# A Software-Defined Networking Framework to Provide Dynamic QoS Management in IEEE 802.11 Networks
## 6 Conclusions  
Nowadays, IEEE 802.11 technology is used in a wide variety of scenarios, such as mobile, vehicular or sensor networks. In all of them, the transmission of real-time and multimedia traffic is very common, and the corresponding applications require that the network supports some minimum QoS requirements. One of the methods to provide it is by giving more channel access opportunities to nodes involved in such sessions. This is the background idea of EDCA, the contention-based medium access mechanism of IEEE 802.11e, that provides long-term QoS.  
However, in some situations it is possible that some multimedia traffic sessions require additional QoS guarantees during short-term intervals. For these situations, in this work we have proposed DEDCA. In DEDCA, stations are classified in three different Terminal Categories (TC): _normal stations_, _requesting stations_ and _giving stations_. By default, all the terminals are classified as _normal stations_, using default \(CW_{min}\) values. Stations that require additional QoS guarantees are called _requesting stations_, and they will modify their \(CW_{min}\) values to increment their channel access opportunities, at the expense of _giving stations_ that they will modify their \(CW_{min}\) value to decrement their channel access opportunities. With the goal of determining how to modify the \(CW_{min}\) value of the _giving_ and _requesting stations_, a mathematical model has been developed. This model is able to determine the number _requesting stations_ and _giving stations_ that are required to manage a certain QoS requirement.  
The previous processes related to the DEDCA mechanism need to be implemented in a centralized way, in order to be able to identify the giving and requesting stations in the network. Controllers of Software-Defined Networks have a centralized control over the network, and they seem to be the ideal elements to implement this mechanism. In this paper, that is the reason we have proposed a SDN framework for IEEE 802.11 networks that implements the proposed DEDCA mechanism. In this framework, the SDN controller is attached to the IEEE 802.11 access points. The communication between the SDN controller and the access points is based on OpenFlow protocol and the flow tables of access points have an appropriate flow entry in order to forward the UDP alarm messages generated by the requesting stations to the SDN controller. On the other hand, the SDN controller will generated _packet_out_ messages with the new \(CW_{min}\) values for _giving_ and _requesting stations_. These messages will be encapsulated in UDP segments by the access points and they will be forwarded to the corresponding stations.  
The proposed SDN framework has been evaluated by simulation using the Estinet network simulator. We have considered an outdoor parking lot, where a surveillance system is installed. The simulations results show that after modifying their \(CW_{min}\) value adequately, the requesting cameras are able to reach the demanding bandwidth. On the contrary, as it was expected, the giving cameras suffer a decrement of the throughput due to the increment of their \(CW_{min}\) value. The remaining cameras are considered normal stations. Consequently, due to the fact that their CWmin value is not modified, their performance is maintained.  
**Author Contributions:** Formal analysis, [PERSON]; Investigation, [PERSON], [PERSON] and [PERSON]; Methodology, [PERSON]; Project administration, [PERSON]; Software, [PERSON] and [PERSON]; Validation, [PERSON]; Writing--original draft, [PERSON], [PERSON] and [PERSON].  
**Funding:** This work has been supported by the AEI/FEDER, UE Project Grants TEC2016-76465-C2-1-R (AIM).  
**Conflicts of Interest:** The authors declare no conflict of interest.