A communication system consisting of network nodes for operating industrial machines and a method for controlling a communication system. The invention relates to a communication system consisting of network nodes (1, 2, 3, 4, 5) belonging to a control and/or drive network (11, 12) wherein control and/or regulating signals are exchanged between network nodes via a closed ring-shaped signal line (6,7) in order to operate industrial machines. A network node (2) exchanges signals with at least one other network node (1, 3) via a bi-directional signal path. At least one network node (2) comprises a switching unit (8) which can be connected to two other network nodes via two bi-directional signal paths (10). The communication system can by configured to form various networks (11,12) by means of a corresponding switching position of the switching units of the network nodes, said networks (11, 12) being provided with separate signal lines (6,7).