Design And Implementation Of Remote Schoolteaching Living Broadcast System Based On Application Layer Multicast

In modern distance learning in order to facilitate rapid long-distance learners to learn, real-time online distance teaching mainly based on video conference are often the first choice .This synchronous teaching-teaching model commonly adopted in the real-time point-to-point transmission technology, so network resources spend less time at the beginning. But with the increase in the number of host access, data transmission load of server increases ,so that more and more the resource of server and network are occupied, and even network congestion resulted from the increasing need of network bandwidth, which affects the expansion of the system. Following the development of computer networks, application-level multicast technology as cutting-edge technology of network multicast has been widely studied and some mature theories come into being . Its most notable feature is that " time focuses and the space distributes ", Single-source sending a package and many terminals receiving it, which adequately makes full use of bandwidth and computer resources to have better data transmission efficiency .It makes up for the shortage of scalability and extencibility etc in real-time network.The features of ALM technology is more suitable for long-range synchronous teaching-teaching mode. In view of this, design and implementation of remote schoolteaching living broadcast system based on application layer Multicast ,which expatiates on the overall framework of system for the design and realization of the process. The medium of teachers live Room uses relatively limited network resources to complete four aspects of distance learning applications, such as presentation of the screen, video live, Document Management / downloads, and news broadcasts.First , this article summarizes an overview of ALM technology and distance learning principles of the present situation ,and moreover, it provides the necessity and feasibility of remote schoolteaching living broadcast system based on ALM. Then it introduced the key technologies used in the development of the system and expatiates on the principle of communication of the ALM platform (MRTP), which designs the system architecture, the module features and its workflow.Then the system uses the advantages of MRTP platform which increase bandwidth utilization rate and reduce the transmission delay .The thesis has a detailed description of design and implementation process as to the screen image transmission module and video messaging transmission module etc.On-screen image transmission module uses algorithm of second intra-frame and extra-frame compressions. First , two adjacent images line by line are compared and recorded the part of changes.Next, having changed data is deaded with by the zlib compression, which reduces the volume of data transmission. After that the frame is splited, and finally the little data segments are tranmissed through the MRTP transmission platform. The video messaging module used the following technology,such as directshow technology adapted to catche video data and audio data, Xvid Video MPEG-4 encoder for video data compression coding, the use of the MP3 audio compression method, time-stamp set by the root server which completed to transmit the data of Audio and video of the two transmission channels in the same channel,so as to achieve synchronization of audio and video transmission. File is downloaded on TCP control channels to verify the reliability. Broadcasting news is the completion of the simultaneous transmission of information.Last, the system is used in college network which gives the evaluation of the results of the experiment. From the test results, data transmitted between the two nodes in the 150-200ms delay, and as a whole the delay is less than 5 seconds, so that the transmission of video images has good results, which ensures real-time synchronization of the system.In short, the system uses for dynamic capture of the screen images and video.After data was compressed, the little segments splitted were carried out transmission ,which reduces the server load and further improves the transmission rate, so as to have a good system and real-time synchronization. In addition, the system for self-adjustment, and no additional hardware, simple to operate, is a typical mode of teaching in different localities of the application for real-time remote teaching to give a great convenience.