05 Fakultät Informatik, Elektrotechnik und Informationstechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6

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1993 - 199927

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Institute: search.filters.UBSInstitut.Institut für Parallele und Verteilte SystemeStart date: 1993End date: 1999

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Now showing 1 - 10 of 27
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    A protocol for preserving the exactly-once property of mobile agents
    (1997) Rothermel, Kurt; Straßer, Markus
    Mobile agents are autonomous objects that can migrate from node to node of a computer network. Mobile agent technology has been proposed for various application areas, including electronic commerce, systems management and active messaging. Many of these applications - especially those for electronic commerce - require agents to be performed 'exactly once', independent of communication and node failures. In other words, once a mobile agent has been launched, it must never be lost before its execution is finished. Moreover, each 'portion' of the agent performed at the visited nodes is performed exactly once. Due to the autonomy of mobile agents, there is no 'natural' instance that monitors the progress of an agent's execution. As a result of that agents may be blocked due to node crashes or network partitioning even if there are other nodes available that could continue processing. In this paper, we will describe a protocol that ensures the exactly once property of agents and additionally reduces the blocking probability of agents by introducing so-called observer nodes for monitoring the progress of agents. This protocol is based on conventional transactional technology, such as defined by X/Open DTP or CORBA OTS. It is implemented in the Mole, a mobile agent system developed at Stuttgart University.
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    Task allocation in distributed multimedia systems based on the host-satellite model
    (1998) Dermler, Gabriel; Iqbal, Ashraf
    Multimedia applications require intermediate processing between media sources and sinks. In addition to end-user machines intermediate computers can be used for performing media processing. This possibility leads to the problem of allocating processing components on various computers. In this paper, we study this problem in the context of star-shaped application graphs which have to be allocated between given end-user machines (satellites) and a central computer (host). The problem is formulated in terms of best achievable bottleneck resource usage. Several approaches are considered including anapproximate scheme and two fast-heuristics. Performance measurements show the efficiency of the considered approaches. A discussion of our approach shows important differences to solutions provided for related problems of graph partitioning and mapping.
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    System mechanisms for partial rollback of mobile agent execution
    (1999) Straßer, Markus; Rothermel, Kurt
    Mobile agent technology has been proposed for various fault-sensitive application areas, including electronic commerce, systems management and active messaging. Recently proposed protocols providing the exactly-once execution of mobile agents allow the usage of mobile agents in these application areas. Based on these protocols, a mechanism for the application-initiated partial rollback of the agent execution is presented in this paper. The rollback mechanism uses compensating operations to roll back the effects of the agent execution on the resources and uses a mixture of physical logging and compensating operations to rollback the state of the agent. The introduction of different types of compensating operations and the integration of an itinerary concept with the rollback mechanism allows performance improvements during the agent rollback as well as during the normal agent execution.
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    ATOMAS : a transaction-oriented open multi agent system; final report
    (1998) Straßer, Markus; Baumann, Joachim; Hohl, Fritz; Schwehm, Markus; Rothermel, Kurt
    The electronic marketplace of the future will consist of a large number of services located on an open, distributed and heterogeneous platform, which will be used by an even larger number of clients. Mobile Agent Systems are considered to be a precondition for the evolution of such an electronic market. They can provide a flexible infrastructure for this market, i.e. for the installation of new services by service agents as well as for the utilization of these services by client agents. Mobile Agent Systems basically consist of a number of locations and agents. Locations are (logical) abstractions for (physical) hosts in a computer network. The network of locations serves as a unique and homogeneous platform, while the underlying network of hosts may be heterogeneous and widely distributed. Locations therefore have to guarantee independence from the underlying hard- and software. To make the Mobile Agent System an open platform, the system furthermore has to guarantee security of hosts against malicious attacks.
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    An agent based framework for the transparent distribution of computations
    (1999) Straßer, Markus; Baumann, Joachim; Schwehm, Markus
    A mobile agent based framework for the transparent distribution and concurrent execution of computations is presented. The framework uses design patterns like the master-slave, abstract factory or the strategy pattern. The architecture of the framework is built on top of a mobile agent system. A performance model allows to identify performance bottlenecks and unbalanced situations within the framework. The framework has been implemented and tested on top of the mobile agent system Mole.
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    A framework for cooperative object recognition
    (1999) Oswald, Norbert; Levi, Paul
