This is something I've often wondered about in the past, but never got around to making any real enquiries - it may be opportune to post the question here, though -
Before the local proliferation of ISP's, many businesses/organisations were faced with issues of authentication on access to their networks, and presumably went the route of implementing their own RADIUS servers, whether through dedicated black-box devices or otherwise. Is this still the case, or have most opted for reliance on their provider in this regard? Do you know of any non-ISP organisations that run their own RADIUS servers/devices?