# Software Defined Networks in Wireless Sensor Architectures
## 1 Introduction
The SDN concept can be applied to Fog Computing, at a more abstract level, allowing centralized control over computation, storage and network resources. [PERSON] et al. [9] propose extending the Fog Computing with the concept of SDN in the application layer, resulting in \"Software Defined Fog\" (SDFog). This approach is able to execute functions in the data plane dealing with the resources on fog nodes. Other emerging technology that enables IT and cloud Computing capabilities at the Radio Access Network (RAN) edge in a close proximity to the end users is the Multi-Access Edge Computing (MEC) [10]. IT provides an ultra-low latency environment and realtime access to radio and network analytics. Then, the use of MEC offers contextual information and specific content, proximity and location awareness, providing a customized mobile broadband experience. Moreover, it collects information from customers in terms of content, location and interests to introduce new services or simply use such information for commercial reasons. MEC is a key enabler for supporting Machine-to-Machine (M2M) and IoT services due to the ubiquitous coverage of cellular networks. For example, providing network scalability and reducing IoT data and signalling, ensuring a fast response to user requests or enabling new services. From the business point of view, MEC enables a secure cloud platform architecture and Application Programming Interfaces (APIs) to allow third players to share and use it dynamically, easily installing and modifying new services. As mentioned before, MEC relies on cloud computing and virtualization technologies including Virtual Machines (VMs) and containers. Nevertheless, a complete cellular system that offers MEC services is supported by Network Function Virtualization (NFV) and SDN, and network slicing attributes that allow flexibility and multi-tenancy support. Then, SDN can complement the use of MEC offering programmability capabilities to authorized tenants at the same time, which allows a flexible and efficient service management. We start with the Wireless Sensor Networks (WSN) [11], which is a technology that has become very important in recent years because of the quick and cheap development of smart sensors. This fact is possible with the innovation in the production chains of Micro-Electro-Mechanical Systems (MEMS). Smart sensors, which are developed following this technology, are smaller, cheaper and limited in terms of processing and computing resources compared to traditional sensors. The main property of these sensors is the low power consumption among others, as information collection from the environment where they are deployed. A smart sensor is based on a processor, a memory, a power supply, a radio and an actuator, which is an electro-mechanical device that is responsible for controlling different components in a system. A WSN topology is comprised from few to thousand sensor nodes that run together in order to gather data from an area or environment. Two types of WSN are defined in [12]: the structured and unstructured. The difference between them is the quantity of sensors that the topology is composed of: the unstructured WSN contains a huge quantity of sensors, while the structured WSN are composed of a small quantity. The main applicability of WSN is categorized in two fields: on one hand, tracking applications and, on the other hand, monitoring applications. The first one includes tracking entities such as animals, humans, vehicles and other types of objects. Monitoring applications include monitoring environmental scenarios, both indoors and outdoors. Next, Software-Defined Sensor Networks (SDSNs) [13] are the result of taking the leading characteristics of WSN and SDN technologies. SDSNs are based on smart nodes as WSN but including the capability of being programmed on demand (as SDN) by loading, in each case, the application that the SDSN will be used for. Therefore, SDSNs are versatile in terms of changing their purposes into several applications [14].