Higher-Level Protocols

Abstract

The CAN standard defines the lower two layers of the ISO reference model, and even those with several gaps and omissions. This is often not enough for the practical operation of a network and the devices attached to it. Interchangeability and portability of devices require further standardization of cables and connectors at the physical layer. Transmission of data units longer than 8 bytes needs to be supported by transport-level protocols. Furthermore, several classes of users need to agree on additional higher-level protocol features, including data types, type encoding, and the definition of commonly used parameters and parameter groups. Also, network management features, addressing of multicast groups and definition of multicast addresses may be subject to standardization. It is not surprising, then, that a number of additional standards have been developed to provide solutions with respect to these problems. These standards typically span across all levels of the protocol stack. They provide specifications for bus lengths and bit rates as well as connectors and cable types at the physical layer. They include a transport-level protocol and a network management protocol. Very often, they also provide standardization of types and parameters and an addressing scheme overlaid on top of CAN identifiers.