On Unstructured File Sharing Networks

Abstract

We study the interaction among users of unstructured file sharing applications, who compete for available network resources (link bandwidth or capacity) by opening multiple connections on multiple paths so as to accelerate data transfer. We model this interaction with an unstructured file sharing game. Users are players and their strategies are the numbers of sessions on available paths. We consider a general bandwidth sharing framework proposed by Kelly [1] and Mo and Walrand [2], with TCP as a special case. Furthermore, we incorporate the Tit-for-Tat strategy (adopted by BitTorrent [3] networks) into the unstructured file sharing game to model the competition in which a connection can be set up only when both users find this connection beneficial. We refer to this as an overlay formation game. We prove the existence of Nash equilibrium in several variants of both games, and quantify the losses of efficiency of Nash equilibria. We find that the loss of efficiency due to selfish behavior is still unbounded even when the Tit-for-Tat strategy is believed to prevent selfish behavior.

A Network Formation Game Approach to Study BitTorrent Tit-for-Tat

“…The results about pairwise stable networks in the homogeneous scenario have already been presented in [6]. This paper presents a new result about the heterogeneous scenario and illustrates extensively the results about the dynamics which were just listed in [6].…”

“…This paper presents a new result about the heterogeneous scenario and illustrates extensively the results about the dynamics which were just listed in [6]. To the best of our knowledge only three other papers [7][8][9] use game theory to study the overlay structure arising from the interaction among selfish peers .…”

“…Note that in [1], for a given peer, the total number of other peers to set up a connection with is fixed. However, we observe that BT clients can benefit from changing their number of connections (an example is shown in [6]). …”

“…Some of the following results (Theorems 1, 2 and 4) can be derived from [13]. Please see Appendix IV in [10] for details. Remark.…”

Performance Improvements of Peer-to-Peer File Sharing

“…In (Qiu & Srikant, 2004), the effect of "Tit-for-Tat" is studied when selfish peers are able to adjust their uploading bandwidth. In (Zhang et al, 2007), an overlay formation game model is used to study the existence of Nash equilibrium and the loss of efficiency when peers can change the number of connections. In (Piatek et al, 2007), it is shown that the "Tit-for-Tat" incentive mechanism is generally not robust to strategic clients.…”