QsNet is a high speed interconnect designed by Quadrics used in HPC clusters, particularly Linux Beowulf Clusters. Although it can be used with TCP/IP; like SCI, Myrinet and Infiniband it is usually used with a communication API such as MPI or SHMEM called from a parallel program.
The interconnect consists of a PCI card in each compute node and one or more a dedicated switch chasses. These are connected with a copper cables. Within the switch chassis are a number of line cards that carry Elite switch ASICs. These are internally linked to form a fat tree topology. Like other interconnects such as Myrinet very large systems can be build by using multiple switch chasses arranged as spine (top-level) and leaf (node-level) switches. Such systems are usually called federated networks.