Dynamics Modeling And Analyzing For Network Service Systems

The P2P (peer-to peer) technology has been influencing the development of the Internet with its good extensibility and effective utilization of resources since its emer-gence in the beginning of the21st century. The development of the Internet began to shift focus from the centralized system to the distributed system. The network service systems, such as file-sharing, instant messaging, social network and streaming service system, have changed the way people live, work, and study. One example is the P2P file-sharing system, with the BitTorrent software as a typical one, which makes full use of users’resources including bandwidth and storage space to share files. Another one is the streaming service system represented by the video-on-demand systems such as Youku, Tudou and iQiYi. The system distributes services to the edge of the Internet by adopting the CDN (content delivery network) technology. Furthermore, by strengthen-ing the interaction between proxy servers using the P2P technology, the stream service system can improve the quality of services (QoS), expand the throughput of the system and reduce the running cost of the network service providers. This dissertation focuses on the two typical network service systems, which are BitTorrent and network stream-ing service system. Structures, main working process and influencing factors of the two systems are analyzed in the dissertation. The influencing factors are mathematically ex-pressed by a series of differential equations. By setting up a dynamic model comprising of the differential equations, the dissertation analyses the evolution of the systems and influence of the factors on the systems as well on each other. The model can work as theoretical support for the study, design, and application of the network service systems.In the dissertation, the structure, main processes and the influence factors of the BitTorrent and streaming service system are analyzed, then the dynamic models are set up to describe the evolution of the BitTorrent and streaming service system. Further-more, we discuss the stability of streaming service system based on the dynamic model. The contribution of this dissertation are listed in the following part.Firstly, a novel dynamic model of BitTorrent P2P file-sharing system is proposed in this thesis. Users of the BitTorrent system, which is a typical application of P2P system, not only download the file but also upload the file to others. This reflects the character of parity, interaction, good extensibility of P2P. The past research put their attention on the evolution of the downloaders’and seeds’number in the BitTorrent sys-tem, and assumed that the main factor influence the evolution is the users’bandwidth, while other influencing factors have been ignored. Instead of studying the macroscopic characteristics of the whole system, the author models one single node in the BitTorrent. The factors that influence the interaction between nodes in the BitTorrent are expressed in mathematical forms, and a dynamic model is set up to describe the interaction be-tween the users of the BitTorrent system in an accurate manner, and also to analyze the influence of the factors on one another.Secondly, a dynamic model of the streaming service system is proposed. The tra-ditional research for the streaming service systems placed emphasis on the algorithms and ignored the interaction between the algorithms. The streaming service system can be seen as a logical network, which is composed of virtual service nodes that repre-sent the streaming service subsystem. Then the factors, such as hardware, user be-havior, algorithms, etc. are analyzed and expressed in mathematical forms. Then the dynamic model of the streaming service system is set up to describe the interaction between clients and the virtual service nodes and also between virtual service nodes. Inter-relations of the influencing factors can also be revealed by the analysis.Thirdly, a criterion for the stability of the streaming service system is proposed in this thesis. The service subsystem is at the edge the Internet, which serve the users directly. The stability of the subsystem influence the user experience directly. We con-sider the subsystem as a whole and analyze the actual conditions, and then define the stability of the streaming service system. Furthermore, based on the model already set up, the criterion for stability of the streaming service system can be gained through analysis.Lastly, an admission control policy based on the stability criterion of the streaming service system is proposed. The admission control policy is a dominant factor in decid-ing whether the users’requests can be admitted by the system. Based on the stability criterion, the author designs an admission control policy under which users’requests will be admitted when the system is stable and rejected when the system is unstable.