Load shared - redundant I/O data source

This variation of the load shared configuration includes a set of redundant nodes running the I/O Servers.

AOS1 and AOS2 are configured as redundant pairs in a load shared scenario. In the event of a failure, one of the nodes hosts all AppObjects in both servers. This set up provides high availability for the execution of AppObjects.

Alternatively, the I/O data level is protected by implementing a pair of remote I/O Server nodes. Each server hosts the corresponding DI client object and I/O Server (DDE/Suitelink or OPC servers) and communication drives.

AppObjects on each engine reference I/O points in the local RDIObject. The RDIObjects switch between I/O Server nodes if a failure in any of those nodes occurs.

Using redundant I/O data sources provides the following benefits:

• The communication protocol between the I/O Server node and the AOS is MX. This protocol is optimized for data transfer over the network, with special emphasis on slow and intermittent networks.

• As the I/O Server uses MX protocol to transfer data, it simplifies configuring OPC communication over the network, and overcomes the deficiencies of DCOM communications.

• Using a platform and an AppEngine on those nodes provides additional diagnostic of conditions associated to the system. These can be historized and alarmed in the same way as with AppObjects.