of other options Inc ClearOS, Smoothwall, Untangle (Lite), PFsense, ZoneCD (discontinued), SoftPerfect Bandwidth Monitor. None in my opinion do what TCAR does in such a simple way.
Am currently looking at purchasing a Mikroti Router 433 Board (with RouterOS), I believe they have a variety of capabilities some of which may help. RouterOS can also be installed on an old PC like IPCOP, Free for 24 Hours after which a license is required. R250)
In my search however I've discovered a few people mentioning using a RADIUS server in conjunction with a NAS (Network Authentication Server) The NAS (as I understand it) would be the Mikrotik Board attached to a Radius server running Radius Software. The best of which seems to be http://www.dmasoftlab.com/cont/home
Here is a diagram to illustrate: http://www.dmasoftlab.com/cont/topologies
At about R2000 for the software alone this is, well, an expensive option for people like myself who like to tinker with and make good use of otherwise old and redundant pc‚Äôs. But if I had the money this setup seems like it would be such a treat esp. for our internet caf√©.
If anyone has any experience of the above I‚Äôd be grateful to hear it as well as if anyone knows of any good / affordable alternatives i.e an upload counter for IPCOP‚Äôs TCAR.