POXN: A New Passive Optical Cross-Connection Network for Low-Cost Power-Efficient Datacenters

Passive optical devices, characterized by low cost, zero energy consumption, and high reliability, are essential building blocks for today's telecom network infrastructure, permeating from conventional backbone transport networks towards next-generation broadband access networks. Motivated by the striking features of passive optical devices, in this paper, we seek their potential applications in emerging datacenter networks to tackle the scalability challenges arising from cost and power. Specifically, we propose passive optical cross-connection networks (POXNs) that enable cost-saving, power-efficient, and reliable communication within datacenters. To support POXNs in warehouse-scale datacenters, we address physical-layer scalability challenges by using advanced interconnection techniques. Next, we propose a distributed polling protocol to address link-layer issues that arise from the broadcast nature of the medium. The performance of our protocol is studied through analysis and simulation. In particular, we develop an analytical model to compute lower and upper bounds on the expected delay of a packet. Numerical results show that the mean packet delay is equal to the lower bound in one regime, while converges to the upper bound in the complementary regime. Results also show that our protocol can achieve high bandwidth efficiency (no less than 85% in our studied case). Additionally, we demonstrate that our protocol can embrace scheduling algorithms that support fairness and QoS. Last, we sketch the roles POXNs can play in various datacenter network architectures in terms of capital and operational cost reductions.