With the increasing availability of flexible wireless 802.11 devices, the potential exists for users to selfishly manipulate their channel access parameters and gain a performance advantage. Such practices can have a severe negative impact on compliant stations. To enable access points to counteract these selfish behaviours and preserve fairness in wireless networks, in this paper we propose a policing mechanism that drives misbehaving users into compliant operation without requiring any cooperation from clients. This approach is demonstrably effective against a broad class of misbehaviours, soundly-based, i.e. provably hard to circumvent and amenable to practical implementation on existing commodity hardware.
The underlying principle behind our approach is to control the attempt rate of misbehaving clients by censoring the generation of MAC layer acknowledgements (ACKs). ACK skipping has been suggested as a means to allocate bandwidth for traffic prioritisation in a network of well-behaved stations @cite_10 @cite_36 @cite_33 , but to the best of our knowledge has not been implemented to date with real devices as this fundamental operation is handled at the firmware level.
@cite_36 @cite_10 @cite_33
2163079953 1590305083 2126820294
The EDCA access mechanism of the upcoming 802.11e standard supports legacy DCF stations, but with substantially degraded performance. The reason being that DCF stations typically compete for access with overly small contention windows (CWs). In this letter we propose a new technique that, implemented at the access points (AP's), mitigates the impact of legacy stations on EDCA. The key idea of the technique is that, upon receiving a frame from a legacy station, the AP skips the ACK frame reply with a certain probability. When missing the ACK, the legacy station increases its CW and thus our technique allows us to have some control over the CW's of the legacy stations. We show by means of an example that this technique improves the overall performance of the WLAN. In recent years the idea of access network has changed radically, and the diffusion of wireless technologies, and especially IEEE 802.11 compliant devices, has made wireless connections increasing popular. Despite the great success of the IEEE 802.11 standard, several problems concerning security, power consumption and quality of service of wireless LANs remain partially unsolved. The QoS issue is especially relevant for multimedia communications, generally needing performance guarantees from the network infrastructure to fulfill application requirements. In this paper we analyze the behavior of the Frame Dropping (FD) mechanism, a QoS mechanism for multimedia communications using simulations, and compare it with that of another well assessed mechanism: Distributed Fair Scheduling (DFS). Simulation results show that, though DFS achieve a better channel utilization, FD behavior is comparable with that of DFS under all the main performance indices, and it exhibits effective traffic differentiation capabilities. Although the EDCA access mechanism of the 802.11e standard supports legacy DCF stations, the presence of DCF stations in the WLAN jeopardizes the provisioning of the service guarantees committed to the EDCA stations. The reason is that DCF stations compete with Contention Windows (CWs) that are predefined and cannot be modified, and as a result, the impact of the DCF stations on the service received by the EDCA stations cannot be controlled. In this paper, we address the problem of providing throughput guarantees to EDCA stations in a WLAN in which EDCA and DCF stations coexist. To this aim, we propose a technique that, implemented at the Access Point (AP), mitigates the impact of DCF stations on EDCA by skipping with a certain probability the Ack reply to a frame from a DCF station. When missing the Ack, the DCF station increases its CW, and thus, our technique allows us to have some control over the CWs of the legacy DCF stations. In our approach, the probability of skipping an Ack frame is dynamically adjusted by means of an adaptive algorithm. This algorithm is based on a widely used controller from classical control theory, namely a Proportional Controller. In order to find an adequate configuration of the controller, we conduct a control-theoretic analysis of the system. Simulation results show that the proposed approach is effective in providing throughput guarantees to EDCA stations in presence of DCF stations.