On the unequal bandwidth share in LonWorks control networks

In the paper, the problem of unequal bandwidth share among the devices introduced by the random scheme of LonTalk Media Access Control protocol is discussed. It is shown that the unfair allocation of communication resources is an unavoidable part of LonTalk operation in most load scenarios. Unfairness in accessing the channel results in a reduction of the bandwidth available to particular nodes. On the other hand, the channel access unfairness increases the mean channel utilization. There is a tradeoff between the access unfairness level and fairness recovery time: the possible inequality in sharing the bandwidth is greater for the light channel load but the fairness recovery time is then faster. Fortunately, the predictive p-CSMA unfairness has not tendency to escalate but is stabilized by the mechanism of a negative feedback.