This part of ISO 11898 specifies characteristics of setting up an interchange of digital information between electronic control units of road vehicles equipped with the controller area network (CAN) at transmission rates above 40 kBit/s up to 125 kBit/s. The CAN is a serial communication protocol which supports distributed control and multiplexing. This part of ISO 11898 describes the fault tolerant behaviour of low-speed CAN applications, and parts of the physical layer according to the ISO/OSI layer model. The following parts of the physical layer are covered by this part of ISO 11898: — medium dependent interface (MDI); — physical medium attachment (PMA). In addition, parts of the physical layer signalling (PLS) and parts of the medium access control (MAC) are also affected by the definitions provided by this part of ISO 11898. All other layers of the OSI model either do not have counterparts within the CAN protocol and are part of the user’s level or do not affect the fault tolerant behaviour of the low speed CAN physical layer and therefore are not part of this part of ISO 11898.