Primary: The main distribution panel, supplies power from the transformer. After stepping down the voltage through the transformer's low-voltage side (0. 4kV), power distribution is achieved through three levels of distribution boxes: the main distribution board, secondary distribution boards, and tertiary distribution boards. Main Distribution Board Serves as the primary. Access layer: It consists of all the LANs which are connected to the switches. This 2-tier architecture is not ideal because it has a single-point failure when a multi-layer switch fails. Three-Tier Hierarchical Architecture. As the name implies, the. The multi-tier model relies on a multi-layer network architecture consisting of core, aggregation, and access layers, as shown in Figure 2-1.