Siemens SIMATIC PCS 7 Function Manual page 59

Components
The use of switches from the SCALANCE series is recommended. Modules for optical and
electrical connection are available for these switches.
Configuration of the switches
For redundant linking of networks, configure one SCALANCE switch as the standby master
and one as the standby slave within a network segment. A redundancy manager (RM) must
be configured in each network segment to enable ring redundancy. Switches and data links
(network cable) connect the redundant networks. The switches configured in this way
exchange data frames with one other and synchronize their operating status (standby master/
standby slave).
You will find details of how to configure switches in the documentation for
Switches SCALANCE X under the following topics:
● Configuration using Web-Based Management and Command Line Interface
● Configuration and diagnostics via SNMP
Availability - redundant terminal bus
The entire transmission route can be configured redundantly. A transmission route remains
operational via a terminal bus if any of the network components fails.
In process mode, one switch automatically takes over the standby master function for linking
the networks. In error-free status, the data link to the other network is active only for the active
standby master. If this data link fails (for example, due to a defective cable), the standby slave
activates its data link.
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA
Fault-tolerant Solutions in PCS 7
3.3 Solutions for communication
Industrial Ethernet
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