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Instead of assigning a separate communication channel - in the form of an electrical line - to each signal to be transmitted, serial bus systems are used to exchange data in the vehicle today. They are characterized by multiple electronic ECUs sharing just one transmission medium to exchange data among one another. First, this results in substantially lower wiring expense; primarily this has a positive impact on costs, space requirements, weight and reliability. Second, information can be distributed to all electronic control units connected in the bus system; this is a basic prerequisite for many modern electronic systems in the motor vehicle.
Although they offer yet other favorable effects - such as accelerated installation due to multiple electronic ECUs sharing one communication medium within a serial bus system - they also raise a number of challenges that the developer must deal with. Above all, these include synchronization of bus nodes, assurance of timely data transmission and addressing. Another challenge is to make serial communication as reliable as possible, despite very harsh environmental conditions that are primarily mechanical, thermal, chemical and electromagnetic in nature.
A large number of communication tasks can be derived from these challenges, which are grouped together in a communication layer so that they can be handled better. The applications residing in the bus nodes utilize this communication layer to communicate, i.e. to exchange data. The structure of the communication layer and handling of the data exchange are simplified by use of the basic reference model for data communication (ISO 7498).
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