49,494 research outputs found

    Performance challenges of decentralised services

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    Decentralised, peer-to-peer based services present a variety of security and privacy benefits for their users, and highly scalable to cater for a growing numbers of users, without extra servers being required of the service operator. This presents a significant advantage for newly emerging mobile applications (with high numbers of users, and limited funds for infrastructure), although performance is a challenge when accessing decentralised services. In this paper, we firstly show the performance of our implementation of a decentralised chunk-based storage platform is constrained by the network. We show the impact of network latency on the performance of this decentralised storage solution, and propose our solution to this, in the form of a federated, intermediary server, thus creating a hybrid decentralised service. This approach offers relatively constant performance as latency increases, due to the use of TCP connectivity, while ensuring the advantages of the decentralised service are not lost in the process

    A Dataflow Language for Decentralised Orchestration of Web Service Workflows

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    Orchestrating centralised service-oriented workflows presents significant scalability challenges that include: the consumption of network bandwidth, degradation of performance, and single points of failure. This paper presents a high-level dataflow specification language that attempts to address these scalability challenges. This language provides simple abstractions for orchestrating large-scale web service workflows, and separates between the workflow logic and its execution. It is based on a data-driven model that permits parallelism to improve the workflow performance. We provide a decentralised architecture that allows the computation logic to be moved "closer" to services involved in the workflow. This is achieved through partitioning the workflow specification into smaller fragments that may be sent to remote orchestration services for execution. The orchestration services rely on proxies that exploit connectivity to services in the workflow. These proxies perform service invocations and compositions on behalf of the orchestration services, and carry out data collection, retrieval, and mediation tasks. The evaluation of our architecture implementation concludes that our decentralised approach reduces the execution time of workflows, and scales accordingly with the increasing size of data sets.Comment: To appear in Proceedings of the IEEE 2013 7th International Workshop on Scientific Workflows, in conjunction with IEEE SERVICES 201

    Performance Analysis of Publish/Subscribe Systems

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    The Desktop Grid offers solutions to overcome several challenges and to answer increasingly needs of scientific computing. Its technology consists mainly in exploiting resources, geographically dispersed, to treat complex applications needing big power of calculation and/or important storage capacity. However, as resources number increases, the need for scalability, self-organisation, dynamic reconfigurations, decentralisation and performance becomes more and more essential. Since such properties are exhibited by P2P systems, the convergence of grid computing and P2P computing seems natural. In this context, this paper evaluates the scalability and performance of P2P tools for discovering and registering services. Three protocols are used for this purpose: Bonjour, Avahi and Free-Pastry. We have studied the behaviour of theses protocols related to two criteria: the elapsed time for registrations services and the needed time to discover new services. Our aim is to analyse these results in order to choose the best protocol we can use in order to create a decentralised middleware for desktop grid

    CBProf: Customisable Blockchain-as-a-Service Performance Profiler in Cloud Environments

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    Blockchain technologies, e.g., Hyperledger Fabric and Sawtooth, have been evolving rapidly during past years and enable potential decentralised innovations in a substantial amount of business applications, e.g. crowd journalism, car-sharing and energy trading. The development of decentralised business applications has to face challenges in selecting suitable blockchain technologies, customising network protocols among distributed peers, and optimising system performance to meet application requirements. Also, manually testing and comparing those different technologies are time-consuming. Therefore, an effective tool is needed for profiling the performance characteristics of blockchain services in different cloud environments. In this paper, we present the Customisable Blockchain-as-a-Service Performance Profiler (CBProf), a tool we developed for automating blockchain deployment and performance profiling in cloud environments. We also provide the implementation and functionality demonstration of this tool

    Working in decentralised service systems: challenges and choices for the Australian aid program

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    The report examined Australia’s support for service systems in decentralised contexts - the evaluation focussed on the health, education and infrastructure (water, sanitation and roads) sectors. Foreword Public services have been decentralised in most countries where Australia provides aid. This means Australia, like other donors, must be willing and able to engage effectively with developing country governments at all levels to improve service delivery. To ensure sustainable improvements, this engagement should carefully coordinate support for governance reforms with assistance to strengthen or expand service delivery systems. As the World Bank has observed, done well, decentralisation can result in more efficient and effective services for communities. However, done poorly, or where the context is inappropriate, decentralisation may have negative effects. This evaluation builds on the Office of Development Effectiveness’s 2009 evaluation of Australian aid for service delivery. It answers important questions about whether Australian aid has appropriately considered the role of subnational authorities, including specific issues identified in 2009. It assesses how well Australian aid has addressed the challenges of decentralisation, with a focus on the major sectors of education, health and infrastructure. This evaluation utilised a clear methodology, applied it consistently, and draws together a range of evidence to provide a balanced account of Australian aid performance. It concludes that Australian aid is beginning to respond to the challenges of supporting service delivery in decentralised contexts, but notes that results are mixed and there is room for further improvement. The evaluation suggests Australia needs to improve its country-level analysis, program planning and design to better address decentralisation. In particular, there is a need to carefully assess short-term service delivery needs against long-term structures and incentives for governments to achieve sustainable service delivery and meet sovereign responsibilities. Australia needs to get the right balance of engagement with different levels of government, and appropriately address both supply and demand aspects of service delivery, especially to improve equity.   &nbsp

