Concurrent round-robin dispatching scheme in a clos-network switch

A Clos-network switch architecture is attractive because of its scalability. Previously proposed implementable dispatching schemes from the first stage to the second stage, such as random dispatching, are not able to achieve a high throughput unless the internal bandwidth is expanded. This paper proposes a concurrent round-robin dispatching (CRRD) scheme for a Clos-network switch, to overcome the throughput limitation of the random dispatching scheme. The CRRD scheme provides high switch throughput without expanding internal bandwidth. CRRD implementation is very simple because only simple roundrobin arbiters are adopted. In CRRD, the round-robin arbiters concurrently perform the matching between requesting cells and output links in each first-stage module to dispatch the cells to available second-stage modules. We show that CRRD achieves 100% throughput under uniform traffic. When the offered load reaches 1.0, the pointers of roundrobin arbiters at the first-stage and second-stage modules are effectively desynchronized and contention is avoided. key words: Packet switch, Clos-network switch, dispatching, arbitration, throughput