# Software-Defined Small Cell-Linked Vehicular Networks: Architecture and Evaluation
## 4 Implementation of the V2x Data Dissemination over diSRsVN and Its Results
### Results Analysis in Comparison with Existing Works  
The diSRsVN architecture is evaluated in comparison with two SDN-based schemes, the hierarchical software-defined VANET (HSDV) [19] and VSDN-based heterogeneous wireless interface (HetSDVN) [18]. These existing schemes were chosen because both use the concept of local controllers to reduce the controller's signaling network traffic. The VSDN architecture in [18] includes a network selection and data dissemination protocol. The network selection is carried out using utility functions and a game theory approach. The controller manages dissemination in HSDV by selecting the next hop that is closest to the destination. Figure 5c shows that the controller manages dissemination in HSDV by selecting the next hop that is closest to the destination. The PDR for HetSDVN and HDSV increases as the number of vehicle density increases (fewer packets are dropped). However, as the vehicle density increases, the proposed architecture's PDR decreases. To summarize, the proposed scheme maintains the PDR regardless of the density of the vehicle nodes. The proposed scheme employs the SDN controller approach; VSDN includes a heterogeneous wireless interface. The proposed architecture improves PDR because the distributed small cell topology discovery reduces the connectivity loss through the network's global view, which is known in advance and updated frequently. The routing paths are predefined in the OpenFlow switch, reducing the flow of messages exchanged between small cell RSU nodes and, as a result, decreasing packet collision. The transmis  
Figure 5: Evaluation performance of the proposed architectures with HSDV, HetSDVN versus vehicle density: (**a**) average throughput; (**b**) E2E delay; (**c**) packet delivery ratio (PDR). sion loads between vehicles and small cell RSU infrastructures are also reduced by the clustering nodes. Since the cluster head would also update flow tables with routing rules received from the distributed small cell RSU controller, the small cell RSU updates route information for previous query dissemination messages from the cluster head. The PDR for the proposed scheme is 94.32 % at a vehicle density of 80, whereas HetSDVN using a heterogeneous wireless interface and HSDV are 91.08 % and 88.04 %, respectively, at a vehicle density of 80. Figure 4(b) shows the average throughput with the vehicle density. When compared to existing SDN-based schemes, the proposed architecture has a higher average throughput. This is because the node vehicles, with the help of the SDN controller's small cell RSU and topology discovery, distribute packets to their destination nodes. HetSDVN with a heterogeneous wireless interface provides stable average throughput as the vehicle density increases, whereas HSDV is lower than the proposed architecture. The best routes predicted by the SDN controller must be chosen in order to achieve higher average throughput. At a vehicle density of 80, HetSDVN with a heterogeneous wireless interface appears to have 92.51 Kbps, whereas HSDV and the proposed architecture have average throughputs of 89.67 Kbps and 103.45 Kbps, respectively. Figure 4(a) shows the average E2E delay. As the number of vehicles increases, the proposed scheme reduces the average E2E delay. This is due to the cluster header having a high probability of selecting a group of vehicles that travel in the same direction when the Hellocluster-controller message is sent. Because the path of disseminating traffic messages is established from the distributed small cell RSU controller based on the topology discovery process, the delay is gradually reduced. The latter is determined after the control message is computed based on the formation of the cluster head with the available number of small cell RSU nodes.