# Software Defined Networking Architecture for Energy Transaction in Smart Microgrid Systems
## 4 SDN Architecture Development for a Transactive Energy Network  
SDN is a standardized network architecture. A typical SDN architecture comprises a single controller and a network of SDN CPEs that are geographically distributed over a large area at a national level. Each SDN CPE is located at a consumer of prosumer premises connected to nationwide network infrastructure or the Internet. Each CPE provides connectivity to its hosts. The network represents the Internet Infrastructure consisting of multiple Internet service providers (ISPs) and interconnected nodes that form the SDN network's data plane. The connection from the SDN switch to the network is not vendor or technology specific and can include technologies such as GSM, wireless, fiber, or satellite connection. Figure 5 below is a diagram of a typical SDN network that can support TESMS. Figure 5 illustrates a typical SDN architecture based on the centralized controller design by [PERSON] et al. [16]. In a star network configuration, the controller is located at the application core, meaning that each SDN CPE's data path (blue line in Figure 5) and control path (red line in Figure 5) follow the same physical communication channel. The consumers and prosumers of the transactive energy network are geographically distributed, which means that the connections between SDN switches operate on a geographically extensive network such as the Internet. The information flow between prosumer and consumer flows through the controller, confirming the extent to which the information is flowing in a start topology. Figure 6 shows the information flow between a consumer and prosumer. A single controller hosted in a centralized location controls all the SDN switches to establish the control path of the SDN architecture. Each SDN switch has a point-to-point connection to the SDN CPE at HQ to complete the data path of the SDN architecture. For transactive energy, most energy trading in the TE process occurs between the SMG, the prosumer, and the consumer, which is site-to-site communication. In addition, the SMG communicates with the regulatory authority for the economic and regulatory validation of the TE process. [PERSON] et al. [28] state that a centralized SDN architecture design faces scalability and reliability challenges. Access bandwidth for control messages (control traffic), controller memory, and processor constraints limit large-scale networks' scalability. Therefore, the increase in network size increases the access bandwidth and controller resource utilization, influencing network reliability due to the potential risk of failure. To optimize the SDN architecture for TESMS, the final design needs to consider the following design considerations,  
1. _Improved reliability in the SDN architecture_ Decentralized controller distribution in the regions optimizes the control traffic between the controller and the nodes. It minimizes the usage and utilization at each controller and the number of POFs. It further improves the end-to-end link availability based on the  
Figure 5: Typical SDN architecture based on the centralized controller design. Figure 6: Information flow between consumer and prosumer. reduced network elements between the nodes. This approach will enhance the reliability of the network. Redundant link configuration at each node improves availability by reducing the failure probability of the communication link. Improving the availability improves the reliability of the network. _Improved flexibility in the SDN architecture_  
A mesh topology enables dynamic communication between SDN nodes to improve network flexibility. This function enables the network to establish multiple routes between SDN nodes. A controller code is then required to determine the optimal data path between SDN nodes dynamically. Adapting to a dynamic environment and determining the optimal data path improve the architecture's flexibility.