The Performability Manager

The authors describe the performability manager, a distributed system component that contributes to a more effective and efficient use of system components and prevents quality of service (QoS) degradation. The performability manager dynamically reconfigures distributed systems whenever needed, to recover from failures and to permit the system to evolve over time and include new functionality. Large systems require dynamic reconfiguration to support dynamic change without shutting down the complete system. A distributed system monitor is needed to verify QoS. Monitoring a distributed system is difficult because of synchronization problems and minor differences in clock speeds. The authors describe the functionality and the operation of the performability manager (both informally and formally). Throughout the paper they illustrate the approach by an example distributed application: an ANSAware-based number translation service (NTS), from the intelligent networks (IN) area

Quality of Service Management using Generic Modelling and Monitoring Techniques

In our previous work, we have presented the performability manager, a distributed environment component that, using a model-based approach, realises and maintains user-requested qos. Generic modelling and monitoring techniques are inevitable for such a model-based approach. The planning of user-requested qos is done by the evaluation of automatically created models out of a library of model components, while achieved qos is checked using monitoring. In this paper we experiment with the generic modelling and monitoring of a multimedia service in an open distributed processing environment. We both use simulation and numerical techniques to evaluate the models. In this particular case study, end-user requested qos is specified by throughput, mean end-to-end delay and delay-jitter. 1 Introduction to quality of service management The Performability Manager (pm) is a distributed environment component which maintains the user-requested Quality of Service (qos) by dynamically reconf..

Dynamic routation in distributed environments

In this paper, we address the issues of communication routing and process allocation in an integrated way, the so-called routations. After the definition of a formal framework for distributed systems and their applications, routations can be defined. Existing routing and allocation algorithms are discussed in a unified way, using this framework. This facilitates the basis for a proper comparison of algorithms. We then propose a routation algorithm based on the A* intelligent tree-search algorithm. Although this algorithm yields optimal routations, it is too slow to be used in practice. We therefore developed three heuristics, each again in three variants, that accomplish the same task, however, with far reduced computational effort. We then propose to use the A* algorithm in combination with one of the heuristics in a real distributed environment. In the appendices we describe the pseudo-codes of the introduced algorithms, as well as an experimental, ANSAware-based, distributed system in which the routations take place using the heuristics we developed

Modelling aspects of model-based dynamic QoS management by the performability manager

The Performability Manager (PM) is a distributed system component which maintains the application-requested Quality of Service (QoS) by dynamically reconfiguring ANSAware-based distributed applications, using a model-based optimization procedure. The PM receives information about the ANSAware-based application from a distributed monitoring process based on JEWEL and DEMON. With this information, and using predefined stochastic Petri net (SPN) models of ANSAware applications, the PM automatically constructs an overall SPN performability model which is subsequently used for the determination of the provided QoS. Based on the analysis results, the PM can decide to initiate on-line system reconfigurations, if such is needed for maintaining the requested QoS. ANSAware provides facilities for these dynamic reconfigurations. In this paper we focus on the modelling aspects of model-based dynamic QoS management by the performability manager. We present an ANSAware-based experimental distributed environment in which the modelling and evaluation aspects are totally automated. We also show the feasibility of the proposed PM by presenting some operational results

Quality of Service Management in Distributed Systems using Dynamic Routation

With the advent of multimedia in computing and communication systems, a new set of requirements has been imposed. Because multimedia applications demand a guaranteed Quality of Service (QoS), the sharing of resources, by means of allocating applications and their communications on computing and communication resources, is an important issue. In this paper, we address the issues of communication routing and process allocation in an integrated way, the so-called routations. It is only in such an integrated way that end-to-end Quality of Service requirements of multimedia end-users can be fulfilled