Siemens SIMATIC PCS 7 Function Manual page 184

Failure, Switchover and Return of Fault-tolerant Components
6.4 OS server
Disrupted network connection to the OS partner server
A disrupted network connection is only detected in the redundancy scheme when:
● There is a fault in the spur line.
● There is a defective connector or network adapter.
● A PC station is identified as faulty.
The terminal bus as a whole and the communication between the AS and OS servers remains
unaffected.
Both OS servers are started and begin processing an activated WinCC project. If a disruption
in the network connection to the OS partner server occurs in this situation, WinCC Redundancy
reacts as follows:
● Both OS servers save the date and time of day of the failure.
● Both OS servers report the failure with a process control message in the message list.
● If the disrupted OS server is a master, the master/standby identification changes.
During the connection failure no online synchronization for alarm logging, operation messages
and user archives can be performed between the two OS servers. As soon as the connection
is restored, this is remedied by following actions:
● Both OS servers save the date and time of day of the restored connection.
● Both OS servers report the return with a process control message in the message list.
● Data from the alarm logging, tag logging and the user archives accumulated during the
● The @RM_MASTER and @RM_MASTER_NAME tags remain unchanged in both servers.
Disrupted network connection between the OS client the OS server
An OS server and the OS client connected to it are processing an activated WinCC project. A
redundant OS partner server has been configured for the OS server in WinCC Redundancy.
The OS server is defined as the preferred server for the OS client. A disrupted network
connection to the OS server may result from a cable break in the spur line from the network
to the OS server. The terminal bus as a whole remains unaffected.
If a connection failure occurs between the OS client and the OS server, WinCC Redundancy
triggers the following reactions:
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connection failure are transmitted to the returning OS server.
Fault-tolerant Process Control Systems (V8.0)
Function Manual, 03/2012, A5E02779471-02