Overhead and ACK-Induced Jitter in Modbus TCP Communication

The MODBUS protocol is widely used at the field level, such as building automation and industrial automation. Among existing implementations of the protocol over different communication infrastructures, MODBUS TCP offers better scal- ability and interoperability than MODBUS RTU and MODBUS CAN, while at the same time, its real-time performance suffers, which limits its adoption in time-critical application domains. In this paper, the overhead and jitter of MODBUS TCP communication are thoroughly evaluated by means of theoretical analysis and experimental campaigns. The results show that, the TCP acknowledgment mechanism is mainly responsible for the round trip time jitter, which in turn may affect the system reliability as well as safety. Instead, its overhead is much more affordable for typical embedded applications.