An analytical framework for the performance evaluation of proximity-aware structured overlays

In this paper, we present an analytical study of proximity-aware structured peer-to-peer networks under churn. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. In earlier work we have demonstrated that this methodology is in fact also well suited to describing structured overlay networks under churn, by showing how we can accurately predict the average number of hops taken by a lookup, for any value of churn, for the Chord system. In this paper, we extend the analysis so as to also be able to predict lookup latency, given an average latency for the links in the network. Our results show that there exists a region in the parameter space of the model, depending on churn, the number of nodes, the maintenance rates and the delays in the network, when the network cannot function as a small world graph anymore, due to the farthest connections of a node always being wrong or dead. We also demonstrate how it is possible to analyse proximity neighbour selection or proximity route selection within this formalism

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

Designs and Analyses in Structured Peer-To-Peer Systems

Peer-to-Peer (P2P) computing is a recent hot topic in the areas of networking and distributed systems. Work on P2P computing was triggered by a number of ad-hoc systems that made the concept popular. Later, academic research efforts started to investigate P2P computing issues based on scientific principles. Some of that research produced a number of structured P2P systems that were collectively referred to by the term "Distributed Hash Tables" (DHTs). However, the research occurred in a diversified way leading to the appearance of similar concepts yet lacking a common perspective and not heavily analyzed. In this thesis we present a number of papers representing our research results in the area of structured P2P systems grouped as two sets labeled respectively "Designs" and "Analyses". The contribution of the first set of papers is as follows. First, we present the princi- ple of distributed k-ary search and argue that it serves as a framework for most of the recent P2P systems known as DHTs. That is, given this framework, understanding existing DHT systems is done simply by seeing how they are instances of that frame- work. We argue that by perceiving systems as instances of that framework, one can optimize some of them. We illustrate that by applying the framework to the Chord system, one of the most established DHT systems. Second, we show how the frame- work helps in the design of P2P algorithms by two examples: (a) The DKS(n; k; f) system which is a system designed from the beginning on the principles of distributed k-ary search. (b) Two broadcast algorithms that take advantage of the distributed k-ary search tree. The contribution of the second set of papers is as follows. We account for two approaches that we used to evaluate the performance of a particular class of DHTs, namely the one adopting periodic stabilization for topology maintenance. The first approach was of an intrinsic empirical nature. In this approach, we tried to perceive a DHT as a physical system and account for its properties in a size-independent manner. The second approach was of a more analytical nature. In this approach, we applied the technique of Master Equations, which is a widely used technique in the analysis of natural systems. The application of the technique lead to a highly accurate description of the behavior of structured overlays. Additionally, the thesis contains a primer on structured P2P systems that tries to capture the main ideas prevailing in the field

On Resilience of Structured Peer-to-Peer Systems

Abstract — In this paper, we propose an approach to analyze the resilience to failures of structured P2P systems. The approach is Markov-chain based, and can be applied to systems with relatively stable size and uniformly distributed nodes. We apply our method to several well-known structured P2P systems. We find that finger neighbors and special neighbors have different influences on the resilience features of P2P systems. More particularly, finger neighbors have significant influence on the average path length while special neighbors influence the hit ratio. Following the above observation, we propose to add some finger neighbor(s) to nodes of the CAN system which originally have no such finger neighbor(s). We use the small-world phenomenon to form the CAN-Small-World (CAN-SW) system. We then apply the proposed Markov-chain based approach to analyze its resilience. We find that the performance of the system under failures or not, has been improved significantly, particularly, in terms of the average path length. I

Resilience of Structured Peer to Peer Systems: Analysis and Enhancement

In this paper, we attempt to provide an extensive and detailed summary of existing work in the area of Structured Peer-to-Peer (P2P) systems resilience. Broadly speaking, resilience of a P2P system is the ability of the system to defend against threats due to system dynamics (in terms of node joins and leaves) and malicious nodes. The coverage in this paper includes resilience metrics, threats, approaches to analyze resilience and enhancements proposed to individual system design features to enhance resilience. Specifically, we first discuss important design features of popular structured P2P systems, the performance metrics and several possible threats and attack scenarios that threaten the performance of structured P2P systems. We then provide a broad overview of approaches to analyze resilience employed by researchers in this area. Following this, we describe an analytical approach developed by us to analyze resilience of structured P2P systems. Our approach is Markov-Chain based and can be applied to analyze systems with relatively stable size and uniformly distributed nodes. We then discuss the insights we obtain on resilience using our analytical approach. Following in the same direction, we then discuss enhancements to individual structured P2P system design features that have been proposed by researchers to increase overall system resilience. We then discuss two of our enhancements, namely CAN-SW (CAN Small World) and RChord (Reverse Chord) to enhance resilience of the CAN and Chord system respectively. Our approaches to design these enhancements derive inspiration from the importance of redundancy and the richness in graph-theory