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.

This paper describes the client-server design, implementation and experimental results for a system that supports real-time visual interaction between a large number of users in a shared 3D virtual environment. The key feature of the system is that server-based visibility algorithms compute potential visual interactions between entities representing users in order to reduce the number of messages required to maintain consistent state among many workstations distributed across a wide-area network. When an entity changes state, update messages are sent only to workstations with entities that can potentially perceive the change -- i.e., ones to which the update is visible. Initial experiments show a 40x decrease in the number of messages processed by client workstations during tests with 1024 entities interacting in a large densely occluded virtual environment. CR Categories and Subject Descriptors: [Computer Graphics]: I.3.7 Three-Dimensional Graphics and Realism -- Virtual Reality. Add...

We explore exploits possible for cheating in real-time, multiplayer games for both client-server and distributed, serverless architectures. We offer the first formalization of cheating in online games and propose an initial set of strong solutions. We propose a protocol that has provable anti-cheating guarantees, but suffers a performance penalty. We then develop an extended version of this protocol, called asynchronous synchronization, which avoids the penalty, is serverless, offers provable anti-cheating guarantees, is robust in the face of packet loss, and provides for significantly increased communication performance. This technique is applicable to common game features as well as clustering and cell-based techniques for massively multiplayer games. Our performance claims are backed by analysis using a simulation based on real game traces. I.

This paper investigates trade-offs of different network topologies and messaging protocols for multi-uservirtual environment systems. We present message distribution techniques appropriate for constructing scalable multi-user systems for a variety of network characteristics. Hierarchical system designs utilizing servers that manage message distribution for entities in separate regions of a virtual environment are described that scale to arbitrary numbers of simultaneous users. Experimental results show that the rate of messages processed by server workstations in this system design are less than using previously described approaches. 1. Introduction With the recent increases in network bandwidth and graphics performance in desktop computers, there is a growing interest in distributed visual simulation systems that allow multiple users to interact in a shared 3D virtual environment. Users on workstations connnected by a wide-area network run an interactive 3D graphics interface program...

This paper is an introductory level tutorial describing how to implement a distributed multi-participant virtual environment (VE). This tutorial is intended for students who are competent programmers and who now wish to implement a distributed multi-participant application. We describe the fundamental concepts of distributed computing for multi-player simulations and provide a concrete example, including C source code available via the Internet. The template program demonstrates a simple multi-player, distributed application, where each player controls the position of a space ship, and communicates the ship's position data over the network. The template uses broadcast communication and a technique called dead-reckoning to improve performance. We give detailed instructions on how to obtain and modify the template, so that students can quickly create their own distributed applications. We conclude by briefly discussing advanced issues which are important when constructing more sophistic...

Virtual environment (VE) applications involve many different tasks, including interfacing with input and output devices, providing responsive user interaction, and simulating a dynamic environment. The variety and number of tasks lends the application to a distributed computing system, where different tasks are performed by different computing resources. A critical issue that arises from such a design is how information is communicated between tasks. In particular, for virtual environments, how information is communicated promptly is the critical issue. In this work, we describe a pattern of communication common between VE tasks which is not addressed by other communication protocols, namely the communication of state information that continuously changes. We describe a new protocol based on an updatable queue abstraction which allows

nd parallelism. In particular, we examine what it means to distribute functionality such as simulation, interaction detection and messaging in a virtual world, how to "scale up" such a world, and how to deal with communication delays. 2 Current Approaches to Distribution Current approaches to architectures for virtual world rely upon either a client-server architecture, or upon a static allocation of processes to processors, which communicate among each other along predetermined paths [4] [5] [12] [13]. These architectures pose two potential problems for scale-up: 1. Point to point models fall apart when object communication is many-to-many. That is, in a simulation with 100 independent but closely interacting entities a point-to-point communication model would mean potentially sending 10,000 distinct messages at each time slice in order to handle interactions properly. 2. In broadcast models, much of the information being communicated between participants is

This paper focuses on the distributed architecture of the collaborative augmented reality system Studierstube. The system allows multiple users to experience a shared 3D workspace populated by multiple applications using seethrough head mounted displays or other presentation media such as projection systems. The system design is based on a distributed shared scene graph that alleviates the application programmer from explicitly considering distribution, and avoids a separation of graphical and application data. The idea of unifying all system data in the scene graph is taken to its logical consequence by implementing application instances as nodes in the scene graph. Through the distributed shared scene graph mechanism, consistency of scene graph replicas and the contained application nodes is assured. Multi-user 3D widgets allow concurrent interaction with minimal coordination effort from the application. Special interest is paid to migration of application nodes from host to host allowing dynamic workgroup management, such as load balancing, late joining and early exit of hosts, and some forms of ubiquitous computing.

Introduction Computer technology has only recently become advanced enough to solve the problems it creates with its own interface. One solution, virtual reality (VR), immediately raises fundamental issues in both semantics and epistemology. Broadly, virtual reality is that aspect of reality which people construct from information, a reality which is potentially orthogonal to the reality of mass. Within computer science, VR refers to interaction with computer generated spatial environments, environments constructed to include and immerse those who enter them. VR affords non-symbolic experience within a symbolic environment. Since people evolve in a spatial environment, our knowledge skills are anchored to interactions within spatial environments. VR design techniques, such as scientific visualization, map digital information onto spatial concepts. When our senses are immersed in stimuli from the virtual world, our minds construct a closure to crea

As military budgets shrink, the Department of Defense (DoD) is turning to virtual worlds (VW) to solve problems and address issues that were previously solved by prototype or field exercises. However, there is a critical void of experience in the community on how to build VW systems. The Naval Postgraduate School’s Network Vehicle Simulator (NPSNET) was designed and built to address this need. NPSNET is a populated, networked, interactive, flexible, three dimensional (3D) virtual world system. This dissertation covers the construction and management of the VW in NPSNET. The system, which uses both standard and non-standard network message formats, is fully networked allowing multiple users to interact simultaneously in the VW. Commercial off the shelf (COTS), Silicon Graphics Incorporated (SGI) workstations, hardware was used exclusively in NPSNET to ensure the usefulness and the portability of the system to many DoD commands. The core software architecture presented here is suitable for any VW.