Systemic Risk and User-Level Performance in Private P2P Communities

Abstract

Abstract-Many peer-to-peer communities, including private BitTorrent communities that serve hundreds of thousands of users, utilize credit-based or sharing ratio enforcement schemes to incentivize their members to contribute. In this paper, we analyze the performance of such communities from both the system-level and the user-level perspectives. We show that both credit-based and sharing ratio enforcement policies can lead to system-wide "crunches" or "crashes" where the system seizes completely due to too little or to too much credit, respectively. We present a theoretical model that identifies the conditions that lead to these system pathologies and we design an adaptive credit system that automatically adjusts credit policies to maintain sustainability. Given private communities that are sustainable, it has been demonstrated that they are greatly oversupplied in terms of excessively high seeder-to-leecher ratios. We further analyze the user-level performance by studying the effects of oversupply. We show that although achieving an increase in the average downloading speed, the phenomenon of oversupply has three undesired effects: long seeding times, low upload capacity utilizations, and an unfair playing field for late entrants into swarms. To alleviate these problems, we propose four different strategies, which have been inspired by ideas in social sciences and economics. We evaluate these strategies through simulations and demonstrate their positive effects.

On the sustainability of credit-based P2P communities

“…In [9,10] another kinds of extended considerations have been done, different from ours, mainly focusing on remedy schemes avoiding crashes or crunches. We did not aim at proposing further mechanisms for preventing systemic risk, as the already developed ones can be applied in the communities we have considered.…”

“…In [10] a model for predicting crashes and crunches was proposed. The idea is to count the number of prosperous leechers and seeders who, given the current situation in the BitTorrent community, have the credit earning potential to be rich in the forthcoming.…”

“…Two sets are introduced, for which we use the main idea of the model in [10]. Our model here is more general as it is using the concept of η, i.e.…”

Dissecting Darknets

“…The active torrents ratio is defined as the ratio of the number of active torrents to the total number of torrents in the community, and is widely used as a key performance indicator to evaluate the activity level and ranking of communities [Chen et al 2012;Jia et al 2013aJia et al , 2013bJia et al , 2014. Figure 14 compares the active torrents ratio of 16 Darknets and 2 public BTs over 60 days.…”

User behaviors in private BitTorrent communities

“…We demonstrate the behavioral differences between users in different groups, we argue the reasons for these differences, and we show the positive and negative effects of these behaviors based on metrics including the seeding time, the upload speed, and the evolution of sharing ratio, which are highly related to user behaviors. Our previous work [5,6,7,8] has dealt with analyzing the advantages and disadvantages of SRE schemes based on theoretical models, simulations, and measurements. This paper complements these works by presenting observations from real world communities with a focus on the user behavior patterns.…”