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The design of the technology modules with PROFIBUS is oriented toward the OSI layer model (Open Systems Interconnection Reference Model). Here, the communication process between two nodes is distributed over seven "layers", from layer 1 ("physical layer", trans-mission technology) to layer 
7 (“application layer”, interface to the application). PROFIBUS uses layers 1, 2 and 7.

References between OSI model and PROFIBUS. The figure shows the definition of the seven OSI layers on the left and the implementation of PROFIBUS on the right.

• Layer 1 defines the physical transmission. With PROFIBUS, there are copper-wire versions (RS485 and MBP) and optical and wireless transmission.
• Layer 2 defines the description of the bus access method, including data security. With PROFIBUS, this is the master-slave method in conjunction with the token method.
• Layer 7 forms the interface to the application and thus represents the link between the application and communication. With PROFIBUS, the communication protocol PROFIBUS DP is used here.

The actual application process lies above layer 7 and is not part of the OSI model.