Abstract. In recent years, the gossip-based communication model in large-scale distributed systems has become a general paradigm with important applications which include information dissemination, aggregation, overlay topology management and synchronization. At the heart of all of these protocols lies a fundamental distributed abstraction: the peer sampling service. In short, the aim of this service is to provide every node with peers to exchange information with. Analytical studies reveal a high reliability and efficiency of gossip-based protocols, under the (often implicit) assumption that the peers to send gossip messages to are selected uniformly at random from the set of all nodes. In practice—instead of requiring all nodes to know all the peer nodes so that a random sample could be drawn—a scalable and efficient way to implement the peer sampling service is by constructing and maintaining dynamic unstructured overlays through gossiping membership information itself. This paper presents a generic framework to implement reliable and efficient peer sampling services. The framework generalizes existing approaches and makes it easy to introduce new ones. We use this framework to explore and compare several implementations of our abstract scheme. Through extensive experimental analysis, we show that all of them lead to different peer sampling services none of which is uniformly random. This clearly renders traditional theoretical approaches invalid, when the underlying peer sampling service is based on a gossip-based scheme. Our observations also help explain important differences between design choices of peer sampling algorithms, and how these impact the reliability of the corresponding service. 1

Abstract — Over the Internet today, computing and communications environments are significantly more complex and chaotic than classical distributed systems, lacking any centralized organization or hierarchical control. There has been much interest in emerging Peer-to-Peer (P2P) network overlays because they provide a good substrate for creating large-scale data sharing, content distribution and application-level multicast applications. These P2P networks try to provide a long list of features such as: selection of nearby peers, redundant storage, efficient search/location of data items, data permanence or guarantees, hierarchical naming, trust and authentication, and, anonymity. P2P networks potentially offer an efficient routing architecture that is self-organizing, massively scalable, and robust in the wide-area, combining fault tolerance, load balancing and explicit notion of locality. In this paper, we present a survey and comparison of various Structured and Unstructured P2P networks. We categorize the various schemes into these two groups in the design spectrum and discuss the application-level network performance of each group.

Currently, researchers designing and implementing largescale overlay services employ disparate techniques at each stage in the production cycle: design, implementation, experimentation, and evaluation. As a result, complex and tedious tasks are often duplicated leading to ine#ective resource use and di#culty in fairly comparing competing algorithms. In this paper, we present MACEDON, an infrastructure that provides facilities to: i) specify distributed algorithms in a concise domainspecific language; ii) generate code that executes in popular evaluation infrastructures and in live networks; iii) leverage an overlay-generic API to simplify the interoperability of algorithm implementations and applications; and iv) enable consistent experimental evaluation. We have used MACEDON to implement and evaluate a number of algorithms, including AMMO, Bullet, Chord, NICE, Overcast, Pastry, Scribe, and SplitStream, typically with only a few hundred lines of MACEDON code. Using our infrastructure, we are able to accurately reproduce or exceed published results and behavior demonstrated by current publicly available implementations.

Peer-to-peer (P2P) technology has undergone rapid growth, producing new protocols and applications, many of which enjoy considerable commercial success and academic interest. Yet, P2P applications are often based on complex protocols, whose behavior is not completely understood. We believe that in order to enable an even more widespread adoption of P2P systems in commercial and scientific applications, what is needed is a modular paradigm in which well-understood, predictable components with clean interfaces can be combined to implement arbitrarily complex functions. The goal of this paper is to promote this idea by describing our initial experiences in this direction. Our recent work has resulted in a collection of simple and robust components, which include aggregation and membership management. This paper shows how to combine them to obtain a novel load-balancing algorithm that is close to optimal with respect to load transfer. We also describe briefly our simulation environment, explicitly designed to efficiently support our modular approach to P2P protocol design.

