# Software Defined Networks in Wireless Sensor Architectures
## 1 Introduction  
Communication technologies have experienced a large evolution since the 1980s to become what are currently Software Defined Networks (SDNs). Nevertheless, there are some concepts that shape the base of this technology. On one hand, these advances are: central control, active networks and network virtualization. On the other hand, the great progress that has been achieved is in the control-data plane separation. Centralized control goes back to the beginning of the 1980s, and it focused on the transport of information over the same channel. This technology offered several advantages in terms of simplicity; however, it was quite fragile, insecure and vulnerable. Active networks [1; 2] appeared during the 1990s. These kinds of networks allow for performing custom assignments in the data packets that travel around the switches. The most popular example of active networks is middleboxes (e.g., firewalls), which are mainly in charge of packet forwarding, proxy functions and application services. Finally, network virtualization [3; 4] plays an important role in the management of setting up these types of networks. Networks virtualization has similarities to computers' virtualization, where different devices can use and share hardware resources to different Operating Systems (OS) in a host. The aim of network virtualization is to isolate multiple logicalnetworks, each of them with addressing and forwarding mechanisms, sharing the same physical infrastructure. Clear instances of network virtualization are Virtual Local Area Networks (VLANs). SDN addresses the shortcoming of the previous technologies by separating the data plane and the control plane. Particularly, switching elements in SDN involve data plane functionality (forwarding) since they are controlled and configured by a centralized controller. Then, controllers serve as central points to gather network view and network information to configure instructions and decisions on how the network resources should behave. Currently, SDN is being investigated in the field of wired provider networks, data centers and research networks among others. Deployment of large SDN testbeds as the one performed by the Ofelia consortium [5] and the Open Networking Foundation (ONF) [6] have increased the interest in this technology. Nevertheless, such deployments are applying to other type of networks in order to solve existing challenges. This paper provides a survey and categorization of some existing wireless networks and the application of SDN to them. For each technology, we overview, classify, contrast and summarize possible SDN solutions to solve challenges as resource allocation and efficient management. New emerging technologies as Fog computing [7; 8], alternatively known as fog networking or \"fogging\", is a term originally introduced by Cisco (San Francisco, CA, United States of America) that follows the SDN principles. Similar to SDN, Fog computing consists of a control and a data plane. The data plane enables computing services located in the edge of the network. Then, Fog Computing provides compute, storage and network services and networking services between end devices and traditional Cloud Computing Data Centers, making reference to the growing difficulties in accessing information. The main feature of Fog Computing is the accentuation on the end-users' proximity and client objectives, dense geographical distribution and local resource pooling to achieve better Quality of Service (QoS). Then, Fog Computing uses multiple cloud platforms introducing a logical architecture from the point of view of processing, considering a federation of cloud platforms with the objective to specify fog-to-fog and fog-to-cloud interfaces. Moreover, Fog networking supports the Internet of Things (IoT) concept overall in the connection between the world population with their devices, taking advantage of its main feature previously described. Examples of this connection includes smartphones, wearable devices and the vehicles' connectivity among others.