## 4 Evaluation
### Experimental Results  
When there is no void, VAA, GPSR and DUA have similar path length, because all of them carry out greedy routing in a void-free scenario. \begin{table}
\begin{tabular}{|l|l|} \hline Simulator & NS-2 version 2.29 \\ Simulation area & 500 x 600m\({}^{2}\) \\ Number of nodes & 100 (predefined scenario) \\ Initial energy & 1,000 J \\ Transmitting energy & 0.06 J \\ Receiving energy & 0.042 J \\ Idle power & 0.02 w \\ Transmission radio range & 40 m \\ Connection type & UDP \\ Duration & 500 seconds \\ Agent and application & CBR over UDP \\ MAC & 802.11 \\ Link bandwidth & 2 Mbps \\ Antenna & Omni Antenna \\ Interface queue & DropTail/PriQueue \\ Mobility & [0]m/s (static) \\ Traffic model & CBR over UDP \\ Data packet size & 32 byte \\ Bacon interval & 5 seconds \\ \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. VAA outperforms GPSR significantly in cases with an open void. GPSR follows an inefficient route if there is an open void on the R side as shown in Figure 15. The packet from the source node 0 destined to the BS (node 24) travels upto node 7 (i.e., \(\text{n}_{0}\rightarrow\text{n}_{7}\), where \"\(\rightarrow\)\" indicates the sequence of nodes strictly monotonically increasing from \(\text{n}_{\text{i}}\), \(\text{n}_{\text{i+1}}\),...,..., \(\text{n}_{\text{i+n}}\)) according to the greedy rule. Greedy forwarding fails in node 7, because node 7 is a void node. After that, it forwards packets according to the perimeter rule to the next face towards node 8 using the right hand rule. Then the packet travels on the respective face of \(\text{n}_{7}\)-\(\text{n}_{6}\)-\(\text{n}_{5}\)-\(\text{n}_{8}\)-\(\text{n}_{5}\)-\(\text{n}_{4}\)-\(\text{n}_{3}\)-\(\text{n}_{2}\)-\(\text{n}_{1}\)-\(\text{n}_{0}\)-\(\text{n}_{1}\)-\(\text{n}_{2}\)-\(\text{n}_{3}\)-\(\text{n}_{9}\)\(\rightarrow\)\(\text{n}_{24}\) nodes. In Figure 16, the open void is in the L side. It is the reverse topology case of Figure 15 (in Figure 15, open void is on the R side). In this topology, GPSR travels \(\text{n}_{0}\)\(\rightarrow\)\(\text{n}_{7}\)-\(\text{n}_{6}\)-\(\text{n}_{5}\)-\(\text{n}_{4}\)-\(\text{n}_{3}\)-\(\text{n}_{9}\)\(\rightarrow\)\(\text{n}_{24}\). This is the best route GPSR can travel, however VAA travels \(\text{n}_{0}\)-\(\text{n}_{1}\)-\(\text{n}_{2}\)-\(\text{n}_{3}\)-\(\text{n}_{9}\)\(\rightarrow\)\(\text{n}_{24}\) 19 hops, still less than the route traveled by GPSR, 27 hops, since GPSR switches to recovery mode after encountering the communication void. However, VAA prevents entering the void and it detours from node 3 toward node 9 in Figure 16.  
The graph in Figure 17 shows GPSR travels the longest path in the open void in R side case (scenario in Figure 15), more than in any other case. However, VAA and DUA travel a similar path (i.e. \(\text{n}_{0}\)\(\rightarrow\)\(\text{n}_{3}\)-\(\text{n}_{9}\)\(\rightarrow\)\(\text{n}_{24}\)) in either case (i.e. open void in L side and R side) but GPSR travels the longer path. Figure 16: Open void on L side. Figure 15: 100 node topology with one communication void. In the case of a closed void, as in Figure 18, GPSR travels the longest route n\({}_{0}\)\(\rightarrow\)n\({}_{7}\)-n\({}_{6}\)-n\({}_{5}\)-n\({}_{4}\)-n\({}_{3}\)-n\({}_{9}\)-n\({}_{24}\), 27 hops. However, DUA and VAA travel n\({}_{0}\)\(\rightarrow\)n\({}_{6}\)-n\({}_{25}\)-n\({}_{30}\)-n\({}_{21}\)-n\({}_{24}\), only 16 hops. Even in a best case scenario (i.e. flipping Figure 18 horizontally) in Figure 19, all three protocols take a similar path. Due to the nature of GPSR, packets go inside the void to node 7, and then come back thus n\({}_{0}\)\(\rightarrow\)n\({}_{7}\)-n\({}_{6}\)-n\({}_{25}\)\(\rightarrow\)n\({}_{30}\)-n\({}_{21}\)-n\({}_{24}\). DUA and VAA do not go inside the void so they detour from node 6, so the route is n\({}_{0}\)\(\rightarrow\)n\({}_{6}\)-n\({}_{25}\)-n\({}_{30}\)-n\({}_{21}\)-n\({}_{24}\). This is still fewer hops than GPSR. The average length of the routing path in VAA is similar in both cases of closed and open void.