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Dynamic modeling approach to analyze user churn in a large P2P downloading system

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The Journal of China Universities of Posts and Telecommunications 2013年第1期20卷 19-25页

作者： HUANG Dan ZHENG Yi chen chang-jia School of Electronics and Information Engineering Beijing Jiaotong University

Characterizing the features of user churn is crucial to the sustainable development of peer-to-peer （P2P） systems where peers join and leave at any arbitrary time. This paper analyzes the user churn in a P2P downloading system named QQXuanfeng by using the fine-grained log analysis over 60 days. It shows that the online and offline duration is related to up （arrive） time and down （depart） time respectively. A continuous ON/OFF process, which exhibits the diurnal patterns of users, is simulated using the churn model. In particular, the dynamic departure rate is proposed to give insight into the distribution of online duration. Further more, considering the heterogeneity of users, we cluster users based on the similarity of redefined user availability. As an example of application of this model, a high availability overlay is constructed and evaluated based on the clustering.

关键词： P2P network user chum clustering

Online social network model with renewal and accelerated growth

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The Journal of China Universities of Posts and Telecommunications 2014年第4期21卷 54-63页

作者： WU Zhe GUO Yu-chun chen chang-jia School of Electrical and Computer Engineering Beijing Jiaotong University

Based on observation of the growing mechanism in Twitter-like online social networks, an online social network （OSN） evolution model was proposed, a renewal mechanism for the old nodes and an accelerated growth mechanism was introduced for the new nodes, comparing with the native copying model. Topological characteristics of the generated networks, such as degree distribution, average shortest-path length and clustering coefficient, are analyzed and numerized. These properties are validated with some crawled datasets of real online social networks.

关键词： online social network network evolution model degree distribution average shortest-path length clustering coefficient

Storage capacity model for cloud download

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The Journal of China Universities of Posts and Telecommunications 2012年第5期19卷 83-91页

作者： XU Ying-ying AO Nai-xiang chen chang-jia School of Electronics and Information Engineering Beijing Jiaotong UniversityBeijing 100044China

With the rise and world wide deployment of cloud utilities, the principle of the cloud download is proposed to provide high-quality file content distribution by using dedicated servers as cloud cache to guarantee the data availability and enhance the data transfer rate. As the system scales up to a large population, how to design appropriate storage capacity of cloud cache is a key challenge for cloud download. In this paper, primary elements impacting on storage capacity are explored through deliberating in large-scale commercial cloud download system, i.e. general user usage pattern and available period. And based on statistical analysis of real-world traces, we formulate storage capacity related to these two elements, which is the original contribution different from all previous works. This model gives guidance of potential system policy design. Finally, the effectivity of this model is demonstrated by simulation results compared with empirical data of practical system.

关键词： cloud download storage capacity model available period usage pattern

Efficient complementary caching for ISP-aware networks

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The Journal of China Universities of Posts and Telecommunications 2012年第5期19卷 66-76页

作者： AO Nai-xiang XU Ying-ying chen chang-jia School of Electronic Information Engineering Beijing Jiaotong UniversityBeijing 100044China

Internet service providers （ISPs） have taken some measures to reduce intolerable inter-lSP peer-to-peer （P2P） traffic costs, therefore user experiences of various P2P applications have been affected. The recently emerging offiine downloading service seeks to improve user experience by using dedicate servers to cache requested files and provide high-speed uploading. However, with rapid increase in user population, the server-side bandwidth resource of offline downloading system is expected to be insufficient in the near future. We propose a novel complementary caching scheme with the goal of mitigating inter-ISP traffic, alleviating the load on servers of Internet applications and enhancing user experience. Both architecture and caching algorithm are presented in this paper. On the one hand, with full knowledge of P2P file sharing system and offiine downloading service, the infrastructure of complementary caching is designed to conveniently be deployed and work together with existing platforms. The co-operational mechanisms among different major components are also included. On the other hand, with in-depth understanding of traffic characteristics that are relevant to caching, we develop complementary caching algorithm with respect to the density of requests, the redundancy of file and file size. Since such relevant information can be real-time captured in our design, the proposed policy can be implemented to guide the storage and replacement of caching unities, Based on real-world traces over 3 months, we demonstrate that the complementary caching scheme is capable to achieve the ＇three-win＇ objective. That is, for l＇2P downloading, over 50% of traffic is redirected to cache; for offline downloading, the average server-dependence of tasks drops from 0.71 to 0.32; for user experience, the average P2P transfer rate is increased by more than 50 KB/s.

关键词： caching inter-ISP traffic server-side load user experience

Cloud download system optimizing by job and notification scheduling

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The Journal of China Universities of Posts and Telecommunications 2014年第4期21卷 47-53,63页

作者： XU Ying-ying chen chang-jia ZHAO Yong-xiang chen Yi-shuai School of Electronics and Information Engineering Beijing Jiaotong University

With expansion of cloud-based applications, it is necessarily for business service provider to deal with how to provision resources to server customers. In cloud download, the service provider faces great challenge on determining when to process job and when to notify the user to meet the conflicting objectives, i.e., the service profit maximization and user satisfaction maximization. An economic model was proposed to find job and notification scheduling strategies for making tradeoffs between user satisfaction and profit of the system, in this model, optimization problems are formulated as follows, profit maximization under a satisfaction target and then satisfaction optimization with a profit bound. By solving these optimization problems, the optimal scheduling strategies are obtained under various quality requirements of service. It is demonstrated that the proposed strategy can obtain better performance than the system without the intelligent scheduling strategy.

