A detailed examination of the overlay construction and maintenance mechanism in BitTorrent

BitTorrent is one of the most important applications on the Internet. Statistics show that it has accounted for more than 1/3 of the Internet bandwidth. Part of BitTorrent's immense success may be attributed to its simple design and effective peer choking and piece selection mechanisms for distributing large files over the Internet. As these mechanisms are performed on the application overlay, how the overlay is constructed and maintained is crucial to their performance. In this paper we divide the overlay construction process into three stages: initial peer set selection, peer set update, and connection management, representing how a peer obtains an initial list of peers in the overlay, how it updates the list, and how it maintains its overlay links. In each stage, several strategies can be selected, yielding a variety of design choices to build and maintain an overlay. The purpose of the paper is to sort them out and find the key choices that improve the performance.