CAN lower- and higher-layer protocols

CAN communication and the Open System Interconnections (OSI) model

The CAN knowledge pages provide technical information on all three CAN (Controller Area Network) data link layer protocol generations (Classical CAN, CAN FD, and CAN XL) and several CAN physical layer options. Additionally, these pages also contain technical descriptions about classic CANopen and CANopen FD as well as other standardized CAN-based higher-layer protocols.

  • CAN lower layers
    • Upper-layer functions provided by the CAN controllers
    • CAN data link layers: Classical CAN, CAN FD, and CAN XL
    • CAN physical coding sub-layer (part of the CAN controller)
    • CAN physical medium sub-layers (transceiver)

  • CAN higher layers

According to the Open System Interconnection (OSI) seven-layer model, the CAN lower layers cover some functions of the transport layer (e.g. automatic retransmission of faulty frames), the data link layer (DLL), and the physical coding sub-layer (PCS) as well as the physical medium attachment (PMA) sub-layer. The other layers are usually referenced as higher-layer protocols (HLP). Often, the CAN-based application layer approaches include functional elements of other higher layers (e.g. session, presentation, transport, or network layers), too. Some of them are accompanied by parameter specifications, which is not in the scope of the OSI model.

The CAN protocols description includes the Classical CAN data link layer (1st generation), the CAN FD data link layer (2nd generation) and the CAN XL data link layer (3rd generation). Classical CAN and CAN FD protocols are internationally standardized in ISO 11898-1. CAN XL protocol is specified in CiA 610-1.

There are several CAN physical media attachment (PMA) sub-layers standardized. They are normally implemented by means of transceivers. Most common is the CAN high-speed transceiver (ISO 11898-2:2016). This includes variants supporting bit-rates up to 1 Mbit/s and those providing tighter symmetry features suitable for higher bit-rates depending on the network design (CAN FD transceiver). The CAN SIC (signal improvement capability) transceiver is specified in CiA 601-4 and CiA 610-3 specifies the CAN SIC XL transceiver. Additional PMAs are standardized in ISO 11898-3 (low-speed, fault-tolerant), ISO 11992-1 (dedicated for truck/trailer links), and SAE J2411 (single-wire CAN).

Besides the lower layers, the CAN knowledge pages give an overview of several higher-layer protocols. This includes, in particular, the classic CANopen application layer (CiA 301) and the CANopen FD application layer (CiA 1301) as well as the related device, interface, and application profiles. Additionally, some basic information on other CAN-based higher-layer protocols (such as Devicenet, Isobus (ISO 11783), ISO 11992 series, and SAE J1939 series) is provided.