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 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 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 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 Adressierung und Semantik von geographischen Nachrichten(2001) Coschurba, PeterIn den letzten Jahren haben mobile Computer eine große Verbreitung gefunden. Zur gleichen Zeit wurden Systeme zur Ortsbestimmung (z.B. GPS) auch für normale Anwender verfügbar. Schnell wurde klar, daß eine Kombination dieser beiden Technologien einen deutlichen Mehrwert für die Nutzer bieten kann. Wenn die Information über den aktuellen Aufenthaltsort des Nutzers vorhanden ist, liegt es nahe diese auch für die Kommunikation zu verwenden. Ähnlich wie beim Multicast ist es auch beim sogenannten GeoCast möglich, mehreren Empfängern eine Nachricht zukommen zu lassen. Nur müssen die Empfänger beim GeoCast keiner Gruppe beitreten. Der Sender spezifiziert viel mehr das Zielgebiet der Nachricht, und alle potentiellen Empfänger, die sich in diesem Gebiet befinden, erhalten die Nachricht. Im Bereich GeoCast sind vor allem zwei Bereiche noch nicht intensiv betrachtet worden. Zum einen ist die Frage der Adressierung des Zielgebietes noch offen. Also wie sehen die Adressierungskonzepte aus, mit denen ein Sender das Zielgebiet spezifizieren kann. Die andere Frage die noch nicht sauber betrachtet wurde, ist die Semantik. Welche Semantik hat eine geographische Nachricht. Was sind Alternativen, und warum sind welche Alternativen am sinnvollsten. Diese Fragen sollen in dieser Arbeit näher betrachtet werden.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.Item Open Access Improving the processing of decision support queries : strategies for a DSS optimizer(2001) Schwarz, Holger; Wagner, Ralf; Mitschang, BernhardMany decision support applications are built upon data mining and OLAP tools and allow users to answer information requests based on a data warehouse that is managed by a powerful DBMS. In this paper, we focus on tools that generate sequences of SQL statements in order to produce the requested information. Our thorough analysis revealed that many sequences of queries that are generated by commercial tools are not very efficient. An optimized system architecture is suggested for these applications. The main component is a DSS optimizer that accepts pre-viously generated sequences of queries and remodels them according to a set of optimization strategies, before they are executed by the underlying database system. The advantages of this extended architecture are discussed and a couple of appropriate optimization strategies are identified. Experimental results are given, showing that these strategies are appropriate to optimize query sequences of OLAP applications.Item Open Access Local feature histograms for object recognition from range images(2001) Leibe, Bastian; Hetzel, Günter; Levi, PaulIn this paper, we explore the use of local feature histograms for view-based recognition of free-form objects from range images. Our approach uses a set of local features that are easy to calculate and robust to partial occlusions. By combining them in a multidimensional histogram, we can obtain highly discriminative classifiers without having to solve a segmentation problem. The system achieves above 91% recognition accuracy on a database of almost 2000 full-sphere views of 30 free-form objects, with only minimal space requirements. In addition, since it only requires the calculation of very simple features, it is extremely fast and can achieve real-time recognition performance.