Fast ping-pong arbitration for input-output queued packet switches

Input-output queued switches have been widely considered as the most feasible solution for large capacity packet switches and IP routers. In this paper, we propose a ping-pong arbitration scheme (PPA) for output contention resolution in input-output queued switches. The challenge is to develop a high speed and cost-effective arbitration scheme in order to maximize the switch throughput and delay performance for supporting multimedia services with various quality-of-service (QoS) requirements. The basic idea is to divide the inputs into groups and apply arbitration recursively. Our recursive arbiter is hierarchically structured, consisting of multiple small-size arbiters at each layer. The arbitration time of an n-input switch is proportional to log₄[n/2] when we group every two inputs or every two input groups at each layer. We present a 256 × 256 terabit crossbar multicast packet switch using the PPA. The design shows that our scheme can reduce the arbitration time of the 256 × 256 switch to 11 gates delay, demonstrating the arbitration is no longer the bottleneck limiting the switch capacity. The priority handling in arbitration is also addressed.