Siemens SIMATIC NET System Manual page 95

Multiple RSTP network areas and MRP ring
Another use case of RSTP+ is the connection of two or more RSTP network areas over one
MRP ring. RSTP+ must be enabled for all devices in the MRP ring that are connected to one
of the RSTP networks. In the example shown here, these are the devices RSW1, RSW2,
RSW3 and RSW4.
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Network structures and network configuration
2.3 Media redundancy
95