    This paper explores the problem of object recognition from multiple observers. The basic idea is to overcome the limitations of the recognition module by integrating information from multiple sources. Each observer is capable of performing appearance-based object recognition, and through knowledge of their relative positions and orientations, the observerrs can coordinate their hypotheses to make object recognition more robust. A framework is proposed for appearance-based object recognition using Canny edge maps that are effectively normalized to be translation and scale invariant. Object matching is formulated as a non-parametric statistical similarity computation between two distribution functions, while information integration is performed in a Bayesian belief net framework. Such nets enable both a continuous and a cooperative consideration of recognition result. Experiments which are reported on two observers recognizing mobile robots show a significant improvent of the recognition results.
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    The shadow approach : an orphan detection protocol for mobile agents
    (1998) Baumann, Joachim; Rothermel, Kurt
    Orphan detection in distributed systems is a well researched field for which many solutions exist. These solutions exploit well defined parent-child relationships given in distributed systems. But they are not applicable in mobile agent systems, since no similar natural relationship between agents exist. Thus new protocols have to be developed. In this paper one such protocol for controlling mobile mobile agents and for orphan detection is presented. The shadow' approach presented in this paper uses the idea of a placeholder (shadow) which is assigned by the agent system to each new agent. This defines an artificial relationship between agents and shadow. The shadow records the location of all dependent agents. Removing the root shadow implies that all dependent agents are declared orphan and are eventually terminated. We introduce agent proxies that create a path from shadow to every agent. In an extension of the basic protocol we additionally allow the shadow to be mobile. The shadow approach can be used for termination of groups of agents even if the exact location of each single agent is not known.
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    Adaptive scheduling of multimedia documents
    (1997) Wirag, Stefan
    Multimedia presentations are applicable in various domains such as advertising, commercial presentations or education. Multimedia presentations are described by multimedia documents. The presentation of multimedia documents require vast system resources due to the huge amount of data that has to be transferred and processed by the computer system. If multimedia documents can be accessed on-line via different types of networks and be presented on various types of terminals, such as PCs or Set-Top-Units, different amounts of resources may be available at presentation time. Hence, it can happen that there are not enough resources to render a multimedia document according to the specification. For usual multimedia documents resource scarcity implies an arbitrarily reduced quality of the presentation or it can even be impossible to start or continue the presentation. To handle resource scarcity in a better way, multimedia documents can be specified flexible so that they can be adapted to different resource situations. Our temporal model provides abstractions to specify flexible multimedia documents on two levels. It is possible to specify multimedia documents with alternative presentation parts. Further on, the presentation behavior of media objects can vary within specified limits. Hence, the temporal model allows to compose presentations which have a defined behavior when resource restrictions occur. The presented adaptive scheduling algorithm uses the flexibility in specifications to adapt presentations at regular intervals to the current resource situation. Hence, the quality of presentations is reduced or increased in a defined manner.
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    Ressourcenreservierung und Task-Plazierung in verteilten Multimedia-Systemen
    (1999) Dermler, Gabriel; Rothermel, Kurt (Prof. Dr.)
    In dieser Arbeit werden grundlegende Aspekte der Dienstgüteerbringung für verteilte Multimedia-Anwendungen untersucht. Aufbauend auf einer Anwendungsmodellierung in Form von Flußgraphen, die aus Verarbeitungskomponenten zusammengesetzt werden, sowie einer Dienstgütearchitektur, die Dienstgütebegriffe auf der Anwendungs- und der Systemebene unterscheidet, werden Konzepte und Lösungen erarbeitet, die eine garantierte und optimierte Bereitstellung von Dienstgüte ermöglichen. Einen Schwerpunkt bilden Protokolle zur Reservierung von Ressourcen, die auf komplexe Flußgraphen anwendbar sind. Die Protokolle erlauben individuelle Dienstgütevorgaben an den Senken eines Flußgraphen und berücksichtigen die Verfügbarkeit von Rechner- und Netzwerkressourcen sowie funktionale Einschränkungen, die durch das Design der Komponenten definiert sind. Ferner sind sie unabhängig von der Verteilung der Komponenten auf Rechnern eines verteilten Systems anwendbar und in der Lage Dienstgütegarantien sicherzustellen. Als ein zweiter Schwerpunkt werden Mechanismen zur Plazierung von Anwendungskomponenten vorgestellt, die eine optimale Ausnutzung von Ressourcen in einem verteilten System sicherstellen. Hierzu werden Algorithmen zur Berechnung günstiger Plazierungen entwickelt und bewertet. Ferner wird ein Protokoll vorgestellt, welches zur Instanziierung eines Flußgraphen verwendet werden kann. Auf der Grundlage der vorgestellten Konzepte wird die Beziehung zwischen der Plazierung eines Flußgraphen sowie der erforderlichen Ressourcenreservierung dargestellt.
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    A comparison of mechanisms for locating mobile agents
    (1999) Baumann, Joachim
    In this paper we present different possible approaches for locating mobile agents and introduce a classification for them. We will use this classification to categorize mechanisms proposed in standards and implemented in mobile agent systems. Then we assess the different mechanisms regarding their fault tolerance, their message complexity and the migration delay they induce. We conclude by combining the different assessments to allow a comparison of all mechanisms.