Communication Via Redundant S7 Connections - Siemens SIMATIC S7-400H System Manual

Communication
11.6 Communication via S7 connections
11.6.2

Communication via redundant S7 connections

Availability
Availability can be enhanced by using a redundant system bus and two separate CPs on a
standard system.
Redundant communication can also be operated with standard connections. For this two
separate S7 connections must be configured in the program in order to implement
connection redundancy. In the user program, both connections require the implementation of
monitoring functions in order to allow the detection of failures and to change over to the
standby connection.
The following figure shows such a configuration.
Figure 11-11 Example of redundancy with fault-tolerant systems and a redundant bus system with
Reaction to failure
Double errors in the fault-tolerant system (in other words, CPUa1 and CPa 2) or in the
standard system (CPb1 and CPb2), and single errors in the standard system (CPUb1) lead
to a total failure of communication between the partners involved (see previous figure).
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redundant standard connections
System Manual, 09/2007, A5E00267695-03
S7-400H