### SDN/NFV-Based Architectures for Industrial OT Networks  
SDN and ETSI NFV are complementary technologies capable of providing one network solution suited for industrial applications that need constant customization and innovation [20; 71; 109]. Figure 6 illustrates a software-defined IIoT-Edge network, taking the case of the Anholt offshore wind farm. The Anholt wind farm is a large offshore wind farm with an installed capacity of 400 MW. The offshore wind farm has 111 Siemens SWP 3.6-120 wind turbines with a generation capacity of 3.6 MW each. Orsted Wind Power, Denmark, operates this offshore wind farm. Each wind turbine has an access network with a nacelle switch and a tower switch. This results in \(\geq\)222 Ethernet switches distributed across the wind farm. These switches handle local data aggregation and transmission. Each tower switch within a wind turbine is connected to the PDC via sub-sea fiber optic cables. This setup ensures robust, high-speed data communication between the distributed wind turbines and the central data-processing hub. Additionally, onsite operations and maintenance (O&M) personnel utilize access points for Internet access, facilitating real-time monitoring and control. The offshore hub-mounted PDC is supported by \(n\) additional Ethernet switches, strategically deployed to manage and route the substantial data flow from the wind turbines to the PDC. Considering all components, a minimum of 250 Ethernet switches are involved in forming the IIoT-Edge network for the wind farm. Within the PDC, NFV instances supplement network functions and enhance the security, efficiency, and management of the network. These SDN/NFV-based architectures are anticipated to be progressively integrated into industrial OT networks due to their multifaceted advantages summarized into four pillars (interoperability, efficiency, cost-benefit assessment, and security), as shown in Figure 7. These architectures demonstrate a robust capability for interoperability with legacy systems, ensuring seamless integration without necessitating extensive overhauls. This capability enables a gradual phase-out or complete overhaul of legacy systems without significant disruptions. However, the integration of SDN/NFV-based architectures can be challenging due to the legacy infrastructure commonly found in industrial environments, which may not be compatible with SDN protocols and architectures. Novel designs must ensure that the new SDN/NFV systems can seamlessly integrate with the existing network of 250 Ethernet switches and various NFV instances, thus maintaining continuity and operational efficiency. Further, they facilitate the customization and configuration of advanced traffic engineering methodologies, which enhance network efficiency and ensure adherence to stipulated QoS requirements. Efficiency is highlighted as a major advantage, with SDN enabling path optimization to reduce latency and increase data transmission speed. In the context of a wind farm, this translates to real-time and rapid response time applications, which are essential for managing the vast amounts of data generated by 111 wind turbines. Enhanced efficiency ensures that the network can handle high data loads more effectively, improving the overall operational performance. The SDN/NFV solutions are recognized for their cost-effectiveness, offering a financially viable alternative to traditional network management approaches. SDN/NFV adoption leads to reduced operational expenditure (OPEX) with one-off capital expenditure (CAPEX). This reduction in costs comes from minimizing manual reconfigurations and physical interventions, which are often time-consuming and costly. The automation of redundant tasks, such as those managed by the PDC in the wind farm, further reduces downtime and troubleshooting efforts, leading to significant cost savings and increased productivity. Lastly, these architectures allow for the implementation of specialized security policies, thereby maintaining the integrity and security of the network.