Smooth switching problem in buffered crossbar switches

Abstract

Scalability considerations drive the switch fabric design to evolve from output queueing to input queueing and further to combined input and crosspoint queueing (CICQ). However, few CICQ switches are known with guaranteed quality of service, and credit-based flow control induces a scalability bottleneck. In this paper, we propose a novel CICQ switch called the smoothed buffered crossbar or sBUX, based on a new design objective of smoothness and on a new rate-based flow control scheme called the smoothed multiplexer or sMUX. It is proved that with a buffer of just four cells at each crosspoint, sBUX can utilize 100% of the switch capacity to provide deterministic guarantees of bandwidth and fairness, delay and jitter bounds for each flow. In particular, neither credit-based flow control nor speedup is used, and arbitrary fabric-internal latency is allowed between line cards and the switch core.