Speedup of Clos packet switches that provide delay guarantees

A multihop Clos fabric may provide the terabit capacity by using the smaller switching elements (SE). When the traffic load is balanced over the switches in a middle stage, all the traffic would get through the fabric, as long as the switch outputs are not overloaded. We derive formulas of the maximum utilization for which certain tolerable delay is guaranteed, and formulas of the minimum speedup for which tolerable delay is guaranteed and 100% switch utilization is achieved in a Clos packet switch. Finally, performances of the architectures comprising cross-bars and shared buffers as SEs are compared and their scalability is discussed.