Control systems like programmable logic controller or motion controller are connected to sensors, actuators and drives on the factory floor via different network topologies. The topology is the method of wiring Ethernet cable in between different equipment so that all field devices are logically connected to the control system.

The network topology methods described below also depends on the type of industrial Ethernet protocol used, because some protocols require a specific connection method and do not allow to use the other described methods. For example, EtherCAT is typically wired in a line topology.

Some protocols do allow a combination of multiple network topology. For example PROFINET and EtherNet/IP combine line and star topology to logically connect all devices to the control system.

• Line Topology: Build as a linear connection from the PLC to devices. Each device has two Ethernet ports to forward the received Ethernet frame.
  Figure 2-1 Line Topology
• Ring Topology: Adds redundancy to the line topology by connecting the last device back to the PLC. With some protocols the PLC sends out the Ethernet frame on both ports. In case there is a ring-break between two devices, for example the Ethernet cable was damaged and there in no link-up between the two devices, the PLC Ethernet frame still reaches all devices in the network with the required process data.
  Figure 2-2 Ring Topology
• Star Topology: Uses multi-port Ethernet switches to distribute Ethernet packets. This is often combined with line topology. Note that typically specific industrial Ethernet protocol specific Ethernet switches need to be used, such that, off-the-self Ethernet switches does not work with an industrial Ethernet protocol or at least performance degradation is expected.