# Performance Evaluation of VANET Routing Protocols in Madinah City
## 5 Results and Analysis
### Average Latency  
The latency graph for fully human-driven traffic distribution with varying traffic densities is shown in Figure 12. It can be seen that latency increases with a higher traffic density. Looking at this graph, it can be observed that the difference between reactive and proactive protocols is not very significant. At a lower traffic density, i.e., less than 3300 vehicles, DSDV outperforms both reactive protocols (AODV and DYMO). Once the vehicle density increases beyond 3300, the reactive protocols provide less latency. The reason behind the increased latency in a higher density is because more nodes will send the acknowledgments to the sender, compared to the lower traffic density, which will take more time to wait and send in order to avoid collisions. For a fully autonomous traffic distribution, as seen in Figure 13, the latency is slightly higher for AODV and DYMO protocols when the traffic density is less than 1900 vehicles. Figure 11: Average trip time for Route 3 in low and high traffic densities. Figure 12: Latency graph for fully human-driven vehicles with varying traffic densities. With increasing traffic density, the DSDV protocol is outperformed by the AODV and DYMO protocols. The difference in latency is about 2.38 milliseconds, with DSDV having significantly higher latency. Therefore, as the traffic density increases, reactive protocols tend to perform better for a fully autonomous traffic scenario. The reason behind the increased latency in the DSDV protocol is the control packet overhead caused by the periodic exchange of packets. As mentioned earlier, the DSDV protocol exchanges control packets regularly to update the routing tables. Since we observe the latency from the time the first 'accident' packet is sent until the last node in the communication range receives the packet and acknowledges it. With high traffic density, there is an increased chance that a DSDV control packet transmission will start while the nodes are reporting the accident. This exact scenario happens in this case. When there is a transmission of control (HELLO) packets, the nodes will wait until the channel is free to transmit the accident or acknowledgment packets, which results in higher latency. In Figure 14, we plot the latency graph for semi-autonomous traffic distribution where 50% of vehicles are human-driven, and the rest are autonomous vehicles. For increasing traffic density, latency for reactive and proactive protocols increases linearly. It is clear that there is no significant difference between the reactive and proactive protocols in this scenario as the density of traffic increases. The analysis of variance presented later further confirms this observation. Figure 14: Latency graph for semi-autonomous vehicles with varying traffic densities. Figure 13: Latency graph for fully autonomous vehicles with varying traffic densities. Figure 15 shows the latency graph with varying traffic distributions under low traffic density. For any traffic distribution, DSDV performs slightly better than reactive protocols at a low traffic density. The difference in latency is about 0.04 milliseconds between reactive and proactive protocols. A latency graph with varying traffic distributions under a high traffic density can be seen in Figure 16. For a fully human-driven traffic distribution, t1, DSDV provides higher latency compared to reactive protocols. For semi-autonomous (t3) or 25% autonomous vehicle (t2) traffic distribution, reactive protocols perform slightly better than DSDV. In 75% autonomous traffic distribution (t4), the DSDV protocol is outperformed by the AODV and DYMO protocols. For a fully autonomous traffic distribution, AODV and DYMO outperform DSDV in high traffic density. The higher latency in the DSDV protocol is due to the control packet overhead. When the control packets (HELLO packets) are sent by any node, the neighboring nodes will not send any data packets as they sense the channel is busy.