Performance comparison between fixed length switching and variable length switching

Fixed length switching (FLS) and variable length switching (VLS) are two main types of switching architecture in high-speed input-queued switches. FLS is based on a cell-by-cell scheduling algorithm, while VLS operates on the variable packet granularity. This paper aims to make a comprehensive comparison between these two switching modes to guide the industrial design and academic research. We use stochastic models, Petri net models, analysis and simulations to investigate various performance measures of interest. Average packet latency, bandwidth utilization, segmentation and reassembly overhead, as well as packet loss are the identified key parameters that influence the outcome of the comparison. The results achieved in this paper are twofold. On one hand, it is shown that FLS enables smaller packet loss and lower packet delay in case of a short packet. On the other hand, VLS favors better bandwidth utilization, reduced implementation complexity and lower average packet delay. We recommend VLS in the conclusion since its disadvantages can be compensated by some methods, while the problems in FLS are difficult to be solved. Copyright q 2007 John Wiley & Sons, Ltd.