1. SDN Controller Placement Problem (CPP): The article discusses the challenge of deploying the optimal number of controllers in a large-scale network environment. CPP involves finding an appropriate trade-off among conflicting performance requirements such as reliability, load balancing, latency, energy efficiency, and computation time.
2. Existing Approaches and Challenges: The article provides a comprehensive review of existing approaches to CPP and identifies their unique solutions, strengths, and weaknesses. It also highlights several challenges in controller placement, including the need for efficient algorithms, attack-awareness, cost-awareness, and energy-awareness while achieving good quality of service.
3. Future Directions: The article suggests future research directions aimed at improving the optimum location and allocation of controllers, particularly for SDN applications in wireless sensor networks (WSNs). These directions include developing more efficient algorithms and addressing the challenges mentioned earlier to enhance network performance, reliability, and scalability.