Multicast-Capable Optical Circuit Switching: When Optical Multicasting Benefits Collective Communications?
Collective communications (CC) and distributed artificial intelligence (AI) training workloads involve substantial one-to-many chunked data transfers. Enabling optical multicast in next-generation optical circuit switching (OCS)-based data centers could streamline such traffic and improve CC efficiency. This paper presents our investigation of when and how to exploit optical multicast for CC and AI training. We discuss the topological property of OCS with multicast capability, showing reduced port-count overhead for the same connectivity degree as its point-to-point (P2P) counterpart. Further, by formulating and addressing the grouped-multicast CC schedule optimization (GMS), we study and compare the completion time of two key types of CC operations in GMS against the P2P schedule under identical port use conditions. Simulations with representative topologies reveal the potential of multicast OCS to enhance CC via a co-design of multicast-based topology and scheduling.