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 context-aware hoarding mechanism for location-dependent information systems(2000) Kubach, Uwe; Rothermel, KurtWhen used in an outdoor environment mobile information systems often suffer from the disadvantages of wireless WANs, especially low bandwidth, high delay, and frequent disconnections. Hoarding is an effective method to overcome these disadvantages by transferring information which is probably needed by the user in advance. In this paper we propose a generic, context-aware hoarding mechanism. When selecting the information to hoard, it considers the user's future location as well as the expected speed of movement. In contrast to existing hoarding mechanisms it is universally applicable for different types of location-dependent, mobile information systems. Its flexibility allows it to rely on different knowledge sources in order to get information about a user's context.Item Open Access Application sharing in teaching context with wireless networks(2001) Burger, Cora; Papakosta, Stella; Rothermel, KurtThe success of teaching is depending on a couple of factors: on how far students are involved into lectures, on the material, its completeness and on co-learning of students. Involvement of students into lectures means, being able to follow the thoughts of the teacher, ask questions and make comments. The material must be presented in a suitable form and essential parts of it have to be available during the whole learning process, for preparing participation in lectures and exercises as well as for exams. For more effective learning and training of social abilities, working in groups of co-learners has to be encouraged. Mobile and ubiquitous computing offer new possibilities to achieve these goals by increasing the awareness in class and supporting an active participation of students. By promoting existing concepts and enabling new ways of application sharing, the project SASCIA (System architecture supporting cooperative and interactive applications) aims at developing a framework for multiple applications to support teaching in collocated, remote and hybrid scenarios. Its core is composed of components to capture and distribute context information about sessions, participants and those applications that are used during a lecture or encounter among students. A configurable floor control was designed to cope with a wide spectrum of applications and learning situations. For some cases, even a control for semantic consistency can be necessary. In combination with a suitable user and session management, a whiteboard for annotations and a recording facility to support latecomers as well as subsequent replay, these components are providing the required functionality. As a consequence, SASCIA offers remote control and viewing facilities to all participants during lectures and co-learning sessions.Item Open Access Spatial aware geographic Forwarding for mobile ad hoc networks(2002) Tian, Jing; Stepanov, Illya; Rothermel, KurtStateless greedy forwarding based on physical positions of nodes is considered to be more scalable than conventional topology-based routing. However, the stateless nature of geographic forwarding also prevents it from predicting holes in node distribution. Thus, frequent topology holes can significantly degrade the performance of geographic forwarding. So far the approaches mostly depend on excessive state maintenance at nodes to avoid forwarding failures at topology holes. In this paper, we propose and analyse spatial aware geographic forwarding (SAGF), a new approach that proactively avoids constant topology holes caused by spatial constraints while still preserving the advantage of stateless forwarding. Geographic source routes (GSR) based on intermediate locations are selected to bypass topology holes. Proactive route selection based on the spatial knowledge is a general approach, and thus can be used with any geographic forwarding algorithms. We evaluate our approach by extending greedy forwarding with spatial knowledge. Simulation results comparing with GPSR show that even simple spatial information can effectively improve the performance of geographic forwarding.Item Open Access A fine-grained addressing concept for GeoCast(2001) Coschurba, Peter; Rothermel, KurtGeoCast provides the functionality of sending messages to everyone in a specific area. So far, only the addressing of larger two-dimensional areas was possible. For the use in an urban environment it is crucial that small and three-dimensional areas can be addressed. For example, GeoCast can then be used to send lecture notes to all in a classroom. In this paper we describe a fine-grained addressing concept for GeoCast that supports such areas. In addition we present an architecture that allows the use of that addressing concept together with the GeoRouting-approach developed by Navas and Imielinski. We also present some modifications necessary to enhance the scalability of GeoCast.Item Open Access AIDA II - Abschlußbericht(2000) Hohl, Fritz; Baumann, Joachim; Rothermel, Kurt; Schwehm, Markus; Theilmann, WolfgangIn diesem Bericht geht es um die Zusammenfassung der Erkenntnisse, die im Verlauf der zweiten Phase des AIDA-Projektes von März 1998 bis Februar 2000 gewonnen wurden. AIDA ist ein Projekt, das von der Deutschen Forschungsgemeinschaft (DFG) finanziert wird. Das Thema dieses Projektes sind Systemmechanismen zur Unterstützung mobiler Agenten, also Einheiten, die aus Code, Daten und Zustand bestehen und sich selbstständig in einem Netzwerk bewegen können. Die Ziele von AIDA II waren die Erarbeitung des Themenbereichs Sicherheit in Mobile-Agenten-Systemen mit Schwerpunkt auf der Sicherheit mobiler Agenten gegenüber böswilligen Hosts, die Implementierung von Terminierungsprotokollen und Waisenerkennungsmechanismen, Abrechnungsmechanismen und schließlich Mechanismen zur Strukturunterstützung für Agentenanwendungen.Item Open Access Architecture of a large scale location service(2001) Leonhardi, Alexander; Rothermel, KurtMany mobile applications require some knowledge about the current geographic locations of the mobile objects involved. Therefore, services exist that can store and retrieve the position of mobile objects in an efficient and scalable way. More advanced location-aware applications, however, require additional functionality, like determining all mobile objects inside a certain geographic area (range query). This functionality is not supported by existing services on a large scale yet. In this paper, we present a generic large-scale location service. We describe the location service model, defining the semantics of position, range and nearest neighbor queries. A hierarchical distributed architecture is presented, which can efficiently process these queries, and the structure of a main-memory database for efficiently storing and retrieving position information on a location server. Finally, through measurements on a first prototype of this architecture, we show the feasibility of such a location service.Item Open Access A map-based dead reckoning protocol for updating location information(2001) Leonhardi, Alexander; Nicu, Christian; Rothermel, KurtAn important aspect of location-aware services is the management of location information. To this end, location information needs to be transferred from a mobile device, which determines this information by means of a local positioning sensor (such as GPS), to a location service, where the location information can be queried by applications. Because bandwidth in wide area mobile communications is still scarce and expensive, it is important to use an update protocol that requires as few messages as possible while still guaranteeing a desired accuracy of the location information. To decrease the number of necessary update messages, so-called dead-reckoning strategies have been proposed. In this paper we give an overview of different variants of dead-reckoning protocols for updating location information and propose a new map-based protocol. While a simple dead-reckoning protocol already reduces the number of update messages by up to 83, the map-based protocol further reduces their number by again up to 60.Item Open Access An enhanced application model for scheduling in grid environments(2003) Ruffner, Christoph; Marrón, Pedro José; Rothermel, KurtApplication scheduling in Grid computing requires information about tasks in each application, as well as a description of the available resources that the scheduler needs, to find an efficient assignment of tasks to resources. In this context, information about applications is provided by the application model. Most current models are restricted to only a few features, but in some cases, such as simulations, which are an important example of Grid applications, more detailed information is available. In this paper, we propose an enhanced application model based on the concept of task refinements, which provide the scheduler with fine-grained information and allow it to determine more efficient schedules than traditional approaches. We backup and show the feasibility of our model by means of experimental evaluations.Item Open Access A dynamic network scenario emulation tool(2002) Herrscher, Daniel; Rothermel, KurtComparative performance measurements of distributed applications and network protocols require the availability of appropriate network environments. Network emulation approaches offer a flexible way to mimic the properties of a variety of networks. Existing emulation tools work either with centralized real-time simulation components, limiting the scenario size and maximum traffic, or focus on the emulation of some network properties at a single point. We propose a tool for the realistic emulation of network links, and show how several emulated links can be combined to reproduce a comprehensive network model. In addition to that, the model can include changing network properties, e.g. emerging from mobile communication partners. This facilitates the distributed emulation of a comprehensive, dynamic network scenario to support repeatable performance measurements.Item Open Access A delay analysis of tree-based reliable multicast protocols(2001) Maihöfer, Christian; Rothermel, KurtWe present a comparative delay analysis of tree-based reliable multicast protocols and show the influence of varying sending rates, group sizes, packet loss probabilities and branching factors of the control tree. Besides the average delivery delay we consider the delay to reliably deliver all packets and the round trip delay. The former two examines the delay between generation of a packet at the sender and correct reception at a randomly chosen receiver or all receivers, respectively. The latter is the delay between generation of a packet at the sender and reception of all acknowledgment packets at the sender. Our numerical results show that all tree-based protocols provide low delays and good scalability. From the four considered protocol classes, NAK-based protocols achieve the best scalability but ACK-based protocols achieve the lowest delays. An important aspect of our work is to be of practical relevance rather than being of only theoretical nature. Therefore, we have compared the analytical results with a RMTP and TMTP simulation. Both show similar results which confirms that our analysis can help to choose a suitable protocol and to tune them for improved performance.