Luc Onana Alima

Efficient broadcast in structured P2P networks

In this position paper, we present an efficient algorithm for performing a broadcast operation with minimal cost in structured DHT-based P2P networks. In a system of N nodes, a broadcast message originating at an arbitrary node reaches all other nodes after exactly N − 1 messages. We emphasize the perception of a class of DHT systems as a form of distributed k-ary search and we take advantage of that perception in constructing a spanning tree that is utilized for efficient broadcasting. We consider broadcasting as a basic service that adds to existing DHTs the ability to search using arbitrary queries as well as dissiminate/collect global information.

The essence of P2P: a reference architecture for overlay networks

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.

Symmetric replication for structured peer-to-peer systems

Structured peer-to-peer systems rely on replication as a basic means to provide fault-tolerance in presence of high churn. Most select replicas using either multiple hash functions, successor-lists, or leaf-sets. We show that all three alternatives have limitations. We present and provide full algorithmic specification for a generic replication scheme called symmetric replication which only needs O(1) message for every join and leave operation to maintain any replication degree. The scheme is applicable to all existing structured peer-to-peer systems, and can be implemented on-top of any DHT. The scheme has been implemented in our DKS system, and is used to do load-balancing, end-to-end faulttolerance, and to increase the security by using distributed voting. We outline an extension to the scheme, implemented in DKS, which adds routing proximity to reduce latencies. The scheme is particularly suitable for use with erasure codes, as it can be used to fetch a random subset of the replicas for decoding.

A framework for structured peer-to-peer overlay networks

Structured peer-to-peer overlay networks have recently emerged as good candidate infrastructure for building novel large-scale and robust Internet applications in which participating peers share computing resources as equals. In the past three year, various structured peer-to-peer overlay networks have been proposed, and probably more are to come. We present a framework for understanding, analyzing and designing structured peer-to-peer overlay networks. The main objective of the paper is to provide practical guidelines for the design of structured overlay networks by identifying a fundamental element in the construction of overlay networks: the embedding of k–ary trees. Then, a number of effective techniques for maintaining these overlay networks are discussed. The proposed framework has been effective in the development of the DKS system, whose preliminary design appears in [2].

Low-Bandwidth Topology Maintenance for Robustness in Structured Overlay Networks

Structured peer-to-peer systems have emerged as infrastructures for resource sharing in large-scale, distributed, and dynamic environments. One challenge in these systems is to efficiently maintain routing information in the presence of nodes joining, leaving, and failing. Many systems use costly periodic stabilization protocols to ensure that the routing information is up-to-date. In this paper, we present a novel technique called correction-on-change, which identifies and notifies all nodes that have outdated routing information as a result of a node joining, leaving, or failing. Effective failure handling is simplified as the detection of a failure triggers a correction-on-change which updates all the nodes that have a pointer to the failed node. The resulting system has increased robustness as nodes with stale routing information are immediately updated. We proof the correctness of the algorithms and evaluate its performance by means of simulation. Experimental results show that for the same amount of maintenance bandwidth correction-on-change makes the system by far more robust when compared to periodic stabilization. Moreover, compared to adaptive stabilization which adjusts its frequency to the dynamism in the system, correction-on-change gives the same performance but with considerably less maintenance bandwidth. As correction-on-change immediately updates incorrect routing entries the average lookup length is maintained close to the theoretical average in the presence of high dynamism. We show how the technique can be applied to our DKS system as well as the Chord system.

Multicast in DKS (N,k,f )overlay networks

In [1] a family of DHT-based infrastructures, termed DKS (N, k, f), with a number of desirable properties is presented. In the current paper, we show how multicast is achieved in DKS (N, k, f) overlay networks. Each multicast group is represented by an instance of DKS (N, k, f), which is created and maintained exactly as the underlying overlay network. Multicast messages are efficiently disseminated thanks to a correcting broadcast algorithm that allow each multicast message to be delivered exactly once to all application layer proccesses despite the presence of erroneous routing information.

A Dynamic Pricing and Bidding Strategy for Autonomous Agents in Grids

In this paper, we propose a dynamic pricing strategy which is used for a market-based resource allocation mechanism in a local Grid. We implement an agent based Grid economy in which the decision-making process regarding task and resource allocation is distributed across all users and resource owners. A Continuous Double Auction is used as the platform for matchmaking where consumers and producers meet. In this paper, we analyze the parameter regime of this pricing mechanism considering different network conditions. Our experiments described in the paper show that using the pricing parameters, the consumers and producers agents can decide the price to influence the way they contribute resources to the Grid or complete the jobs for which they need resources. These agents are individually capable of changing the degree of their task usage and resource contribution to the Grid.

Hybrid Resource Discovery Mechanism in Ad Hoc Grid Using Structured Overlay

Resource management has been an area of research in ad hoc grids for many years. Recently, different research projects have focused resource management in centralized, decentralized or in a hybrid manner. In this paper, we discuss a micro economic based, hybrid resource discovery mechanism. The proposed mechanism focuses on the extension of a structured overlay network to manage the (dis)appearance of matchmakers in the grid and to route the messages to the appropriate matchmaker in the ad hoc grid. The mechanism is based on the emergent behavior of the participating nodes and adapts with respect to changes in the ad hoc grid environment. Experiments are executed on PlanetLab to test the scalability and robustness of the proposed mechanism. Simulation results show that our mechanism performs better than previously proposed mechanisms.

Market Formulation for Resources Allocation in an Ad-Hoc Grid

An ad hoc grid is a spontaneous formation of cooperating heterogenous computing nodes which attempts to provide computing resources on demand to every participant. In this paper, we study market formulation for resource allocation in an ad-hoc Grid. Continuous Double Auction (CDA) protocol with discriminatory pricing policy is selected as the market protocol and a novel bidding mechanism is presented to determine ask/bid prices. We study the performance of our bidding mechanism and compare it with three other mechanisms from the literature. The performances are investigated in the terms of price stability, throughput, and load balancing. The experimental results show that our mechanism outperforms other bidding mechanisms in similar conditions.

Ant Colony Inspired Microeconomic Based Resource Management in Ad Hoc Grids

Ad hoc grids are inherently complex and are dynamic systems. This is due to decentralized control, heterogeneity in resources of the participating nodes, variations in resource availability and user defined access and use polices for the resources. On the other hand, the universe is full of complex adaptive systems such as the immune system, sand dune ripples, and ant foraging etc. The participants in these systems apply simple local rules, resulting in robustness and self-organization. In this paper, we present an ant colony inspired, microeconomic based resource management system for ad hoc grids. The mechanism is based on the emergent behavior of the participating nodes and adapts itself to changes in the ad hoc grid environment. The mechanism enables the ad hoc grid to self-organize itself under varying workload of the participating nodes. Experiments are executed on PlanetLab to test the scalability and robustness of the proposed mechanism.