A Survey of Routing Techniques for Mobile Collaborative Virtual Environment Applications <s> Peer-to-peer Network based CVEs <s> We present a spatial model of group interaction in virtual environments. The model aims to provide flexible and natural support for managing conversations among large groups gathered in virtual space. However, it can also be used to control more general interactions among other kinds of objects inhabiting such spaces. The model defines the key abstractions of object aura, nimbus, focus and adapters to control mutual levels of awareness. Furthermore, these are defined in a sufficiently general way so as to apply to any CSCW system where a spatial metric can be identified - i.e. a way of measuring position and direction. Several examples are discussed, including virtual reality and text conferencing applications. Finally, the paper provides a more formal computational architecture for the spatial model by relating it to the object oriented modelling approach for distributed systems. <s> BIB001 </s> A Survey of Routing Techniques for Mobile Collaborative Virtual Environment Applications <s> Peer-to-peer Network based CVEs <s> 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 3-D virtual environment that incorporates both the IEEE 1278 distributed interactive simulation DIS application protocol and the IP multicast network protocol for multiplayer simulation over the Internet. <s> BIB002 </s> A Survey of Routing Techniques for Mobile Collaborative Virtual Environment Applications <s> Peer-to-peer Network based CVEs <s> This paper describes and analyzes SCORE, a scalable multicast-based communication protocol for large-scale virtual environments (LSVE) on the Internet. Today, many of these applications have to handle an increasing number of participants and deal with the difficult problem of scalability. We propose an approach at the transport layer, using multiple multicast groups and multiple agents. This approach involves the dynamic partitioning of the virtual environment into spatial areas and the association of these areas with multicast groups. It uses a method based on the theory of planar point processes to determine an appropriate cell size, so that the incoming traffic at the receiver side remains with a given probability below a sufficiently low threshold. We evaluate the performance of our scheme and show that it allows to significantly improve the participants' satisfaction while adding very low overhead. <s> BIB003 </s> A Survey of Routing Techniques for Mobile Collaborative Virtual Environment Applications <s> Peer-to-peer Network based CVEs <s> Content-based publish-subscribe middleware is emerging as a promising answer to the demands of modern highly dynamic distributed computing by providing the necessary decoupling and flexibility. The majority of currently available systems implement event dispatching on top of an overlay network with a tree topology. However, they fail to provide any mechanism to maintain it in the presence of failures, thus hampering their applicability in dynamic scenarios. In this paper, we present a novel approach to reconfiguring the overlay topology by exploiting a distributed hash table. Our algorithm supports arbitrary tree topologies and deals very well with the dynamicity of network scenarios by limiting the impact of reconfigurations induced by topology changes. These results are confirmed by simulations, which validate the applicability of our approach in reconfigurable publish-subscribe middleware. Beyond publish-subscribe, the algorithm is applicable in a wide range of contexts and provides a general way to maintain an overlay network with a controlled topology in dynamic environments. <s> BIB004 </s> A Survey of Routing Techniques for Mobile Collaborative Virtual Environment Applications <s> Peer-to-peer Network based CVEs <s> The scalability of large-scale networked virtual environments (NVEs) such as today's massively multiplayer online games (MMOGs) faces inherent limits imposed by client-server architectures. We identify an emerging research direction that applies peer-to-peer (P2P) networks in order to realize more scalable and affordable NVEs. The central issue for P2P-based NVE (P2P-NVE) systems is to correctly and efficiently maintain the topology of all participating peers by solving the neighbor discovery problem. We also propose the Voronoi-based overlay network (VON), a simple and efficient design that maintains the P2P topology in a fully-distributed, low-latency, and message-efficient manner. Simulation results show that by bounding the per-node resource consumption, VON can be fundamentally more scalable than existing methods while achieving high topology consistency and reliability <s> BIB005
In peer-to-peer systems, each avatar directly communicates its update information to all other participants on the network. In such a model, there is no central server and no single point of failure, since all nodes play client and server roles. A number of well-known applications, namely DIVE  , MiMaze BIB002 , NPSNET [26] , SPLINE [27], SCORE BIB003 , and VON BIB005 are extensively described; other, less common applications like MASSIVE BIB001 , Federated peer-to-peer  , and SimMud  . Federated peer-to-peer  uses hybrid architecture, where nodes are organized into various groups, and managed by a multicast reflectors scheme. SimMud  proposes a solution based on DHT Pastry  structured network to support massive online multiplayer games. The VE is divided into regions, with each region managed by a super node, and playing the root role for the multicast region tree. Any user action is received by the root and delivered to all multicast members. Network latency is affected, since communication between nodes operates under DHT BIB004 . MASSIVE BIB001 (Model, Architecture, and System for Spatial Interaction in Virtual Environments) proposes a technique to limit the number of connections as the number of users increases, in order to reduce network traffic. Each object is associated with an Aura that defines the area in the VE in which the object can publish. Objects can communicate only when their Auras overlap. MASSIVE was developed to handle mainly scalability and network heterogeneity. To the best of our knowledge, NPSNET [26] (Naval Postgraduate School NPS) and SPLINE [27] (Scalable Platform for Large Interactive Networked Environment), represent the most well wellknown peer-to-peer CVE prototypes. NPSNET [26] was developed in 1990 for large-scale military simulations using the Model-View-Controller (MVC) pattern to offer reusability and simplicity. NPSNET uses SIMNET and DIS [26] as networking technique solutions to interoperate with other simulation systems. The virtual environment is divided into a welldefined hexagonal cells structure, with each cell having its own multicast group so as to save network bandwidth. NPSNET has been designed with special focus on military simulation application. An improvement version of NPSNET called DIVE  (Distributed Interactive Virtual Environment) was developed at the Swedish Institute of Computer Science. DIVE uses RTP (Real-time Transport Protocol) for stream data and SRM (Saleable Reliable Multicast) for non-stream-based data communication. The network traffic is reduced by means of the SRM protocol, since there is no need to send keepalive message. The SRM protocol is able to detect missing data packets on reception. We classify DIVE under the hybrid architecture category since there is a central node called DIVESERVER, which is needed to supply the initial connection; however, Frécon et al classified it as a peer-topeer system.