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...

Despite intense and wide-spread research in both virtual environments (VEs) and usability, the exciting new technology of VEs has not yet been closely coupled with the important characteristic of usability -- a necessary coupling if VEs are to reach their full potential. Although numerous methods exist for usability evaluation of interactive computer applications, these methods have well-known limitations, especially for evaluating VEs. Thus, there is a great need to develop usability evaluation methods and criteria specifically for VEs. Our goal is to increase awareness of the need for usability engineering of VEs and to lay a scientific foundation for developing high-impact methods for usability engineering of VEs. The first step in our multi-year research plan has been accomplished, yielding a comprehensive multi-dimensional taxonomy of usability characteristics specifically for VEs. This taxonomy was developed by collecting and synthesizing information from literature, conferences, World Wide Web (WWW) searches, investigative research visits to top VE facilities, and interviews of VE researchers and developers. The taxonomy consists of four main areas of usability issues: Users and User Tasks in VEs, general user and task characteristics and types of tasks in VEs

. Floor control allows users of networked multimedia applications to utilize and share resources such as remote devices, distributed data sets, telepointers, or continuous media such as video and audio without access conflicts. Floors are temporary permissions granted dynamically to collaborating users in order to mitigate race conditions and guarantee mutually exclusive resource usage. A general framework for floor control is presented. Collaborative environments are characterized and the requirements for realization of floor control will be identified. The differences to session control, as well as concurrency control and access control are elicited. Based upon a brief taxonomy of collaboration-relevant parameters, system design issues for floor control are discussed. Floor control mechanisms are discerned from service policies and principal architectures of collaborative systems are compared. The structure of control packets and an application programmer's interface are proposed and...

Existing Cooperative Virtual Environments present the same shared world to each of the cooperating users. This is analogous to the use of strict-WYSIWIS in early 2D interfaces. Research in the area of shared 2D interfaces has shown a strong trend to support individual tailoring of the shared views, and move away from the strict-WYSIWIS abstraction. This paper argues that the development of Cooperative Virtual Environments can gain from the experience of research into in shared 2D interface systems, and presents a model to manage the use of subjective views in Cooperative Virtual Environments. Keywords WYSIWIS, Shared interfaces, view coupling, VR INTRODUCTION Early 2D multi user interface systems supported shared interfaces by presenting exactly the same image of the application to all users. This simple replication of the system's image secured a founding abstraction for multi user interfaces: What You See is What I See (WYSIWIS). However, the early applications based on this abst...

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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.

This paper introduces the notion of context-aware mobile hypermedia. Contextawareness means to take the users' context such as location, time, objective, community relations etc. into account when browsing, searching, annotating, and linking. Attributes constituting the context of the user may be sensed automatically and/or be provided by the user directly. When being mobile the user may achieve context-aware hypermedia support on a variety of small and medium sized computing platforms such as mobile phones, PDAs, tablet PCs and laptops.

This paper presents a world model for location-aware and user-aware services in ubiquitous computing environments. It can be dynamically organized like a tree based on geographical containment, such as user-room-floor-building, and each node in the tree can be constructed as an executable software component. The model is unique to existing approaches because it can be managed by multiple computers in an ad-hoc manner and it can provide a unified view of the locations of not only physical entities and spaces, including users and objects, but also computing devices and services. A prototype implementation of this approach was constructed on a Java-based mobile agent system. This paper presents the rationale, design, implementation, and applications of the prototype system. 1

. Research areas that require interactive visualization of simulation data

Visualisations of virtual worlds by current Cooperative Virtual Environments (CVEs) are identical for each user, albeit from a different viewpoint. Users cannot tailor their representation of the virtual scene or the degree to which they are aware of other user's activities. This paper describes the implementation of a mechanism to support subjective views of shared virtual worlds, and describes how this mechanism is utilised to enhance an existing 3D application. Keywords CVE, VR, Subjective Views, Database, View coupling, Visualisation, Q-PIT 1 Background And Motivation Cooperative Virtual Environments (CVEs) support the population of generic 3D spaces by a number of users. Such systems include DIVE[3], dVS [5], and MASSIVE [7], and allow users to navigate through the shared space and interact with objects and other users. Each of the CVEs provide a range of functionality and services which may be utilized by application developers in creating shared 3D applications. Many of the ...