Basics And Terminology Of Fault-Tolerant Communication - Siemens SIMATIC S7-400H System Manual

14.2

Basics and terminology of fault-tolerant communication

Overview
Increased demands on the availability of an overall system require increased reliability of the
communication systems, which means implementing redundant communication.
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 enhanced by duplicating component
units and all bus components, or by 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 reserve 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
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 communication endpoints, communication can no longer be
guaranteed.
S7-400H
System Manual, 03/2012, A5E00267695-11
14.2 Basics and terminology of fault-tolerant communication
Communication
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