Analysis of Peer-to-Peer File Dissemination amongst Users of Different Upload Capacities

In recent years, overlay networks have proven an effective way of disseminating a file from a single source to a group of end users via the Internet. A number of algorithms and protocols have been suggested, implemented and studied. In particular, much attention has been given to peer-to-peer (P2P) systems such as BitTorrent, Slurpie, SplitStream and Bullet. The key idea is that the file is divided into M parts of equal size and that a given user may download any one of these either from the server or from a peer who has previously downloaded it. More recently, a scheme based on network coding has been suggested. Here, users download linear combinations of file parts rather than individual file parts. Performance evaluation of such systems has typically been limited to comparing one system relative to another. Our results give the minimal time required to fully disseminate a file of M parts from a server to N end users. In the scheduling literature this completion time is referred to as makespan. We thus provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system.

Optimal Scheduling of Peer-to-Peer File Dissemination

Jochen Mundinger

Peer-to-peer (P2P) overlay networks such as BitTorrent and Avalanche are increasingly used for disseminating potentially large files from a server to many end users via the Internet. The key idea is to divide the file into many equally-sized parts and then let users download each part (or, for network coding based systems such as Avalanche, linear combinations of the parts) either from the server or from another user who has already downloaded it. However, their performance evaluation has typically been limited to comparing one system relative to another and typically been realized by means of simulation and measurements. By contrast, we provide an analytic performance analysis that is based on a new uplink-sharing version of the well-known broadcasting problem. Assuming equal upload capacities, we show that the minimal time to disseminate the file is the same as for the simultaneous send/receive version of the broadcasting problem. For general upload capacities, we provide a mixed integer linear program (MILP) solution and a complementary fluid limit solution. We thus provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the performance of a decentralized strategy, providing evidence that the performance of necessarily decentralized P2P file dissemination systems should be close to this bound and therefore that it is useful in practice.

2007

Analysis of peer-to-peer file dissemination

Jochen Mundinger

In recent years, overlay networks have proven a popular way of disseminating potentially large files from a single server S to a potentially large group of N end users via the Internet. A number of algorithms and protocols have been suggested, implemented and studied. In particular, much attention has been given to peer-to-peer (P2P) systems such as BitTorrent, Slurpie, SplitStream, Bullet and Avalanche. The key idea is that the file is divided into M parts of equal size and that a given user may download any one of these -- or, for Avalanche, linear combinations of these -- either from the server or from a peer who has previously downloaded it. However, performance analysis of P2P systems for file dissemination has typically been limited to comparing one system relative to another and typically been realized by means of simulations and measurements. We give the minimal time to fully disseminate the file of M parts from a server to N end users in a centralized scenario. In the scheduling literature this completion time is referred to as makespan. We thereby provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the part of the loss in efficiency that is due to the lack of centralized control in practice. Using simulation as well as direct computation, we show that even a simple and natural randomized strategy disseminates the file in an expected time that grows with N in a similar manner to the minimal time achieved with a centralized controller. This suggests that the performance of necessarily decentralized P2P file dissemination systems should still be close to our performance bound.

2006

Sampling Cluster Endurance for Peer-to-Peer based Content Distribution Networks

Several types of Content Distribution Networks are being deployed over the Internet today, based on different architectures to meet their requirements (e.g., scalability, efficiency and resiliency). Peer-to-peer (P2P) based Content Distribution Networks are promising approaches that have several advantages. Structured P2P networks, for instance, take a proactive approach and provide efficient routing mechanisms. Nevertheless, their maintenance can increase considerably in highly dynamic P2P environments. In order to address this issue, a two-tier architecture called Omicron that combines a structured overlay network with a clustering mechanism is suggested in a hybrid scheme. In this paper, we examine several sampling algorithms utilized in the aforementioned hybrid network that collect local information in order to apply a selective join procedure. Additionally, we apply the sampling algorithms on Chord in order to evaluate sampling as a general information gathering mechanism. The algorithms are based mostly on random walks inside the overlay networks. The aim of the selective join procedure is to provide a well balanced and stable overlay infrastructure that can easily overcome the unreliable behavior of the autonomous peers that constitute the network. The sampling algorithms are evaluated using simulation experiments as well as probabilistic analysis where several properties related to the graph structure are revealed.

2007