WinCC OA Redundancy

A report control block can be used only by one client at once. Both WinCC OA redundancy partners share the same RCB, however only the active client receives values from the device. In case of a redundancy switch-over the client which is going to be passive has to release the RCB before the other client can use it.

Depending on the used RCB type the behavior is different in case of a redundancy switch-over:

• URCB - is released immediately
• BRCB - is not available for the other client till the time period defined at the ReserveTms data point element expires. Therefore, the value for ReserveTms must be defined as low as possible (1 second).

The actual switch-over time depends on the reason for the connection loss. E.g. both partners must detect the connection loss. Whereas the WinCC OA client detects a connection failure immediately, how fast a IED detects the connection loss and releases the RCB depends on the device type.

Therefore, it is recommended to use BRCBs for transmitting important data. The IED stores BRCBs in a buffer. In case of a connection loss, the reports are transmitted in chronological order after connection reestablishment. Depending on the configuration of ReadCompleteBuffer the complete buffer or only reports accumulated during downtime are retrieved.

Dynamic datasets must not be used in a redundant system.