# Improved Road Segment-Based Geographical Routing Protocol for Vehicular Ad-hoc Networks
## 3 Improved Road Segment-Based Geographical Routing Protocol
### Routing Process, Flowchart and Algorithms
Furthermore, in the simulation, the process of packet forwarding continued until the packet reached the destination or passed over 10 hops (Time to Live (TTL) = 10 hops). * Simulation Time: The time for simulation was set at 500s for each round, and the settling time was set at 40 seconds to avoid the transmit behaviors from the results. The confidence interval was set 95%. * Positioning and range: A GPS receiver was attached to each vehicle, and the communication range of each vehicle was at least 300 m, which helped them to determine their position. Moreover, this communication range covered the area of the segment. Vehicles exchanged their information, such as position and direction, with others in the transmission range to maintain the neighbor table. Hello messages helped them to update these tables periodically. * Cooperative Awareness Messages (CAMs): Vehicular nodes sent CAMs, as characterized in the standard. Each CAM contained information like their physical location, destination (if applicable), current velocity, and direction. The header of a CAM contained the ID and location of the source, as well as the packet generation time and expiration time. For the simulations, the test space was set to \(2\times 2\) km\({}^{2}\) on-road area within the Chicago city road map, as shown in Figure 4. In this map, there are intersections and road segments. We thought about the obstacles among all the road segments wherever no line-of-sight (LOS) was experienced. As represented in Table 3, 350 vehicle nodes were used in the simulations. The typical speed of considered vehicular nodes was in the range of 40-100 km/h. ### Simulation Results

In this section, the simulation results of ISR are discussed in terms of the packet delivery ratio (PDR) and end-to-end delay with increasing numbers of vehicle nodes in the network and different speeds for vehicles. The elaborated description of the considered metrics is as follows. The PDR is defined as the ratio of data packets successfully received at the destination over a total number of packets that were sent from the source vehicle. It showed a successful transmission rate of the routing protocol. The end-to-end delay is defined as the how much time the protocol took to send data to the destination from the source, including processing at each intermediate vehicular node. Basically, it is the sum of sending buffer time, retransmission, medium access delay due to interface queue, propagation delay, and relay selection delay. Hop link disconnection is defined as the failure of message transmission during one hop communication in any forwarding path. The data throughput is defined as the amount of data successfully moved from source to destination per unit time. It is measured in bits per second for each vehicular node involved as source node in communication in the overall vehicular network implementation. #### 4.1.1 Number of Nodes Analysis

The first simulation result had increasing numbers of vehicle nodes to analyze the data delivery ratio of the proposed routing protocol, and we compared the results with a clustering protocol, the TASR [24] protocol, and a beacon-based virtual backbone in the VBRP [25]. The TASR protocol is a cluster-based routing protocol, but its cluster heads are present on the corners of its cluster, which became outdated here due to the high mobility of the nodes. On the other hand, the VBRP is a position-based protocol that has a network overhead issue due to the continuous beacon messages in

Figure 4: Fragmented city map of Chicago city. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Network Simulator & NS-2-34 \\ Simulation Area & 2 km \(\times\) 2 km \\ Traffic type & CBR \\ Simulation Time & 500 s \\ MAC protocol & IEEE 802.11p \\ No of Vehicle Nodes & 100–350 \\ Packet Size & 512 bytes \\ Transmission range & 300 m \\ Vehicle speed & 10–100 km/h \\ Mobility Model & SUMO-MOVE \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Major simulation setup parameters.