Adaptive routing in Clos networks

We describe a method of controlling a three-stage Clos nonblocking switch where 'speculative' self-routing over the Clos fabric is augmented with reservations over a control network that connects controllers in the input and output stages of the switch. The effect is that most connections succeed over the speculative path, while those subject to contention are processed over the control network. We present simulation results which indicate that the inclusion of a control network yields significant benefits under heavily nonuniform traffic conditions.