From Table 1 it is observed that the dominant delay for the whole authentication time is the network latency. It has clearly observed from Table 1 that flat layer RADIUS server model takes less authentication time than RADIUS based tree structures. Also, it is observed that the authentication time increases most likely in linear along with the depth of the tree structure. In particular, the authentication time of 3 hops away tree structure exhibits 3 times more delay than the flat layer RADIUS server model.