Bringing QoS Over Wireless LAN into Focus

Introduction The reliable delivery of latency-sensitive voice and video streams mandates the use of transport mechanisms with very low packet loss, jitter, and delay. IP PBX systems already incorporate the necessary mechanisms to deliver these services over local area networks (LANs) and wide area networks (WANs). The introduction of corporate Wi-Fi networks and wireless clients introduces a disruptive new variable in the transportation of latency-sensitive streams, one that must be properly managed and controlled to provide a satisfactory user experience. The underlying protocols for Quality-of-Service (QoS) over Wi-Fi were standardized several years ago, and enterprise wireless LANs now incorporate the relevant standards. However, adhering to the standards alone is not sufficient to build a superior multimedia-enabled wireless LAN. Rather, the network vendor needs to understand the fundamentals of how these protocols work, and then implement network configuration adjustments that dynamically and automatically tune the network to deliver end-to-end QoS. In this paper, we will briefly examine Wi-Fi QoS standards, and see the role these play in delivering end-to-end QoS. The paper will conclude with a detailed explanation of Aruba's self-tuning QoS mechanisms and how they ensure the reliable delivery of latency-sensitive voice and video streams. Most networks, including wireless LANs, operate far below capacity most of the time: there is little to no congestion and all traffic experiences good performance. QoS policies become important where offered traffic exceeds the capability of network resources, i.e., QoS provides predictable behavior for those exceptional occasions and points in the network where congestion is experienced. During overload conditions QoS mechanisms grant some traffic high priority, while making fewer resources available to lower-priority clients. For instance, increasing the number of voice users on the network may entail delaying or dropping data traffic. The wireless layer in a Wi-Fi network segment is shared across multiple clients, and the medium is bandwidth limited. The 20 or 40MHz of wireless spectrum occupied by a Wi-Fi RF channel is shared by an access point, its associated clients, and by all other access points and clients in the vicinity that are using the same channel. Out of all of the devices within radio range of each other, only one client or access point (AP) can transmit at any time on any channel. Even without QoS requirements, there must be a protocol to manage access to the wireless channel, and for this Wi-Fi uses carrier-sense, multiple-access with collision avoidance (CSMA/CA). Prior …