Aaron Harwood

Using a distributed quadtree index in peer-to-peer networks

Peer-to-peer (P2P) networks have become a powerful means for online data exchange. Currently, users are primarily utilizing these networks to perform exact-match queries and retrieve complete files. However, future more data intensive applications, such as P2P auction networks, P2P job-search networks, P2P multiplayer games, will require the capability to respond to more complex queries such as range queries involving numerous data types including those that have a spatial component. In this paper, a distributed quadtree index that adapts the MX-CIF quadtree is described that enables more powerful accesses to data in P2P networks. This index has been implemented for various prototype P2P applications and results of experiments are presented. Our index is easy to use, scalable, and exhibits good load-balancing properties. Similar indices can be constructed for various multidimensional data types with both spatial and non-spatial components.

Peer-to-peer-based resource discovery in global grids: a tutorial

An efficient resource discovery mechanism is one of the fundamental requirements for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involves searching for the appropriate resource types that match the users application requirements. Various kinds of solutions to grid resource discovery have been suggested, including centralized and hierarchical information server approaches. However, both of these approaches have serious limitations in regard to scalability, fault tolerance, and network congestion. To overcome these limitations, indexing resource information using a decentralized (e.g., peer-to-peer (P2P)) network model has been actively proposed in the past few years. This article investigates various decentralized resource discovery techniques primarily driven by the P2P network model. To summarize, this article presents a: summary of the current state of the art in grid resource discovery, resource taxonomy with focus on the computational grid paradigm, P2P taxonomy with a focus on extending the current structured systems (e.g., distributed hash tables) for indexing d-dimensional grid resource queries,1 a detailed survey of existing work that can support rf-dimensional grid resource queries, and classification of the surveyed approaches based on the proposed P2P taxonomy. We believe that this taxonomy and its mapping to relevant systems would be useful for academic and industry-based researchers who are engaged in the design of scalable grid and P2P systems.

A distributed quadtree index for peer-to-peer settings

We describe a distributed quadtree index for enabling more powerful access on complex data over P2P networks. It is based on the Chord method. Methods such as Chord have been gaining usage in P2P settings to facilitate exact-match queries. The Chord method maps both the data keys and peer addresses. Our work can be applied to higher dimensions, to various data types, i.e., other than spatial data, and to different types of quadtrees. Finally, we can use other key-based methods than the Chord method as our base P2P routing protocol and index scale well. The index also benefits from the underlying fault-tolerant hashing-based methods by achieving a nice load distribution among many peers. We can seamlessly execute a single query on multiple branches of the index hosted by a dynamic set of peers.

SLA-Based Coordinated Superscheduling Scheme for Computational Grids

The service level agreement (SLA) based grid superscheduling approach promotes coordinated resource sharing. Superscheduling is facilitated between administratively and topologically distributed grid sites via grid schedulers such as resource brokers and workflow engines. In this work, we present a market-based SLA coordination mechanism, based on a well known contract net protocol. The key advantages of our approach are that it allows: (i) resource owners to have finer degree of control over the resource allocation which is something that is not possible with traditional mechanisms; and (ii) superschedulers to bid for SLA contracts in the contract net, with focus on completing a job within a user specified deadline. In this work, we use simulation to show the effectiveness of our proposed approach

Decentralised Resource Discovery Service for Large Scale Federated Grids

Efficient resource discovery mechanism is one of the fundamental requirement for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery involves searching for resources that match the users application requirements. Various kinds of solutions to grid resource discovery have been developed, including the centralised and hierarchical information server approach. However, these approaches have serious limitations in regards to scalability, fault-tolerance and network congestion. To overcome such limitations, we propose a decentralised grid resource discovery system based on a spatial publish/subscribe index. It utilises a distributed hash table (DHT) routing substrate for delegation of d-dimensional service messages. Our approach has been validated using a simulated publish/subscribe index that assigns regions of a d-dimensional resource attribute space to the grid peers in the system. We generated the resource attribute distribution using the configurations obtained from the top 500 supercomputer list. The simulation study takes into account various parameters such as resource query rate, index load distribution, number of index messages generated, overlay routing hops and system size. Our results show that grid resource query rate directly affects the performance of the decentralised resource discovery system, and that at higher rates the queries can experience considerable latencies. Further, contrary to what one can expect, system size does not have a significant impact on the performance of the system, in particular the query latency.

