Research On Distribution Technology Of Unstructured Peer-to-Peer Video-on-Demand System

Large-scale media distribution technology of VoD(Video-on-Demand) has broad application scenarios.There are some requirements of high bandwidth and long duration for multimedia streams due to diversity requests from users and real-time data transmission from video sequences.So how to provide large-scale media service in a scalable way has been a core issue in the multimedia research area with the growing number of users and videos.In the traditional C/S(Client/Service) system,the centralized server can easily become the bottleneck.IP Multicast reduces the workload of source server and transmission network by having,multiple peers sharing the media streams, however,its deployment on the interact is still limited due to several fundamental concerns.CDN(Content Distribution Network) pushes the service and content to the edge of the internet by utilizing agent cache nodes,but there are also some bottlenecks because of the expensive deployments.P2P mode can provide users with highly flexible interactive environments.Since P2P introduces the sharing of bandwidth,storage and other resources among peers,it has completely changed the VoD service mode,significantly reduced the server load,and greatly improved the utilization of network resources.But the scalability and large-scale application of P2P VoD system remains to be restricted by the dynamic of peers.How to improve the quality and efficiency of data transfer for large-scale P2P VoD applications has become a "hot spot" in the research community of P2P VoD system. Based on the characteristics of real-time data transfer,peer interaction,diversity requests of resources,and VCR operations,this thesis investigates the distribution technology of unstructured P2P VoD,including three aspects:(1) Unstructured-based P2P VoD service architecture,which is used to address the low utilization of data source and remaining bandwidth,as well as uncontrollable playback delay.(2) High bit-rate video transfer scheduling scheme,which is used to meet the requirements on high quality video service for high-level users.(3) Incentive in large-scale P2P VoD distribution,which takes full account of real-time data,heterogeneous request and unequal content from upstream and downstream.Unstructured-based P2P VoD service architecture.The dissertation proposes a P2P VoD system with unstructured topology for the consideration of scalability,and the overlay topology is a data-driven network.The scheme of asynchronous data transfer specializes in effective mining of available video data source at the cost of playback continuity.And it could also reduce the impacts on playback performances from discrete distribution of resources.In view of the contradictions between the characteristics of non-real-time in asynchronous transfer and the real-time in video playback,a novel priority strategy is introduced to establish a compromising selecting algorithm for peers, and to solve the continuity issues for VoD system on condition of meeting normal data transfer and acceptable download rate for multiple peers.The theoretical analysis of server workload points out the relationship between server stress and the peer buffer size as well as the ratio of high priority.The simulation results further show the benefits in terms of continuity,hunch delay and server stress in random and sudden scenarios.Compensation-assisted scheduling in high-quality P2P VoD distribution.To solve the data scheduling issues for high bit-rate streams,we take the analysis and summary from two perspectives of heterogeneous resources and network restrictions in large-scale applications,and propose solutions based on the delay of peer locating and data transfer. An estimate algorithm for peer buffer size is introduced from the research on the update delay in centralized locating strategy.Under accurate locating conditions,the algorithm can lower the update frequency of peers,and then reduce the workload of directory server and update delay of peer locating.Further more,the compensation-assisted strategy,as well as the collaborate process of compensation stream and cache strategy of compensation server,are given to solve resource "hunger" caused by the link jam and asymmetry.The simulation results show that the introduction of compensation strategy can improve the system playback performance on the premise that the server workload is acceptable.Incentive in large-scale P2P VoD distribution.To solve the free-riding issues among peers and stimulate more peers to contribute their bandwidth and storage,an incentive based on the service differentiation by the contribution of peers is proposed for unstructured P2P VoD systems.In this incentive,the contribution of a peer was measured by peer contribution considering both the requirement of real-time video playback and the resource inequality of peers.Meanwhile,a service differentiation scheme was introduced in data transfer scheduling based on the contribution measure of requesting peer and the request queue length of supplying peers.Also,an identification mechanism was presented to avoid possible whitewashing behaviors of peers.Simulation results show that the proposed incentive is effective to constrain the selfish behaviors of peers,and improve the performances of demanded video playback.The works in this thesis have been supported by the China Next Generation Internet "P2P-based digital media business research and application experiment".It is expected that the research results can be applied to the statistical analysis on application and network performance for P2P VoD,and can provide a reference for deployments of large-scale P2P VoD application.