Response To Failure; Redundant S7 Connections - Siemens SIMATIC S7-400H Manual

Communication Functions

Response to failure

Only a double error within a fault-tolerant system (e.g. CPUa1 and CPa2 in a
system) in the case of a two-fiber ring leads to total failure of communications
between the redundant systems concerned (refer to Figure 8-3).
If a double error (CPUa1 and CPb2, for example) occurs in the first case of a
redundant electrical bus system (see Figure 8-4), a this results in a complete
failure of communication between the systems involved.
In the case of a redundant electrical bus system with CP redundancy (see
Figure 8-5), only a double error within a fault-tolerant system (CPUa1 and CPUa2,
for example) or a triple error (CPUa1, CPa22 and bus2, for example) will result in a
complete failure of communication between the systems involved.

Redundant S7 connections

Interruptions of a connection unit while communication requests are being
processed will lead to extended runtimes.
8.4.2 Communications between Fault-Tolerant Systems and a
Fault-Tolerant CPU
Availability
Availability can be enhanced by using a redundant system bus and by using a
fault-tolerant CPU on a standard system.
If the communication partner is a fault-tolerant CPU, fault-tolerant connections can
also be configured here,in contrast to a CPU 416, for example.
8-12
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07