Technology overview

As all modern communication technologies, CAN-based networks follow the internationally standardized Open Systems Interconnect (OSI) reference model as defined in ISO 7498-1. For CAN technology, this model has been adapted. The CAN reference model comprises the CAN physical layer (layer-1), the CAN data link layer (layer-2), and the CAN application layer (layer-7). Some layer-7 solutions include also network and transport layer functionality. All these communication services and protocols specify just the communication behavior. The application functionality may be described in standardized profile specifications. In order to verify the correctness of implementations standardized conformance test plans are necessary. A manufacturer-independent certification based on these test plans minimizes compatibility problems.

Bus-line and topology

The CAN physical layer is partly implemented in transceiver chips. The Medium Access Unit (MAU) specification (e.g. ISO 11898-2) defines among others the voltage levels on the bus lines and the maximum data rate. Another part of the physical layer, the Physical Signaling, defines the bit-timing behavior, the data encapsulation, etc. It is implemented in the CAN protocol controller chip.

Services and protocols

The CAN data link layer defines basic communication services and protocols implemented in the CAN protocol controller chip. The CAN-based higher layer uses these services and protocols to map the higher communication services and protocols. They are normally implemented in software available as protocol stack firmware in object or source code. Additional functionality, e.g. safety-related communication, may be implemented in specific protocol stacks.

Device and application profiles

In order to provide a communication interface that is standardized on the level of parameter semantic, the device needs to follow a standardized profile specification. Device profiles specify the parameter meaning and grouping for a single physical device. Application profiles specify the same for a set of virtual devices; and several virtual devices may be implemented in a physical device.