This thesis presents a new design and implementation of the DHash distributed hash table based on erasure encoding. This design is both more robust and more efficient than the previous replication-based implementation [15]. DHash uses

This paper presents Rosebud, a new Byzantine faulttolerant storage architecture designed to be highly scalable and deployable in the wide-area. To support massive amounts of data, we need to partition the data among the nodes. To support long-lived operation, we need to allow the set of nodes in the system to change. To our knowledge, we are the first to present a complete design and a running implementation of Byzantine-fault-tolerant storage algorithms for a large scale, dynamic membership. We deployed Rosebud in a wide area testbed and ran experiments to evaluate its performance, and our experiments show that it performs well. We show that our storage algorithms perform equivalently to highly optimized replication algorithms in the wide-area. We also show that performance degradation is minor when the system reconfigures.

Abstract. Current research in peer to peer systems is lacking appropriate environments for simulation and experimentation of large scale overlay services. This has led to a plethora of custom made simulators that waste development resources and hinder fair comparisons between different approaches. In this paper we present a new simulation / experimentation framework for large scale overlay services with three main contributions: i) provide a unifying approach to simulation / experimentation that eases the transition from simulation to network testbeds, ii) it clearly distinguish between the design of overlay algorithms (key based routing), and the applications and services built on top of them, iii) offer a layered and modular architecture with clear hotspots, and pervasive use of design patterns. We have used PlanetSim to implement and evaluate overlay networks such as Chord and Symphony, and overlay services such as Scribe application level multicast, and keyword query systems over distributed hash tables. 1

self-organizing substrate for distributed applications and support powerful abstractions such as distributed hash tables (DHTs) and group communication. However, in most of these systems, lack of control over key placement and routing paths raises concerns over autonomy, administrative control and accountability of participating organizations. Additionally, structured p2p overlays tend to assume global connectivity while in reality, network address translation and firewalls limit connectivity among hosts in different organizations. In this paper, we present a general technique that ensures content/path locality and administrative autonomy for participating organizations, and provides natural support for NATs and firewalls. Instances of conventional structured overlays are configured to form a hierarchy of identifier spaces that reflects administrative boundaries and respects connectivity constraints among networks.

Large highly distributed data sets are poorly supported by current query technologies. Applications such as endsystembased network management are characterized by data stored on large numbers of endsystems, with frequent local updates and relatively infrequent global one-shot queries. The challenges are scale (10 3 to 10 9 endsystems) and endsystem unavailability. In such large systems, a significant fraction of endsystems, and their data, will be unavailable at any given time. Existing methods to provide high data availability despite endsystem unavailability involve centralizing, redistributing or replicating the data. At large scale these methods are not scalable. We advocate a design that trades query delay for completeness, incrementally returning results as endsystems become available. We also introduce the idea of completeness prediction, which provides the user with explicit feedback about this delay/completeness trade-off. Completeness prediction is based on replication of compact data summaries and availability models. This metadata is orders of magnitude smaller than the data. Seaweed is a scalable query infrastructure supporting online aggregation and completeness prediction. Seaweed is built on a distributed hash table (DHT) but unlike previous DHT based approaches it does not redistribute data across the network. It exploits the DHT infrastructure for failure resilient metadata replication, query dissemination, and result aggregation. We analytically compare Seaweed’s scalability against other approaches and present an evaluation of the Seaweed prototype running on a large-scale network simulator driven by real-world traces. 1.

The success of the P2P idea has created a huge diversity of approaches, among which overlay networks, for example, Gnutella, Kazaa, Chord, Pastry, Tapestry, P-Grid, or DKS, have received specific attention from both developers and researchers. A wide variety of algorithms, data structures, and architectures have been proposed. The terminologies and abstractions used, however, have become quite inconsistent since the P2P paradigm has attracted people from many different communities, e.g., networking, databases, distributed systems, graph theory, complexity theory, biology, etc. In this paper we propose a reference model for overlay networks which is capable of modeling different approaches in this domain in a generic manner. It is intended to allow researchers and users to assess the properties of concrete systems, to establish a common vocabulary for scientific discussion, to facilitate the qualitative comparison of the systems, and to serve as the basis for defining a standardized API to make overlay networks interoperable.