Computation of Response Time Distributions for Messages on the Controller Area Network

The response time of messages is an important parameter for the design of in-vehicle networks based on the controller area network (CAN). The message transmission on CAN is affected by several non-deterministic factors such as stuff bits that are added to CAN frames depending on the message payload or changing phases among the asynchronous CAN nodes because of clock drifts. The resulting probabilistic nature of message response times on CAN is captured by the response time distribution (RTD) that quantifies the probability of experiencing each possible response time of a CAN message. This paper proposes an original method for the exact RTD computation for each message on CAN, taking into account bit stuffing and clock drifts among CAN nodes. The proposed method features a recursive algorithm for evaluating the backlog caused by interfering messages and averages over all possible transmission scenarios. Validation experiments using different CAN message sets show a very high correlation of the computed RTDs and measured RTDs from a hardware setup in the order of 98 %. To the best of our knowledge, this is the first method for the exact RTD computation for non-preemptive communication systems such as CAN.