Patrick Wüchner

Finite-source M/M/S retrial queue with search for balking and impatient customers from the orbit

The present paper deals with a generalization of the homogeneous multi-server finite-source retrial queue with search for customers in the orbit. The novelty of the investigation is the introduction of balking and impatience for requests who arrive at the service facility with a limited capacity and FIFO queue. Arriving customers may balk, i.e., they either join the queue or go to the orbit. Moreover, the requests are impatient and abandon the buffer after a random time and enter the orbit, too. In case of an empty buffer, each server searches for a customer in the orbit after finishing service. All random variables involved in the model construction are supposed to be exponentially distributed and independent of each other. The primary aim of this analysis is to show the effect of balking, impatience, and buffer size on the steady-state performance measures. Concentrating on the mean response time, several numerical examples are investigated by the help of the MOSEL-2 tool used for creating the model and calculating the stationary characteristics.

Combined contention and TDMA-based communication in wireless sensor networks

Wireless sensor networks usually consist of a large number of very small, energy-constrained sensor nodes. The nodes capture information from their immediate environment to send it to a destination node (sink) in a timely manner. This work proposes a combined contention and TDMA-based approach for load balancing and a discrete-time Markov model that allows to study the trade-off between energy consumption and transfer delay in clustered wireless sensor networks. Our investigations show that the length of the TDMA frame needs to be configured close to the minimum that is capable of transferring the offered load for optimizing energy efficiency and minimizing the delay.

The Impact of Retrials on the Performance of Self-Organizing Systems

ABSTRACT This article describes the application of the theory of retrial queues in capturing certain aspects of self-organizing behavior that arises, for example, in Peer-to-Peer networks. It can be shown that retrials have a fair effect on the performance of such self-organizing systems, and thus, should be taken into account adequately during the design and evaluation of these systems. Moreover, it can be shown that there is a notable difference between finite-source and infinite-source retrial queueing models. The main goal of this paper is to show the practical applicability of retrial queues and some of their varieties.

Modeling of Self-Organizing Systems: An Overview

This paper gives a systematic overview on modeling formalisms suitable for modeling self-organizing systems. We distinguish between micro-level model- ing and macro-level modeling. On the micro level, the behavior of each entity and the interaction between different object must be described by the model. Macro- level modeling abstracts from the individual entities and only looks at the behav- ior of the system variables of interest. The differentiations between discrete and continuous time and between discrete and continuous state space lead to different descriptions of the model.

In memory of dr. gunter bolch

The MMB Special Interest Group mourns for a highly valued member. Gunter Bolch died on May 29, 2008 in Erlangen, after a serious illness. He was very open minded, a beautifully moderate person, and a friend in its truest meaning. With MMB, he shared his academic passion of performance modelling, in general, and queueing networks, in particular.

Modeling of Self-Organizing Systems

A goal of computing and networking systems is to limit administrative requirements for users and operators. A technical systems should be able to configure itself as much as possible to increase the usability. This leads to the design of self-organizing systems. Self-organizing systems emerge as an increasingly important area of research, not only for computer networks but also in many other fields. For analyzing properties of complex systems, a mathematical model for these systems may be useful. Whether a model with discrete time or with continuous time fits better, depends on the properties of the system and which analysis should be done in the model. In this paper we give a comparison between discrete and continuous models and we give a formal definition for modeling continuous complex systems. Then this theory is applied to model slot-synchronization in wireless networks.