Elastic optical ring with flexible spectrum ROADMs: An optical switching architecture for future data center networks

Abstract

Data center networks (DCN) are facing significant increase in both scale and bandwidth requirement, and various intra-DCN optical circuit switching architectures have been proposed to handle the inter-rack traffic. As the size of data centers are becoming larger, ring based architectures have received considerable interests, because a ring can provide connectivity to a large number of racks that are distributed far apart in a data center. However, due to the specific data center traffic pattern, fixed spectrum allocation scheme in existing ring based DCNs will lead to low spectrum utilization and hence low system throughput. In this paper, we propose to introduce flexible spectrum allocation into ring based intra-DCN optical switching, so that spectrum utilization can be improved. We design an elastic ring intra-DCN optical circuit switching architecture with flexible spectrum reconfigurable optical add-drop multiplexers (FS-ROADMs). Adopting flexible spectrum allocation in elastic ring, a spectrum allocation problem which is essentially a very complex yet interesting optimization problem arises. For a given set of inter-rack traffic requests, we develop an integer linear program formulation as well as a heuristic algorithm to solve the flexible spectrum allocation problem. We study how the inter-rack traffic pattern may affect the system performances in both fixed and elastic ring cases. For elastic ring, we also analyze and evaluate the computational complexity in solving the spectrum allocation problem. Our results demonstrate that, to handle uneven inter-rack traffic pattern in DCNs, elastic ring can remarkably improve system throughput, though its computational complexity of spectrum allocation problem is slightly higher than that of the fixed ring.