# A Software-Defined Networking Framework to Provide Dynamic QoS Management in IEEE 802.11 Networks
## 5 Related Works  
Much of the research in wireless SDN has focused in IEEE 802.11 networks. An important feature of SDN-enabled WLANs is virtualization. The ability to slice the network, based on users, subnets or traffic, allows many benefits [10]. Another research interest in this area is related to mobility management. For example, Odin [11] is an SDN framework that proposes to simplify the implementation of authentication, authorization and accounting (AAA), by moving to a centralized architecture, which eases to implement mobility managers and to mitigate the hidden terminal problems. On the other hand, there have been multiple research efforts in multi-hop networks. Figure 9: Throughput using the proposed DEDCA mechanism. CAM11, CAM9 and CAM12 switch to high-demanding transmission mode after CAM11 launches an ALARM. Ref. [12] proposed an architecture for wireless mesh networks with traffic management functionality. In this architecture, the control plane is composed by four modules: global overview manager, routing path computation, traffic scheduling, and lastly spectrum allocation to configure radio resources. In addition to this, routers are also equipped with a monitor module to send neighbor connectivity information to the global overview manager at the controller and a radio frequency tuning module for assigning the radio frequency to transmit the data and control traffic. Regarding QoS management in SDN networks, the rule placement and caching in SDN switches have been studied in [13; 14]. Given a set of sessions with certain QoS requirements, instead of installing all the forwarding rules and QoS requirement rules in every switch, the authors of [13] divide a session into several independent sub-sessions with different subsets of QoS requirement rules, which are scattered across multiple switches, to reduce the TCAM usage. In [14], the authors studied the rule caching problem in SDN in order to minimize the amount of TCAM and remote controller processing cost. Finally, in [15] authors studied a problem in which the load balancing of the control plane traffic and the cost of stablishing the control channel are jointly considered when selecting the protection paths for control channels. Simulation results show that the algorithm has high efficiency in resource utilization. The main contribution of this work refers to the media access control mechanism of 802.11 networks. An analytical model of the IEEE 802.11 CSMA/CA mechanism was presented in [16; 17]. Based on a complex bi-dimensional Markov Chain, this model has been widely used in the literature as a theoretical corpus to calculate different set of parameters related to CSMA/CA performance evaluation. The model has also been extended to include priorities [18], high traffic conditions [19] and loss channels [20]. With regard to the modification of the \(CW_{min}\) value, different solutions have been proposed. These works differ in the parameters that are used to calculate the new value, where the modification is calculated (in the access point or the stations) or when the \(CW_{min}\) value is updated. In [21], the \(CW_{min}\) value of each Access Category defined in IEEE 802.11e is adapted according to the traffic load and channel conditions. A higher value is set when the channel is estimated to be congested and a smaller value is set when the channel load is estimated to be low. The \(CW_{min}\) value is obtained at each station (that is, in a distributed way), considering the instantaneous collision rate (calculated using the number of collisions and the number of packets sent during a period of time) experimented during the update period. Therefore, there does not exist any coordination between the stations that increase and decrease their \(CW_{min}\) values. On the contrary, in our proposal, the mechanism that determines how to modify the \(CW_{min}\) value of the stations is implemented in a centralized way. Ref. [22] proposes a \(CW_{min}\) adaptation mechanism which takes place periodically at the access point.