FastReChain: Highly Responsive and Low-Overhead Centralized Route Scheduling in Clos Datacenter Networks

Abstract: Ever since Clos topologies were used in datacenter networks (DCNs), a practical centralized scheduling algorithm that supports dynamic scheduling has been absent. The introduction of optical switches in DCNs as a future-proof solution exacerbates this problem due to several properties of optical switches, such as the fact that they are generally bufferless and therefore rely on centralized scheduling, and that they have long switching times and therefore require the number of rearrangements to be minimized. In this paper, we propose a centralized scheduling algorithm that achieves theoretical maximum throughput even in one-rate bidirectional Clos networks, while producing schemes with near-minimal numbers of rearrangements. It is the only algorithm that directly supports bidirectional Clos networks and has a time efficiency high enough to support dynamic scheduling to date. For static minimal rewiring, its running time ranges from a fraction to a few hundredths of other algorithms, and the number of rearrangements has also been steadily improved, allowing for more frequent adjustments and less impact on ongoing communications. In addition, the algorithm is very flexible and can support various functional requirements in real-world environments. We achieve this result through the replacement chain concept and bitset optimization.