Experimental evaluation of the service time for industrial hybrid (wired/wireless) networks under non-ideal environmental conditions

In industrial communication systems, the unavailability of models of real components, in particular of their behavior in the presence of non-ideal channels, often leads to consistent differences between theoretical/simulative analysis and experimental results. In this paper we consider a hybrid (Ethernet/IEEE 802.11) network employing access points from different vendors and measure a specific performance index, namely the service time, for various transmission rates focusing on the effects of both internal component behaviors and channel conditions. The obtained results show how, in case of small payload packets transmitted on noisy channels, the choice of a fixed low transmission rate guarantees better service times. Indeed, decreasing the transmission rate on the wireless segment below 54 Mb/s reveals effective, since it limits the occurrence of packet errors and the consequent retransmissions reducing the service time variability to the intrinsic randomness of the employed devices.