Siemens SIMATIC PCS 7 Function Manual page 40

Fault-tolerant Solutions in PCS 7
3.3 Solutions for communication
● Electrical
● Optical
● Electrical/optical combination
The communication connections are grouped in three areas:
● Terminal bus
● Plant bus
● Fieldbus
In PCS 7, we recommend that the bus systems are set up in a ring structure. The ring structure
makes the bus "fault-tolerant", since it can compensate for the failure of a bus line.
Redundant communication connections
Redundant communication connections can be formed on all levels of the process control
system.
When a communication error occurs, communication automatically switches over from the
active connection to the backup connection. Both connections use the same media and
protocols. The failover has no effect on the user program running in the CPU.
Overview of the redundant and fault-tolerant bus systems
In PCS 7 systems, you can configure fully redundant bus systems with redundant components
for the following bus systems:
● Redundant, fault-tolerant terminal bus (Page 49)
● Redundant, fault-tolerant plant bus (Page 59)
● Redundant PROFIBUS DP (Page 62)
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Fault-tolerant Process Control Systems (V8.0)
Function Manual, 03/2012, A5E02779471-02