Fixed-length switching vs. variable-length switching in input-queued IP switches

Abstract

Many large-scale, high speed routers adopt input-queued switches with virtual output queuing (VOQ) for preventing head of line (HOL) blocking. Switching based on cell-by-cell scheduling algorithms (fixed-length switching) have been widely studied for years, while a new idea of transferring IP packet based on a packet-by-packet scheduling algorithm (variable-length switching) has been proposed recently. Fixed-length and variable-length switching can be significantly different in performance and implementation complexity. This paper establishes experiments at the aim of evaluating one design issue: whether it should be fixed-length switching or variable-length switching. We investigate various performance measures of interest: bandwidth utilization, packet loss, segmentation and reassembling overhead, as well as average packet latency. The focus of the paper is on identifying key parameters that influence the outcome of this comparison, and on quantifying the potential benefits of each switching mode.