    Harmonisation, decentralisation and local governance: Enhancing aid effectiveness

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    During the last decades, international development assistance was often marked by overlaps, duplication of efforts and rivalry between multitudes of donor organisations. In order to translate the principles of the Paris Declaration into practice in the field of Local Governance and Decentralisation (LGD), different donor organisations have joined forces on headquarter level and formed a working group, the Development Partners Working Group for Local Governance and Decentralisation (DPWG-LGD), which is operating since 2006. InWEnt is hosting the secretariat of the group since 2008 and assigned Wageningen International to organise two lead donor workshops. The workshop drew a cross section of delegates who comprised development partners, consultants, academicians, members of parliament and local governance practitioners. The partner countries included Rwanda, Ghana, Tanzania and Uganda whose experiences were mutually re-enforcing and beneficial

    Self-organising agent communities for autonomic resource management

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    The autonomic computing paradigm addresses the operational challenges presented by increasingly complex software systems by proposing that they be composed of many autonomous components, each responsible for the run-time reconfiguration of its own dedicated hardware and software components. Consequently, regulation of the whole software system becomes an emergent property of local adaptation and learning carried out by these autonomous system elements. Designing appropriate local adaptation policies for the components of such systems remains a major challenge. This is particularly true where the system’s scale and dynamism compromise the efficiency of a central executive and/or prevent components from pooling information to achieve a shared, accurate evidence base for their negotiations and decisions.In this paper, we investigate how a self-regulatory system response may arise spontaneously from local interactions between autonomic system elements tasked with adaptively consuming/providing computational resources or services when the demand for such resources is continually changing. We demonstrate that system performance is not maximised when all system components are able to freely share information with one another. Rather, maximum efficiency is achieved when individual components have only limited knowledge of their peers. Under these conditions, the system self-organises into appropriate community structures. By maintaining information flow at the level of communities, the system is able to remain stable enough to efficiently satisfy service demand in resource-limited environments, and thus minimise any unnecessary reconfiguration whilst remaining sufficiently adaptive to be able to reconfigure when service demand changes

    Spectrum sharing security and attacks in CRNs: a review

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    Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundament al approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR - specific security mechanisms are presented with some open research issues and challenges

    Observing the clouds : a survey and taxonomy of cloud monitoring

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    This research was supported by a Royal Society Industry Fellowship and an Amazon Web Services (AWS) grant. Date of Acceptance: 10/12/2014Monitoring is an important aspect of designing and maintaining large-scale systems. Cloud computing presents a unique set of challenges to monitoring including: on-demand infrastructure, unprecedented scalability, rapid elasticity and performance uncertainty. There are a wide range of monitoring tools originating from cluster and high-performance computing, grid computing and enterprise computing, as well as a series of newer bespoke tools, which have been designed exclusively for cloud monitoring. These tools express a number of common elements and designs, which address the demands of cloud monitoring to various degrees. This paper performs an exhaustive survey of contemporary monitoring tools from which we derive a taxonomy, which examines how effectively existing tools and designs meet the challenges of cloud monitoring. We conclude by examining the socio-technical aspects of monitoring, and investigate the engineering challenges and practices behind implementing monitoring strategies for cloud computing.Publisher PDFPeer reviewe

    A general purpose programming framework for ubiquitous computing environments

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    It is important to note that the need to support ad-hoc and potentially mobile arrangements of devices in ubiquitous environments does not fit well within the traditional client/server architecture. We believe peer-to-peer communication offers a preferable alternative due to its decentralised nature, removing dependence on individual nodes. However, this choice adds to the complexity of the developers task. In this paper, we describe a two-tiered approach to address this problem: A lower tier employing peer-to-peer interactions for managing the network infrastructure and an upper tier providing a mobile agent based programming framework. The result is a general purpose framework for developing ubiquitous applications and services, where the underlying complexity is hidden from the developer. This paper discusses our on-going work; presenting our design decisions, features supported by our framework, and some of the challenges still to be addressed in a complex programming environment
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