Multi-Step Scheduling Strategy in Input-Queued Switches

Input Queued switches are increasingly used in ATM switches and high performance routers. It has been proved that combining VOQ (virtual output queueing) technology and some weighted scheduling algorithms, such as LQF (longest queue first) and OCF (oldest cell first), the switch throughput can reach 100% for all cell arrivals with independent distributions. But the algorithms of LQF and OCF are so complicated that they cannot be easily implemented in hardware. A multi step scheduling strategy proposed in this paper makes it possible to implement the weighted scheduling algorithms in hardware. It is also proved that the switches based on the LQF by introducing the multi step scheduling strategy can still get 100% throughput and the better delay property for arrivals with independent distributions.