05 Fakultät Informatik, Elektrotechnik und Informationstechnik

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

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Start date: 2000End date: 2001Subject: search.filters.subject.004Author: search.filters.author.Rothermel, Kurt

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Now showing 1 - 8 of 8
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    Application sharing in teaching context with wireless networks
    (2001) Burger, Cora; Papakosta, Stella; Rothermel, Kurt
    The 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.
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    A context-aware hoarding mechanism for location-dependent information systems
    (2000) Kubach, Uwe; Rothermel, Kurt
    When 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.
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    AIDA II - Abschlußbericht
    (2000) Hohl, Fritz; Baumann, Joachim; Rothermel, Kurt; Schwehm, Markus; Theilmann, Wolfgang
    In 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.
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    Architecture of a large scale location service
    (2001) Leonhardi, Alexander; Rothermel, Kurt
    Many 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.
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    A fine-grained addressing concept for GeoCast
    (2001) Coschurba, Peter; Rothermel, Kurt
    GeoCast 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.
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    A map-based dead reckoning protocol for updating location information
    (2001) Leonhardi, Alexander; Nicu, Christian; Rothermel, Kurt
    An 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.
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    A delay analysis of tree-based reliable multicast protocols
    (2001) Maihöfer, Christian; Rothermel, Kurt
    We 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.
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    A comparison of protocols for updating location information
    (2000) Leonhardi, Alexander; Rothermel, Kurt
    The detailed location information of mobile objects, for example that of a user with a mobile computer or phone, is an important input for many location-aware applications. However, constantly updating the location information for thousands of mobile objects is not feasible. Update protocols for location information therefore use the special properties of this information to transmit it as efficiently as possible, that is requiring only few update messages, while still being effective in returning the location information with the desired accuracy. Different classes of such update protocols are described in this paper and a new combined protocol is proposed. To be able to compare their effectiveness and efficiency, we present an analysis for the minimum and average resulting accuracy of the location information on the receiver and the number of messages transmitted between them. We also present some simulation results, which we have performed to back up our analysis.