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.

We present Avocado, our object-oriented framework for the development of distributed, interactive VE applications. Data distribution is achieved by transparent replication of a shared scene graph among the participating processes of a distributed application. A sophisticated group communication system is used to guarantee state consistency even in the presence of late joining and leaving processes. We also describe how the familiar dataflow graph found in modern stand-alone 3D-application toolkits extends nicely to the distributed case. 1.

MASSIVE is a distributed virtual reality system. It provides rich facilities to support user interaction and cooperation via text, audio and graphics media, and interaction is controlled by a spatial model of interaction. The communications architecture is based on processes communicating via typed connections which have interfaces on both ends and which integrate RPCs, attributes and streams in a common context. A spatial interface trading service, the aura manager, has been developed to support interface trading in a spatial context. The concepts embodied in the aura manager can be useful in other interface trading situations, especially where notions of "space" and "meeting" may be applied.

This paper describes how Dynamic WindowConstrained Scheduling (DWCS) can guarantee real-time service to packets from multiple streams with different performance objectives. We show that: (1) DWCS can guarantee that no more than x packets miss their deadlines for every y consecutive packets requiring service, as long as the minimum aggregate bandwidth requirement of all real-time packet streams does not exceed the available bandwidth, (2) using DWCS, the delay of service to realtime packet streams is bounded even when the scheduler is overloaded, (3) DWCS can ensure that the delay bound of any given stream is independent of other streams, and (4) a fast response time for best-effort packet streams, in the presence of real-time packet streams, is possible. Furthermore, if a feasible schedule exists, each stream is guaranteed a minimum fraction of available bandwidth over a finite window of time. 1. Introduction Many real-time, distributed applications, such as telemedicine, virtual env...

Groupware toolkits let developers build applications for synchronous and distributed computer-based conferencing. This chapter describes four components that we believe toolkits must provide. A run-time architecture automatically manages the creation, interconnection, and communications of both centralized and distributed processes that comprise conference sessions. A set of groupware programming abstractions allows developers to control the behavior of distributed processes, to take action on state changes, and to share relevant data. Groupware widgets let interface features of value to conference participants be added easily to groupware applications. Session managers let people create and manage their meetings and are built by developers to accommodate the group’s working style. We illustrate the many ways these components can be designed by drawing on our own experiences with GroupKit, and by reviewing approaches taken by other toolkit developers.

We present EMMIE (Environment Management for Multiuser Information Environments), a prototype experimental user interface to a collaborative augmented environment. Users share a 3D virtual space and manipulate virtual objects that represent information to be discussed. We refer to EMMIE as a hybrid user interface because it combines a variety of different technologies and techniques, including virtual elements such as 3D widgets, and physical objects such as tracked displays and input devices. See-through headworn displays overlay the virtual environment on the physical environment, visualizing the pervasive “virtual ether” within which all interaction occurs. Our prototype includes additional 2D and 3D displays, ranging from palm-sized to wall-sized, allowing the most appropriate one to be used for any task. Objects can be moved among displays (including across dimensionalities) through drag & drop. In analogy to 2D window managers, we describe a prototype implementation of a shared 3D environment manager that is distributed across displays, machines, and operating systems. We also discuss two methods we are exploring for handling information privacy in such an environment. 1.

Bamboo is a portable system supporting real-time, networked, virtual environments. Unlike previous efforts, this design focuses on the ability for the system to dynamically configure itself without explicit user interaction, allowing applications to take on new functionality after execution. In particular, this framework facilitates the discovery of virtual environments on the network at runtime. Fundamentally, Bamboo offers a compatible set of mechanisms needed for a wide variety of real-time, networked applications. Also included is a particular combination of these mechanisms supporting a dynamically extensible runtime environment. This paper serves as a general introduction to Bamboo. It describes the system's architecture, implementation, and future directions. It also shows how the system can facilitate the rapid development of robust applications by promoting code reuse via communitywide exchange.

Although avatars may resemble animated communicating interface agents, they have for the most part not profited from recent research into autonomous systems. In particular, even though avatars function within conversational environments (for example, chat or games), and even though they often resemble humans (with a head, hands, and a body) they are incapable of representing the kinds of knowledge that humans have about how to use the body during communication. Their appearance does not translate into increased communicative bandwidth. Face-to-face conversation among humans, however, does make extensive use of the visual channel for interaction management where many subtle and even involuntary cues are read from stance, gaze and gesture. We argue that the modeling and animation of such fundamental behavior is crucial for the credibility and effectiveness of the virtual interaction in chat. By treating the avatar as a communicative agent, we propose a method to automate the...

This paper describes an experiment to assess the anxiety responses of people giving five minute presentations to virtual audiences consisting of eight male avatars. There were three different types of audience behaviour - an emotionally neutral audience that remained static throughout the talk, a positive audience which exhibited friendly and appreciative behaviour towards the speaker, and a negative audience, which exhibited hostile and bored expressions throughout the talk. A second factor was immersion: half of the 40 subjects experienced the virtual seminar room through a head-tracked head-mounted display and the remainder on a desktop system. Responses were measured using standard Personal Report of Confidence as a Public Speaker (PRCS) which was elicited prior to the experiment and after each talk. Several other standard psychological measures such as SCL-90-R (for screening for psychological disorder), the SAD and the FNE were also measured prior to the experiment. Other response variables included subjectively assessed somaticisation and a subject self-rating scale on performance during the talk. The subjects gave the talk twice each to a different audience, but in the analysis only the results of the first talk are presented - thus making this a between-groups design. The results show that posttalk PRCS is significantly and positively correlated to PRCS measured prior to the experiment in the case only of the positive and static audiences. For the negative audience, prior PRCS was not a predictor of post-PRCS which was higher than for the other two audiences and constant. The negative audience clearly provoked an anxiety response irrespective of the normal level of public speaking confidence of the subject. The somatic response also showed a higher level of anx...

This paper explores interconnecting outdoor AR systems with a VR system to achieve collaboration in both domains simultaneously. We envisage multiple mobile users of wearable AR systems interacting with a stationary VR facility via a wireless network. An application in simulated combat training is described, where the AR users are soldiers with wearable computers, and the VR system is located at a command and control centre. For soldiers, AR provides enhanced information about the battlefield environment, which may include the positions and attributes of simulated entities for the purpose of training outdoors at low cost. At the same time a complete picture of the battlefield, including real and simulated troops and vehicles, is available via the VR system. As soldiers move about, their GPS and digital compass hardware provide the remote VR user and other AR users with the means to track their position in real-time. We describe a working system based on our modular Tinmith-II wearable computer, which interacts with a combat simulator to create a synthetic battle environment for safe training and monitoring.