We consider a challenging class of highly interactive virtual environments, also known as Real-Time Online Interactive Applications (ROIA). Popular examples of ROIA include multi-player online computer games, e-learning and training based on real-time simulations, and other challenging applications. ROIA combine high demands on scalability and real-time user interactivity with the problem of an efficient and economic utilization of resources, which is difficult to achieve due to the changing number of users. This paper proposes a generic scalability model for ROIA that analyzes the application performance during runtime and predicts the demand for load balancing, i.e., when to add/remove resources or redistribute workload. We prove the practical relevance of the model by incorporating it into our RTF-RMS resource management system where it is used to predict the influence of different load-balancing actions on the application scalability. Our model is utilized by RTF-RMS for finding efficient load-balancing actions and thresholds for how often these actions should be applied. We report experimental results on the load balancing of a multi-player online game using predictions from the scalability model.

We consider a challenging class of emerging, highly interactive virtual environments which we call Real-Time Online Interactive Applications (ROIA). Popular examples include multi-player online computer games, e-learning and training applications based on real-time simulations, etc. ROIA combine tough demands on the level of scalability and highly intensive user interactivity with real-time QoS requirements on distributed performance. A major problem in this context is the efficient and economic utilization of server resources for distributed service provision, which is very difficult to achieve due to the variable numbers of users. In this paper, we propose a novel combination of two platforms that address this challenge by utilizing Cloud Computing for ROIA provision: we extend the Real-Time Framework (RTF) by the novel Cloud resource management system RTF-RMS. RTF is a high-level development platform that provides suitable management and scalability mechanisms for ROIA. RTF-RMS is a resource management system on top of RTF that implements workload analysis and distribution techniques. We illustrate how RTF-RMS interacts with RTF and describe how both platforms are used together to scale application servers up and down during runtime to conform to a changing number of users.

Large-scale Massively Multiplayer Online Games (MMOGs) and other networked applications pose challenging performance requirements such as low response times (down to 100 ms for action games like First-Person Shooters) and high update rates (up to 50 Hz). They require multi-server architectures in order to scale to higher player numbers (up to 105 in a single application session). During the application development process, it is necessary to study performance properties such as response time to user actions or CPU consumption in order to optimize the application. To analyse performance properties, the application developer needs to (i) model these properties, (ii) collect information about the variables of interest, and (iii) process the collected information to study the results. In this paper, we propose a novel tool set (Netlag) that supports the collection and processing of variables of interest in the context of MMOGs. The tool set consists of a C++ library that allows to collect and store information in a generic way, as well as a Java application that visualises the collected information. As a case study, we conduct how Netlag is used to evaluate the performance and scalability of an example MMOG application. Furthermore, we describe measurements of the overhead introduced by Netlag which demonstrate that its application intrusion is minimal, thus proving its good applicability for MMOGs and other networked applications.

This paper deals with networked applications in the emerging field of online virtual worlds. Example applications include, e.g., Massively Multiplayer Online Computer Games (MMOG), networked e-learning, training and simulations, etc. Highly interactive virtual worlds bring a new security challenge: the multiple participants of such applications do not always show cooperative and intended behavior, but rather may act in an illegal way (cheating) which is harmful for other participants, thus intentionally or accidentally procuring illicit advantages for themselves. The paper studies the new challenge of cheating in virtual-world applications in three areas: a) system and application programming, b) economics, and c) law. The main contributions of our work are as follows: 1) We present a systematic classification of cheating threats in virtual worlds, and describe software solutions that help prevent them in future Internet-based applications; 2) We enhance the classical economic analysis of crime and punishment for applying it to virtual worlds; 3) We describe our development approach for networked virtual worlds and its implementation as the Real-Time Framework (RTF) which has been designed at the University of Muenster; 4) Finally, we explore the law aspects of cheating in virtual applications in the context of the legal system in Germany. The consideration of informatics aspects together with the corresponding problems of economics and law allows us to tackle virtual-world security in a holistic, systematic manner.