On caching and prefetching of virtual objects in distributed virtual environments

Advances in networking technology and the establishment of the Information Superhighway have rendered the virtual library a concrete possibility. We are currently investigating user experience in walking through a large virtual environment in the context of Internet. This provides users with the ability to view various virtual objects from different distances and angles, using common web browsers. To deliver a good performance for such applications, we need to address several issues in different research disciplines. First, we must be able to model virtual objects effectively. The recently developed techniques for multi-resolution object modeling in computer graphics axe of great value here, since they are capable of simplifying the object models and therefore reducing the time to render them. Second, with the limited bandwidth constraint of the Internet, we need to reduce the response time by reducing the amount of data requested over the network. One alternative is to cache object, models of high affinity. Prefetching object models by predicting those which axe likely to be used in the near future and downloading them in advance will lead to a similar improvement. Third, the Internet often suffers from disconnection. A caching mechanism that allows objects to be cached with at least their minimum resolution will be useful to provide at least a coarse view of the objects to a disconnected viewer for improved visual perception. In this paper, we propose a multi-resolution caching mechanism and investigate its effectiveness in supporting virtual walkthrough applications in the Internet environment. The caching mechanism is further complemented with several object prefetching mechanisms for predicting future accessed objects. The performance of our proposed mechanisms and their feasibilities are quantified -via simulated experiments.