In this paper, we consider cloud-assisted Peer-to-Peer (P2P) video streaming systems, in which a given video stream is divided into several sub-streams called stripes and those stripes are delivered to all subscribers through different spanning trees of height two, with the aid of cloud

capacity. We call such a low latency delivery of stripes a 2-hop delivery. This paper proves that if the average capacity of the peers equals to the bit rate of the video stream and the video stream is divided into a stripes, then 2-hop delivery of all stripes to n peers is possible if the capacity assisted by the cloud is 3n/a. If those peers have a uniform capacity, then the amount of cloud assistance necessary for the 2-hop delivery reduces to n/a.

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In UMTS (universal mobile telecommunications system) networks upgraded with HSPA (high speed packet access) technology, the high access bandwidth and advanced mobile devices make it applicable to share large files among mobile users by peer-to-peer applications. To receive files quickly is essential for mobile users in file sharing applications, mainly because they are subject to unstable signal strength and battery failures. While many researches present peer-to-peer file sharing architectures in mobile environments, few works focus on decreasing the time spent in disseminating files among users. In this paper, we present an efficient peer-to-peer file sharing design for HSPA networks called AFAM — Adaptive efficient File shAring for uMts networks. AFAM can decrease the dissemination time by efficiently utilizing the -bandwidth of mobile nodes. It uses an adaptive rearrangement of a node's concurrent uploads, which causes the count of the node's concurrent uploads to lower while ensuring that the node's -bandwidth can be efficiently utilized. AFAM also uses URF — Rarest First policy for the block selection and receiver selection, which achieves real rarest-first for the spread of blocks and effectively avoids the “last-block” problem in file sharing applications. Our simulations show that, AFAM achieves much less dissemination time than other protocols including BulletPrime and a direct implementation of BitTorrent for mobile environments.

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To address the digital divide in developing countries, fixed wireless access (FWA) networks have the potential to quickly provide economical access over a wide area within a radius of tens of kilometers. The conventional synchronous variable-multiple collision avoidance (v-MCA) system, which is referred to as a non-precedence (NP) system, can be operated over a network of any size without the need to use frame-length restrictions. However, it has a potential drawback of rapid degradation of the throughput due to the intervention of the round trip time, which is proportional to the network length and bandwidth. The advanced synchronous v-MCA system incorporating total precedence (TP) transmission of frames provides high throughput regardless of network length and bandwidth. In this paper, after showing the medium access control mechanisms of the NP and TP systems, their theoretical calculation models are discussed in detail. Then, their system performances are evaluated and overlooked by comparing theoretical and simulated results. The TP system provides an ultimate maximum throughput performance regardless of network length and total bandwidth, while maintaining the low delay characteristics of a contention-based access scheme.

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In PONs, an optical subscriber unit (OSU) is shared by users. Since the /download speed depends on the available bandwidth of the OSU, the utilization ratio of OSU bandwidth must be equally distributed to offer fair /download speeds. A dynamic load-balancing (DLB) method to distribute OSU’s traffic load equally in λ-tunable WDM/TDM-PONs has been realized by monitoring the buffer depth of each OSU. However, it is difficult to monitor the traffic load if the OSU has an unused capacity. This paper proposes a novel DLB method for λ-tunable WDM/TDM-PONs. The proposed method makes the traffic load of OSU uniform by monitoring the traffic volume itself, even if some available capacity is present. In addition, to quickly determine the optimal OSU-ONU assignments, a determination algorithm based on the proposed method is derived from Jain’s fairness index. The proposed method is validated by simulations based on a measured traffic model.

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A web-based system for sharing and integration of crop data and weather data called CROWIS was developed to allow users their experimental data and download the merged and integrated data in spreadsheet format. The system was designed based on a hybrid of MVC (Model, View and Controller) and SOA (Service Oriented Architecture) design pattern and composed of a web application and three services of MetBroker, Google Maps and Rice Data Service. User can crop data in spreadsheet format, and then these data are merged with data from other locations in the database. Crop data can be queried from Rice Data Service and be integrated with weather data by way of MetBroker based on specified locations and then be downloaded as a spreadsheet file. By using Google Maps service, user can register the latitude and longitude information of a new location. Successful uploading of 37 spreadsheet rice data files indicated that the and merging function of CROWIS is operational. A total of 184 rice properties of 151072 records containing information of 6486 different varieties and lines collected from 256 different experiment locations from 1980 to 2004 had been stored in rice database. The results of various combinations of rice data queries and data integrations with weather data indicated that CROWIS is robust and stable enough for users to download merged rice data and/or integrated data files. With this system, people in experimental fields can easily share and integrate their most recent and valuable experimental data sets. Researchers and modelers can easily obtain the merged and integrated data. These data are helpful to test and verify existing models, improve parameter estimations and simplify construction of new models. The system is accessible at http://www.agmodel.org/CROWIS/

