Analysis of Mean Access Delay in Variable-Window CSMA

The paper addresses the problem of the mean access delay characteristics in term of the channel load for networked sensor/control systems in LonWorks/EIA-709 technology. The system modelling is focused on the Media Access Control protocol that provides the load prediction and determines the key network characteristics. The network model assumes the consistency of load prediction between the nodes, and that the Transaction Control Sublayer does not introduce limitations on the data transmission. The latter means that the numbers of concurrent outgoing transactions being in progress are unlimited. Furthermore, it is assumed that the destination addresses of transmitted messages are distributed rather than concentrated on particular nodes. The analytical approach based on Markov chains is applied. The calculation of transition probabilities of the Markov chain is exemplified by the load scenario where all the transactions are acknowledged, unicast, and the optional collision detection is enabled. On the basis of the stochastic analysis, the probabilities of a successful transmission and collision, respectively, are computed. Furthermore, the numerical results of the mean access delay are reported. The simulative validation of analytical results is provided.