Siemens SIMATIC PCS 7 Function Manual page 62

Fault-tolerant Solutions in PCS 7
3.3 Solutions for communication
Configuration - ring structure
The following figure represents a fault-tolerant plant bus in a ring structure with switches.
The following automation systems can be used:
● AS 41xH
Availability - ring structure
In this system, one CP 443-1 may fail in each subsystem of the AS without this affecting the
complete system.
The plant bus (identified by an * in the following figure) is equipped with switches for fault-
tolerant operation. Each OS server is wired to two switches. The bus can be separated at any
location. The overall system remains functional even if a switch fails. The redundant OS partner
server then communicates via the functional switch. The same scenario applies to the switches
that each have a CP of a subsystem of the H system connected.
To guard against the failure of all switches, however, the redundant double ring described in
the following section can be used.
62
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA