# Software-Defined Small Cell-Linked Vehicular Networks: Architecture and Evaluation
## 4 Implementation of the V2x Data Dissemination over diSRsVN and Its Results  
### Disseminate V2V Message Based C-V2X over diSRsVN  
In this section, we review the simulation setup of the scenario to handle the dissemination of speed notification. The simulation evaluation uses the omnet++ simulator [29]. To integrate the OpenFlow protocol and SDN technology, we import the OpenFlow Module for omnet++ 5.4+ and INET 3.6 [29]. The VeinsLTE [30] and SimuLTE [31] frameworks were also imported into omnet++ to run the simulation of the proposed architecture. We outline the simulation parameters in Table 2.  
As the diSRsVN architecture is based on the SDN approach, the INET framework provides modules that apply and implement the SDN concept. This paper examines an initial model presented in [32] and applies two basic SDN elements, the SDN centralized controller and distributed small cell-enabled OpenFlow switches. They manage the basic openFlow messages for flow establishment and component communication [32].  
We use the traffic simulators called simulation of urban mobility (SUMO) version 0.30 [33] to simulate real-world traffic conditions. SUMO is a microscopic traffic simulator with features, such as collision-free vehicle movement. The open street map is used to download the real-time traffic scenario (OSM) [34] of a section of San Francisco, California, USA.  
To obtain trace files, the osm file is converted and processed using SUMO simulator tools. The latter is fed into omnet++ to run simulations. The vehicle density ranges between 10 and 100 vehicles. The vehicle's speed ranges from 15 to 40 km/h. Small cell-linked RSUs are available in threes and are equipped with both DSRC and cellular interfaces (LTE-V2X). The transmission range is 500 m to the cluster head. The fixed query transmission time and the information broadcast time are both set to 10 ms. The small cell-linked RSU query processing time is set to 10 ms. For IEEE 802.11p, we set a transmission range of 500 m, a data rate of 6 Mbps, and a carrier frequency of 5.890e9 MHz. The simulation time is approximately 400 s. The results are saved with an average of five realizations. For vehicle movement, we configure the freeway mobility model. Another network simulation framework is Veins [30] which was used to simulate a vehicular application with RSU unit (TraCIDemoRSU11p). During the simulation, every vehicle is sending data to another, selected randomly. There is a pause interval chosen between \([0,1]\) s, and after that, the accident count mobility traces is about 1 in the chosen area. This accident count is enough to allow the Veins cars to propagate the accident packet for an amount of time selected between [10; 60] s. We considered a low varying traffic density because of the additional computation of small cells and distributed SDN controller to study the effect of increasing the number of vehicles. The clustering of vehicles in their respective small cells-linked RSUs clusters provides stable connectivity between the clusters' vehicles, which fastens the transmission packets after the distributed controllers compute the global network topology. The input values for radio medium are the default value as defined in the TraCIDemoRSU11p application of the Veins framework. The propagation parameters used were extracted from [35].