In our quest to better understand network tra#c dynamics, we examine Internet chat systems. Although chat as an application does not contribute huge amounts of tra#c, chat systems are known to be habit-forming. This implies that catering to such users can be a promising way of attracting them, especially in low bandwidth environments such as wireless networks.

In previous work [24], Fractal Point Processes (FPPs) have been proposed as novel tools for understanding, modeling and analyzing diverse types of self-similar traffic behavior. We apply the FPP models in the context of network traffic modeling and performance analysis. Two qualitatively different fractal data sets (Bellcore Ethernet traces) are characterized by FPP models. Comparison of model-driven and trace-driven queueing simulation results show that the matched models yield close agreement with the traces over a wide range of system parameters. We also show that under suitable conditions, the FPP models yield Gaussian processes. Queueing simulation shows that the FPP models can be computationally efficient alternatives for generating fractional Gaussian noise processes. Finally, we divide fractal traffic into two types, applicationlevel fractal traffic and network-level fractal traffic, and argue that each type has radically different implications for the design and control of fut...

For the performance analysis of ATM networks carrying Variable Bit Rate (VBR) MPEG video sequences there is a need for appropriate video traffic models. In this paper, we discuss Markov chain models for this specific type of traffic with respect to several statistical properties and their ability to predict cell losses at buffers of ATM multiplexers. We intentionally selected a simple model class to check for its appropriateness to model a complex traffic type. The results of this paper show that Markov chain models can be used efficiently for MPEG video traffic under the following conditions. The Group of Pictures (GOP) generation process should be modeled rather than the frame process. If the performance measures depend on the correlation properties of the video traffic the scene process should also be considered in the course of the model development. 1 Introduction In B-ISDNs on the basis of the ATM, a major part of the traffic will be generated by multimedia sources like teleco...

The diversity in web object types and their resource requirements contributes to the unpredictability of web service provisioning. In this paper, an efficient admission control algorithm, PACERS, is proposed to provide different levels of services based on the server workload characteristics. Service quality is ensured by periodical allocation of system resources based on the estimation of request rate and service requirements of prioritized tasks. Admission of lower priority tasks is restricted during high load periods to prevent denial-of-services to high priority tasks. A double-queue structure is implemented to reduce the effects of estimation inaccuracy and to utilize the spare capacity of the server, thus increasing the system throughput. Response delays of the high priority tasks are bounded by the length of the prediction period. Theoretical analysis and experimental study show that the PACERS algorithm provides desirable throughput and bounded response delay to the prioritized tasks, without any significant impact on the aggregate throughput of the system under various workload.

We investigate the performance of CBR traffic in the context of large-scale networks, where many connections and switches coexist and interact. We develop a framework for simulating such networks, decoupling the influence of breadth and depth. Our results are briefly as follows: we found that a Poisson stream is a good approximation to a superposition of many CBR streams with differing phases and bandwidths. Delays incurred by a reference stream with cross traffic composed of many CBR streams with different bandwidths and phases do not exceed a few cell times even under heavy load, which means that buildout buffers of 10 to 20 cells seem to be sufficient after traversing 20 switches. CBR traffic can be efficiently served by the First Come First Served (FCFS) scheduling discipline, which has the least implementation cost. Surprisingly, the Round Robin (RR) and Weighted Round Robin (WRR) disciplines perform worse than FCFS, despite their greater implementation complexity. We also compare an analytical approximation method, based on...

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Motivated by telecommunication applications, we investigate ways to estimate the parameters of a nonhomogeneous Poisson process with linear rate over a finite interval, based on the number of counts in measurement subintervals. Such a linear arrival-rate function can serve as a component of a piecewise-linear approximation to a general arrival-rate function. We consider ordinary least squares (OLS), iterative weighted least squares (IWLS) and maximum likelihood (ML), all constrained to yield a nonnegative rate function. We prove that ML coincides with IWLS. As a reference point, we also consider the theoretically optimal weighted least squares (TWLS), which is least squares with weights inversely proportional to the variances (which would not be known with data). Overall, ML performs almost as well as TWLS. We describe computer simulations conducted to evaluate these estimation procedures. None of the procedures differ greatly when the rate function is not near 0 at either end, but when the rate function is near 0 at one end, TWLS and ML are significantly more effective than OLS. The number of measurement subintervals (with fixed total interval) makes surprisingly little difference when the rate function is not near 0 at either end. The variances are higher with only two or three

We develop a practical, multiple time scale model for MPEG video traffic whose accuracy and relatively low computational complexity make it well suited for real-time traffic generation experiments on broadband networks. The major feature of our approach is the decomposition of the frame size sequence into simple slow and fast time scale components. This accurately captures aspects of queueing behavior that are difficult to model otherwise. The model also exploits the existence of deterministic patterns that are due to the MPEG coding scheme. We also present a novel modeling approach based on spatial renewal processes (SRP). This model gives exact matches to any desired marginal distribution and any convex non-increasing autocorrelation function. In particular, it can match subexponentially decaying autocorrelations (i.e., can capture long range dependence), something no other model of comparable complexity can do. A SRP is suited for on-line model construction, since it involves no sea...

A significant discovery from this work is that although video traffic has complicated short- and longrange dependence in the time domain, the corresponding wavelet coefficients are no longer long-range dependent in the wavelet domain. Therefore, a "short-range" dependent process can be used to model video traffic in the wavelet domain. In this work, we develop such wavelet models for VBR video traffic. The strength of the developed wavelet models includes (1) it provides a unified approach to model both long-range and short-range dependence in video traffic simultaneously, (2) it has the ability to reduce the temporal dependence so significantly that the wavelet coefficients can be modeled by either independent or Markov models, and (3) the model results in a computationally efficient method on generating high quality video traffic. Key words: wavelet, long-range dependence, short-range dependence, traffic modeling, VBR video traffic. Topics: video networking, B-ISDN and ATM, admission control. I.

Compression of digital video is the only viable means to transport real-time full-motion video over BISDN/ATM networks. Traffic streams generated by video compressors exhibit complicated patterns which vary from one compression scheme to another. In this paper we investigate the traffic characteristics of video streams which are compressed based on the MPEG standard. Our study is based on 23 minutes of video obtained from an entertainment movie. A particular significance of our data is that it contains all types of coded frames, namely: Intra-coded (I), Prediction (P), and Bidirectional (B) MPEG frames. We describe the statistical behavior of the VBR stream using histograms and autocorrelation functions. A procedure is developed to determine the instants of a scene change based on the changes in the size of successive I frames. It is found that the length of a scene can be modeled by a geometric distribution. A model for an MPEG traffic source is developed in which frames are generated...