I've got a Cisco 3005 Concentrator. On my groups I've configured the "Idle Timeout" to be 15 minutes. The groups are not getting disconnected after 15 minutes. Also these groups are being authenticated through Microsoft IAS Server.
Are there any other settings for "Idle Timeout" that need to be configured also?
The problem is more likely to be that the connections are not really "idle" for fifteen minutes. Microsoft Networking protocols tend to send information around on a very regular basis, even when the users are not actively using their systems. Putting a protocol analyzer on the network, or on one of the client machines would be a good way to see what traffic may be getting sent in the background when the machines are otherwise idle.