Siemens SIMATIC PCS 7 Function Manual page 52

Fault-tolerant Solutions in PCS 7
3.3 Solutions for communication
For example, a broken cable in the connection between the modules is tolerated and
communication remains uninterrupted.
If the terminal bus experiences problems, no process data are sent from the servers to the
clients.
Fault-tolerant communication solutions
The following solutions are available to guard against failure of the terminal bus:
● Ring structure in an electrical network. The connection to the switches is electrical.
● Ring structure in an optical network with switches and FO cables. The connection to the
switches is electrical or optical.
● Ring structure in a combined network with optical and electrical switches and FO cables.
The connection to the switches is electrical.
● Ring structures as optical, electrical and combined networks with transfer rates up to 1
Gbps based on the modular switches
Configuration
In the following figure, the terminal bus is shown as a ring with switches as an example. The
OS servers are connected to the switches in a distributed pattern in order to take optimal
advantage of the switch functionality. The probability of OS server failure due to the failure of
a switch and the bus load are thereby reduced.
The log data of the control process is secured and continuously available if you use two OS
clients each equipped with a line printer for printing the message sequence reports.
Note
If a switch fails, the connection to the associated nodes will also fail. Therefore, redundant
servers must not be connected to the same switch.
52
Fault-tolerant terminal bus
Industrial Ethernet
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA