## 2 Related Work
### SDN Based WSN Routing Approaches  
A common issue in previous research is that simple models and concepts have been put forward with simulations that are simple or not even realized. There is no systematic realization or explanation as detailed on algorithms of a controller for SDN routing is relatively vague [30]. Recently, many prototypes are practically implemented because of wireless networks as explained in [31]. SDWSNs have enabled the programmable control and virtualization of equipment in networks through the decoupling of data and the control plane [32]. In a logically centralized controller, the control intelligence is implemented after taking it out of the data plane devices that use the standard interfaces to interact with data plane devices. The software programs are performed by network operators to optimize network resource usage and automatically manage data plane devices. This architecture is used to ensure up-to-date control schemes for the future management of SDWSNs [33]. In [34], a SDN based published/subscriber system (SDNPS) is designed for a load balancing issue that helps to reduce end-to-end latency. A framework for a SDWSN was proposed by [PERSON] in [35] where the forwarding is executed by sensor node only. The energy consumption is reduced through the implementation of a controller as a base station in this framework. The sensor nodes in a SDWSN reconfigure their properties and functionalities dynamically through the loading of multiple programs on demand regarding real-time sensing requests. The issues mentioned above are tackled by emerging SDWSNs that act as a compelling solution. A variety of sensing nodes are undertaken by considering the activated programs because such nodes are equipped with different types of sensors. The energy consumption of transmitters is minimized by designing an efficient SDWSN as proposed in [36]. In this article, the energy transmitters are used to transmit energy to sensor nodes. For an optimal replacement of energy transmitters, a trade-off is made between maximum energy charged and fair energy distribution. It may not result in energy efficient routing protocols. An energy-efficient routing algorithm for SDWSN has been proposed in [37] by dynamically assigning and selecting the different types of tasks and control nodes respectively. The particle swarm optimization method was utilized to select the selection of some control nodes in SDWSN. The nodes assign the tasks on the base of their residual energy. Thus, there is a difficulty in determining the precise number of required control nodes as well the number of nodes under one particular control node. [PERSON] [38] proposed a framework called Improved SDWSN for a SDN-based network to enhance network reliability. The proposed framework helps to resolve the network management of WSN in the Industrial Internet of Things (IIoT) and improves network reliability. They also claimed to address node failure issues, especially related to energy consumption, but they do not use any energy aware algorithm to control the energy consumption of nodes. In [14], an energy efficient routing algorithm is proposed for a SDN-based WSN network. The authors assume that the controller knows the initial data of all network nodes and the controller establishes a flow table based on distance. They assume that the controller can access each node by hop. After establishing the flow table, the controller sends to each node directly, which is impractical in a large network. An SD-EAR energy aware routing algorithm [39] is designed to reduce the flooding and broadcasting issue of WSN network. The authors divide the network into a different zone and each zone is handled by the SDN controller, but the selection of the zone head is vague. A routing algorithm is proposed for a SDN network in [40]. The controller collects the node information through multihop communication. A controller generates the flow table based on hop count and energy.