High performance and scalable transport protocols for ad hoc wireless networks

Capacity of the wireless network is very limited. High performance transport protocols are highly desired to efficiently utilize the scarce wireless resources. The two most important metrics for evaluating transport layer protocols are efficiency and fairness. In this dissertation, we show that TCP (the most important transport protocol) experiences significant unfairness problems in the ad hoc wireless networks, even it performs well in the "last hop wireless networks such as the wireless LAN. We investigate this problem at different layers, namely the MAC layer, network layer and transport layer. Solutions at different layers are proposed to enhance TCP fairness.; Besides significant unfairness, TCP also experiences serious efficiency problems in a MANET. The existing schemes are mostly targeting at preventing TCP from wrongly reacting to packet losses caused by link failures (e.g. by freezing TCP states). In this dissertation, we improve TCP efficiency in another way as improving the path availability from end to end. Path availability can be greatly improved by utilizing multi-path routing. Multi-path routing maintains several paths to the same destination simultaneously. Thus, the probability that all paths from the source node to the destination node are broken is effectively reduced.; However, even we can carefully tune the transport protocols to efficiently utilize bandwidth, the "flat ad hoc network structure suffers scalability limits and cannot scale well. Recent research has demonstrated its performance bottleneck through both theoretical analysis and simulation experiments and testbed measurements. This is further exacerbated by heavy routing overhead of ad hoc routing protocols when the network size grows to be large. In this dissertation, we design methodologies to build a hierarchical ad hoc network using different types of radio capabilities at different hierarchical levels. Various schemes regarding topology management of the wireless backbone network and scalable routing strategies are proposed and evaluated.