Supplementary information
15.7 Basics and terminology of fault-tolerant communication
CPU 410-5H Process Automation
256 System Manual, 09/2014, A5E31622160-AB
Basics and terminology of fault-tolerant communication
Overview
When more stringent requirements for overall plant availability exist, it is necessary to
increase the reliability of the communication, i.e., by configuring the communication
redundantly as well.
Below you will find an overview of the fundamentals and basic concepts which you ought to
know with regard to using fault-tolerant communications.
Redundant communication system
The availability of the communication system can be increased by duplicating
subcomponents, duplicating all bus components, or using a fiber-optic ring.
On failure of a component, the various monitoring and synchronization mechanisms ensure
that the communication functions are taken over by the standby components during
operation.
A redundant communication system is essential if you want to use fault-tolerant
S7 connections.
Fault-tolerant communication
Fault-tolerant communication is the deployment of S7 communication SFBs over fault-
tolerant S7 connections.
Fault-tolerant S7 connections need a redundant communication system.
Redundancy nodes represent extreme reliability of communication between two fault-tolerant
systems. A system with multi-channel components is represented by redundancy nodes.
Redundancy nodes are independent when the failure of a component within the node does
not result in any reliability impairment in other nodes.
Even with fault-tolerant communication, only single errors/faults can be tolerated. If more
than one error occurs between two communication end points, communication can no longer
be guaranteed.
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