Error signaling instead of message acknowledgement
In contrast to communication concepts with node-oriented transmission, CAN as a message-oriented protocol uses the principle of error signaling. Each network node checks every message transmitted on the bus with respect to errors. As soon as a transmitting or receiving network node detects an error, it signals this to all other nodes by transmitting an error message (error frame). This contains a bit combination of six bits with the same polarity (which is usually permitted), normally as a dominant bit sequence.
All network nodes detect the error signal and cancel the segments of a message already received. Consistent data is thus ensured for all nodes of the network.
As soon as a transmitting node has transmitted or received an error frame, it immediately attempts to transmit the previously transmitted message again with another bus arbitration process.
The error signaling mechanism ensures that the message transfer with all nodes of a network is error-free and consistent. As error signaling takes place immediately after an error is detected, very short error recovery times are guaranteed.
The fact that the bus is only additionally occupied when an error has been detected also has the advantage of a considerably lower additional bus load.