In this paper, the reliability performance of 128 128 optical cross-connects (OXCs) based on microelectrooptomechanical systems (MEOMS) switch matrices is considered. First, we compare a strictly nonblocking wavelength selective switch with a strictly nonblocking three-stage Clos architecture. The probability of maintenance of free operation has been investigated for both OXC structures. We present our calculation results for such commonly used reliability measures as mean time between failures (MTBF),mean downtime (MDT) per year, and steady-state unavailability. It is shown that the reliability performances of the considered OXCs are far from that requested. In this paper, we also investigate possibilities of improving the reliability performance of the considered OXCs by introducing shared redundancy of the MEOMS matrices. We propose two different protection schemes: one for the wavelength selective switch  and another for the three-stage Clos architecture. It is shown that the proposed protection schemes significantly improve the reliability performance for both cases. Finally, we compare the performance of the all-optical version of the OXC based on MEOMS matrices with the optoelectronic version of the OXC based on electronic cross-point switch matrices. It is shown that from a reliability viewpoint, the optical cross-connect based on MEOMS matrices is better than that with electrical cross-point switches. The influence of capacity expansion on the system reliability is discussed.
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