Sandwich Tree: A new datacenter network based on passive optical devices

Most datacenter network designs overwhelmingly use expensive and power-consuming electronic switches or expensive active optical switches with long reconfiguration time. In this paper, we explore architectural solutions to leverage the design elements of Passive Optical Cross-Connection Networks with Multiple Planes (POXN/MPs) and Passive Optical Cross-Connection Networks with Multiple Planes and Bundled Ports (POXN/MP-BPs), both of which consist primarily of passive optical fabrics and optical transceivers that replace groups of switches in hierarchical networks. Through simple physical interconnections, our proposed architectures allow datacenter network (DCN) to incrementally scale out in network capacity. From developed formulas for calculating cost and power consumption, we demonstrate that POXN/MP-BPs can significantly reduce the cost and power consumption of datacenter networks compared to the traditional DCNs. To lower overhead and adapt to the types of real datacenter scenarios that are possible with POXN/MP-BPs, we propose the new Multiple Channels with Bundled Ports Distributed Access Protocol (MCBDAP), which outperforms the Multiple Channels Distributed Access Protocol (MCDAP) for POXN/MP in terms of bandwidth efficiency, especially for those applications involving higher proportions of inter-rack traffic than intra-rack traffic.