Software-defined networking (SDN) decouples data and control plane, i.e., forwarding elements are remotely configured by centralized controllers instead through distributed control protocols. Wireless sensor networks (WSNs) have mostly been controlled in a distributed way, but its configuration challenges are complex and can be theoretically better solved with network-wide knowledge – the solution just needs to be configured on the distributed sensor nodes. This calls for SDN in WSNs and so that software-defined WSNs (SD-WSNs) have been proposed. In this survey, we explain basics of WSN and SDN, describe fundamentals of SD-WSNs and how SDN can improve the operation of WSN. Furthermore, we outline the open challenges that need to be investigated in more detail and discuss lessons learned during the preparation this survey.

Introduction

Software-defined networking (SDN) is an emerging networking architecture that gives the opportunity to overcome the current limitations of the network infrastructure [1, 2]. It decouples the network’s control plane and data plane. That means an intelligent controller configures forwarding elements with finegrained forwarding rules for data packets of different flows. The controller obtains sufficient information to fulfill that task so that distributed control protocols among forwarding elements are no longer needed. Furthermore, the controller may interact with applications to optimize the network. A wireless sensor network (WSN) consists of sensor nodes with communication, computing, and sensing capabilities. Sensor nodes mostly have batteries that limit their lifetimes. They are often randomly deployed over a larger area for monitoring purposes. Therefore, communication and sensing ranges are controlled to ensure communication with other nodes and to cover the entire area with the desired application. In the past, self-organized management with distributed control has been the intuitive approach for running WSNs. Thereby, energy saving was always an important goal to extend the lifetime of the network. Software-defined WSNs (SD-WSNs) have been recently proposed with the objective that WSNs can particularly profit from SDN. The operation of sensor nodes should be simplified to save energy and to manage the WSN through a powerful controller which has a view on the entire network rather by distributed control protocols. The controller is able to manage the network and applications while saving energy and to deliberately balance the residual energy of the network to maximize its lifetime. A significant difference to SDN in a datacenter is that the controller in a WSN communicates with distant sensor nodes over possibly multiple hops rather than over a dedicated control network. In this survey, we give an introduction to SDN in wireline networks and to non-SDN WSNs, we describe the architecture of SD-WSNs, illustrate their operation, point out advances and research challenges. We also compare SDN-based and non SDN-based WSNs. General requirements for deploying SDN in WSNs are surveyed in [3, 4]. Ndiaye et al. [4] focused on how WSN management can be performed by SDN. Kobo et al. [3] concentrated on the architectural view of SDN in WSNs. The authors of [5, 6] provided a survey on the application of SDN in wireless networks. However, non of these papers surveyed what can be controlled by SDN in WSNs and how applying SDN in WSNs is different from wireline networks This work is structured as follows. Sec.2 reviews the basic concepts of WSNs. Sec. 3 describes the basic concepts of SDN. The basics for SD-WSN are described in Sec. 4. Advances in WSNs through SDN are reviewed in Sec. 5. Sec. 6 states challenges in SD-WSN. Lessons learned are reviewed in Sec. 7 and Sec. 8 concludes this survey.