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Carrier Sense Media Access (CSMA) protocol is a widely used algorithm to control the access of a computer to the shared media (channel). There are several variants derived from this Media Access Control (MAC) method, such as non-persistent CSMA, 1-persistent CSMA, p-persistent CSMA, and CSMA/CD etc. These algorithms are successful in time-insensitive network, such as Ethernet. But for the fieldbus-based real-time control system that is time-sensitive, they are no longer adequate. To meet the real-time requirements, Echelon Corporation proposed a novel CSMA algorithm, the predictive p-persistent CSMA protocol. In this paper, we evaluate the performance of this protocol by a discrete-event simulation. A node-centric simulation model based on event-driven simulation language - SMPL - is designed using what we call "FSM-to-EVENT" method. Also, some techniques are presented to achieve this purpose. Finally, the experiments and results, including the comparison with other protocols, are described.