# A Geographical Heuristic Routing Protocol for VANETs
## 5 Performance Evaluation
### Performance Comparison
When greedy-DTN and MMMR work with GHR, with tailored configurations according to the vehicle density, both protocols decrease their percentage of packet losses. Nonetheless, the behavior between greedy-DTN and MMMR remains the same. That is, GHR-MMMR outperforms GHR-greedy-DTN in the three vehicle densities, and the difference in the packet losses decrease as the vehicle density increases. It is important to notice that GHR-greedy-DTN improves the default operation of MMMR, i.e., it always selects the best neighbor (\(\alpha\rightarrow\infty\)) and it always applies \"carry and forwarding\" when there is not a closer node to the destination (\(\beta\rightarrow\infty\)). This means that the use of Tabu and simulated annealing is able to improve the straightforward routing criterion of greedy-DTN to improve the MMMR's results reached by using a combination of four parameters instead of only the distance to the destination. Figure 7b shows the average end-to-end delay for the received packets. iAODV is the routing protocol with the lowest delay because it establishes end-to-end routes to reach destination. MMMR is able to reduce the delay compared to greedy-DTN because MMMR takes into account the congestion in the path through the available bandwidth metric, the vehicle density to avoid void areas and the trajectory to select nodes that approach the destination. The use of GHR with the routing protocols increases notably the delay with low vehicle density because Tabu is used with carry and forwarding (\(\beta\rightarrow\infty\)). As we explained in previous sections, when Tabu forbids nodes, the set of possible next forwarding nodes is reduced. Consequently, nodes have to apply \"carry and forwarding\" more often. The delay of GHR configurations in intermediate vehicle density is closer to the default operations of MMMR and greedy-DTN than in low density, because the recovery simulated annealing (\(\beta=3\)) is applied by GHR in intermediate density; hence, \"recovery and forwarding\" (which introduces high delay) is used less often. Finally, the GHR configuration for high vehicle density decreases the delay compared with the default protocol operation, because this configuration does not apply \"carry and forwarding\" (\(\beta=0\)). The average number of hops is depicted in Figure 7c. iAODV needs the smallest number of hops to reach the destination because its algorithm builds a shortest path between the source and destination. On the other hand, MMMR needs more hops than greedy-DTN since the latter only selects the closest node to destination while MMMR considers other parameters and prefers more stable nodes, but requiring more hops to reach the destination. Regarding the GHR configuration, there are two reasons for the increment in the average number of hops. First the use of Tabu forces routing protocols to search alternative routes, typically longer than the ones obtained by the default operations of greedy-DTN and MMMR. The second reason for the increment in the number of hops for GHR configurations in intermediate and high vehicle densities is the use of recovery simulated annealing and aggressive recovery, respectively. The difference in the percentage of idle time, shown in Figure 7d, is related to the number of hops and the signaling traffic. AODV (green bar) is the most demanding protocol in terms of bandwidth compared to the default operation of greedy-DTN and MMMR (blue and red bars, respectively) because of the high number of signaling messages that AODV needs to operate. This fact is evident in the scenario with high vehicle density in which there is a broadcast storm of signaling messages. Greedy-DTN requires less bandwidth than MMMR because MMMR needs more hops than greedy-DTN. Furthermore, the signaling messages of greedy-DTN are shorter than the ones of MMMR because MMMR needs to transmit information about speed, direction, vehicle density and idle time into the hello messages.