The communications network termed "terminal bus" connects your clients to the servers and the servers with one another. You can set up such networks using standard components from SIMATIC NET such as switches, onboard interface modules, network cards, communication modules, cables etc. A ring design avoids communication failures if, for example, the line is damaged or interrupted at a particular point. If you want to increase the availability even further, the terminal bus can also be divided redundantly between two rings. Each PCS 7 station is connected to one of two Industrial Ethernet interfaces on each of the two separate rings. The basis of this parallel redundancy protocol (PRP) according to IEC 62439-3 is the double transmission of the message frames in two separate networks (Ring 1, Ring 2).