Fundamentals And Basic Concepts - Siemens SIMATIC S7-400H System Manual

Communication

11.2 Fundamentals and basic concepts

11.2 Fundamentals and basic concepts
Overview
Rising demands on the availability of an overall system make it essential to improve the
fail-safety of communication systems, including implementation of redundant communication.
You will find below 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 redundancy of the media,
duplication of component units, or duplication of all bus components.
On failure of a component, the various monitoring and synchronization mechanisms ensure
that the communication functions are taken over by the standby components while the
system stays in 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 are only possible when using redundant communication
systems.
Redundancy nodes
Redundancy nodes represent the fail-safety 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/fault occurs between communication endpoints, communication can no longer
be guaranteed.
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System Manual, 09/2007, A5E00267695-03
S7-400H