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Wolff, Robin; Roberts, David J.; Otto, Oliver
doi: 10.1162/1054746041422280pmid: N/A
Event management must balance consistency and responsiveness above the requirements of shared object interaction within a Collaborative Virtual Environment (CVE) system. An understanding of the event traffic during collaborative tasks helps in the design of all aspects of a CVE system. The application, user activity, the display interface, and the network resources, all play a part in determining the characteristics of event management. Linked cubic displays lend themselves well to supporting natural social human communication between remote users. To allow users to communicate naturally and subconsciously, continuous and detailed tracking is necessary. This, however, is hard to balance with the real-time consistency constraints of general shared object interaction. This paper aims to explain these issues through a detailed examination of event traffic produced by a typical CVE, using both immersive and desktop displays, while supporting a variety of collaborative activities. We analyze event traffic during a highly collaborative task requiring various forms of shared object manipulation, including the concurrent manipulation of a shared object. Event sources are categorized and the influence of the form of object sharing as well as the display device interface are detailed. With the presented findings the paper wishes to aid the design of future systems.
Wolff, Robin; Roberts, David J.; Otto, Oliver
doi: 10.1162/1054746041422280pmid: N/A
Event management must balance consistency and responsiveness above the requirements of shared object interaction within a Collaborative Virtual Environment (CVE) system. An understanding of the event traffic during collaborative tasks helps in the design of all aspects of a CVE system. The application, user activity, the display interface, and the network resources, all play a part in determining the characteristics of event management. Linked cubic displays lend themselves well to supporting natural social human communication between remote users. To allow users to communicate naturally and subconsciously, continuous and detailed tracking is necessary. This, however, is hard to balance with the real-time consistency constraints of general shared object interaction. This paper aims to explain these issues through a detailed examination of event traffic produced by a typical CVE, using both immersive and desktop displays, while supporting a variety of collaborative activities. We analyze event traffic during a highly collaborative task requiring various forms of shared object manipulation, including the concurrent manipulation of a shared object. Event sources are categorized and the influence of the form of object sharing as well as the display device interface are detailed. With the presented findings the paper wishes to aid the design of future systems.
Hosseini, Mojtaba; Georganas, Nicolas D.
doi: 10.1162/1054746041422325pmid: N/A
IP Multicasting has been a crucial requirement of many scalable networked virtual environments by providing an efficient network mechanism through which a sender can transmit its information to a large number of receivers without having to send multiple copies of the same data over a physical link. The widespread deployment of IP Multicast has been slow due to some yet unresolved issues, prompting recent efforts in the development of multicasting protocols at the application layer instead of at the network layer. Most of these protocols address the case of a single source streaming media to a large number of receivers in applications such as video-on-demand or live broadcast. Collaborative and distributed virtual environments exhibit different characteristics that in turn necessitate a different set of requirements for application layer multicast protocols. This paper presents an introduction to application layer multicasting as it relates to distributed and collaborative virtual environments and the development of our own end system multicast protocol for multi-sender virtual teleconference applications.
Hosseini, Mojtaba; Georganas, Nicolas D.
doi: 10.1162/1054746041422325pmid: N/A
IP Multicasting has been a crucial requirement of many scalable networked virtual environments by providing an efficient network mechanism through which a sender can transmit its information to a large number of receivers without having to send multiple copies of the same data over a physical link. The widespread deployment of IP Multicast has been slow due to some yet unresolved issues, prompting recent efforts in the development of multicasting protocols at the application layer instead of at the network layer. Most of these protocols address the case of a single source streaming media to a large number of receivers in applications such as video-on-demand or live broadcast. Collaborative and distributed virtual environments exhibit different characteristics that in turn necessitate a different set of requirements for application layer multicast protocols. This paper presents an introduction to application layer multicasting as it relates to distributed and collaborative virtual environments and the development of our own end system multicast protocol for multi-sender virtual teleconference applications.
