Game-Theoretic Analysis of (Non-)Refundable Fees in the Lightning Network

In PCNs, nodes that forward payments between a source and a receiver are paid a small fee if the payment is successful. The fee is a compensation for temporarily committing funds to the payment. However, payments may fail due to insufficient funds or attacks, often after considerable delays of up to several days, leaving a node without compensation. Furthermore, attackers can intentionally cause failed payments, e.g., to infer private information (like channel balances), without any cost in fees. In this paper, we first use extensive form games to formally characterize the conditions that lead to rational intermediaries refusing (or agreeing) to forward payments. A decision made by an intermediary to forward or not depends on the probability of failure, which they approximate based on past experience. We then propose and analyze an alternative fee model that allows the sender to determine and pay a fraction of the fee to intermediaries in a non refundable manner. A rational sender chooses the fraction such that the intermediaries' utility for forwarding the payment exceeds their utility for not forwarding. Our simulation study, based on real world Lightning snapshots, confirms that our novel mechanism can increase the probability of successful payments by 12 percent and decrease routing fees for senders by about 6 percent if all nodes behave rationally. Furthermore, previously cost free probing attacks now require that the attacker pays 1500 satoshis for every 1 million satoshis inferred. Finally, we propose a modification to the Hash Time Locked Contract to enable secure payments of the non refundable fees

On the Dynamic Resources Availability in Grids

This paper has been submitted to the Grid'2007 conference.Currently deployed grids gather together thousands of computational and storage resources for the benefit of a large community of scientists. However, the large scale, the wide geographical spread, and at times the decision of the rightful resource owners to commit the capacity elsewhere, raises serious resource availability issues. Little is known about the characteristics of the grid resource availability, and of the impact of resource unavailability on the performance of grids. In this work, we make first steps in addressing this twofold lack of information. First, we analyze a long-term availability trace and assess the resource availability characteristics of Grid'5000, an experimental grid environment of over 2,500 processors. Based on the results of the analysis, we further propose a model for grid resource availability. Our analysis and modeling results show that grid computational resources become unavailable at a high rate, negatively affecting the ability of grids to execute long jobs. Second, through trace-based simulation, we show evidence that resource availability can have a severe impact on the performance of the grid systems. The results of this step show evidence that the performance of a grid system can rise when availability is taken into consideration, and that human administration of availability change information results in 10-15 times more job failures than for an automated monitoring solution, even for a lowly utilized system

Towards ServMark, an Architecture for Testing Grid Services

Technical University of Delft - Technical Report ServMark-2006-002, July 2006Grid computing provides a natural way to aggregate resources from different administrative domains for building large scale distributed environments. The Web Services paradigm proposes a way by which virtual services can be seamlessly integrated into global-scale solutions to complex problems. While the usage of Grid technology ranges from academia and research to business world and production, two issues must be considered: that the promised functionality can be accurately quantified and that the performance can be evaluated based on well defined means. Without adequate functionality demonstrators, systems cannot be tuned or adequately configured, and Web services cannot be stressed adequately in production environment. Without performance evaluation systems, the system design and procurement processes are limp, and the performance of Web Services in production cannot be assessed. In this paper, we present ServMark, a carefully researched tool for Grid performance evaluation. While we acknowledge that a lot of ground must be covered to fulfill the requirements of a system for testing Grid environments, and Web (and Grid) Services, we believe that ServMark addresses the minimal set of critical issues

Systemic Risk and User-Level Performance in Private P2P Communities

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 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. © 1990-2012 IEEE

Fast download but eternal seeding: The reward and punishment of Sharing Ratio Enforcement

Many private BitTorrent communities employ Sharing Ratio Enforcement (SRE) schemes to incentivize users to contribute their upload resources. It has been demonstrated that communities that use SRE are greatly oversupplied, i.e., they have much higher seeder-to-leecher ratios than communities in which SRE is not employed. The first order effect of oversupply under SRE is a positive increase in the average downloading speed. However, users are forced to seed for extremely long times to maintain adequate sharing ratios to be able to start new downloads. In this paper, we propose a fluid model to study the effects of oversupply under SRE, which predicts the average downloading speed, the average seeding time, and the average upload capacity utilization for users in communities that employ SRE. We notice that the phenomenon of oversupply has two undesired negative effects: a) Peers are forced to seed for long times, even though their seeding efforts are often not very productive (in terms of low upload capacity utilization); and b) SRE discriminates against peers with low bandwidth capacities and forces them to seed for longer durations than peers with high capacities. To alleviate these problems, we propose four different strategies for SRE, which have been inspired by ideas in social sciences and economics. We evaluate these strategies through simulations. Our results indicate that these new strategies release users from needlessly long seeding durations, while also being fair towards peers with low capacities and maintaining high system-wide downloading speeds. © 2011 IEEE

Decentraliseer- en beheers?

Gedistribueerde computersystemen – van het Web via peer-to-peer systemen tot aan de sociale media en de Cloud – zijn alom tegenwoordig, en ons bestaan hangt er schijnbaar vanaf. De mate van decentralisatie van systemen, dat wil zeggen van de spreiding van functionaliteit en autoriteit, heeft gevolgen voor hun effectiviteit en efficiëntie. In deze rede wordt onderzoek naar gedistribueerde computersystemen in de context van decentralisatie beschouwd