# A Geographical Heuristic Routing Protocol for VANETs
## 5 Performance Evaluation
### Performance Comparison  
In this section, we show how an adequate configuration of GHR can enhance the performance of geographical routing protocols. In addition to using the MMMR routing procedure to score the neighbors of a node, a case widely studied in the two previous sections, in this section, we employ a basic routing criterion, which is based only on the distance to the destination to choose the next forwarding node. This approach is generally called greedy-DTN [4], and it is widely used as a reference for comparison with more sophisticated DTN protocols [4]. Moreover, we compare our proposed GHR with these two routing algorithms, i.e., GHR-MMMR, GHR-greedy-DTN, against a modified version of AODV called irresponsible AODV (iAODV) [33], which was especially adapted for VANETs because it reduces the number of route request signaling messages to establish an end-to-end path. iAODV is a representative example of topology-based routing protocols. Figure 7 shows the results of the four metrics used in this paper for the three protocols that we have compared, GHR-MMMR, GHR-greedy-DTN and iAODV, with red, blue and green bars, respectively. The default operations of MMMR, greedy-DTN and iAODV are the bars with solid fill (first, second and fifth bars). The results for MMMR and greedy-DTN when they are assisted with the best configuration of GHR, which depends on the vehicle density, are represented in red and blue bars with different filling patterns for each vehicle density. Figure 7: Performance comparison of the best GHR configurations using MMMR and greedy-DTN as the scoring algorithms and iAODV. (**a**) Percentage of packet losses; (**b**) average end-to-end packet delay; (**c**) average number of hops; (**d**) percentage of idle time. The percentage of packet losses in Figure 7a lets us see that the default MMMR operation (solid red bar), without GHR assistance, outperforms the default operation of greedy-DTN and iAODV in the three vehicle densities. The reason is the more elaborate scoring metric that considers, in addition to the distance, the trajectory of the neighbor, the vehicle density and the available bandwidth. If the trajectory of a neighbor approaches the destination, then it would be useful if the node implements \"carry and forwarding\". A high vehicle density increases the probability of finding a suitable next forwarding hop. Finally, it is important that a neighbor has enough available bandwidth for a packet transmission. However, the reader can notice that the importance of the three additional parameters of MMMR with respect to greedy-DTN decreases when the vehicle density increases because it is easier for greedy-DTN to find good forwarding candidates. Regarding iAODV, we can see that it only reaches the greedy-DTN marks with low vehicle density. In this vehicle density, nodes can build and maintain end-to-end routes without mutual interference due to the low signaling traffic. For the intermediate vehicle density, iAODV is able to decrease the percentage of packet losses with respect to its low density results because it can find more routes and maintain a reasonable signaling overhead since it does not use the aggressive flooding of the route request message of the original AODV. However, iAODV is not able to follow the results obtained by default greedy-DTN nor MMMR, because these two protocols use a simple and effective routing strategy. More importantly, greedy-DTN and MMMR need very few signaling messages to operate compared to iAODV, which turns into idler communication channels for data transmissions. Despite the more efficient route construction mechanism of iAODV, broadcast storms of route request/reply messages arise when the number of vehicles is high. As a consequence, the performance of iAODV decreases considerable contrary to the behavior of the geographical routing protocols, which decreases the percentage of packet losses.