high-level protocol for CAN-bus:Fieldbus networks from the OSI network modelpoint-of-view usually only have the layers 1 (PhysicalLayer), 2 (Datalink Layer) and 7 (ApplicationLayer) implemented. The intermediate layers arenot needed because a fieldbus network usually consistsof a single network segment only (no need forTransport and Network Layer, layer 3 and 4) andhas no notion of 'sessions' (layer 5) or a need fordifferent internal data 'presentation' (layer 6).The CAN (Controller Area Network) fieldbus definesonly the layers 1 and 2 (ISO11898); in practicethese are completely handled by the CANhardware, significantly reducing the implementationeffort for developers of the fieldbus node firmware.However, a high level protocol is necessary in order to define how the CAN message frame's 11-bit identifier and 8 data bytes are used. Building CANbased industrial automation systems guaranteeing interoperability and interchangeability of devices of different manufacturers requires a standardized application layer and 'profiles', standardizing the communication system, the device functionality and the system administration:
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