this paper presents a methodto calculate the capacity, efficiency and measurement update cycle in Supervisory control and data acquisition (SCADA) systems when thesesystems using token passing bus protocol as a mac protocol in medium access control sub layer. After driving the proper formula for parameters the simulations results will be discussed and compared with results in polling protocol.Finally according to the most important criteria a suitable cost function for optimal operation of such system will be derived and with the results of minimizing this cost function an optimum number of remote in specific condition and parameter are obtained. These calculations will leadremotes tocommunicate with MTU without violating the channel efficiency.
