Time Stamp Consistency In Large-Scale Distributed Virtual Environment

Distributed Virtual Environment has been widely used in many fields such as mili-tary simulation, multi-player online video games, distance education and electronic com-merce because of its cost-efficiency, repeatability and safety. Time Stamp ConsistencyproblemisoneoftheessentialandkeyissuesinDistributedVirtualEnvironment, toavoidthe inconsistency phenomena such as the incorrect message order and the disordered timestampswhicharecausedbythemessagetransmissiondelay,manytimestampconsistencycontrol methods are applied to keep the consistency among all nodes. However, withthe increasing scale of Distributed Virtual Environment, the existing consistency controlmethods have to compromise the system functionality while maintaining the system con-sistency, which limits the applicability of Distributed Virtual Environment systems. Tomeet the requirements of large-scale Distributed Virtual Environment, this dissertationfirst analyzes the key attributes about large-scale, high real-time and delay uncertainty inDistributed Virtual Environment, and then studies some new consistency control methodsto improve overall system performance in many different scenarios. The main contribu-tions of the dissertation are as follows.(1)To tackle the contradiction relationship between time stamp consistency require-mentandresponsivenessrequirementinDistributedVirtualEnvironment,thisdissertationproposes a novel method called Asynchronous Time Consistency (ATC) Control Methodbased on call-back clock, which can improve the system responsiveness without com-promising the system functionality. The basic idea of this method is to utilize the asyn-chronism of different nodes'clocks to re-distribute the system time resources and get abreakthroughinkeepingabsolutetimestampconsistencyunderasynchronouslocal-timessituation. In the case that only partial delay information is perceived, we overcome thetechnical difficulty of fast iteration method and improve the overall system performancewhile meeting the consistency requirements.(2)To solve the problem about different responsiveness requirements in large-scaleDistributed Virtual Environment, this dissertation proposes a novel consistency controlmethod to optimize the worst system satisfaction degree of responsiveness requirementsfor Cooperative Distributed Virtual Environment, and a new consistency control method to improve the usability and fairness for Competitive Distributed Virtual Environment re-spectively. On the basis of absolute time stamp assurance, the methods provide a goodsupport to meet the different responsiveness requirements. In the method for CooperativeDistributed Virtual Environment, we define a new metric to quantify the worst systemsatisfaction degree, and realize a distributed request-response mechanism to optimize theperformance of nodes with different responsiveness requirements. In the method for Co-operative Distributed Virtual Environment, we keep the system consistency by consid-ering usability and fairness simultaneously, and maintain the functionality of the systemwith different responsiveness requirements.(3)To solve the interaction efficiency problem while keeping the consistency of con-tinuous model entities in Distributed Virtual Environment, this dissertation proposes anovelintervalconsistencycontrolmethodbasedonestimatingnetworkdelay. Themethodutilizes the strategy that receiver nodes are responsible for choosing the event delay to re-lievetherestriction relationshipamongallreceivernodesimposedbytheexistingintervalconsistency control methods. Moreover, the time stamp consistency and interval consis-tency are kept simultaneously due to the same delay strategy for all local events and re-mote events. For adjusting the parameters properly during the run time, this dissertationproposes a B-tree based network delay estimation method, which solves the contradic-tion problem between efficiency and accuracy in the estimating process and improve theinteraction performance effectively.(4)To study the impact on the consistency made by mapping all clients to properservers in multi-server infrastructure Distributed Virtual Environment, this dissertationproposes a new optimal mapping method based on balanced load cutting for the case thatclients migrate occasionally, and an irregular cutting based distributed mapping methodfor the case that clients migrate frequently. In the balanced load cutting based optimalmapping method, we reveals the three factors to affect the mapping results: balancing theworkload of servers, maintaining the physical world integrity and maintaining the virtualworld integrity. Hence, we achieve a breakthrough to get the optimal result with polyno-mialcomplexityandimprovethemappingresulteffectively. Intheirregularcuttingbaseddistributed mapping method, by utilizing the irregular cutting of Voronoi cells inoscula-tion, we capture the dynamic property of clients in the virtual world and greatly decrease the costs of Distributed Virtual Environment systems for migration of clients. As a re-sult, the above methods improve the consistency and overall performance of multi-serverinfrastructure Distributed Virtual Environment effectively.