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The widespread use and increasing popularity of broadband service has prompted a focus on the measurement and analysis of its empirical performance in recent studies. The worldwide view of broadband performance has been examined over the short term with Speedtest.net, but research in this area has not yet provided a long-term evolutionary insight on how DSL, Cable, and Fiber access technologies have influenced on user experience. In this study, we present 6 years of measurement results, from 2006 to 2011, of broadband performance with fast developing broadband networks in Korea. With 57% Fiber penetration in 2011, our data consist of a total of 29M test records and 10M subscribers. Over the 6 years, we have observed a 2.9-fold improvement in download speed (57Mbps), 2.8-fold increase in speed (38Mbps), and 0.7-fold decrease in latency due to the high penetration rate of Fiber broadband service and the advanced Cable modem technology. In addition, we carried out longitudinal analysis of various aspects of services, providers, regions, and cost-performance. We believe that the evolutionary Korean broadband measurement results can shed light on how high-speed access technologies are substantially enhancing on end-to-end performance.

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The peer-assisted streaming paradigm has been widely employed to distribute live video data on the internet recently. In general, the mesh-based pull approach is more robust and efficient than the tree-based push approach. However, pull protocol brings about longer streaming delay, which is caused by the handshaking process of advertising buffer map message, sending request message and scheduling of the data block. In this paper, we propose a new approach, mesh-push, to address this issue. Different from the traditional pull approach, mesh-push implements block scheduling algorithm at sender side, where the block transmission is initiated by the sender rather than by the receiver. We first formulate the optimal bandwidth utilization problem, then present the mesh-push approach, in which a token protocol is designed to avoid block redundancy; a min-cost flow model is employed to derive the optimal scheduling for the push peer; and a push peer selection algorithm is introduced to reduce control overhead. Finally, we evaluate mesh-push through simulation, the results of which show mesh-push outperforms the pull scheduling in streaming delay, and achieves comparable delivery ratio at the same time.

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Peer-to-Peer (P2P) file distribution systems can efficiently disseminate massive contents, such as disk images of operating systems, from a server to many users in a piece-by-piece manner. In particular, the BitTorrent protocol optimizes each peer's download speed by applying the tit-for-tat (TFT) strategy, where each peer preferentially uploads piece(s) to peer(s) from which it can download missing pieces faster. To the best of our knowledge, however, the optimality of TFT-based P2P file distribution has not been studied sufficiently. In this paper, we aim to understand the optimal scheduling in TFT-based P2P file distribution. First, we develop a discrete-time model of TFT-based P2P file distribution and formulate its optimal scheduling as a two-step integer linear programming problem. The first step is to minimize the average file retrieval time among peers, and the second step is to improve fairness among peers. We analyze the optimal solution obtained by the existing solver and reveal the characteristics of the optimal scheduling. Specifically, we show that it is crucial to distribute pieces from the server indirectly to peers with large capacity via those with small capacity.

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In this paper, we describe the large-scale database system using the Hadoop distributed file system to store sensor data from the mobile robot or intelligent house. By this approach, we would able to construct a more flexible database for the accumulated long sensor various information. And we mention about the RT-Component to data from distributed sensors.

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This paper proposes a method to reduce the playback suspension in a Video-on-Demand system based on the Peer-to-Peer technology (P2P VoD). Our main contribution is twofold. The first is the proposal of a hierarchical P2P architecture with the notion of dynamic swarms. Swarm is a group of peers to have similar playback position and those swarms are connected with an overlay so that requested pieces are forwarded from a swarm to another swarm in a bucket brigade manner, where the forward of pieces is regulated by the super-peer (SP) of each swarm. The second contribution is the proposal of a match making scheme between requests and uploaders. The simulation result indicates that the proposed scheme reduces the total waiting time of a randomized scheme by 24% and the load of the media server by 76%.

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With the popularity of BitTorrent-like P2P applications, improving its performance has been an active research area. Super-seeding, a special policy for the initial seeder, improves the efficiency in producing multiple seeds and reduces the uploading bytes of content initiators, thus being highly expected as a promising solution for improving downloading performance while decreasing uploading cost. However, the overall impacts of super seeding upon BitTorrent performance remain a question and have not been analyzed so far in literature. In this paper, we present an analytical and experimental study over the performance of super-seeding scheme. We attempt to answer the following questions: whether and how much super-seeding saves uploading cost, whether the overall downloading time is decreased by super-seeding, and in which circumstances super-seeding performs worse. Based on the seeding process, our analytical study gives formulas on the new piece distribution time, average downloading time and minimum distribution time for heterogeneous P2P file distribution system with super-seeding. Robust evidence supporting the use (or not) of super-seeding is given based on our worldwide Internet experiments over wide distribution of 250 PlanetLab nodes. With a well-designed experimental scenario, we study the overall download time and cost of super seeding scheme under varying seed bandwidth and peer behavior. Results show that super-seeding can save an ratio of 20% and does help speeding up swarms in certain modes. Tentative conclusions about the effectiveness of super-seeding and its optimal working circumstances are given with inside mechanism analyzed and negative factor identified. Our work not only provides reference for the potential adoption of super-seeding in BitTorrent and other P2P applications, but also much insights for the tussle of enhancing of Quality of Experience (QoE) and saving cost for a large-scale BitTorrent-like P2P commercial application.

