The ability to perform traffic differentiation is a promising feature of the current Medium Access Control (MAC) in Wireless Local Area Networks (WLANs). The Enhanced Distributed Channel Access (EDCA) protocol for WLANs proposes up to four Access Categories (AC) that can be mapped to different traffic priorities. High priority ACs are allowed to transmit more often than low priority ACs, providing a way of prioritising delay sensitive traffic like voice calls or video streaming. Further, EDCA also considers the intricacies related to the management of multiple queues, virtual collisions and traffic differentiation. Nevertheless, EDCA falls short in efficiency when performing in dense WLAN scenarios. Its collision-prone contention mechanism degrades the overall throughput to the point of starving low priority ACs, and produce priority inversions at high number of contenders. Carrier Sense Multiple Access with Enhanced Collision Avoidance (CSMA ECA) is a compatible MAC protocol for WLANs which is also capable of providing traffic differentiation. Contrary to EDCA, CSMA ECA uses a contention mechanism with a deterministic backoff technique which is capable of constructing collision-free schedules for many nodes with multiple active ACs, extending the network capacity without starving low priority ACs, as experienced in EDCA. This work analyses traffic differentiation with CSMA ECA by describing the mechanisms used to construct collision-free schedules with multiple queues. Additionally, evaluates the performance under different traffic conditions and a growing number of contenders. (arXiv's abstract field is not large enough for the paper's abstract, please download the paper for the complete abstract.)
Great efforts have been directed towards parameter adjustments in EDCA, mostly to ensure QoS for high priority ACs while maintaining low delay and losses @cite_17 @cite_16 @cite_18 . For example, by dynamically adjusting the AIFS for each AC it is possible to maintain traffic differentiation while avoiding the starvation of low priority ACs. This is especially relevant in WLANs where all ACs are required to have effective throughput, like in @cite_16 . Further, by randomising the AIFS values it is possible to increase the channel utilisation in EDCA @cite_18 .
@cite_18 @cite_16 @cite_17
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In this paper, we propose an adaptive tuning algorithm for wireless medical applications to in order to meet medical-grade quality of service (QoS). The conventional IEEE 802.11e protocol is designed to satisfy a certain level of QoS, which is insufficient for medical-grade QoS. In the proposed algorithm, we adaptively tune the AIFS value of the IEEE 802.11e protocol for enhancing the overall network performance while providing the required medical-grade QoS. In our scenario, as representative applications, we consider medical alarms, ECG transmission, and TCP file transfer. We categorize these three applications according to their urgency. Then, we compare the performance of the proposed scheme with the conventional IEEE 802.11e protocol. Supporting real-time and interactive traffic in addition to traditional data traffic with a best-effort nature represents a constantly rising need in any kind of telecommunications environment. The IEEE 802.11 based WLAN (Wireless Local Area Network) environment does not represent an exception. This is why at different protocol layers, and primarily at the MAC layer, many efforts are being put by both the research community and the standardization bodies to design effective mechanisms for user QoS (Quality of Service) differentiation. Although early results are coming into sight, such as, for example, the IEEE 802.11e standard release, still a thorough research activity is required. Aim of the present paper is to contribute to the cited research issue by proposing an improvement to the "static" traffic prioritisation mechanism foreseen by the IEEE 802.11e MAC (Medium Access Control) protocol. This latter shows a twofold drawback. First, there is no certainty that QoS requirements relevant to a given application are always fulfilled by the "statically" associated priority. Second, resource requests of the applications are not adapted to the (usually highly) variable traffic conditions of a distributed WLAN environment. The algorithm we propose is specifically tailored to "dynamically" assign 802.11e MAC priorities, depending on both application QoS requirements and observed network congestion conditions. It is carefully designed, implemented into a system simulation tool, and its highly effective behaviour assessed under variable traffic and system conditions.