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...

In ATM networks congestion control plays an essential role to support different quality of service guarantees for a large variety of traffic types. While for real-time communications, such as CBR and VBR services, a preventive open-loop congestion control mechanism is applied, a reactive closed-loop mechanism has been suggested for the ABR service class, which was introduced aiming at data communication applications. This paper presents a performance analysis of the ratebased congestion control mechanism developed by the ATM Forum. Using a differential equation approach for the computation of the evolution of the allowed cell rate and the buffer content during steady state, we derive closed-form expressions to estimate the maximum buffer lengths. These expressions can be formulated for steady-state conditions as well as for transient phases. In our approach, scenarios with and without priority for the resource management cells are considered. From numerical examples we conclude that an...

this paper, two models dealing with the call retrial phenomenon are presented. The first model considers a base station with a finite customer population and repeated attempts. A Markovchain modeling is proposed and a recursive solution of the state probabilities is presented. The second model focuses on the use of the guard channel concept to prioritize the handover traffic. Again, the retrial phenomenon plays an important role. The influence of the repeated attempt effect on the quality of service experienced by the mobile customers is discussed by means of numerical results

In ATM network environments, congestion control plays an important role to support different quality of service guarantees for a large variety of traffic types. While for real-time communications, like CBR and VBR services, a preventive open-loop congestion control mechanism is applied, a reactive closed-loop mechanism has been suggested for the ABR service class, which was introduced mainly for data communications. This paper presents an analysis to evaluate the performance of the rate-based congestion control mechanism developed by the ATM Forum. We derive formulae to compute the evolution of the allowed cell rate and the resulting buffer content during steady state. Therefore, we focus on traffic scenarios consisting of single sources as well as of homogeneous mixes of ABR sources. From numerical examples we can conclude that an appropriate setting of the control parameters is important to achieve a reasonable performance of the rate-based control mechanism, especially to obtain low...

This paper is a condensed introduction to self-similarity, self-similar processes, and the estimation of the Hurst parameter in the context of time series analysis. It gives an overview of the literature on this subject and provides some assistance in implementing Hurst parameter estimators and carrying out experiments with empirical time series. 1 Introduction The subject of self-similarity and the estimation of statistical parameters of time series in the presence of long-range dependence are becoming more and more common in several fields of science. Up to now there are only a few text books available, e.g. in [2], which give a comprehensive overview of the techniques and estimators. The intention of this paper is not to close this gap but to provide some basic information about self-similarity, self-similar processes, and estimators of the so-called Hurst parameter H. It gives a rather condensed introduction to self-similarity and contains a number of referenced papers which can ...

: This study investigates the properties of arti#cial recurrent neural networks. Particular attention is paid to the question of how these nets can be applied to the identi#cation and control of non-linear dynamic processes. Since these kind of processes can only insu#ciently be modelled by conventional methods, di#erent approaches are required. Neural networks are considered to be useful for this purpose due to their ability to approximate a wide class of continuous functions. Among the numerous network structures, especially the recurrentmulti-layer perceptron #RMLP# architecture is promising from application point of view. This network architecture has the wellknown properties of multi layer perceptrons and moreover these nets have the ability to incorporate temporal behavior. Departing from the original process description the applicability of RMLPs is investigated and di#erent learning algorithms for this network class are outlined. Furthermore, besides the conventional...

The investigation of feedback controls for telecommunication networks has recently gained considerable interest. The reason is the definition of a new ATM service category, the so-called Available Bit Rate service, whose primary goal is the economical support of applications with vague requirements for throughputs and delays. One class of possible feedback controls is formed by the rate-based mechanisms. Feedback from the network switches to the end systems gives users the information necessary to appropriately adjust their transmission rates. This type of control has been investigated to some extent in the existing literature, assuming a constant transmission rate on a bottleneck link. In this paper, we present a discrete-time analysis of a feedback control policy, taking into account a bottleneck link capacity that varies according to a general probability distribution. The control policy we look at belongs to the class of explicit rate control mechanisms considered for the Available...

: In this paper we present a fast ray-tracing technique with scalable approximation accuracy for field strength prediction in cellular mobile network planning. Automatic network design methods, like the Adaptive Base Station Positioning Algorithm (ABPA), [2, 3], perform a huge number of field strength estimations and require therefore a fast and accurate approximation. However, common prediction techniques either give only rough estimations or are too complex for fast evaluation, cf. [7]. The proposed new ray-tracing technique obtains its speed-up by taking advantage of the topological information inherent in the used triangulation data structure of the investigated terrain. By that, it is possible to apply simple mathematics and algorithms to trace individual rays. The applicability of the fast ray-tracing technique is demonstrated for both a single transmitter scenario and in conjunction with ABPA. Keywords: mobile communication, network planning, base station location, field stren...

Well investigated are growing context-sensitive languages (GCSL), i. e. languages defined by grammars that have only growing rules, where the left side of a growing rule is shorter than its right side. GCSL is characterized by quasi growing context-sensitive grammars (QGCSG), i. e. the rules therein are growing only with respect to a valuation of all the strings by a homomorphism to natural numbers with addition. In this paper we introduce weak growing context-sensitive grammars (WGCSG), i. e. grammars that are growing with a weighted valuation of all strings, where the weights are the values of a position valuation. Here we evaluate a string by summing up every product of a symbol value with its position value. For every position valuation which does not agree with the beginning of any exponential function, the corresponding class of WGCSGs characterizes CSL, shown by a somehow tricky proof. Such a valuation function is called unsteady. On the other hand all WGCSG related to steady ...

This paper discusses and compares the performance of three easy-to-implement congestion detection schemes for ATM switches supporting the ABR service category.