Fundamentals And Basic Concepts; Redundant Communication System; Fault-Tolerant Communications - Siemens SIMATIC S7-400H Manual

Communication Functions
8.1

Fundamentals and Basic Concepts

Overview
Fault-tolerant controllers make it possible for controllers, including their I/O, to
feature redundancy. With growing demands on the availability of an overall system
it is necessary to raise the fault tolerance of communications – in other words,
communications have to be configured so that they are also redundant.
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 subcomponents, or duplication of all bus components.
Monitoring and synchronization mechanisms ensure that should one component
fail, communications in routine operation are continued by means of standby
components.
A redundant communications system is a requirement for the configuration of
fault-tolerant S7 connections.

Fault-tolerant communications

Fault-tolerant communications means the use of SFBs in S7 communications via
fault-tolerant S7 connections.
Fault-tolerant S7 connections are only possible with the use of redundant
communications systems.
Redundant nodes
Redundant nodes represent the fault tolerance of communications between two
fault-tolerant systems. A system with multi-channel components is represented by
redundant nodes. The independence of a redundant node is given when the failure
of a component within the node does not result in reliability constraints in other
nodes.
8-2
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07