关键词： cloud download economic model optimization scheduling strategy user satisfaction

Scheduling piece requests blindly and randomly for peer-to-peer live streaming

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The Journal of China Universities of Posts and Telecommunications 2010年第2期17卷 76-84页

作者： chen Yi-shuai chen chang-jia ZHAO Yong-xiang LI Chun-xi School of Electrical and Information Engineering Beijing Jiaotong University Beijing 100044 China

The design of piece scheduling algorithm is fundamental in mesh-based peer-to-peer （P2P） live streaming systems. This article regards the piece propagation process in P2P live streaming system as a conflict process, where peers compete to get the piece as soon as possible to meet the tight timing requirement of the live system. In this vision, the authors reduce the piece scheduling problem as a conflict resolution problem, and propose a blind random scheduling method to resolve it. The algorithm can be described as： 1） pieces are scheduled independently; 2） conflicts are resolved by the random back off algorithm. The theoretical analysis and simulation results prove that the algorithm scales well with the network size, and can obtain near-optimal in-time delivery of pieces. The algorithm is also easy to implement in the real-world system.

关键词： peer-to-peer live streaming conflict resolution exponential back off piece scheduling

Model of downloading strategy from peers and server for saving server bandwidth in P2P VoD system

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The Journal of China Universities of Posts and Telecommunications 2011年第5期18卷 76-86,101页

作者： WEI Ting DENG Guang-qing chen chang-jia ZHU Wei School of Electronic and Information Engineering Beijing Jiaotong University Beijing 100044 China Department ofPPLive P2P-CDN R＆D Shanghai 201203 China

In peer-to-peer （P2P） video on demand （VoD） system, once the P2P downloading rate cannot satisfy the need of playback, server is quickly referred to for help in providing enough bandwidth. Thus the switch of downloading from other peers （P2P） and server （HTTP） exists. This paper uses the proportion of P2P downloading amount （PPDA） during the video watching process to measure server load. This article is interested in finding a better strategy or switch rule between P2P and HTTP downloading for saving server bandwidth. The authors suggest and model a kind of switch rule based on local buffer amount, using mathematical theory of Brownian motion. It can effectively alleviate the impact of P2P rate fluctuation, reduce the switch times and improve the PPDA by at least 3%-5% on the basis of the former switch rule, which means substantial cost can be saved. Particularly the PPDA is related with the ratio of playback bit rate to the HTTP downloading rate which means the PPDA can be restricted by controlling the ratio in the real-world system. Though the result comes from constant bit rate （CBR） video supposition, it provides perspective and method for variable bit rate （VBR） application, and valuable insights for the future development of P2P VoD system.

关键词： P2P VoD downloading server load

Cost-effective deployment of distributed cloud based on generic expense model

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The Journal of China Universities of Posts and Telecommunications 2013年第5期20卷 9-15,29页

作者： AO Nai-xiang XU Ying-ying HUANG Dan ZHAO Yong-xiang chen chang-jia School of Electronic Information Engineering Beijing Jiaotong University

Distributed cloud architecture which consists of many cloud computing-storage resources （CCSRs） distributed across a geographic large-area has been widely implemented. It has received significant attention from academia. However, little effort has been taken to examine changes in operating cost-structure brought by distributed cloud scheme, or explore how to reap economic benefits from its geo-diversity. To tackle such issue, this paper formulated cost optimizations for cloud platforms based on a generic expense model of distributed cloud, taking into account major components of operating cost. The best deployment schemes were obtained through numerical simulation. The optimal amount of edge CCSRs and their corresponding placements were found to be determined by the ratio among various overhead components. Both model study and numerical simulation shed light on practical deployment of distributed cloud with high cost-effectiveness.

关键词： distributed network cost-effective optimization numerical simulation

Inferring playback rate and rate resets of P2P video streaming transmissions by piecewise line envelope approximation

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The Journal of China Universities of Posts and Telecommunications 2009年第2期16卷 58-62,79页

作者： LI Chun-xi chen chang-jia School of Electronics and Information Engineering,Beijing jiaotong University,Beijing 100044,China [a]School of Electronics and Information Engineering Beijing jiaotong University Beijing 100044 China

Conventionally, P2P video is regarded as CBR traffic. However, our measurements have shown that the rate reset cannot be neglected in a practical IPTV system because each rate reset often leads to performance degradation. Thus, addressing the problem of inferring playback rate and rate reset in a P2P video system is significant. In this article, an algorithm termed piecewise linear envelope approximation （PLEA） is proposed, in which a follow-up time is introduced to smooth rate fluctuations in a small time scale and to adapt rate jumps in a large time scale automatically. With the PLEA algorithm, discontinuity introduced by blind segmentations adopted by current methods is avoided. Furthermore, unlike existing algorithms in which both segmentation and combinations are performed in multiple runs, only a single computation path is involved in the PLEA algorithm. This makes PLEA algorithm amenable to implementation of low complexity by either software or hardware. Both theoretical analysis and experiment based on measured data show that the PLEA outperforms existing algorithms based on segmentation.

关键词： P2P video playback rate rate reset convex hull linear program