We used an open source based freeRADIUS (version 2.1.8) on ubuntu (version 10.04.4) as RADIUS servers.
According to the structure of RADIUS servers, we can apply different configurations of connectivity of RADIUS servers. For considering WAN (Wide Area Network) connectivity between RADIUS servers we emulate network links between each RADIUS servers and 100ms delay.
We compared Flat layer RADIUS server model with RADIUS based tree structure models (three hops away and two hops away models) in eduroam.