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As one innovative research that heavily depends on the network virtualization for its realization and deployment on an Internet-scale, we propose an approach to utilize user resources in information-centric network (ICN). We try to fully benefit from the in-network cache that is one attractive feature of ICN by expanding the in-network cache indirectly based on the user resources. To achieve this, in this paper, we focus on how to encourage users to contribute their resources in ICN. Through simulations, we examine a feasibility of our approach and an effect of user participation on the content distribution performance in ICN. We also briefly discuss how the network virtualization technique can be utilized for our research in terms of its evaluation and deployment.

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To promote a development of models of multilevel physiological systems, it is crucial to establish a framework to share and reuse modes among researchers. For providing such a space, databases in Physiome.jp were renovated, and interoperability with tools for modelling and simulation was enhanced. The PH Database includes three databases for models, morphological data and time series data. If the sharing level of data is set as "public", any users visited the cite can view and download it. Logged in users also can share models only to specific users. This function can be used for team development of models. We demonstrated that PhysioDesigner, a modelling platform for multilevel physiological systems, can directly access the PH Database and can search, download and models. Such interoperability with tools boost up the usability of the PH Database and make it easier for researchers to utilize it in their research activities.

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The video database system in local area community is able to search of scene by keyword .A high convenience user interface which can , edit and search the video file easily, is realized in this system.

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In this study, a low-cost, power-saving and reliable Multiple Server Backup System (MSBS) was configured and tested. The MSBS is based on a Dynamic Backup Server System (DBSS) and is able to recover many different server functions. To configure the DBSS, the mode segmentation method is introduced to simplify system control design and improve applicability to other systems. Experiments based on a mail server showed that the DBSS has sufficient ability to deal with various types of issues, including software and hardware failures. Furthermore, it is important to evaluate the virtual server performance in recovering target server functions. The well-known clock time inaccuracy problem of the virtual server is solved using the network access method regardless of the failure.

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In this paper, we propose a method to enhance the download efficiency of BitTorrent protocol with the notion of structures in the set of pieces generated from a shared file and the swarm of peers downloading the same shared file. More specifically, as for the set of pieces, we introduce the notion of super-pieces called clusters, which is aimed to enlarge the granularity of the management of request-and-reply of pieces, and as for the swarm of peers, we organize a clique consisting of several peers with similar

capacity, to improve the smoothness of the flow of pieces associated with a cluster. As is shown in the simulation results, the proposed extensions significantly reduce the download time of the first 75% of the downloaders, and thereby improve the performance of P2P-assisted video streaming such as Akamai NetSession and BitTorrent DNA.

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Recently, flight control of unmanned aerial vehicles (UAVs) in non-global positioning system (GPS) environments has become increasingly important. In such an environment, visual sensors are important, and their main roles are self-localization and obstacle avoidance. In this paper, the concept of a multi-camera UAV system with multiple cameras attached to the body is proposed to realize high-precision omnidirectional visual recognition, self-localization, and obstacle avoidance simultaneously, and a two-camera UAV is developed as a prototype. The proposed flight control system can switch between visual servoing (VS) for collision avoidance and visual odometry (VO) for self-localization. The feasibility of the proposed control system was verified by conducting flight experiments with the insertion of obstacles.

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Drivers can make driving plans and save traveling time if they can download real-time pictures taken at each driver's point of interest (POI). We designed a system that provides pictures taken by other drivers at a driver's POI. In one naive system design, vehicles send picture data to a central server via a cellular network whenever they take a picture. However, sending all pictures taken by vehicles to the server leads to high processing loads on the server and major amounts of cellular network traffic. In this paper, we propose a scalable data sharing system that uses VANETs and a cellular network for providing a picture taken at POI. For realizing the system, we propose a data

control method. In this method, all vehicles exchange metadata via VANETs to know the existence of pictures taken by other vehicles and reduce the traffic for uploading pictures taken under a similar condition of other pictures. We evaluate the performance of the proposed method through simulations. The simulation results show that the proposed method reduces the cellular network traffic to 36% in comparison with a system that sends all pictures received by the server to meet all driver POI picture requests.

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