| The growing interest in using the IEEE 802.11 protocol in mesh topologies necessitates a rigorous understanding of its behavior and performance in such settings. This dissertation makes several contributions towards this end.; We first develop an analytical model that closely follows the basic access protocol, taking queueing and retransmissions into account. Using this model, we derive expressions for the probability of packet collision and maximum throughput in mesh topologies. The analysis, supported by simulations, shows that nodes may saturate at very small load due to cascading effects resulting from retransmissions. Thus, these results show that the basic access method of IEEE 802.11 may exhibit unstable behavior in mesh topologies.; Next, we study the optional Request-to-Send/Clear-to-Send (RTS/CTS) channel reservation mechanism. We show that this mechanism does not prevent a considerable number of DATA packet collisions in mesh topologies, even under idealized conditions, due to the presence of so-called masked nodes---nodes that cannot overhear control packets due to other on-going transmissions. We demonstrate the existence and impact of masked nodes by conducting real experiments on a small wireless testbed. These experiments, together with detailed queueing-theoretic analysis and extensive simulations, reveal that masked nodes can cause a packet collision probability of 10% to 15% and significantly affect throughput and delay performance.; Finally, we uncover a subtle problem with the RTS/CTS mechanism that may lead to inter-dependencies unnecessarily prohibiting nodes from transmitting over long periods of time. We refer to this problem as "false blocking." False blocking propagates in the network causing performance degradation, network-wide congestion, and even temporary deadlocks. We propose a backward-compatible solution to the false blocking problem, called RTS Validation. We analyze the RTS Validation using a continuous-time Markov chain methodology. The analysis, supported by simulations, shows that RTS Validation sharply reduces the probability of false blocking, stabilizes the network at high load, and increases the peak throughput by as much as 50%.; In summary, this dissertation establishes that local transmission strategies in wireless networks may lead to unexpected interactions, which can have significant impact on global network performance. These interactions must be taken into consideration in the design of future protocols for wireless networks. |
