Redundant Ring topology with all devices dual attached
In highly critical applications, it may be necessary to dual attach all devices (outstations and PCs) to the network to provide a very high level of redundancy. This provides maximum reliability but also generates maximum cost and complexity.
Most vendors of Industrial Ethernet products support a version of the ‘redundant ring’ technology described above. It should be noted that the protocols used are not based on a standard and are generally not interoperable amongst the different switch manufacturers.