Modem unreliable hang up.

I Have an Windows 2K server installation which unfortunately has to rely on a dialup connection for mail and internet access. The modem is configured to drop its connection to the ISP after 1 min (but have tried up to 10mins) of idle time. About 30% of the time it doesn’t drop its connection because there is some sort of traffic even though all email is collected or there are no browser sessions active.

How do I track down the source of the traffic and how do I prevent it from holding the modem connection up. I suspect the answer lies with the ISA server and logs but don’t really know where to start.

Any help or pointer to white paper, FAQ etc would be gratefully rx’d.