Hermann Schloss

Elastic Consistency in Decentralized Distributed Virtual Environments

Distributed virtual environments like online games or 3D virtual worlds have become very popular in the last few years and a more substantial surge in popularity and use is expected. Because of the huge number of users, such environments will undergo a change of infrastructure from a centralized to a decentralized one, making higher demands on consistency issues. This paper addresses consistency problems which may occur in distributed virtual environments and introduces the elastic consistency model to tackle these problems. According to elastic consistency, different consistency levels setting up a trade-off between consistency and responsiveness of the environment should be introduced in order to provide an efficient way of interaction on a global scale.

HyperVerse: simulation and testbed reconciled

When dealing with dynamic large-scale topologies such as those underlying Peer-to-Peer (P2P) Distributed Virtual Environments (DVEs), one inescapably reaches the point where either: a) simulations lack human behaviour and assessment or where b) practical experiments on a small scale do not yield significant results. The restrictions resulting from the separation of simulation and testbed environments hinder a comprehensive assessment and efficient development of adaptive algorithms and techniques for DVEs as they are investigated in our HyperVerse research project. In this paper, we present a hybrid evaluation system designed to combine the advantages of simulations and testbeds. The proposed infrastructure exhibits great flexibility particularly alluring in view of the multitude of potential research in the context of DVEs.

P2P-Based Avatar Interaction in Massive Multiuser Virtual Environments

The idea of the 3D Web as a global scale Distributed Virtual Environment (DVE) currently is very popular and a lot of research work is done in this field. In the course of the HyperVerse project we have developed a two-tier Peer-To-Peer (P2P) architecture as basic infrastructure for a federated, open and scalable 3D Web. Our approach relies on a concept that incorporates a loosely-structured P2P network overlay of user clients and a highly-structured overlay that connects a federation of reliable server machines constituting a reliable backbone service. A central problem when intending to build a massive virtual online environment is how avatar interaction as well as tracking and provision of avatar positions can be realized in a globally scalable manner. This paper presents a hybrid avatar interaction scheme developed for HyperVerse that incorporates the user clients and the backbone service for avatar position tracking. The backbone is used as reliable fall-back service, while the avatar tracking is handled in a pure P2P fashion whenever possible. This way backbone overload is prevented in a self-organizing manner whenever client density tends to overburden the backbone infrastructure.

The SEMPA prototype - using XAML and web services for rich interactive Peer-to-Peer applications

Currently one can see a surge of evolving technologies supporting the creation of Rich Internet Applications. All of these approaches however traditionally address the classic Client/Server scenario in which a dedicated Web Server acts as application provider for thin clients. This paper argues, that there are many scenarios in which a Peer-to-Peer approach enabling every application/process to export parts of its graphical user interface in a lightweight and interoperable way would be more desirable. This work-in-progress paper presents the lightweight middleware prototype SEMPA, proving that these scenarios can be supported by combining the readily available technologies eXtensible Application Markup Language (XAML) and Web Services.

HERA: Design Framework for Decentralized Distributed Virtual Environments and Games

Distributed Virtual Environments such as Massive Multiplayer Online Games or Virtual Worlds have become very popular in the last few years and a more substantial surge in popularity and use is expected. Because of the huge number of users most of these environments have to cope with scalability problems. The change of the basic infrastructure from a centralized client-server to a decentralized peer-to-peer architecture mitigates these problems. However it makes the handling of management and consistency issues more complicated. To address these issues we have developed HERA - a design framework for decentralized distributed virtual environments. In this paper we present HERAs Area of Interest handling as well as its consistency provision and introduce a 2D online game application based on the HERA framework.

CARMA Based MST Approximation for Multicast Provision in P2P Networks

The Minimum Spanning Tree (MST) problem is one of the most popular and important problems in the research area of distributed computing and networks. Contrary to the theoretical models where we usually have a global knowledge of all nodes and the corresponding distances for MST construction, in a realistic network (e.g., Internet) a node always has to rely on local knowledge only, that is it neither knows all other nodes nor exact distances between these nodes. In this paper we propose an approach for MST approximation based on local knowledge of a small subset of existing nodes by using the CARMA metric as a distance substitute. According to the evaluation results, our approach achieves a good MST approximation with respect to a communication cost and avoids extraneous communication needed for latency measurements.

Self-organizing collaborative filtering in global-scale massive multi-user virtual environments

Due to the huge amount of available information in todays society, it becomes more and more difficult for the consumer to locate the most useful information for a specific topic. Recommender systems using collaborative filtering (CF) are a popular technique for reducing information overload and finding useful information on the Internet. However, in massive global-scale multi-user virtual environments different approaches are required from those used within the currently dominant centralized infrastructures or lately investigated P2P approaches. Within this paper we present a novel collaborative filtering algorithm used within the HyperVerse -- a P2P-based self-organizing middleware service for massively distributed virtual worlds -- to generate and manage recommendations for HyperVerse object favorites. Due to its global extent considering users and possible ratings, using a monolithic database-backed recommendation service or huge profile- or item-rating-matrices does not scale in our scenario. The decentralized approach presented within this paper creates per user ratings in an adaptive and transparent way by comparing public favorites of passer-by users with personal peer data, weighted by self-adjusting buddy lists.

SimCon - a simulation and visualization environment for overlay networks and large-scale applications

A substantial number of massive large-scale applications require scalable underlying network topologies. Nowadays structured Peer-to-Peer overlay networks meet these requirements very well. But there is still a need to decide which of these overlay networks is most suitable for providing the best possible performance for a certain application. This paper describes SimCon - a simulation environment for overlay networks and large-scale applications. SimCon allows the comparison of different overlay networks with respect to predefined metrics derived from requirements of the considered application. This approach allows determining which overlay network meets the needs of a given application best, which in turn is a great support for developers of large-scale applications.

Using Epidemic Hoarding to Minimize Load Delays in P2P Distributed Virtual Environments

Distributed Virtual Environments (DVEs) have grown popular in various fields of application. Apart from providing great collaborational opportunities in an immersive setting, large-scale DVEs pose severe scalability challenges. Although P2P approaches have proven to be effective for tackling many of these issues, still load delay problems remain in regions with high object or avatar density. In this article we present and evaluate a hoarding approach that is suitable to minimize such delays in P2P-based DVEs with a real-time distribution of dynamic data. The prediction of what data shall be hoarded is based on an epidemic aggregation algorithm working solely with local knowledge. Evaluation results that have been obtained using a DVE simulation environment will be presented.

Performance Evaluation of GP3 - A Grid-Based Spatial Index Infrastructure

Looking at the evolution of the Internet in recent years one can observe that Massive Multiuser Virtual Environments(MMVEs) have grown increasingly popular. Especially the idea of a ”3D Web” as a combination of a MMVE and today’s WWW provides a lot of exciting opportunities in terms of user experience and interactivity. From an infrastructural perspective, the global provision of such a scenario is much more than another evolutionary step in content visualization. Such a 3D Web rather poses severe technical challenges to the underlying infrastructure, especially with respect to scalability. The HyperVerse project aims at the provision of a globally scalable federated infrastructure being able to handle these requirements. One component of this infrastructure is the structured Peer-to-Peer overlay GP3. This paper presents a detailed performance evaluation of this overlay network, providing simulation results as well as formal proofs for the upper bound complexity.