Networked virtual environments

The problem of resource bottlenecks is encountered in almost any distributed virtual environment or networked game. Whenever the demand for resources – such as network bandwidth, the graphics pipeline, or processing power – exceeds their availability, the resulting competition for the resources leads to a degradation of the system’s performance. In a typical client-server setup, for example, where the virtual world is managed by a server and replicated by connected clients which visualize the scene, the server must repeatedly transmit update messages to the clients. The computational power needed to select the messages to transmit to each client, or the network bandwidth limitations often allow only a subset of the update messages to be transmitted to the clients; this leads to a performance degradation and an accumulation of errors, e.g. a visual error based on the positional displacement of the moving objects. This thesis presents a scheduling algorithm, developed to manage the objects competing for system resources, that is able to achieve a graceful degradation of the system’s performance, while retaining an output sensitive behavior and being immune to starvation. This algorithm, called Priority Round-Robin (PRR) scheduling, enforces priorities based on a freely definable error metric, trying to minimize the overall error. The output sensitivity is a crucial requirement for the construction of scalable systems, and the freely definable error metric makes it suitable to be employed whenever objects compete for system resources, in client-server and peer-to-peer architectures as well. Therefore Priority Round-Robin scheduling is a substantial contribution to the development of distributed virtual environments and networked online-games.