Extended Equal Service and Differentiated Service Models for Peer-to-Peer File Sharing

Peer-to-Peer (P2P) systems have proved to be the most effective and popular file sharing applications in recent years. Previous studies mainly focus on the equal service and the differentiated service strategies when peers have no initial data before their download. In an upload-constrained P2P file sharing system, we model both the equal service process and the differentiated service process when peers' initial data distribution satisfies some special conditions, and also show how to minimize the time to get the file to any number of peers. The proposed models can reveal the intrinsic relations among the initial data amount, the size of peer set and the minimum last finish time. By using the models, we can also provide arbitrary degree of differentiated service to a certain number of peers. We believe that our analysis process and achieved theoretical results could provide fundamental insights into studies on bandwidth allocation and data scheduling, and can give helpful reference both for improving system performance and building effective incentive mechanism in P2P file sharing systems

Analyzing Peer Selection Policies for BitTorrent Multimedia On-Demand Streaming Systems in Internet

The adaptation of the BitTorrent protocol to multimedia on-demand streaming systems essentially lies on the modification of its two core algorithms, namely the piece and the peer selection policies, respectively. Much more attention has though been given to the piece selection policy. Within this context, this article proposes three novel peer selection policies for the design of BitTorrent-like protocols targeted at that type of systems: Select Balanced Neighbour Policy (SBNP), Select Regular Neighbour Policy (SRNP), and Select Optimistic Neighbour Policy (SONP). These proposals are validated through a competitive analysis based on simulations which encompass a variety of multimedia scenarios, defined in function of important characterization parameters such as content type, content size, and client interactivity profile. Service time, number of clients served and efficiency retrieving coefficient are the performance metrics assessed in the analysis. The final results mainly show that the novel proposals constitute scalable solutions that may be considered for real project designs. Lastly, future work is included in the conclusion of this paper.Comment: 19 PAGE

Autonomic Management of Maintenance Scheduling in Chord

This paper experimentally evaluates the effects of applying autonomic management to the scheduling of maintenance operations in a deployed Chord network, for various membership churn and workload patterns. Two versions of an autonomic management policy were compared with a static configuration. The autonomic policies varied with respect to the aggressiveness with which they responded to peer access error rates and to wasted maintenance operations. In most experiments, significant improvements due to autonomic management were observed in the performance of routing operations and the quantity of data transmitted between network members. Of the autonomic policies, the more aggressive version gave slightly better results

Response of Fresh Food Suppliers to Sustainable Supply Chain Management of Large European Retailers

This article analyses new supply chain management (SCM) strategies of the largest retail distribution chains in Europe within the context of differing sustainability concepts and approaches. An analysis is carried out of the strategic plans of such retailers, as well as recent developments in the sector. We begin by identifying the priority actions of retailers and then evaluating, by means of a survey, how small horticultural marketing firms (mainly cooperatives) in southeast Spain respond to the needs of these retailers. Subsequently, an analysis is carried out on these small marketing firm exporters to identify the relative weight which they assign to the variables assessed, while also considering the existing relationships between said weighted variables and business profits. Our results show that retailers tend to establish more simplified supply chains (that is, shorter and more vertical), essentially demonstrating their interpretation of a sustainable supply chain. In contrast, horticultural marketing firms have concentrated more on tactical and operational issues, thereby neglecting environmental, social and logistics management. Thus, their success rate in meeting the sustainability demands of their customers can be considered medium-low, requiring a more proactive attitude. Improved and collaborative relations, and the integration of sustainability concepts between suppliers (marketing firms) and their clients could contribute to successfully meeting sustainability demands. From the point of view of the consumer, close supplier–retail relationships have solved food safety issues, but the implementation of sustainability in other supply chain activities and processes is a pending issue. We propose strategic approximation and collaboration to bridge the gap between the varying sustainability demands in the supplier–retail relationship within perishable supply chains. Although this article specifically addresses fresh vegetable supply chains, the results may be extrapolated to other agri-food chains with a similar structure

Improving file distribution performance by grouping in peer-to-peer networks

It has been shown that the peer-to-peer paradigm is more efficient than the traditional client-server model for file sharing among a large number of users. Given a group of leechers who wants to download a single file and a group of seeds who possesses the whole file, the minimum time needed for distributing the file to all users can be calculated based on their bandwidth availabilities. A scheduling algorithm has been developed so that every leecher can obtain the file within this minimum time. Unfortunately, this mechanism is not optimal with regard to the average download time among the peers. In this paper, we study how to reduce the average download time without prolonging the time needed for all leechers to obtain the file from a theoretical perspective. Based on the bandwidth capacities, the seeds and leechers are divided into different groups. We identify the necessary conditions for grouping to bring about benefits. We also study the impact on performance when leechers leave the system before the downloading process is complete. To evaluate our mechanism, we conduct extensive simulations and compare the performance with a BitTorrentlike file sharing algorithm. The results show that our grouping protocol successfully reduces the average download time over a wide range of system configurations. © 2009 IEEE.published_or_final_versio