This paper explores the issues involved in designing and developing network software architectures for large scale virtual environments. We present our ideas in the context of NPSNET-IV, the first 3D virtual environment that incorporates both the IEEE 1278 Distributed Interactive Simulation (DIS) application protocol and the IP Multicast network protocol for multi-player simulation over the Internet.

The development of multi-user networked virtual worlds has become a major area of interest in the computer and communications fields. However, there has been little effort to provide a coherent framework for understanding distributed virtual environments (VEs). In this paper we discuss VEs in the context of how communications, views, data, and processes are distributed while emphasizing those aspects critical to scaling environments. We find most of the systems described in this paper scale to accommodate a handful of users. We also discuss why systems which demand strong data consistency, causality, and reliable communications at the same time while supporting real-time interaction are not likely to scale very well. Furthermore, if the systems are to be geographically dispersed, then highspeed, multicast communication is required. . KEYWORDS: Virtual Reality, Distributed Interactive Simulation, Internet Protocol Multicast, Distributed Interactive Entertainment, Large-scale Virtual E...