## 5 Results and Discussion
### Experimental Details
After the successful construction of topology in Mininet, a tool is needed to evaluate the topology through real distributed network traffic.D-ITG (distributed internet traffic generator) is one tool that replicates real packets of various protocols. Through D-ITG, different packet streams can be generated, and statistics are collected on the logging server. In D-ITG, there are different modules responsible for their function. In the network, one host has to act as a log to collect all the data regarding D-ITG traffic. The D-ITG log sample information is shown in Figure 6. One host sends a UDP packet to another host, and in the end, the decoder analyzes the data collected by log. D-ITG also provides the feature of analyzing information in real time. In our case, we wrote bash files for TCP and UDP traffic. When Mininet topology is created, every host also accesses the shell. On another terminal, we ran the bash file of D-ITG so traffic can be generated in the network. Finally, let us discuss the SDN controller, the crucial component of the system. The ONOS controller is selected for our study. The reason is that the author of our base paper also uses this controller, and it is an open-source controller. The second ONOS controller is compatible with Mininet. It is an open-source controller providing next-generation SDN/NFV solutions. There is no major challenge in connecting the ONOS controller with the Mininet topology. It is recommended for clustering or making groups of controllers, so in our method we have to create groups of controllers, so this will be the best choice for this experiment. In [13], they created VM for every controller, and one VM machine is used as a click modular router [55], which is used to develop the communication fabric of controllers. Figure 7 shows the concept; they use Core i7--7700k @4:20 GHz with 64 GB of RAM for the experiments. Virtual machines are configured with 4-core CPUs and 12 GB of RAM. Also, the whole experimental network is constructed over a Dell Power Edge M640 Server consisting of two Intel Xeon Gold 6126 @ 2.6 GHz processors and 384 GB (6 \(\times\) 64) by [13]. Due to limited computational resources, we changed some experimental strategies. \begin{table}
\begin{tabular}{p{128.0 pt} p{128.0 pt}} \hline \hline
**Notation** & **Descriptions** \\ \hline _Dist_ & Distance \\ \hline _SP_ & Source point (source node) \\ \hline _DP_ & Destination Point (end node) \\ \hline _La_ & Latitude in radians \\ \hline _Lo_ & Longitude in radians \\ \hline \(r\) & Radius (6,378,137 m) \\ \hline _v\({}_{l}\)_ & Velocity of signal (\(1.97\times 10^{8}\)) m/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Important notations used to calculate delay and their description. It is similar to the original one with a bit of change. We created 20 peer controllers for the experiment and one central controller. Despite assigning every controller a complete resource equal to a computer, we made all controllers on one system. All controllers are connected in topology; between these peer controllers and the central controller, one OpenFlow switch is connected to provide communication. Figure 7 shows our concept. This switch is the replacement of the click modular router. At first, the SDN controller collects the service rate of peer controllers. The service rate to peer controllers is assigned from 1 k to 30 k/s. After collecting the service rate, the central controller decides whether the network is heterogeneous. It is determined based on the service rate of peer controllers. If the ratio of maximum and minimum service rates is less

Figure 6: D-TTG log showing information about UDP packet transfer from H1 to H2. Figure 7: Peer controllers forming groups on the basis of service rate and connected to the central controller via OpenFlow switch. than two, the network is considered a homogeneous network and heterogeneous otherwise. If the system is homogeneous, the central controller randomly selects any controller to fulfill the flow request.