Supplementary information 
  18.10 Communication via S7 connections 
CPU 410 Process Automation/CPU 410 SMART 
System Manual, 05/2017, A5E31622160-AC 
327 
 
Figure 18-9  Example of linking standard and fault-tolerant systems in a redundant bus system 
If the plant bus is configured as a duplex fiber-optic ring, the communication of the systems 
involved is maintained if a break of the two-fiber fiber-optic cable occurs. The systems then 
communicate as if they were connected to a bus system (linear structure); see following 
figure. 
 
Figure 18-10  Example of linking of standard and fault-tolerant systems in a redundant ring 
Response to failure 
Duplex fiber-optic ring and bus system
 
S7 connections are used here in which the connection ends on the CPU of the subsystem, 
here CPUa1. For this reason, an error in the fault-tolerant system, e.g., CPUa1 or CPa1, as