On the relevance of long-range dependence in network traffic

There is much experimental evidence that network traffic processes exhibit ubiquitous properties of self-similarity and long-range dependence, i.e., o f correlations over a wide range of time scales, However, there is still co nsiderable debate about how to model such processes and about their impact on network and application performance. In this paper, we argue that much r ecent modeling work has failed to consider the impact of two important para meters, namely the finite range of time scales of interest in performance e valuation and prediction problems, and the first-order statistics such as t he marginal distribution of the process, We introduce and evaluate a model in which these parameters can be controlled. Specifically, our model is a m odulated fluid traffic model in which the correlation function of the fluid rate matches that of an asymptotically second-order selfsimilar process wi th given Hurst parameter up to an arbitrary cutoff time lag, then drops to zero, We develop a very efficient numerical procedure to evaluate the perfo rmance of a single-server queue fed with the above fluid input process. We use this procedure to examine the fluid loss rate for a wide range of margi nal distributions, Hurst parameters, cutoff lags, and buffer sizes, Our mai n results are as follows. First, we find that the amount of correlation tha t needs to be taken into account for performance evaluation depends not onl y on the correlation structure of the source traffic, but also on time scal es specific to the system under study. For example, the time scale associat ed with a queueing system is a function of the maximum buffer size. Thus, f or finite buffer queues, we find that the impact on loss of the correlation in the arrival process becomes nil beyond a time scale we refer to as the correlation horizon, This means, in particular, that for performance-modeli ng purposes, we may choose any model among the panoply of available models (including Markovian and self-similar models) as long as the chosen model c aptures the correlation structure of the source traffic up to the correlati on horizon, Second, we find that loss can depend in a crucial way on the ma rginal distribution of the fluid rate process. Third, our results suggest t hat reducing loss by buffering is hard for traffic with correlation over ma ny time scales. We advocate the use of source traffic control and statistic al multiplexing instead.