Abstract — Over the Internet today, computing and communications environments are significantly more complex and chaotic than classical distributed systems, lacking any centralized organization or hierarchical control. There has been much interest in emerging Peer-to-Peer (P2P) network overlays because they provide a good substrate for creating large-scale data sharing, content distribution and application-level multicast applications. These P2P networks try to provide a long list of features such as: selection of nearby peers, redundant storage, efficient search/location of data items, data permanence or guarantees, hierarchical naming, trust and authentication, and, anonymity. P2P networks potentially offer an efficient routing architecture that is self-organizing, massively scalable, and robust in the wide-area, combining fault tolerance, load balancing and explicit notion of locality. In this paper, we present a survey and comparison of various Structured and Unstructured P2P networks. We categorize the various schemes into these two groups in the design spectrum and discuss the application-level network performance of each group.

Abstract — In this paper, we present the mathematical analysis of two important performance measures for a BitTorrent (BT) like P2P file sharing system, namely, average file downloading time and file availability. For the file downloading time, we develop a model using the “stochastic differential equation ” approach, which can capture the system more accurately than some previous approach [17] and can capture various network settings and peers behavior. We study the steady-state behavior and obtain the closed-form solutions for performance measures which allow us to carry sensitivity analysis on various performance measures for various system parameters. We then extend this model to consider multiclass peers wherein some peers are behind firewalls which may impede the uploading service. We also present the mathematical model to study the file availability of a BT-like system. The model helps us gain the understanding of why the “rarest-first ” chunk selection policy is used in today’s BT protocol. We propose a novel chunk selection algorithm to enhance the overall system file availability. Extensive simulations are carried to validate our analysis. I.

Abstract — In this paper, we propose to model the dynamics of BitTorrent (BT) P2P file sharing systems using the stochastic differential equation method. Unlike previous approach, our method can capture more realistic network environment and peers behavior. Closed-form solutions of various performance measures such as the average number of downloaders, seeders, the system throughput and file downloading time are derived. We also validate our mathematical results via simulation and show that not only our mathematical model can closely track the dynamics of BT-like systems, but the model has a much higher accuracy than previous proposed methods. Also, many important properties can be derived from the close-form solution such as performance scalability, sensitivity of the measurements to various system parameters. We believe the proposed method can provide better understanding in the design and analysis of BT-like P2P systems. I.

In this paper, we present the mathematical analysis of two important performance measures for a BitTorrent (BT) like P2P file sharing system, namely, average file downloading time and file availability. For the file downloading time, we develop a model using the “stochastic differential equation ” approach, not only it captures the system more accurately than some previous approach [18], but also allows us to capture various network settings and peers behavior. We study the steady-state behavior and obtain the closed-form solutions for performance measures such as the average number of peers, the average system throughput, average file downloading time. These analytical results allow us to carry sensitivity analysis on various performance measures for various system parameters. We then extend this model to consider multiclass peers wherein some peers are behind firewalls which may impede the uploading service. We also present the mathematical model to study the file availability of a BT-like system. The model helps us gain the understanding of why the “rarest-first ” chunk selection policy is used in today’s BT protocol. We show under some situations this policy may not be good in practice and propose a novel chunk selection algorithm to enhance the overall system file availability. Extensive simulations are carried to validate our analysis. Keywords: Peer-to-peer, BitTorrent, Modeling, Performance evaluation, File availability 1

Many P2P systems have been designed without taking into account an important factor: a large fraction of Internet users nowadays are located behind a network address translator (NAT) or a firewall, making them unable to accept incoming connections (i.e. unconnectable). Peers suffering from this limitation cannot fully enjoy the advantages offered by the P2P architecture and thus they are likely to get a poor performance. In this work, we present a mathematical model to study the performance of a P2P swarming system in the presence of unconnectable peers. We quantify the average download speeds of peers and find that unconnectable peers achieve a lower average download speed compared to connectable peers, and this difference increases hyperbolically as the percentage of unconnectable peers grows. More interestingly, we notice that connectable peers actually benefit from the existence of peers behind NATs/firewalls, since they alone can enjoy the bandwidth that those peers offer to the system. Inspired by these observations, we propose a new policy for the allocation of the system’s bandwidth that can mitigate the performance issues of unconnectable peers. In doing so, we also find an intrinsic limitation in the speed improvement that they can possibly achieve.

BitTorrent is a widely deployed peer-to-peer protocol that provides scalable file sharing capabilities. While Bit-Torrent applications contribute to the demand for high speed broadband access, they also contribute to the undesirable 80/20 effect wherein 80 % of the bandwidth is consumed by 20 % of the users. In this study we explore the impact that BitTorrent users can have on a DOCSIS cable network. We began the study by capturing packet traces of BitTorrent applications operating on two commercial DOCSIS cable networks. Next we developed for the ns-2 simulation tool a configurable mix of BitTorrent, Web browsing, and VoIP workloads and verified that the behavior of the simulated BitTorrent workloads to be consistent with the behavior observed on the commercial network. In this simulated environment, we show that as few as 15 BitTorrent users can significantly reduce the service quality experienced by other subscribers.