# Software Defined Networking Architecture for Energy Transaction in Smart Microgrid Systems
## 4 SDN Architecture Development for a Transactive Energy Network
A redundant configuration only requires two links, \(x\) and \(y\),  
Figure 6:3  
And so, the total link availability is expressed as follows,  
Figure 6:4  
For time (\(t\)) = 100%, the failure rate \(\lambda_{x}\) and \(\lambda_{y}\) will be the difference between the availability \(A_{x}\) and \(A_{y}\),  
Figure 6:5  
With low-availability links, a redundant configuration can provide a significant improvement in the total availability of the node,  
An SDN network with a mesh topology requires a specific control algorithm approach. A controller's default flow decision procedure in an SDN network is based on the principle that there is a single link between the nodes and core node, i.e., only one path from one host (application or user connected to the SDN node) to another host. A mesh topology allows multiple paths between hosts, and the controller needs to determine the best or shortest path between hosts. The Floyd\(-\)Warshall algorithm is the best and most famous algorithm to find the shortest path between every node because it is effective and accurate. For the SDN controller in a TESMS network, the following steps in Table 1 are used in an algorithm that is based on the Floyd\(-\)Warshall algorithm. Literature research found multiple methods to improve security, including cyber-attack mitigation techniques, application-filtered flow control, and data encryption. According to [PERSON] et al. [37], encrypting the data packet is one of the most common and proven methods to secure data and ensure integrity. A virtual private network (VPN) is a secure method to encrypt the data between nodes using IPsec. The design considerations showed that reliability, flexibility, and security could be improved. By taking each design consideration into account for an SDN design for TESMS, the following steps in the design were followed:  
* Decentralized controller placement by placing an SDN controller in each region. The number of network nodes between the hosts reduces, so the number of potential network failures reduces. The usage and utilization at each controller are limited to the number of nodes in the regional network, improving the resource allocation in the SDN controller. * A redundant link configuration at each link improves the availability of each SDN node. Each node will have two links to the Internet, using any combination of media and technologies available. This list includes GSM, fiber, wireless, and satellite. * A mesh configuration that allows site-to-site connectivity. Site-to-site communication reduces the number of network nodes between SDN nodes, improving the SDN architecture's availability and reliability. * A VPN connection between SDN nodes improves the security of the SDN architecture. Encrypting the data protects architectural integrity. In Figure 7, each design consideration is included. * Each region has its designated controller that allows direct data flow between participants, decentralizing the SDN controller and allowing site-to-site communication for a mesh network configuration. * Each remote site has two network connections to the Internet for redundant connectivity from each SDN node, adding redundancy to each remote site. * Each controller also connects to the regional HQ for regulatory data flow and TE transaction updates to the regulator database. * The region definition is not limited to geographical or political definitions and can also include local municipalities and private gated communities or complex estates. The information flow between the consumer and prosumer is now directly between the SDN nodes. Figure 8 shows the control path and data paths are logically separated and that the consumer and prosumer can establish a direct path for the information flow during the transaction of energy. Figure 7 below illustrates the decentralized mesh SDN architecture.