Scalable and Fair Admission Control for On-Chip Nanophotonic Crossbars

Advances in CMOS-compatible photonic elements have made it plausible to exploit nanophotonic communication to overcome the limitations of traditional NoCs. Amongst the architectures proposed to exploit nanophotonic technology for on-chip communication networks, optical crossbars have been shown to provide high performance in terms of bandwidth and latency. Generally, optical crossbars provide a huge volume of network resources that are shared among cores. In this paper, we present a fair and efficient admission control mechanism for shared wavelengths and buffer space in an optical crossbar. We model the buffer management and wavelength assignment as a utility-based convex optimization problem, whose solution determines the admission control policy. Thanks to efficient convex optimization techniques, we obtain the globally optimal solution of the admission control optimization problem using simple and yet efficient iterative algorithms. Then, we cast our solution procedure as an iterative algorithm to be implemented inside a central admission controller. Our experimental results corroborate the efficacy of using such an admission controller to manage the shared resources of the system. It also confirms that the proposed admission control algorithm works well for various traffic patterns and parameters, and promisingly evinces tractable scalability properties as the number of cores in the crossbar increases.