In optical-grooming networks, the capacity fairness issue can be resolved by utilizing a call admission control mechanism. Existing call admission control schemes are generally based on one of the four different techniques, namely static bandwidth reservation (SBR), static threshold setting (STS), mathematical statistics (MS), and Markov decision processing without buffer implementation (NB). However, irrespective of the technique used, a tradeoff exists between the network fairness and the network throughput. Accordingly, this article presents a conditional-preemption call admission control (CP-CAC) scheme designed to increase the network throughput while simultaneously maintaining the fairness. The CP-CAC method is based on a dynamic threshold setting concept and is implemented using a single connection buffer (C-Buf) and a set of virtual buffers (V-Bufs). In general CAC mechanisms, if the residual bandwidth is sufficient to satisfy a new request but some requests are already buffered, the new request can be treated in two different modes, i.e. with-preemption (WP) or without-preemption (NP). In contrast, in the CP-CAC scheme proposed in this study, a conditional-preemption (CP) mode is proposed in which statistical information about the blocking probability is used to determine the preempt (or not) decision. The simulation results show that compared to the NB call admission control mechanism, the proposed CP-CAC scheme improves the network throughput without sacrificing the fairness. In addition, the average waiting time induced by the buffer implementation is just 0.25 time units. Finally, it is shown that the proposed method ensures fairness in a variety of common network topologies, including 6 × 6 mesh-torus, NSF, and Cost 239.
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