OSI 7-Layer Model Compliance

• Both protocols use a simplified 3 layer version of the OSI 7 Layer model called EPA (Enhanced Performance Architecture)

• DNP adds a Transport layer to permit single-function messages larger than a data link frame

• Every 101 Profile single-function message is sent as a single data link frame

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Slide 10 of 30

In DNP all application layer functions are implemented as application layer messages encapsulated in data link frames.

101 supports a mechanism to specify a set of application functions (e.g. poll requests) in a data link layer message containing no application data. This improves efficiency, but blurs the separation of application and data link functionality.