# A Geographical Heuristic Routing Protocol for VANETs
## 5 Performance Evaluation
### Evaluation of the Recovery Phase in GHR
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Metric** & **Number of Density** & **Forwarding Factor** & **Pairwise** & \(p\)**-Value** \\ \hline \multirow{2}{*}{\% packet losses} & 150 & \(\infty\) & (\(\beta=3\), \(\beta=0\)) & 0.279 \\  & 150 & 3 & (\(\beta\rightarrow\infty\), \(\beta=0\)) & 0.336 \\  & 250 & 3 & (\(\beta=3\), \(\beta=0\)) & 0.562 \\ \hline Average number of hops & 150 & \(\infty\) & (\(\beta=3\), \(\beta=0\)) & 0.106 \\ \hline \multirow{2}{*}{\% of idle time} & 150 & 3 & (\(\beta=3\), \(\beta=0\)) & 0.068 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Pairwise comparison of the performance metrics in which there is a difference among recovery techniques for the GHR protocol (i.e., \(p\)-value \(<\) 0.05 in Table 6). The table shows only the results for metrics and pairs of recovery values with the absence of statistically-significant differences (i.e., \(p\)-value \(\geq\)0.05). Figure 6: Performance evaluation of the recovery techniques (_RT_) included in our proposed GHR. The three _RT_ are: carry and forwarding (\(\beta\rightarrow\infty\)), Simulated Annealing (SA) (\(\beta=3\)) and aggressive recovery (\(\beta=0\)). We compare them with two forwarding techniques (_FT_): best node selection (\(\alpha\rightarrow\infty\)) and SA (\(\alpha=3\)). (**a**) Percentage of packet losses; (**b**) average end-to-end packet delay; (**c**) average number of hops; (**d**) percentage of idle time. The behavior of the recovery techniques in terms of packet losses can be seen in Figure 6a. The carry and forwarding strategy (\(\beta\to\infty\)) is the best option for the low vehicle density. As the value of \(\beta\) increases, the percentage of packet losses becomes significantly higher in this density. In the intermediate density, for the classical forwarding to the best node (\(\alpha\to\infty\)), SA recovery and the aggressive recovery (\(\beta=0\)) reach the same level of packet losses (see the first row in Table 7) between them, but they do not improve the default carry and forwarding (\(\beta\to\infty\)). Only the SA recovery (\(\beta=3\)) has a better performance than the default carry and forwarding for SA annealing forwarding (\(\alpha=3\)) in the intermediate density. Moreover, in this scenario (150 vehicles), this approach (\(\alpha=3\), \(\beta=3\)) has the same packet losses as the default selection of the best node with carry and forwarding (\(\alpha\to\infty\), \(\beta\to\infty\)). In the high vehicle density, the three recovery mechanisms behave very similarly as the classical forwarding (\(\alpha\to\infty\)). On the other hand, for the SA forwarding process (\(\alpha=3\)), carry and forwarding (\(\beta\to\infty\)) is again the best strategy when SA is used. However, contrary to the low density scenario, the other two recovery values of \(\beta\), which are similar between them (see the third row in Table 7), are close to the percentage of packet losses of SA forwarding with \(\beta\to\infty\). The average end-to-end delay is related with the value of the recovery factor \(\beta\). As can be seen from Figure 6b, when the \(\beta\) value decreases, the average end-to-end delay decreases, as well, for the two forwarding techniques. The reason is that the low \(\beta\) values produced use the buffer less often than carry and forwarding, which is the main cause of high delays. \(\beta=0\) has the lowest delay because it uses the buffer only when there is not any legal neighbor. This aggressive recovery leads to a decrease around two seconds with respect to the carry and forwarding technique in the three vehicle densities. More importantly, this decrement comes with none or very little degradation in the percentage of packet losses for intermediate and high densities, respectively. From Figure 6c, we can realize that applying a recovery factor \(\beta<\infty\), the average number of hops increases because the packets are forwarded more times than with carry and forwarding.