Thoughts about redundancy in fieldbus systems anchored in OSI Layer-4 and applied to the Lontalk Protocol on neuron based network nodes

Fault-tolerance in fieldbus systems can be accomplished on different OSI layers. Nowadays most fieldbus systems supporting redundancy at the physical layer are based on layer 2 characteristics. Some examples like MIL-STD-1553B, Profibus, CAN, XR-III are presented at the beginning, giving an insight into the state of the art. A new approach for network redundancy is introduced, utilizing inherent fault-tolerance capabilities in the OSI reference model. In more detail we concentrate on Layer-4, the transport layer, which establishes a reliable end to end communication. Detecting duplicate data packets is a service provided in this layer and this service will be the basis for our thoughts about redundancy. An enhanced LONWORKS based network node is presented capable of handling multiple redundant communication media.