Optimal Scheduling of Peer-to-Peer File Dissemination

TL;DR

This paper presents an analytical framework for optimal scheduling in P2P file dissemination, providing bounds and strategies that approach theoretical performance limits, enhancing understanding beyond prior simulation-based evaluations.

Contribution

It introduces a new uplink-sharing model for P2P dissemination, offering MILP and fluid solutions, and analyzes decentralized strategies against performance bounds.

Findings

Minimal dissemination time matches the broadcast problem with equal upload capacities.

MILP and fluid models provide lower bounds for dissemination time.

Decentralized strategies perform close to the theoretical bounds.

Abstract

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. In 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.