Physics-inspired Performace Evaluation of a Structured Peer-to-Peer Overlay Network

In the majority of structured peer-to-peer overlay networks a graph with a desirable topology is constructed. In most cases, the graph is maintained by a periodic activity performed by each node in the graph to preserve the desirable structure in face of the continuous change of the set of nodes. The interaction of the autonomous periodic activities of the nodes renders the performance analysis of such systems complex and simulation of scales of interest can be prohibitive. Physicists, however, are accustomed to dealing with scale by characterizing a system using intensive variables, i.e. variables that are size independent. The approach has proved its usefulness when applied to satisfiability theory. This work is the first attempt to apply it in the area of distributed systems. The contribution of this paper is two-fold. First, we describe a methodology to be used for analyzing the performance of large scale distributed systems. Second, we show how we applied the methodology to find an intensive variable that describe the characteristic behavior of the Chord overlay network, namely, the ratio of the magnitude of perturbation of the network (joins/failures) to the magnitude of periodic stabilization of the network

NATCracker: NAT Combinations Matter

In this paper, we report our experience in working with Network Address Translators (NATs). Traditionally, there were only 4 types of NATs. For each type, the (im)possibility of traversal is well-known. Recently, the NAT community has provided a deeper dissection of NAT behaviors resulting into at least 27 types and documented the (im)possibility of traversal for some types. There are, however, two fundamental issues that were not previously tackled by the community. First, given the more elaborate set of behaviors, it is incorrect to reason about traversing a single NAT, instead combinations must be considered and we have not found any study that comprehensively states, for every possible combination, whether direct connectivity with no relay is feasible. Such a statement is the first outcome of the paper. Second, there is a serious need for some kind of formalism to reason about NATs which is a second outcome of this paper. The results were obtained using our own scheme which is an augmentation of currently-known traversal methods. The scheme is validated by reasoning using our formalism, simulation and implementation in a real P2P network

A GPU-enabled solver for time-constrained linear sum assignment problems

This paper deals with solving large instances of the Linear Sum Assignment Problems (LSAPs) under realtime constraints, using Graphical Processing Units (GPUs). The motivating scenario is an industrial application for P2P live streaming that is moderated by a central tracker that is periodically solving LSAP instances to optimize the connectivity of thousands of peers. However, our findings are generic enough to be applied in other contexts. Our main contribution is a parallel version of a heuristic algorithm called Deep Greedy Switching (DGS) on GPUs using the CUDA programming language. DGS sacrifices absolute optimality in favor of a substantial speedup in comparison to classical LSAP solvers like the Hungarian and auctioning methods. We show the modifications needed to parallelize the DGS algorithm and the performance gains of our approach compared to a sequential CPU-based implementation of DGS and a mixed CPU/GPU-based implementation of it

IMPACT OF FOLIAR-APPLIED DORMANCY-BREAKING AGENTS ON FLOWERING BEHAVIOR, YIELD, FRUIT QUALITY, AND SOME CHEMICAL CONSTITUENTS OF “EIN SHAMER” APPLE TREES

Objective: This investigation was carried out during the two successive seasons of 2016 and 2017 to investigate the effect of Dormex, mineral oil, potassium nitrate, calcium nitrate, and thiourea on bud break, growth, yield, and some chemical constituents of “Ein Shamer” apple (Malus sylvestris, Mill) variety. Methods: The trees were grown in loamy sand soil, and sprayed with six treatments (Dormex (4%), mineral oil (5%), potassium nitrate (8%), calcium nitrate (8%), and thiourea (2%) and control. Results: In general, it was found that all studied growth parameters, date of flower bud break, percentage of bud break, fruit-setting, fruit weight, fruit size, fruit number/tree, yield/tree (kg), and some chemical constituents of leaves (total chlorophyll, total carbohydrates, total protein, nitrogen, phosphorous, and potassium contents) and some chemical constituents of fruits total soluble solids (T.S.S.), T.S.S./acid ratio, Vitamin C, water content %, total free amino acids, total carbohydrates, total sugars, and reducing sugars) were increased with the application of the different treatments. Conclusion: The best results were obtained from the treatment of Dormex at 4% and mineral oil (5%). On the contrary, the same treatment decreased total acidity and total phenols in fruits as compared to the control. It could be recommended to use Dormex at 4% and mineral oil (5%) for improving bud break, growth, yield, and chemical constituents of apple trees or fruits

Mesmerizer: A Effective Tool for a Complete Peer-to-Peer Software Development Life-cycle

In this paper we present what are, in our experience, the best practices in Peer-To-Peer(P2P) application development and how we combined them in a middleware platform called Mesmerizer. We explain how simulation is an integral part of the development process and not just an assessment tool. We then present our component-based event-driven framework for P2P application development, which can be used to execute multiple instances of the same application in a strictly controlled manner over an emulated network layer for simulation/testing, or a single application in a concurrent environment for deployment purpose. We highlight modeling aspects that are of critical importance for designing and testing P2P applications, e.g. the emulation of Network Address Translation and bandwidth dynamics. We show how our simulator scales when emulating low-level bandwidth characteristics of thousands of concurrent peers while preserving a good degree of accuracy compared to a packet-level simulator

Comparing Maintenance Strategies for Overlays

In this paper, we present an analytical tool for understanding the performance of structured overlay networks under churn based on the master-equation approach of physics. We motivate and derive an equation for the average number of hops taken by lookups during churn, for the Chord network. We analyse this equation in detail to understand the behaviour with and without churn. We then use this understanding to predict how lookups will scale for varying peer population as well as varying the sizes of the routing tables. We then consider a change in the maintenance algorithm of the overlay, from periodic stabilisation to a reactive one which corrects fingers only when a change is detected. We generalise our earlier analysis to underdstand how the reactive strategy compares with the periodic one.Comment: 10 pages, 8 figure

An Analytical Study of a Structured Overlay in the presence of Dynamic Membership

In this paper, we present a complete analytical study of dynamic membership (aka churn) in structured peer-to-peer networks. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. We demonstrate that this methodology is in fact also well suited to describing structured overlay networks by an application to the Chord system. For any rate of churn and stabilization rates, and any system size, we accurately account for the functional form of: the distribution of inter-node distances, the probability of network disconnection, the fraction of failed or incorrect successor and finger pointers and show how we can use these quantities to predict both the performance and consistency of lookups under churn. Additionally, we also discuss how churn may actually be of different 'types' and the implications this will have for structured overlays in general. All theoretical predictions match simulation results to a high extent. The analysis includes details that are applicable to a generic structured overlay deploying a ring as well as Chord-specific details that can act as guidelines for analyzing other systems

A User-Centric Adaptive Story Architecture – Borrowing from Acting Theories.

Interactive virtual environments are becoming increasingly popular for their utility in education, virtual training, and entertainment. These applications often rely on a scenario that is revealed to the user as he/she interacts with synthetic objects and characters that inhabit virtual worlds. Current interactive narrative architectures used in the interactive entertainment industry often use decision trees, which are hard to author and modify. Some interactive entertainment productions are starting to use more generative techniques, such as plan-based or goal-based narrative. In this paper, I present an interactive narrative architecture that extends current research in interactive narrative by integrating a user modeling and user behavior analysis technique, which I argue facilities a more engaging and fulfilling experience. I have implemented the architecture within an interactive story called Mirage. The architecture resulted from an iterative design and development process involving a team that included film and theatre professionals. During this design and development process, I have experimented and evaluated different narrative techniques, which resulted in the proposed architecture