Recently there is an increasing interest in using directional antennas and multi-channel for Ad-hoc wireless networks. The two techniques can also be used for infrastructure local area networks. In this paper, we present the architecture and the MAC layer design for a Multi-Channel Multi-Sector Directional Antenna Wireless Local Area Network (MCMSDA WLAN). This paper has three key components. First, we describe the network architecture and propose a TDMA-based MAC layer. Second, we formulate the channel time allocation problem as an optimization problem and introduce a Lagrangian Relaxation based load-balancing algorithm as a solution. The simulation study shows that the algorithm obtains good sub-optimal solution very quickly. Finally, we propose two methods to accelerate the load-balancing process further.