Configuring Redundancy

Redundancy for the KNX driver in unicast communication supports the traditional redundancy model for Plant SCADA I/O devices as described in the I/O Server Redundancy section of Plant SCADA help.

Redundancy in multicast communication is different from the traditional redundancy model for Plant SCADA I/O devices. In this case one I/O device represents an entire KNX network.

The use of IP multicasting as the communications medium between IP router devices means that only one connection per network interface is possible. In this context, only one I/O device can be defined per I/O server, unless the server supports multiple interfaces and the LocalIPAddress parameter is used to bind different I/O devices to different interfaces.

The use of IP multicast, and thus the lack of a direct connection to the KNX IP router devices, means that the I/O server is very limited in the extent to which it can signal a device to be offline.

The KNX driver will only signal a device as offline under the following conditions:

A media disconnect event is received by the socket, i.e. network cable pulled out

All of the group addresses on the device has timeout and become bad

It is possible for two I/O devices on two servers to be configured as a redundant pair. In this case, the two devices will act as a hot-standby, with both servers maintaining a live cache.