## 5 RC-LARR: RSU-Assisted Cloud-Based Location-Aware Hybrid Routing  
In this section, the cloud-based routing protocol for the proposed SD-VANET architecture is presented. All scenarios to find the destination node are discussed in detail. Further, the workings of routing are discussed. Figure 2 illustrates all the possibilities of finding the destination node. The RSU was placed on the divider of the road to obtain maximum coverage. Figure 1: An illustration of the system model with the infrastructure for a hierarchical SD-VANET. Figure 2: Routing scenarios. A is the sender node and B, C, D are the possible destination nodes. According to these possible nodes, the following four types of scenarios are possible. As shown in Figure 2, there are four possibilities for finding the destination node. In this figure, A is the sender node and B, C, D are the possible destination nodes. According to these possible nodes, the following four types of scenarios are possible. 1. The destination node is found in the range of the sender vehicle: Suppose that the sender node wants to communicate with the destination node, as shown in Figure 3.  
The sender node broadcasts the \"hello\" control message to all the vehicles in its range. If the destination node is available in the range, the destination node will send a reply. Figure 4 shows the communication process. 2. The destination node is found in the range of the RSU but outside the range of the sender: The destination node is outside the range of the sender node, but the destination node is inside the range of the same RSU in which the sender node is available, as shown in Figure 5.  
Figure 4: Communication between source node and destination node when the destination node is found in the range of the sender vehicle. Figure 3: The destination node is inside the range of the sender node. In this case, the sender node sends the route request to the RSU. The RSU checks its routing table. The RSU sends the route information to all the intermediate nodes, the sender node, and the destination node. Figure 6 illustrates the communication process. 3. The destination node is outside the range of the parent RSU but in the range of a neighboring RSU: In this case, the destination node is outside the range of the parent RSU, but inside the range of a neighboring RSU, as illustrated in Figure 7.  
Figure 5: The destination node is inside the range of the parent RSU but outside the range of the sender node. Figure 6: Communication between source node and destination node when the destination node is found in the range of the RSU but outside the range of the sender. Figure 7: The destination node is outside the range of the parent RSU but inside the range of a neighboring RSU. If the parent RSU fails to get the route itself, then it broadcasts the route request to all its neighboring RSUs to find the route. Figure 8 shows the detailed communication process. 4. The destination is not in the range of neighboring RSUs: If neither the parent RSU nor neighboring RSUs get the route for further communication, the parent RSU forwards the route request to the cloud as it has overall network information to find routes. Figure 9 illustrates the representation of the scenario. Figure 10 displays the communication process. All of these situations use the RSU as a control plane layer 1 part. Its job is to store data about vehicles in its coverage area so that it can keep a localized view of the network topology. If both the sender and destination nodes fall within the coverage area of the same RSU, the RSU will undertake the task of route calculation. Subsequently, the calculated route will be transmitted to the source node, the destination node, and any intermediate nodes that exist along the route. Figure 2:0 Communication between source node and destination node when the destination node is outside the range of the RSU but in the range of a neighboring RSU. Figure 2:1 The destination node is outside the range of neighboring RSUs.