A serverless 3D world

Online multi-participant virtual-world systems have attracted significant interest from the Internet community but are hindered by their inability to efficiently support interactivity for a large number of participants. Current solutions divide a large virtual-world into a few mutually exclusive zones, with each zone controlled by a different server, and/or limit the number of participants per server or per virtual-world. Peer-to-Peer (P2P) systems are known to provide excellent scalability in a networked environment (one peer is introduced to the system by each participant), however current P2P applications can only provide file sharing and other forms of relatively simple data communications. In this paper, we present a generic 3D virtual-world application that runs on a P2P network with no central administration or server. Two issues are addressed by this paper to enable such a spatial application on a P2P network. First, we demonstrate how to index and query a 3D space on a dynamic distributed network. Second, we show how to build such a complex application from the ground level of a P2P routing algorithm. Our work leads to new directions for the development of online virtual-worlds that we believe can be used for many government, industry, and public domain applications.

Stable High-Capacity One-Hop Distributed Hash Tables

Most research on Distributed Hash Tables (DHTs) assumes ephemeral, lightly loaded deployments. Each node has a lifetime of a few hours and initiates a lookup once every few seconds or minutes. However, in giant internet data centers, each node has a lifetime of weeks or months and initiates hundreds or thousands of lookups every second. In such an environment, one-hop DHTs are superior to multi-hop DHTs. They use lookup bandwidth more efficiently. We qualify conflicting research to show that a single onehop DHT can indeed scale to at least a few hundred thousand nodes in stable, high-capacity enterprise networks. Two new designs are presented: One Hop Sites (1HS), a high-capacity DHT tailored for site redundancy; and the One Hop Federation (1HF), a global, hierarchic DHT that resolves an open latency problem. For both, the analysis a) confirms linear scalability to at least a few hundred thousand nodes and b) identifies the most sensitive design parameters.

Improving performance in delay/disruption tolerant networks through passive relay points

In this paper, we study the case of a limited number of mobile nodes trying to communicate in a large geographic area, forming a delay/disruption tolerant network (DTN). In such networks the mobile nodes are disconnected for significantly long periods of time. Traditional routing protocols proposed for mobile ad hoc networks or mesh networks, which assume at least one path between each source and destination, are ineffective in DTNs. One approach to improve communication is through gossip based protocols because these protocols do not rely on a fixed path. Another approach is to control the movement of the mobile nodes and/or use special mobile nodes called ferry nodes. Others try to employ a fixed infrastructure including stationary relay points. One scheme in stationary relay point approach is to use base stations as relay points which need their own power supply. In this paper, we study a passive approach where mobile nodes deposit/retrieve messages to/ from known stationary locations in the geographic region. Messages are delivered from a source by being deposited at one or more locations that are later visited by the destination. A proposed implementation of our approach using read/writable passive Radio Frequency Identification (RFID) tags, one per point location, is considered in this work. Passive RFID technology is desirable because it operates wirelessly and without the need for attached power. Our simulation results indicate that our approach can achieve competitive message delay and delivery rates. We also demonstrate several techniques for optimizing the stationary relay node placement, namely relay pruning, probability based relay distribution and a genetic algorithm; the genetic algorithm is shown to provide the best solutions to this problem.

Mining Micro-blogs: Opportunities and Challenges

This chapter investigates whether and how micro-messaging technologies such as Twitter messages can be harnessed to obtain valuable information. The interesting characteristics of micro-blogging services, such as being user oriented, provide opportunities for different applications to use the content of these sites to their advantage. However, the same characteristics become the weakness of these sites when it comes to data modelling and analysis of the messages. These sites contains very large amount of unstructured, noisy with false or missing data which make the task of data mining difficult. This chapter first reviews some of the potential applications of the micro-messaging services and then provides some insight into different challenges faced by data mining applications. Later in this chapter, characteristics of a real data collected from the Twitter are analysed. At the end of chapter, application of micro-blogging services is shown by three different case studies.

Distributed scheduling schemes for wireless mesh networks: A survey

An efficient scheduling scheme is a crucial part of Wireless Mesh Networks (WMNs)—an emerging communication infrastructure solution for autonomy, scalability, higher throughput, lower delay metrics, energy efficiency, and other service-level guarantees. Distributed schedulers are preferred due to better scalability, smaller setup delays, smaller management overheads, no single point of failure, and for avoiding bottlenecks. Based on the sequence in which nodes access the shared medium, repetitiveness, and determinism, distributed schedulers that are supported by wireless mesh standards can be classified as either random, pseudo-random, or cyclic schemes. We performed qualitative and quantitative studies that show the strengths and weaknesses of each category, and how the schemes complement each other. We discuss how wireless standards with mesh definitions have evolved by incorporating and enhancing one or more of these schemes. Emerging trends and research problems remaining for future research also have been identified.