Realizing software-defined wireless networks

Fueled by the increasing popularity of wireless enabled mobile end-devices and the advent of the Internet-of-Things networks, the demand for wireless access technology is growing rapidly. Today, many hotels and cafés—and sometimes also entire cities—already offer free WiFi services. Moreover, several mobile operators operate massive WiFi HotSpot, as well as HotSpot 2.0, deployments for traffic offloading, i.e., reducing the stress on their cellular networks. Specifically, WiFi (also known as IEEE 802.11 or WLAN) stands as an attractive inexpensive wireless alternative to cellular access technologies due to its simplistic MAC layer design, reduced costs due to its prevalence in consumer off-the-shelf devices, and operation in the unlicensed spectrum. Supporting the ever increasing number of WiFi capable devices across residential, public, and enterprise networks is non-trivial. In particular, the (last) wireless hop is often critical for network performance, as it can contribute a non-negligible delay and may constitute a bandwidth bottleneck. Thus, future WiFi architectures are challenged by optimized medium utilization, mobility support, and network management. The latter challenge is integrating wired, cellular, and WiFi networks seamlessly. While today point solutions exist for some of the WiFi-specific network challenges, commodity off-the-shelf hardware is outside the purview of such ossified, expensive, and vertically integrated solutions. Software-Defined Networking (SDN) is a new paradigm which introduces programmability to overcome network ossification. The key idea of SDN is to decouple the control and data plane to consolidate and outsource the control over a set of network devices to a logically centralized software controller. This allows the control plane to evolve independently of the data plane, enabling faster innovations. SDN is also an enabler for a second paradigm shift in the Internet: Network Functions Virtualization (NFV). Modern networks include many middleboxes to provide a wide range of network functions to improve performance as well as security. NFV aims to virtualize these network functions, and replace dedicated hardware appliances by software applications running on generic compute resources. The resulting orchestration flexibilities can be used for a faster and cheaper service deployment. SDN can be exploited to steer flows through the appropriate network functions. Decoupling data plane and control plane operations, à la Software-Defined Networking, can greatly simplify network management and improve the overall performance and utilization of wired networks. However, SDN and NFV have not yet received as much attention in the context of wireless networks, due to fundamental differences between wireless and wired networks. First and foremost, wireless networks feature many peculiarities and knobs that often do not exist in wired networks. For example, wireless networks need interfaces for flexible resource allocation, client mobility, client-based load balancing, and fine/grained traffic engineering is paramount. Furthermore, today’s trend towards Bring-Your-Own-Device (BYOD), implies that the network has to accommodate a more diverse set of user device types of different generations. Moreover, today’s home networks, unlike enterprise networks, typically suffer from a non-existing dedicated control channel, rendering fine-grained centralized control challenging. But, applying the SDN and NFV concepts of softwarization and virtualization to WiFi networks has the potential to render WiFi ready for its future. However, little is known today on how to introduce and benefit from the concepts in WiFi networks. In this thesis, we present a Software-Defined Wireless Network (SDWN) approach which combines SDN and NFV with wireless access technology. With our SDWN approach we