Study In Wireless Streaming-Media Service With Hybrid Network Based On Content Delivery Network(CDN)

Nowadays the demand of the multi-media service is rapidly rising,which leads to the contradiction between the huge load on the system and the limited resource in the wireless environment as well as the poor user experience in the multi-media service.To get rid of the difficulty,a new multi-media framework which can be adapted to the wireless environment is urgently needed,to release the traffic load and improve the user experience.This thesis designs a wireless multi-media service framework based on CDN technology and converged network.This framework is primarily based on the converged network of the broadcasting and cellular system.The converged network can realize the large-scale coverage and high-speed transmission of broadcasting system,as well as the multi-user access and the end-to-end service of cellular network at the same time.The broadcasting system can take charge of pushing data,the cellular network can realize the data pulling.The converged network of them can decrease the expense of the network resource.Besides,the thesis introduces CDN proxy servers into the structure of the framework,to receive and store data from both broadcasting and cellular systems.Users can access the multi-media service directly from the CDN proxy server,so that the traffic load cased by large amount of user requests can be furthermore decreased.To evaluate the framework's performance,a simulation platform is also designed based on the OMNET++ framework.With a static system content set,it can be used to study system capacity and average system delay under different network scenarios.The results show the advantage of the system to have a better performance.As the storage size of the CDN proxy server increases,the system capacity and the average system delay can increase and decrease in a form of logistic curve.Increasing the transmission speed of the broadcasting channel can also increase the system capacity markedly at the beginning,but when the speed turns bigger,the curve of the system capacity turns out to be flat.It can decrease the average system delay in the form of a logistic curve.As for the topology of the system,increasing the number of the CDN proxy servers in the region of a cell can efficiently increase the system capacity linearly,and show the advantage of the broadcast system.In reality,the system content set can be updated as the time varies.New contents can arrive and old contents would be eliminated.The time interval of updating the system content set can influence the system performance in a negative exponential way.The broadcast mechanism needs to be adjusted according to the update state of the system content set.It is found that,when the the system content set updates frequently,no matter the broadcast interval is too long or too short,it would bring poor system capacity.To optimize the broadcast interval,the relationship between the system capacity and the system content set update interval is studied to determine the relationship between the system capacity and the broadcast interval under different system content set update state.The optimized broadcast interval can maximize the system capacity and gain a low average system delay at the same time.