05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access A protocol for preserving the exactly-once property of mobile agents(1997) Rothermel, Kurt; Straßer, MarkusMobile 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.Item Open Access System mechanisms for partial rollback of mobile agent execution(1999) Straßer, Markus; Rothermel, KurtMobile 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.Item Open Access ATOMAS : a transaction-oriented open multi agent system; final report(1998) Straßer, Markus; Baumann, Joachim; Hohl, Fritz; Schwehm, Markus; Rothermel, KurtThe 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.Item Open Access The shadow approach : an orphan detection protocol for mobile agents(1998) Baumann, Joachim; Rothermel, KurtOrphan 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.Item Open Access TIEMPO: an authoring and presentation system for interactive multimedia(1995) Wirag, Stefan; Wahl, Thomas; Rothermel, KurtThe composition of interactive multimedia titles is a challenge for all advanced multimedia authoring tools. When non-interactive titles were specified by aligning the media items on a temporal axis such as time lines or tracks, now interactive multimedia titles require a non-linear temporal model. Thus, authoring becomes more complex, and the structure of a title is more difficult to visualize. TIEMPO addresses two areas: First, a temporal model satisfying the specification needs of interactive multimedia; Secondly, an interface for easy and rapid authoring of multimedia titles. This paper presents the architecture and design principles of the TIEMPO authoring and presentation environment.Item Open Access A robust and efficient mechanism for constructing multicast acknowledgment trees(1999) Rothermel, Kurt; Maihöfer, ChristianA great variety of todays networked applications require a reliable multicast service. A number of the proposed reliable multicast protocols use a positive acknowledgment scheme, which returns ACKs to the sender to confirm correct delivery. To avoid the well-known implosion problem in the case of large receiver groups, often a tree-based approach is used, i.e., receivers are organized in a tree and ACK messages are passed along the edges of this so-called ACK tree. For building up this tree variations of the Expanding Ring Search (ERS) scheme have been proposed. However, our simulations show that ERS scales poorly. In this paper, we propose an alternative scheme for building up ACK trees. This scheme is based on a so-called token repository service, wherena token represents the right to connect to a certain node in the corresponding ACK tree. Nodes that want to join a group just request a token for this group from the (distributed) token repository service. Our simulations show that our scheme causes a much lower message overhead than ERS. Moreover, the quality of the resulting ACK trees in terms of delay and reliability is in many cases higher if generated with our scheme.Item Open Access AIDA I - Abschlußbericht(1998) Hohl, Fritz; Baumann, Joachim; Rothermel, Kurt; Schwehm, Markus; Straßer, MarkusIn diesem Bericht geht es um die Zusammenfassung der Erkenntnisse, die im Verlauf der ersten Phase des AIDA-Projektes bis September 1997 gewonnen wurden. AIDA ist ein Projekt, das von der Deutschen Forschungsgemeinschaft (DFG) finanziert wird. Das Thema dieses Projektes sind mobile Agenten, also Einheiten, die aus Code, Daten und Zustand bestehen und sich selbständig in einem Netzwerk bewegen können. Das Ziel von AIDA I war es, auf der Grundlage eines allgemeinen Verarbeitungsmodells flexible Systemmechanismen für verteilte, agentenbasierte Systeme zu entwickeln.Item Open Access Representing time in multimedia systems(1993) Wahl, Thomas; Rothermel, KurtAs multimedia systems deal with a variety of temporally interrelated media items, synchronization is an important issue in those systems. One part of synchronization is the representation of temporal information. In contrast to traditional computing tasks, multimedia imposes new requirements on the representation of time. Specifically, a fine-grained and a flexible temporal model is required. Therefore, a number of temporal models have been suggested by various authors. This paper evaluates and classifies a selection of the most common existing models applying fundamental statements of the time theory and temporal logic. Learning from the deficits of the existing models, a new temporal model based on interval operators is proposed for multimedia systems.Item Open Access Verbundprojekt PoliFlow : Abschlußbericht(1999) Kindler, Thomas; Kulendik, Ottokar; Rothermel, Kurt; Schneider, Kerstin; Siebert, Reiner; Soyez, TobiasIn den letzten Jahren fanden Groupware- und Workflow-Systeme ein große Beachtung bei Herstellern, Anwendern und Wissenschaftlern. Nach anfänglich unkritischer Euphorie wurden in den letzten Jahren jedoch auch einige Schwachstellen der noch jungen Technologien erkannt. Von der Behebung dieser Schwachstellen wird die weitere Entwicklung maßgeblich beeinflußt werden. In der Förderinitiative POLIKOM wurde untersucht, wie diese Technologien im Anwendungsbereich der öffentlichen Verwaltung effektiv und effizient eingesetzt werden können. Im Projekt PoliFlow wurden Mechanismen und Modelle entworfen, mit denen einige existentiellen Mängel in den Bereichen Sicherheit und Flexibilität behoben werden konnten. Hierbei wurden die Beschreibungsmodelle für Workflows um spezifische Aspekte und die Ausführungsmodelle um entsprechende Funktionalitäten erweitert. Um diese erweiterte Funktionalität in verschiedene bestehende Systeme integrieren zu können, wurden Referenzarchitekturen entworfen, die auf eine Vielzahl bestehender Modelle und Systeme übertragbar sind. Weitere erfolgreiche Konzepte wurden zur Integration von Workflow und synchroner Telekooperation sowie zur zuverlässigen Ausführung langlebiger Prozesse entwickelt. Eine weitere Schwachstelle der Technologie war die mangelnde Unterstützung heterogener System- und Anwendungsumgebungen. Um eine große Verbreitung dieser strategischen und hoch integrierten Informationssysteme zu erreichen, müssen die beteiligten Personen von unterschiedlichen Rechnern und Netzen eine entsprechende Zugangsmöglichkeit erhalten. Mit der Realisierung des Stuttgarter Workflow- und Telekooperationssystems (SWATS), bei dem neueste Intra-/Internet-Technologien (wie Java und CORBA) berücksichtigt wurden, konnten auch diese Anforderungen erfüllt werden. Darüber hinaus bildete das Grundsystem von SWATS die Basis zur Integration der Prototypen aus den oben genannten Arbeitsbereichen.Item Open Access Analysis of distribution schemes for the management of location information(1999) Kubach, Uwe; Leonhardi, Alexander; Rothermel, Kurt; Schwehm, MarkusNew applications in the area of mobile computing make heavy use of knowledge about the application's run-time environment. Applications running on mobile devices in particular exploit knowledge about their current geographical position or query for the location of other interesting objects. To manage such queries some applications provide a location service specifically tailored for their needs. The efficient and application-independent handling of such queries calls for a global and universal location service. Considering a large number of users and queries to be handled, a distributed implementation of a location service is necessary. This paper analyses three schemes for the partitioning of location information and derives a performance model for these partitioning schemes. Finally, an example for the application of the analysis' results is presented for a universal location service within the Nexus system, an infrastructure for location aware mobile computing.