# Application-Aware SDN-Based Iterative Reconfigurable Routing Protocol for Internet of Things (IoT)
## 2 Characteristics of SDN Architectures:  
The exiting SDN-Based WSNs architectures are divided into the following categories:  
* Distributed SDN-based WSNs Architecture: Although SDN-based WSNs are developed to achieve the centralized control but here, the distributed SDN-based WSNs architectures means the network architectures that contain a single controller and complete absence of distributed controllers. The distributed SDN-based WSNs architectures provide multiple SDN controllers to be deployed within WSNs and perform over central networking behaviour by shifting the control plane functionality to SDN controllers. These multiple controllers react as clusters leading nodes and take responsibilities of SDN-based CHs. These SDN controllers are rich in computational and energy resources and offer relief to normal sensor nodes by skipping complex computations [10; 11]. Overall combinations of these multiple SDN-controllers maintains a logical integrated network global view and implement the network reconfigurations to execute the sophisticated traffic engineering for WSNs. At the earlier stages of research on SDN-based WSNs architectures, only a few solutions were available, which allows the distributed deployment of multiple SDN controllers otherwise, the majority of existing solutions offers only a single  
Figure 1: The General Architecture of Software Defined Network (SDN) [9]. centralized SDN controller to maintain the central control. The design and implementation of communications protocols for complex distributed clustering SDN-based WSNs model is still an open challenge. Some of the state-of-the-art distributed SDN-based WSNs architectures are SDWN, Sensor OpenFlow and Mininet-WiFi [12; 13; 14]. * Centralized SDN-based WSNs Architecture: This type of network model depicts an SDN-based WSN architecture enabling central network configurations with the help of the SDN controller, which maintains the overall record of the whole network that results in the efficiency of network management. These centralized SDN-based solutions manage dictations over sensor nodes with multiple sensing units to prioritized the application-sensing and active modes' participation according to their residual energy resources. QoS and security enhancement are other critical features for SDN-based WSNs architectures achieved at the control plane while enabling SDN integration at all levels of the design. Smart and CRLB are examples of centralized SDN-based WSNs Architecture [15]. * Hybrid SDN-based WSNs Architecture: The hybrid SDN-based WSNs Architecture is designed to achieve flexibility and cost-effectiveness at the same time. These architectures consist of few controllers deployed within the network for long distant nodes while these networks can manage networking responsibilities, even the failure of distributed controllers. This architecture can behave fully centralized at the time to carry on SDN-based WSNs networking architecture. Some of the hybrid management systems include Sensor Network Management System (SNMS) and Wireless Sensor Network Management System (WSNMS) [16]. * Mobility Management SDN-based WSNs Architecture: The new application spectrum of conventional WSNs contains many networking solutions for mobility-based networks. These networks are facing more connectivity and central management control as compared to static WSNs. In the management of sensor nodes mobility, while maintaining a global view of reasonable network topology, the SDN-controller needs to support node mobility, which consists of unreliable wireless links and continuous reconfigurations of routing traffic engineering [17]. The sensor nodes in the SDN-based WSNs are capable of mobility that helps in packets transmission and task execution, which makes it obligatory to monitor and manage the particular movement of sensor nodes in the entire network. Mobility management of SDN-based WSNs architectures also needs to deal with high mobility nodes entering and leaving the networks.