A control system and method thereof is provided. The control system includes switch devices that operate on supplied power, each switch device includes multiple switch-side ports and a communication processing unit for relaying data, input to any of the switch-side ports on a basis of destination information set for the data, a relay device that includes first ports coupled to corresponding switch-side ports of the switch devices and second ports selectively coupled to the first ports and that relays the data, input to any of the second ports, to any of the first ports, and a control device that controls the switch devices and the relay device, where the control device includes a port monitoring unit, a port-assignment control unit, and a power control unit.