An improved medium access control protocol for real-time applications in WLANs and its firmware development

The IEEE 802.11 Wireless Local Area Network (WLAN), commonly known as Wi-Fi, has emerged as a popular internet access technology and researchers are continuously working on improvement of the quality of service (QoS) in WLAN by proposing new and efficient schemes. Voice and video over Internet Protocol (VVoIP) applications are becoming very popular in Wi-Fi enabled portable/handheld devices because of recent technological advancements and lower service costs. Different from normal voice and video streaming, these applications demand symmetric throughput for the upstream and downstream. Existing Wi-Fi standards are optimised for generic internet applications and fail to provide symmetric throughput due to traffic bottleneck at access points. Performance analysis and benchmarking is an integral part of WLAN research, and in the majority of the cases, this is done through computer simulation using popular network simulators such as Network Simulator ff 2 (NS-2) or OPNET. While computer simulation is an excellent approach for saving time and money, results generated from computer simulations do not always match practical observations. This is why, for proper assessment of the merits of a proposed system in WLAN, a trial on a practical hardware platform is highly recommended and is often a requirement. In this thesis work, with a view to address the abovementioned challenges for facilitating VoIP and VVoIP services over Wi-Fi, two key contributions are made: i) formulating a suitable medium access control (MAC) protocol to address symmetric traffic scenario and ii) firmware development of this newly devised MAC protocol for real WLAN hardware. The proposed solution shows signifocant improvements over existing standards by supporting higher number of stations with strict QoS criteria. The proposed hardware platform is available off-the-shelf in the market and is a cost effective way of generating and evaluating performance results on a hardware system

Virtual PCF: Improving VoIP over WLAN performance with legacy clients

Abstract Voice over IP (VoIP) is one of the fastest growing applications on the Internet. Concurrently, 802.11 Wireless LANs (WLANs) have become ubiquitous in residential, enterprise, campus and public networks. Currently the majority of traffic on WLANs is data traffic but as more people use wireless networks as their primary access medium, a greater portion of traffic will be real-time traffic such as VoIP traffic. Unfortunately 802.11 networks are designed to handle delay-insensitive, bursty traffic and perform poorly for VoIP streams. Experimental and analytical results have shown that a single 802.11b access point operating at the maximum 11 Mbps rate can support only 5 to 10 VoIP connections simultaneously. Intuitively, an 11 Mbps link should support approximately 85 bi-directional 64Kbps (G.711) streams. The reason for this under-utilization lies primarily in the Distributed Coordination Function (DCF) used by 802.11 MAC layer. The problem can be addressed by using the optional Point Coordination Function (PCF). However PCF is not widely implemented in commodity hardware nor likely to be. There is a similar problem with the proposed 802.11e standard for quality of service. To solve these problems we propose Virtual PCF, a legacy-client compatible solution to increase the number of simultaneous VoIP calls. We implement Virtual PCF, a scheme which employs a variety of techniques to improve both uplink and downlink VoIP QoS. This alleviates delays and packet loss due to DCF contention and doubles the number of supported VoIP sessions