This paper presents the detailed design and performance analysis of MACA-P, a RTS/CTS based MAC protocol, that enables simultaneous transmissions in wireless mesh networks. The IEEE 802.11 DCF MAC prohibits any parallel transmission in the neighborhood of either a sender or a receiver (of an ongoing transmission). MACA-P is a set of enhancements to the 802.11 MAC that allows parallel transmissions in situations when two neighboring nodes are either both receivers or transmitters, but a receiver and a transmitter are not neighbors. The performance of MACA-P in terms of system throughput is obtained through a simulation of the protocol using ns and is compared with the 802.11 RTS/CTS MAC. Experiments with the base MACA-P protocol reveal the need for certain enhancements, especially to avoid the drawbacks associated with attempts at parallel transmissions in scenarios where such parallelism is not feasible. Studies with the enhanced MACA-P protocol also demonstrate how significant performance gains in wireless mesh network performance may be realized if the radio transceiver behavior is modified in tandem with the MAC protocol.