Distributed cell scheduling algorithms for virtual-output-queued switches

Abstract

Input buffered switches most efficiently use memory and crossbar bandwidth. Virtual output queueing (VOQ) is required to circumvent the head-of-line blocking limiting the throughput to 58.6%. For the slotted access control to the switch fabric, weighted arbitration algorithms achieve 100% throughput with lowest delays under all admissible traffic. Following the arbitration decision, distributed QoS-aware cell schedulers decide locally in each input port upon the next cell to forward. We treat cell scheduling algorithms employed in VOQ switches, in contrast to output queueing (OQ). We show that typical scheduling properties also hold under the VOQ architecture and give representative quantitative performance results.