In the Flat Layer RADIUS server model, we assumed that every node in the network must know about all other nodes in the network. In the Flat Layer RADIUS server model, each node (RADIUS server) directly communicates with each other, without using any intermediate RADIUS proxy servers. To evaluate the performance of the Flat Layer RADIUS server model and compare with tree structure model, we setup experiments by using open source based freeRADIUS (version 2.1.8) and ubuntu (version 10.04.4) as RADIUS server. Table I shows the authentication time comparison between the tree structure and the Flat Layer RADIUS models. Note that the authentication time includes request forwarding process, authentication process, network latency and response forwarding process. Table II shows request processing time of three stages in authentication process. From Table I, we can observe that Flat Layer RADIUS server model takes less authentication time than RADIUS-based tree structures.