Siemens ESM - Manual (Page 37)

Network Topologies with OSM/ESM
Industrial Ethernet OSM/ESM
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3.3 Redundant Coupling of Network Segments
The standby-sync port of an OSM/ESM with 8 ports allows the connection of two
Industrial Ethernet OSMs or ESMs with one operating as standby master (DIP
switch "Stby off") and the other as standby slave (DIP switch "Stby on"). With this
mode, pairs of OSMs/ESMs can be used for redundant coupling of OSM/ESM or
OLM rings.
With network management, the OSM/ESM can also be configured so that several
rings or networks can be interconnected at the same time with two OSMs/ESMs
(see OSM/ESM Network Management, User Manual /1/).