high-level protocol for CAN-bu

high-level protocol for CAN-bus:Fieldbus networks from the OSI network model
point-of-view usually only have the layers 1 (Physical
Layer), 2 (Datalink Layer) and 7 (Application
Layer) implemented. The intermediate layers are
not needed because a fieldbus network usually consists
of a single network segment only (no need for
Transport and Network Layer, layer 3 and 4) and
has no notion of 'sessions' (layer 5) or a need for
different internal data 'presentation' (layer 6).
The CAN (Controller Area Network) fieldbus defines
only the layers 1 and 2 (ISO11898); in practice
these are completely handled by the CAN
hardware, significantly reducing the implementation
effort 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: