ICP DAS USA VERION 1.0 MSM-508FCS - Manual (Page 32)

Industrial Ethernet Layer 2 Managed Switch User Manual
TDRS4050601 25
Two Rings Coupling with Two Phase Recovering
Redundant coupling gives one more chance to keep connection alive when any
connection between 2 rings has been broken. It is much safe than Single Coupling, but it
takes 3 more switches to form Redundant Coupling.
Be sure to use port 5 (interconnection port) to form two phase recovering coupling and
only ring pair 2 can be used in this topology.