Goldin, Alexander; Gotsman, Craig
doi: 10.1162/1054746041422352pmid: N/A
Message filtering is important for distributed multiagent systems, where a large number of dynamic agents participate in the system activity, but a typical agent is interested in only a very small dynamic subset of the other agents. The agent must be constantly informed on the status of this subset, and this is achieved by message passing between relevant agents. Message filtering is required to reduce the communications load on the system, which could be prohibitive if each agent must communicate with all others in order to obtain the information it needs. This paper deals with the case of a multiagent virtual environment, where each agent has a location in 2D space, and is interested in a small subset of the other agents, either those within a fixed range—as treated by previous authors, or the k other agents nearest to it—treated here for the first time. Furthermore, we treat the case of a fully distributed system, where no central server(s) are available to coordinate between the agents. The main challenge is then to design protocols that perform significant message filtering, yet enable each agent to maintain a consistent image of the other agents it is interested in. These protocols are useful in multi-agent games, simulations, and other virtual environments in which the geometric relationships between agents are important. They could also be useful for mobile-commerce and cellphone-based gaming applications.
Goldin, Alexander; Gotsman, Craig
doi: 10.1162/1054746041422352pmid: N/A
Message filtering is important for distributed multiagent systems, where a large number of dynamic agents participate in the system activity, but a typical agent is interested in only a very small dynamic subset of the other agents. The agent must be constantly informed on the status of this subset, and this is achieved by message passing between relevant agents. Message filtering is required to reduce the communications load on the system, which could be prohibitive if each agent must communicate with all others in order to obtain the information it needs. This paper deals with the case of a multiagent virtual environment, where each agent has a location in 2D space, and is interested in a small subset of the other agents, either those within a fixed range—as treated by previous authors, or the k other agents nearest to it—treated here for the first time. Furthermore, we treat the case of a fully distributed system, where no central server(s) are available to coordinate between the agents. The main challenge is then to design protocols that perform significant message filtering, yet enable each agent to maintain a consistent image of the other agents it is interested in. These protocols are useful in multi-agent games, simulations, and other virtual environments in which the geometric relationships between agents are important. They could also be useful for mobile-commerce and cellphone-based gaming applications.
Linebarger, John M.; Kessler, G. Drew
doi: 10.1162/1054746041422316pmid: N/A
As collaboration in virtual environments becomes more object-focused and closely coupled, the frequency of conflicts in accessing shared objects can increase. In addition, two kinds of concurrency control “surprises” become more disruptive to the collaboration. Undo surprises can occur when a previously visible change is undone because of an access conflict. Intention surprises can happen when a concurrent action by a remote session changes the structure of a shared object at the same perceived time as a local access of that object, such that the local user might not get what they expect because they have not had time to visually process the change. A hierarchy of three concurrency control mechanisms is presented in descending order of collaborative surprises, which allows the concurrency scheme to be tailored to the tolerance for such surprises. One mechanism is semioptimistic; the other two are pessimistic. Designed for peer-to-peer virtual environments in which several threads have access to the shared scene graph, these algorithms are straightforward and relatively simple. They can be implemented using C/C++ and Java, under Windows and Unix, on both desktop and immersive systems. In a series of usability experiments, the average performance of the most conservative concurrency control mechanism on a local LAN was found to be quite acceptable.
Linebarger, John M.; Kessler, G. Drew
doi: 10.1162/1054746041422316pmid: N/A
As collaboration in virtual environments becomes more object-focused and closely coupled, the frequency of conflicts in accessing shared objects can increase. In addition, two kinds of concurrency control “surprises” become more disruptive to the collaboration. Undo surprises can occur when a previously visible change is undone because of an access conflict. Intention surprises can happen when a concurrent action by a remote session changes the structure of a shared object at the same perceived time as a local access of that object, such that the local user might not get what they expect because they have not had time to visually process the change. A hierarchy of three concurrency control mechanisms is presented in descending order of collaborative surprises, which allows the concurrency scheme to be tailored to the tolerance for such surprises. One mechanism is semioptimistic; the other two are pessimistic. Designed for peer-to-peer virtual environments in which several threads have access to the shared scene graph, these algorithms are straightforward and relatively simple. They can be implemented using C/C++ and Java, under Windows and Unix, on both desktop and immersive systems. In a series of usability experiments, the average performance of the most conservative concurrency control mechanism on a local LAN was found to be quite acceptable.
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