Siemens SIMATIC CPU 410 System Manual page 335

Note
The number of connection resources required on the CPs depends on the network used.
If you implement a duplex fiber-optic ring (see figure below), two connection resources are
required per CP. In contrast, only one connection resource is required per CP if a double
electrical network (see figure after next) is used.
Figure 18-16 Example of redundancy with fault-tolerant system and redundant ring
Configuration view ≠ Physical view
Figure 18-17 Example of redundancy with fault-tolerant system and redundant bus system
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC
18.11 Communication via fault-tolerant S7 connections
Supplementary information
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