Fault-tolerant switched local area networks

The RAIN (Reliable Array of Independent Nodes) project at Caltech is focusing on creating highly reliable distributed systems by leveraging commercially available personal computers, workstations and interconnect technologies. In particular the issue of reliable communication is addressed by introducing redundancy in the form of multiple network interfaces per compute node. When using compute nodes with multiple network connections the question of how to best connect these nodes to a given network of switches arises. We examine networks of switches (e.g. based on Myrinet technology) and focus on degree-two compute nodes (two network adaptor cards per node). Our primary goal is to create networks that are as resistant as possible to partitioning. Our main contributions are: (i) a construction for degree-2 compute nodes connected by a ring network of switches of degree 4 that can tolerate any 3 switch failures without partitioning the nodes into disjoint sets; (ii) a proof that this construction is optimal in the sense that no construction can tolerate more switch failures while avoiding partitioning; and (ii) generalizations of this construction to arbitrary switch and node degrees and to other switch networks, in particular to a fully-connected network of switches.