Topology optimization of interconnection networks

This paper describes an automatic optimization tool that searches a family of network topologies to select the topology that best achieves a specified set of design goals while satisfying specified packaging constraints. Our tool uses a model of signaling technology that relates bandwidth, cost and distance of links. This model captures the distance-dependent bandwidth of modern high-speed electrical links and the cost differential between electrical and optical links. Using our optimization tool, we explore the design space of hybrid Clos-torus (C-T) networks. For a representative set of packaging constraints we determine the optimal hybrid C-T topology to minimize cost and the optimal C-T topology to minimize latency for various packet lengths. We then use the tool to measure the sensitivity of the optimal topology to several important packaging constraints such as pin count and critical distance

I. Introduction

Interconnection networks are today used in a variety of applications such as switch and router fabrics [6], and memory-processor interconnect [11]. Large scientific computers such as ASCI White [1], have thousands of processors and large internet routers, such as the Avici TSR, are scalable to thousands of ports. These applications, and many others, demand networks that can be incrementally expanded from small (less than ten node) configurations to large (many thousands of nodes) configurations.