Halo: An Efficient and Scalable Distributed Control Strategy for AWGR-Based Optical Networks

Optical networks based on arrayed waveguide grating routers (AWGRs) present a promising solution for rapidly evolving data centers (DCs). However, the contention issue remains a significant challenge to their widespread adoption. Existing control strategies typically rely on time-slots that are both synchronized across the network and of fixed duration. This results in the fixed switching granularity. The determination of time-slot duration often involves a trade-off between flexibility and control overhead. In this paper, we propose Halo, a distributed control strategy that avoids contention without relying on time-slots. Halo decentralizes the scheduling tasks across the network. Each node independently issues <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Grants</i>, which are passed sequentially among source nodes with communication demands. The node holding the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Grant</i> is allowed to transmit a batch of data to the issuing node. Once the demand is no longer present, or the transmitted packet count exceeds a threshold, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Grant</i> is forwarded to the next node. As a result, synchronization operations among nodes is unnecessary, allowing the switching granularity to become flexible. Experimental results demonstrate that Halo significantly outperforms existing control strategies. In trace-based simulations, it achieves up to a 75.13% reduction in flow completion time (FCT). Additionally, we developed a prototype system and executed several real applications to demonstrate the practical feasibility of the Halo.