The proliferation of peer-to-peer (P2P) file sharing protocols is due to their efficient and scalable methods for data dissemination to numerous users. But many of these networks have no provisions to provide users with long term access to files after the initial interest has diminished, nor are they able to guarantee protection for users from malicious clients that wish to implicate them in incriminating activities. As such, users may turn to supplementary measures for storing and transferring data in P2P systems. We present a new file sharing paradigm, called a Graffiti Network, which allows peers to harness the potentially unlimited storage of the Internet as a third-party intermediary. Our key contributions in this paper are (1) an overview of a distributed system based on this new threat model and (2) a measurement of its viability through a one-year deployment study using a popular web-publishing platform. The results of this experiment motivate a discussion about the challenges of mitigating this type of file sharing in a hostile network environment and how web site operators can protect their resources.
Much of the previous work on developing P2P storage systems that provide block storage across multiple nodes is based on distributed hash tables @cite_19 @cite_5 @cite_28 . These approaches have the same deficiencies as the BitTorrent model: peers download file blocks directly from other peers, thereby losing anonymity, and the systems do not provide mechanisms to provide long term availability for less popular files after peers disconnect from the network. Other systems are focused on providing anonymous and secure P2P data storage @cite_6 . The POTSHARDS system provides secure long-term data storage when the content originator no longer exists using secret splitting and data reconstruction techniques to handle partial losses @cite_17 ; their approach assumes multiple, semi-reliable storage backends that are willing to host a client's data. The Freenet anonymous storage system uses key-based routing to locate files stored on remote peers @cite_10 . As discussed in @cite_19 , Freenet's anonymity limits both its reliability and performance: files are not associated with any predictable server, and thus unpopular content may disappear since no one is responsible for maintaining replicas.
@cite_28 @cite_6 @cite_19 @cite_5 @cite_10 @cite_17
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In a Peer-to-Peer (P2P) file-sharing system, a node finds and retrieves its desired file. If multiple nodes cache the same file to provide others, we can achieve a dependable file-sharing system with low latency and high file availability. However, a node has to spend costs, e.g., processing load or storage capacity, on caching a file. Consequently, a node may selfishly behave and hesitate to cache a file. In such a case, unpopular files are likely to disappear from the system. In this paper, we aim to reveal whether effective caching in the whole system emerges from autonomous and selfish node behavior. We discuss relationship between selfish node behavior and system dynamics by using evolutionary game theory. Through theoretic analysis, we show that a file-sharing system can be robust to file disappearance depending on a cost and demand model for caching even if nodes behave selfishly. Furthermore, we also conduct several simulation-based analysis in terms of network structures, evolving network, load balancing, and system stability. As a result, we demonstrate that a file-sharing system with good properties, i.e., robustness to file disappearance, low search latency, well load-balancing, and high stability, can be achieved independent of network structures and dynamics. We study the 'service capacity' of peer to peer (P2P) file sharing applications. We begin by considering a transient regime which is key to capturing the ability of such systems to handle bursty traffic, e.g., flash crowds. In this context our models, based on age dependent branching processes, exhibit exponential growth in service capacity, and permit the study of sensitivity of this growth to system policies and parameters. Then we consider a model for such systems in steady state and show how the average delay seen by peers would scale in the offered load and rate at which peers exit the system. We find that the average delays scale well in the offered load. In particular the delays are upper bounded by some constant given any offered load and even decrease in the offered load if peers exit the system slowly. We validate many of our findings by analyzing traces obtained from a second generation P2P application called BitTorrent. In this paper, a simple mathematical model is presented for studying the performance of the BitTorrent (1) file sharing system. We are especially interested in the distribution of the peers with different states of the download job completedness. With the model we find that in the stable state the distribution of the download peers follows a U-shaped curve, and the parameters such as the departure rate of the seeds and the abort rate of the download peers will influence the peer distribution in different ways notably. We also analyze the file availability and the dying process of the BitTorrent file sharing system. We find that the system's stability deteriorates with the clustering of the peers, and BitTorrent's built-in "tit-for-tat" unchoking strategy could not help to preserve the integrity of the file among the download peers when the size of the community is small. An innovative peer selection strategy which enables more peers to finish the download job and prolongs the system's lifetime is proposed, in which the peers cooperate to improve the stability of the system by making a tradeoff between the current download rate and the future service availability. Finally, experimental results are presented to validate our analysis and findings. Peer-to-peer networks provide better scalability for the filesharing applications they underlie. Unlike traditional server-based approach such as FTP, maintaining a constant QoS with a fixed number of servers seems feasible, whatever the number of peers involved. However, a P2P filesharing network sometimes happens to saturate, notably in a semi-P2P filesharing architecture or during flashcrowds phase, and scalability may fail. Even "smart" networks can encounter the whole file but one piece downloaded case, which we call starvation. We suggest a simple and versatile filesharing model. It applies to all pieces-oriented filesharing protocols used in softwares such as MlDonkey or BitTorrent. Simulations of this model show that starvation may occur even during flashcrowds. We propose a theoretical explanation for the so-called starvation phenomenum.