On Nonblocking Folded-Clos Networks in Computer Communication Environments

Folded-Clos networks, also referred to as fat-trees, have been widely used as interconnects in large scale high performance computing clusters. The switching capability of such interconnects in computer communication environments, however, is not well understood. In particular, the concept of nonblocking interconnects, which is often used by system vendors, has only been studied in the telephone communication environment with the assumption of a centralized controller. Such "nonblocking'' networks do not support nonblocking communications in computer communication environments where the network control is distributed. This paper theoretically analyzes the conditions for folded-Clos networks to achieve nonblocking communications in computer communication environments with various routing schemes including deterministic routing and adaptive routing, and establishes nonblocking conditions.