Siemens SIMATIC PCS 7 Function Manual page 53

Note
Redundant linking of network segments
The redundant linking of two network segments is only possible when the linking switches
are capable of acting as standby manager.
Example:
● Linking with SCALANCE X414-3E
● For Gigabit Ethernet: Linking with SCALANCE X408-2
Redundant, fault-tolerant terminal bus with redundant linking of network segments (rings)
One pair of redundancy-capable network adapters is used for each PC station in each server
to be connected to the terminal bus (for example, OS server, BATCH server, domain
controller), (see section "Connecting PC stations to the terminal bus (Page 46)"). Team-
capable network adapters are required for this configuration. They work in " INTEL Team
mode" with only one logical network address. Each network adapter is connected to one of
the redundant terminal bus rings (bus1/bus2). The link between the redundant network
segments (rings) is implemented using two switches in each network.
Fault-tolerant Process Control Systems (V8.0)
Function Manual, 03/2012, A5E02779471-02
Fault-tolerant Solutions in PCS 7
3.3 Solutions for communication
53