Configuring Redundancy

The IEC870IP driver supports redundant communication with devices at the I/O server level.

The following diagrams shows the configuration of a simple redundant system with a pair of I/O servers connected to an IEC-60870-5-104 device. The physical device is represented on both I/O servers.

Both I/O servers establish a TCP/IP connection to a device and periodically send test link messages to confirm that it is still online.

As the IEC 60870-5-104 standard specifies that only one master station can perform data interrogation on a device at a time, redundancy is managed through the implementation of START DT/STOP DT requests.

The I/O server with the highest priority connection to the I/O device sends a START DT request to the device to commence data interrogation. If the test link determines the connection to the device has stopped working, the second I/O server assumes highest priority and sends a START DT request.

If the initial server then comes back online, it once again assumes highest priority and issues a START DT request. This will prompt the other server to send a STOP DT request.

Note: You can adjust the rate of transmission used for test link message via the driver parameter Communication Parameters.