A main unit of a director-class switch including a wire-based backplane located in a chassis, having a plurality of slots configured to receive switch boards. The wire-based backplane includes a plurality of harnesses each including first and second cartridges, a plurality of interface port units mounted on each of the first and second cartridges and cables connecting each of the interface port units of the first cartridge to each of the interface port units of the second cartridge. The harnesses are mounted in the chassis such that the interface port units face ends of the slots in a manner configured to mate with corresponding connectors of switch boards inserted into the slots. A plurality of interface port units are mounted in each slot. Each cartridge includes interface port units which are located in a plurality of different slots.