Title: The SRAWAN MAC Protocol to support Real-Time Services in Long Distance 802.11 Networks
Abstract:
The wireless communications market has grown rapidly since the introduction of 802.11 wireless local area networking (WLAN) standards in the 1990s. The 802.11 MAC was designed to be used in an indoor environment like small offices, home environment. It is based on CSMA/CA (carrier sense multiple access with collision avoidance) where flows cannot be guaranteed quality of service. The 802.11e provides QoS mechanisms to 802.11 WLANs to support bandwidth-sensitive applications such as voice and video. Despite, it was not tested well in long distance links. The challenge of using 802.11 hardware beyond its intended use, has shown in Digital Gangetic Plains project by forming long distance links using high gain antennas which spread the signal for tens of kilometers. Due to contention based channel access, huge round trip time in long distance links and hidden node problem, the 802.11 MAC protocol does not work well in long distance networks. In this thesis work, we try to overcome the above all mentioned problems by coming up with new MAC protocol to operate on point-to-multipoint long distance links.
We have designed, implemented and evaluated the new MAC protocol SRAWAN (Sectorized Rural Area Wireless Access Network) that gives better performance and QoS compared to the 802.11 MAC. The significant challenge here is while preserving the cost benefits of off the shelf 802.11 hardware, we need to implement new MAC protocol on top of the existing Atheros hardware. This we have done by taking the advantage of flexibilities provided by Atheros Madwifi driver of AR5212 chipsets. Outdoor experimental results shown that SRAWAN outperformed CSMA/CA by more than 40% for point-to-multipoint long distance links. We have implemented a fair scheduling among different flows by using the WFQ (Weighted Fair Queuing) scheduling discipline on top of the SRAWAN MAC protocol. This report also presents the performance evaluation of a WFQ scheduling scheme on SRAWAN MAC and shows that it provides guaranteed services. Experimental results shown better throughput results and also given quality of service for guaranteed bandwidth services when compared to very inefficient round-robin (RR) scheduling discipline or normal 802.11. WFQ scheduling algorithm also provides many more VoIP sessions (Ex: For a GSM6.10 codec, 802.11b provides 40 conversations) when compared with normal 802.11 MAC(11 conversations for same settings).