Spatio-temporal Consistency In P2P Based Distributed Virtual Environment

With the development of the computer networks and virtual environment technology, research on the theory and application of distributed virtual environment (DVE) has become a hotspot of computer networks technology. Owing to the advantages of peer-to-peer (P2P) techonology in real-time property, security, scalability and load-balancing, it's a trend to use P2P technology instead of the traditional client/server (C/S) architecture to conctruct DVE system.The states of Avatar objects are computed and distributed by local nodes in P2P- based DVE system. Spatio-temporal consistency is still a problem to be solved in such system due to the lack of global administration services of central server. Spatially, three requirements as follows should be satisfied. First, the interactive node discovered by each node should keep consistent with the truth. Second, different replicas of the same avatar object's state should keep consistency with each other. Three, the event message and the state message received by each node should keep consistent with the truth. Temporally, the above three requirements should be satisfied real-timely. Therefore, spatio-temporal consistency could be divided into three subproblems which are the node discovery, synchronization of interaction among nodes and cheat-proofing of nodes' interaction.Aiming at the spatio-temporal consistency of P2P-based distributed virtual environment, further research is done concerning the cooperative behaviors among nodes. Furthermore, corresponding measures are put forward to solve some problems in point.1. In order to improve the topological consistency, real-time property and scalability of node discovery in P2P-based distributed virtual environment, a hormone-based node discovery model named HP2PON is proposed by referring to the hormone mechanism in biological incretion system. According to the model, node discovery is actualized by the diffusion of hormone message in the network. Meanwhile, an analysis framework of node discovery in P2P-based DVE system is put forward. According to this framework, local awareness of the network can be reenforced by guaranteeing the global connectivity, neighbors' encapsulation property, AOI neighbors' encapsulation property and the periodical checking to the weak areas. On the basis of the framework, a fully distributed node discovery model with high topological consistency named SimWorld is proposed. Experiments and analysis proved that both HP2PON and Simworld model has approximate 100% topological consistency.2. In order to improve the real-time property, load-balancing and scalability ofthe synchronize mechanism in the P2P-based DVE, this paper proposes single point computing synchronize model. The task of global state's computing is assigned uniformly to all the nodes in the system, and for each object there is only one source to compute its state. The interval of round is set by the user, and the slow node will be booted out of the system. The experiment and analysis prove that the traffic in single point computing synchronize model is approximately twice as much as the traffic in C/S, only two application level hops are needed in each round, at the same time, the bandwidth consumption and the computing task are distributed in all of the nodes uniformly.3. In order to improve the real-time property, load-balancing and scalability of cheat-proofing mechanism in the P2P-based DVE, this paper proposes single proxy computing model. The computing and distributing tasks of each avatar's state are managed by a corresponding proxy node in the model. And due to the random assignment of proxy node, there is no profit relation between the proxy node and the controlling node of the same avatar object, and there is also no profit relation between the proxy node of avatar a and the nodes which control the avatars interacting with avatar a. so the model effectively proof the cheatings. The experiment and analysis prove that single point computing synchronize model can successfully proof several protocol cheatings, while the traffic in single proxy computing model is approximate three to four times as much as the traffic in C/S, and only two application level hops are needed in each round.