Study Of Scalabilty And Rolbustness Of Streaming Media Multicast System

Application Layer Multicast built on overlay network which is based on TCP/IP architecture is proposed to solve the deployment of large scale streaming media application in Internet. The multicast functions in application layer multicast are implemented by end hosts that are in charge of data storage and transmission. Due to the heterogeneity and P2P transmission style of end hosts in multicast system, the performance of application layer multicast is unsteady with high link stress, transmission delay and low efficiency of multicast. The study of scalability and robustness in large scale streaming media multicast has significance in theory and application.Some achievements have been made in study of scalability and robustness in streaming media system based on application layer multicast. We have done some research work based on these fruits.We propose a hierachical model of application layer multicast based on single data stream——SHMHD, end hosts are organized in different level with the time sequence of cached data packet. Multicast data are split and transmitted in more fine grained style, which makes better use of bandwidth. Redundant mapping mechanism for bandwidth is adopted to avoid the possible congestion in data transmission. Simultaneously, the constrain mechanism based on uploaded data volume of out-degree is proposed to improve the contribution rate of end hosts. To improve the reliability of data transmission, SHMHD reduces the size of parent set and increases the available bandwidth to optimize the hierachical structure. Experiment results show that SHMHD achieves higher data receive rate and shorter transmission path compared with NICE, SHMHD is more adapted to the variance of bandwidth distribution and video bitrate than NICE.Combined multiple description coding with multi-tree topology, we propose a method——MSD to acquire the maximum synchronizing description set. End hosts join the multi-tree multicast with the lowest delay, and acquire optimal synchronizing description set with acceptable delay by maximum covering algorithm. Depending on the asynchronous feature of descriptions, MSD utilizes the asynchronous multi-level cache management mechanism to make the best use of capability of end hosts and achieve higher data receive rate.Experiment results show that MSD achieves better video quality with acceptable transmission delay and control overhead compared with CoopNet, and is scalable and self-adaptive to dynamic and heterogeneous overlay network.A hierachical multicast mechanism based on self-adaptive multiple description coding——HMDC is proposed to synchronize the acquired descriptions from different parents. Based on bandwidth statistical model, MSD adjusts the bitrate and number of description in self-adaptive multiple description coding to meet the demands of heterogeneous end hosts, and improves the multi-level controlled synchronous mode to lower the system delay and dithering. The distributed algorithm for uniform distribution of descriptions is proposed to accelerate the convergence of multicast process.Maximum description set and query set can be acquired by improved maximum covering algorithm to achieve high robustness. Emulation experiment shows that performance of HMDC has been improved significantly with a little bit higher control traffic overhead. In HMDC, the data receive rate is higher and link stress is lower than CoopNet, and HMDC is scalable and robust in dynamic and heterogeneous overlay network.