This mode of operation is known as multi-cast. The unique identifier also determines the priority of the message. The lower the numerical value of the identifier, the higher the priority. The higher priority message is guaranteed to gain bus access as if it were the only message being transmitted. Lower priority messages are automatically re-transmitted in the next bus cycle, or in a subsequent bus cycle if there are still other, higher priority messages waiting to be sent.
Arbitration is explained in more detail later.
An Example Using a much simplified system in a car as a general example, Figure 1 below shows a CAN bus with four nodes. Assume that node 2 is connected to a sensor that is monitoring the engine revolutions and, at defined intervals, needs to transmit the RPM information. The controller in node 2 initiates the transmission of a message containing the RPM data. The message and its appropriate identifier are passed to the CAN chip in the node. The use of NRZ ensures compact messages with a minimum number of transitions.