The Design And Implementation Of Distributed Synchronous Online Teaching System

A distributed synchronous online teaching system is designed and implemented in this dissertation, which is a distance teaching system applied on Internet, transmitting multimedia data in real-time, such as video, audio, PowerPoint courseware, and graphic data etc. With the rapid development of network and multimedia technologies, this kind of system has become increasingly needed, within which, an interactive real-life teaching environment is build through Internet, however, which is still plagued by many problems, such as variability in throughput, packet loss and delay due to the network congestion.The flux and the reliability of the system have been studied in this paper, and the main research is summarized as following:1. A three layer network structure including a central server and proxies for the system is designed, setting those proxies in LANs the server in Internet. The scheme solves the problem of connecting through the proxy's initial link by transmitting data received from the server to other users , and the same time reducing both the data flux and workload of the server.2. Data transfer of this system is carried out in one-to-more way through the multicast technology. Ethernet supports multicast on the hardware while Internet does not, thus this just implement the multicast within LANs and the unicast between LANs, in which a proxy is required to set in LANs.3. An distributed synchronous online teaching application protocol (DSOTAP) is proposed in this paper, which is based on the TCP/IP protocol and provides a format for the video datagram, which transmitting control information via the TCP segment and the multimedia data via the UDP datagram.4. Fail-silent fault is tackled by using the physical redundancy to enhance the reliability of the system, and the idea of CDN network is adopted to guarantee the state consistency.5. User interface is unique in the software of the client that has many functions of the system supported by many technologies. However, software in the server is simpler. By doing so, the system make full use of the computers of the clients, greatly reducing the workload of the server and improving the reliability of the system.