## 4 Methodology
### TMR Routing Protocol
If this condition is not met for all available paths, this means that the data packets have no efficient route to the final destination. Therefore, the RSU has to wait for a backoff time and later try again to find a route when the destination vehicle is closer. In this way, excessive data traffic, particularly normal messages, can be reduced to mitigate the pressure on the network and therefore avoid network congestion. Vehicles' mobility might harm the precision of the RTT calculation in terms of its aberration, and this is one of the limitations of the algorithms that use RTT. Several techniques utilize RTT in various data communications systems as discussed in [36]. RTT variation relies on the communication model, whether being short-term or long-term transmissions. In VANETs, data communication between RSU and OBU is usually for a short term, where RTT will be updated quite often. This accordingly avoids the RTT inaccuracy happening when vehicles have high speed on the road. In [37], the effect of mobility speed has a limited effect on the RTT calculation as the data packets carrying information can travel back and forth at speeds that are much higher than the node speed. This is valid, particularly in small networks having a shorter path for data packets to traverse. On the other hand, and as in [38], RTT increases with wider networks as having more nodes in the network increases the queuing delay, and this, in turn, would reduce the data packets' transmission speed. In this case, the data packet traveling speed will be comparable with the vehicle speed, and as a result, RTT accuracy will reduce. To overcome such constraints, it is recommended to have more RSUs in crowded regions such as urban areas to have less distance where packets have to travel, and therefore RTT will reduce. On the contrary, in a high way, particularly between cities, having fewer RSUs can work efficiently as the number of vehicles is relatively small. Therefore, RTT will be short, which in turn increases the data packets' transmission speed compared to the vehicle speed. RTT can be calculated through a few ICMP echo requests and response packets between the source node (RSU) and the destination node (vehicle) as suggested in [39]. ## 5 Experiment Setup and Performance Analysis

To evaluate the performance of TMR, we used NS-3 (version 3.30.1) on Ubuntu 20.04.2 LTS operating system to obtain simulation results. Performance is measured by quantitative metrics of end-to-end delay, packet delivery ratio, packet loss ratio, throughput, and routing overhead. During the simulations, we considered different network configurations with randomly distributed vehicular nodes in a square shape connected roads with 1 km length bidirectional double lane in each direction. Different network loads in terms of having various packet sizes, number of concurrent connections, and different environmental configurations, including mobility speed, number of nodes, and more, are considered to scrutinize the network's performance. Table 1 shows the simulation parameters. Experiments are all set to parameter assumptions in Table 1 unless otherwise noted. The results indicate the efficiency of our protocol, even as the number of nodes increases. As TMR uses stationary RSU nodes in its network topology, there was an effort to implement a fair simulation environment for all the protocols. As the result of the same consideration, there was the same number of stationary nodes at the same position in the network for all the simulations. ### Performance Metrics

Hereafter, we present the formulas used to measure the performance metrics [11; 40]:

1. End-to-end Delay (E2E): End-to-End Delay refers to the time taken by the packet to be transmitted across the network from source to destination. It is generally represented in seconds. \[E2E\left(\text{in Seconds}\right)=\frac{\sum_{i=1}^{n}(R_{i}-S_{i})}{n}\] (1) The \(R_{i}\) represents the simulator time at the receiving end when the packet delivered.