Redundancy allocation problem is one of the most important problem in Reliability area. In this problem the reliability and availability of the systems maximized via allocating redundant components to sub-systems. a systems operates normally in its operational mode but fails in either opened or shorted modes. this paper presents a repairable k_out_of_n systems network model with common cause failures. We used Biographic Based Optimization algorithm for solving the presented problem. تفاصيل المقالة