Siemens SIMATIC CPU 410 System Manual page 327

Figure 18-9
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
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC
Example of linking standard and fault-tolerant systems in a redundant bus system
Supplementary information
18.10 Communication via S7 connections
327