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We propose a novel medium access control (MAC) algorithm using pure directional transmission and reception for mobile wireless ad hoc networks with directional antennas. Recent research results show that there are significant gains in throughput to be realized with directional transmission and reception (compared with omnidirectional) (Su Yi et al., MobiHoc, 2003), however; no specific reservation/scheduling algorithms are presented. To the best of our knowledge, all previous work assumed omnidirectional reception at certain stages of the algorithms. However, the omni-receive requirement makes the protocol vulnerable to jamming. We assume no omni-antennas or omni-directional reception capability at all. The proposed algorithm exploits the beamforming capabilities of smart antennas to tailor resource access according to the services desired for individual traffic flows while limiting interference, probability of detection and jamming in the network. Specifically, we present a TDMA-based MAC algorithm for load-dependent negotiation of slot reservations. Our new protocol offers four significant advantages: (1) it assumes directional transmission/reception; (2) it is distributed, that is, it relies on local information only; (3) it allocates slots to different links dynamically based on demand; (4) power control is easily carried out during neighbor discovery and reservation, as well as the data transmission period, with very little overhead. We believe that it is the first work on pure directional transmission and reception in ad hoc networks. The algorithm can be used in many commercial and military applications.