Leveraging Commodity Photonics to Reduce Datacenter Network Latency

Abstract

Most datacenter network (DCN) designs focus on maximizing bisection bandwidth rather than minimizing server-to-server latency. They are, therefore, ill-suited for important latency-sensitive applications, such as high performance computing, realtime analytic systems and high-frequency financial trading. Although there are a number of existing approaches to reduce network latency, they are only partially effective, workload dependent, and often require network protocol changes.

In this thesis, we explore architectural approaches to building a low-latency DCN and introduce Quartz, a new optical design element consisting of a full mesh of switches connected by an optical ring. We can reduce the network latency of a hierarchical or random network by replacing portions of it with a Quartz ring. Our analysis shows that, in a standard 3-tier DCN, replacing high port-count core switches with Quartz can significantly reduce switching delays, and replacing groups of top-of-rack and aggregation switches with Quartz can significantly reduce congestion-related delays from cross-traffic. We overcome the complexity of wiring a complete mesh by using low-cost optical multiplexers that enable us to efficiently implement a logical mesh as a physical ring. We evaluate our performance using both simulations and a small working prototype. Our evaluation results confirm our analysis, and demonstrate that it is possible to build low-latency DCNs using inexpensive commodity elements without significant concessions to cost, scalability, or wiring complexity.