Practical TCP/IP and Ethernet Networking for Industry

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• Message formats must be the same for all nodes (as there is no presentation

layer)

MiniMAP and the Fieldbus protocol standards use the reduced OSI model with only

three layers. Similarly other industrial protocols such as the Allen Bradley Data Highway

Plus protocol, Modbus Plus and the HART smart instrumentation protocols have all

standardized on the three layers only.

One of the challenges with the use of the OSI model is the concept of interoperability

and the need for definition of another layer above the application layer, called the ‘user’

layer.

Figure 2.12

‘Collapsed’ OSI stack

However, ...