Reliable control protocol for crossbar arbitration

We describe an incremental request-grant protocol between line cards comprising virtual output queues and a central arbitration unit in a crossbar-based packet switch. Moreover, we introduce a method to make this protocol reliable in the presence of transmission errors that might lead to permanent inconsistency of the queue state information maintained by the arbiter. The protocol employs a "census" mechanism that travels the round-trip distance from line card to arbiter and back. We prove that it detects any inconsistency as well as its precise magnitude, enabling immediate corrective action.