Fault tolerance analysis of Extended Pruned Vertically Stacked Optical Banyan networks with link failures and variable group size

Vertically stacked optical banyan (VSOB) networks are attractive for serving as optical switching systems due to the good properties of banyan network structures (such as the small depth and self-routing capability), and it is expected that using the VSOB structure will lead to a better fault-tolerant capability because it is composed of multiple identical copies of banyan networks. In the Extended Pruned Vertically Stacked Optical Banyan (EP-VSOB) network, the number of pruned planes has always been considered as √(N), and a few extra planes (regular banyan) has been added with this pruned planes. In this paper, we present the results of blocking analysis of EP-VSOB network incorporating link-failures in which the number of pruned planes can be 2^x, where 0 ≤ × ≥ log₂ N, in addition to the variable extra planes. This generalization helps us trade-off between different constraints and performance metrics. Our simulation results show that for some given performance requirements (e.g. cost, speed or blocking probability), we can choose a network that has lower switch count compared to N - plane pruned crosstalk-free optical banyan networks. Our result also reveals a fact that by accepting small link failure probability, the blocking behavior of EP-VSOB network is very similar to that of a fault-free one, which demonstrates our expectation of good fault-tolerant property of VSOB networks. Simulation results also show that the blocking probability does not always increase with the increase of link-failures; blocking probability decreases for certain range of link-failures, and then increases again.