MODBUS TCP BACKBONE THROUGHPUT ANALYSIS FOR NOISY IEEE 802.11 WIRELESS CHANNEL

The use of high-speed wireless IEEE 802.11 channels (802.11n/ac/ax) for the Modbus TCP backbone in automated control systems of industrial enterprises (APCS) requires an assessment of backbone performance under communication channel operating conditions, taking into account the specific features of APCS operation, where a high level of bit errors is present in the communication channels. Based on an analysis of the algorithmic structure of the backbone and transmission timing diagrams in a wireless channel, analytical relationships were obtained for calculating transaction time and backbone throughput for a real wireless channel. An analysis of the backbone throughput for typical operations was carried out, taking into account different levels of bit error rate (BER) in the wireless communication channel.Classes of Modbus TCP backbone operations (simple and composite) are identified. It is shown that composite operations are formed as a composition of a certain number of simple operations. Unlike models with ideal communication channels, models for real channels take intoaccount frame retransmission mechanisms and additional delays associated with bit errors during information transmission. The obtained expressions for operation execution time and throughput make it possible to assess the real performance of the Modbus TCP backbone for wireless channels with errors.The performed throughput calculation demonstrates a significant impact of bit errors on the backbone throughput for single-channel and multi-channel implementations of the Modbus TCP backbone based on wireless channels of the IEEE 802.11 family. The obtained analytical relationships for the execution time of typical operations and backbone throughput represent a tool for selecting optimal configurations in the design and modernization of industrial networks based on wireless implementations of the Modbus TCP backbone within the framework of the “Industry 4.0” concept.