Research On QoS Of Network For Interactive Collaboration Environment Of Distance Education

In this dissertation, the structure of a modern distance education model is createdin a network-based virtual learning environment by means of computer networkingand multimedia technology. Computer Supported Cooperative Learning(CSCL)combined with the idea of Computer Supported Cooperative Working makes it mucheasy for users to communicate and cooperate more conveniently and widely andbecomes a technical foundation of modern distance education. First, the current state of CSCL based interactive learning environment isintroduced;and the architecture, the key techniques for CSCL, including thecollaborative model, collaborative awareness and concurrency control strategy arethen given. Secondly, the function and implementation of a virtual classroom thatconsists of electronic blackboard, cooperative browser, courseware on demand andreal-time multimedia tools are described. It can work together with m-learning systembased on WLAN. The problem of sharing information between heterogeneous devicesis solved.Interactive learning environment needs communication network to providetransmission service with some degree of quality. According to architecture and thefeature of the network, a layer model of QoS(Quality of Service) can be set up, everylayer has its quality parameters and appropriate mechanism to guarantee QoS, theselayers work cooperatively to meet the requirement for QoS in distance education. Inaccordance with the features of multimedia communication in interactive learningenvironment, how to improve the quality of transmission service in application layerand network layer is studied respectively. At application layer, a new BWTA(Burrows-Wheeler Transform Algorithm)compression algorithm is proposed, whichcan reduce the quantity of redundant information and, therefore, bandwidthrequirement of applications is efficiently decreased. At network layer, aimed at one ofnext generation backbone techniques, MPLS(Multiprotocol LabelSwitching)networks, a framework of MPLS-based traffic engineering is put forward,which uses offline optimization and online routing jointly. According to the trafficdemands between sources and destinations, offline optimization computes optimalbandwidth allocation on links;based on the optimal bandwidth allocation, a path setbetween sources and destinations is calculated, which is used in online routingalgorithms and, in this way, global optimum performance of network is achieved;atthe same time, a flexible routing mechanism is provided. In the existing MPLS basedtraffic engineering routing algorithms, only routing traffic with the guaranteedbandwidth request is dealt with, the best-effort traffic which is the majority in thecurrent Internet is neglected. The framework constructed in this dissertation, onlinerouting algorithm of the QoS of traffic with the guaranteed bandwidth and best-efforttraffic is considered simultaneously. Also in this dissertation, an edge admissioncontrol mechanism originally proposed in [94] is improved. In the advancedadmission algorithm, a new approach of computing available bandwidth is used in theadmission decision, which is simple and effective in practice. The improvedadmission control algorithm will guarantee the bandwidth request and will not admittraffic to cause serious performance degradation of others.