## 4 Methodology
### TMR Routing Protocol
However, it results in having more data congestion and collision especially when network nodes frequently broadcast emergency messages or cooperative awareness messages (CAM). In Figures 32 and 33, increasing the number of nodes would improve the utilization of the network. This continues until the number of nodes reaches 70, which is the optimum. Beyond that optimum number of nodes, more data packets will result in traffic data jams and hence the performance degrades monotonically. Based on Table 7, TMR degrades PLR by 13.2 and 7.1 percent in comparison with QMR and ISR, respectively. The end-to-end delay increases drastically when the number of nodes goes beyond the optimum value as depicted in Figure 34. The chance of having lengthy routes increases when there are lots of intermediate nodes. TMR mechanism drops those lengthy routes and, therefore, end-to-end delay is minimal. In Figure 35, the routing overhead increases slightly with the number of nodes because the throughput in this range increases. When the number of nodes is greater than the optimum number, the throughput diminishes as a result of the traffic problems occurrence. In this range, data retransmissions increase and accordingly more routing packets are sent to accommodate those retransmissions. Figure 34: Comparison of QMR, ISR, and proposed protocol TMR for end-to-end delay with number of nodes. Figure 35: Comparison of QMR, ISR, and proposed protocol TMR for routing overhead with number of nodes. Figure 33: Comparison of QMR, ISR, and proposed protocol TMR for PLR with number of nodes. ## 6 Routing Protocol Analysis

In VANETs, energy consumption is not a challenge due to the availability of a significant source of energy. The network nodes could use the vehicle battery. As a result, methods that use energy consumption to measure the traffic condition of the network, such as ETE [42] and FF-AOMDV, are not accurate and do not achieve high performance in VANETs. Moreover, using other methods that rely on successful data delivery probabilities, such as the ETX method, would impose high overhead on the network in terms of sending an excessive amount of link probe packets (LPP) [43]. This, in turn, would add more traffic load to the network, which causes traffic problems such as data packet congestion. On the other hand, RTT measures the status of the network and, therefore, routes can be selected, avoiding those congested paths without the need to add extra overhead. In addition, the route optimization process based on RTT is impossible to frequent topological change in VANETs, which is not the case with using ETX and ETE methods. This feature is more obvious with vehicles having high mobility speeds. The data path from the sender node to the receiver end may encounter congestion or collision. Algorithms designed based on one-way delay such as [44; 45; 46; 47] rely on the delay only in the reverse path, which may be vulnerable to various traffic challenges compared to the forwarding path. On the other hand, RTT consist of both forwarding and reverse-path delays, and this provides more accuracy. The main difficulty with the routing protocols designed based on the delay to represent the state of the links' condition is their dependency on the clock synchronization [48]. The clock of all the nodes should be synced to calculate the accurate RTT; otherwise, the performance could be impacted by the accuracy of the calculated RTT. Another difficulty is the placement of the RSU devices in the network. To optimize the network performance, the number and position of RSU nodes need to be determined precisely. RSU devices play a key role in the network topology, and it is more likely to be placed where there is a physical obstacle to provide steady coverage as well as where vehicles are operating at a high mobility speed [49]. Table 8 provides the required characteristics for each protocol. In this comparison, protocols such as EGSR, QMR, and ISR are dependant on the GPS, which may cause a bigger routing packet size.