Siemens SIMATIC CPU 410 System Manual page 336

Supplementary information
18.11 Communication via fault-tolerant S7 connections
Configuration view = Physical view
Figure 18-18 Example of fault-tolerant system with additional CP redundancy
Configuration view = Physical view
You decide during configuration if the additional CPs are used to increase resources or
availability. This configuration is typically used to increase availability.
Note
Internal and external interface
Communication between fault-tolerant systems can be either via internal interfaces or via
external interfaces (CP).
The partial connections of an S7 H connection cannot be configured over an external and
internal interface
Response to failure
With a duplex optic-fiber ring, only a double error within a fault-tolerant system, e.g., CPUa1
and CPa2 in one system, leads to total failure of communication between the systems
involved (see Figure 11-14).
If a double error, e.g., CPUa1 and CPb2, occurs in the first case of a redundant electrical
bus system (see Figure 11-15), this results in a total failure of communication between the
systems involved.
In the case of a redundant electrical bus system with CP redundancy (see Figure 11-16),
only a double error within a fault-tolerant system, e.g., CPUa1 and CPa2, or a triple error,
e.g., CPUa1, CPa22, and bus2, will result in a total failure of communication between the
systems involved.
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CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC