## 1 Introduction
### Contributions of the Present Paper  
In the present paper, software defined energy aware routing (SD-EAR) and SDN divide the completely distributed structure of a sensor network into clusters or zones where each controller is in charge of one zone. The controllers are aware of the topologies of the associated zone, and also keep track of peripheral nodes. Peripheral nodes in a zone are nodes that have some portion of radio circle outside the zone. SD-EAR particularly aims at proposing an energy-efficient routing protocol along with a sleeping strategy to promote energy preservation in the network. Its novelties are as follows:  
Figure 1: Structure of a software defined network (SDN).  
1. Normally in a WSN, whenever a source needs to establish a route to a sink, it mostly applies blind flooding [27; 33; 38; 39] or gossiping [38; 39]. In flooding, each router retransmits the route-request (RREQ) generated by a source to all of its neighbors, whereas the gossiping technique enables the routers to select a subset of neighbors to rebroadcast the route-request packet. Both of these suffer from redundancies that unnecessarily eat up energies in routers. In SD-EAR, since the SDN controller of each zone is aware of the zonal topology, it is capable of finding all of the possible paths between a given source and a destination through the depth-first traversal technique if both the source and destination are within the same zone. Among all of these paths, one optimal path is selected by a fuzzy controller named FUZZ-OPT-ROUTE, which is embedded within each SDN controller. If the destination is not within same zone as the source, then the SDN controller of the source zone instructs the source to send a request for discovering the route to the destination or to all of the peripheral nodes in the zone, through the optimum paths selected by the FUZZ-OPT-ROUTE embedded in the SDN controller of the source. Routers perform similar to the source. SD-EAR gives special weight to the presence of alternative nodes in live communication paths. As a result, the broadcasting of a route-request is eliminated irrespective of intra-zone or inter-zone communication, resulting in huge message saving.
2. An alternative node \(n_{v}\) of a node \(n_{u}\) in a live communication route R, should be such that energy efficiency as well as the lifetime of R should not decrease after replacing \(n_{u}\) with \(n_{v}\). This provides a facility to improve the residual energy and lifetime of a route. It may happen that after replacing the least energy node with an alternative, the new minimum energy becomes higher than the previous minimum. In that case, the new minimum will depend upon other nodes in the route except the one with the previous minimum energy. Assuming all of these nodes to be equally likely, we consider both the minimum and average residual energy to compute the residual energy effect of a route. Please note that the alternatives for a node are searched if its battery is almost exhausted.
3. A sleeping strategy is also proposed where nodes that request to go to sleep are granted sleep by the SDN controller of the zone, provided the situation demands so. All of these help to greatly reduce the energy consumption in the network, and increase network throughput. Also, the provision of forceful sleep is introduced in which if all of the neighbors of a node are suffering from exhausted battery, then \(n_{u}\) is directed by the SDN controller to go to sleep. All of these result in great energy saving by avoiding the broadcasting of route-requests during route discovery as well as rediscovery.