Im Sommersemester 2012 wurde die Online Community auditorium von Informatik-Studenten der TU Dresden entwickelt. Die Online Plattform bietet den Studierenden und Mitarbeitern einen Anlaufpunkt für alle Fragen und Antworten rund um das Studium. Der Fokus lag darin, eine zentrale Anlaufstelle für die studentischen Belange zu schaffen, um das vorhandene Wissen besser teilen zu können und für später zu archivieren.

This paper presents a general-purpose distributed lookup service, denoted Passive Distributed Indexing (PDI). PDI stores entries in form of (key, value) pairs in index caches located at mobile devices. Index caches are filled by epidemic dissemination of popular index entries. By exploiting node mobility, PDI can resolve most queries locally without sending messages outside the radio coverage of the inquiring node. For keeping index caches coherent, configurable value timeouts implementing implicit invalidation and lazy invalidation caches implementing explicit invalidation are introduced. Inconsistency in index caches due to weak connectivity or node failure is handled by value timeouts. Lazy invalidation caches reduce the fraction of stale index entries due to modified data at the origin node. Similar to index caches, invalidation caches are filled by epidemic distributions of invalidation messages. We evaluate the performance of PDI for a mobile P2P file sharing a mobile instant messaging application. Simulation results show that with the suitable integration of both invalidation mechanisms, up to 80% of the lookup operations return correct results and more than 90% of results delivered by PDI index caches are up-to-date.

This paper introduces an efficient numerical algorithm for transient analysis of deterministic and stochastic Petri nets (DSPNs) and other discrete-event stochastic systems with exponential and deterministic events. The proposed approach is based on the analysis of a general state space Markov chain (GSSMC) whose state equations constitute a system of multidimensional Fredholm integral equations. Key contributions of this paper constitute the observations that the transition kernel of this system of Fredholm equations is piece-wise continuous and separable. Due to the exploitation of these properties, the GSSMC approach shows great promise for being effectively applicable for the transient analysis of large DSPNs with concurrent deterministic transitions. Moreover, for DSPNs without concurrent deterministic transitions the proposed GSSMC approach requires three orders of magnitude less computational effort than the previously known approach based on the method of supplementary variables.

This paper introduces an efficient numerical algorithm for the steady-state analysis of deterministic and stochastic Petri nets (DSPNs) without structural restrictions on the enabling of deterministic transitions. The method rests on observation, at equidistant time points, of the continuous-time Markov process that records tangible markings of the DSPN and remaining firing times associated with deterministic transitions. This approach results in the analysis of a general state space Markov chain whose system of stationary equations can be transformed into a system of Volterra equations. The techniques of this paper are also applicable to queueing networks, stochastic process algebras, and other discrete-event stochastic systems with an underlying stochastic process which can be represented as a generalized semi-Markov process with exponential and deterministic events.

In this paper, we introduce a unified approach for the adaptive control of 3G mobile networks in order to improve both quality of service (QoS) for mobile subscribers and to increase revenue for service providers. The introduced approach constantly monitors QoS measures as packet loss probability and the current number of active mobile users during operation of the network. Based on the values of the QoS measures just observed, the system parameters of the admission controller and packet scheduler are controlled by the adaptive performance management entity. Considering UMTS, we present performance curves showing that handover failure probability is improved by more than one order of magnitude. Moreover, the packet loss probability can be effectively regulated to a predefined level and provider revenue is significantly increased for all pricing policies.

This paper describes a Petri Net-based model for workflow management in distributed cancer therapy, a domain which is characterized by the involvement of several geographically distributed departments and a long-term treatment. The approach uses hierarchical Petri-Nets; tokens, places and transitions are objects conform to the CORBA/IDL-model to facilitate implementation in a heterogeneous environment. During treatment, generic organizational nets are dynamically refined with disease-specific subnets obtained from an oncological knowledge base to adapt the net in a patient-specific way. This refinement task is mainly processed by a Knowledge Refinement Manager which has been added to a commercial workflow architecture. Currently, a prototype implementing the model, called HEMATOWORK, is developed at Leipzig University.

Im Sommersemester 2012 wurde die Online Community auditorium von Informatik-Studenten der TU Dresden entwickelt. Die Online Plattform bietet den Studierenden und Mitarbeitern einen Anlaufpunkt für alle Fragen und Antworten rund um das Studium. Der Fokus lag darin, eine zentrale Anlaufstelle für die studentischen Belange zu schaffen, um das vorhandene Wissen besser teilen zu können und für später zu archivieren.