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Kinds of Server Terms modified by Server Selected AbstractsImpact of mixed-parallelism on parallel implementations of the Strassen and Winograd matrix multiplication algorithmsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2004F. Desprez Abstract In this paper we study the impact of the simultaneous exploitation of data- and task-parallelism, so called mixed-parallelism, on the Strassen and Winograd matrix multiplication algorithms. This work takes place in the context of Grid computing and, in particular, in the Client,Agent(s),Server(s) model, where data can already be distributed on the platform. For each of those algorithms, we propose two mixed-parallel implementations. The former follows the phases of the original algorithms while the latter has been designed as the result of a list scheduling algorithm. We give a theoretical comparison, in terms of memory usage and execution time, between our algorithms and classical data-parallel implementations. This analysis is corroborated by experiments. Finally, we give some hints about heterogeneous and recursive versions of our algorithms. Copyright © 2004 John Wiley & Sons, Ltd. [source] The role of electronic preprints in chemical communication: Analysis of citation, usage, and acceptance in the journal literatureJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 5 2003Cecelia Brown This study characterizes the usage and acceptance of electronic preprints (e-prints) in the literature of chemistry. Survey of authors of e-prints appearing in the Chemistry Preprint Server (CPS) at http://preprints.chemweb.com indicates use of the CPS as a convenient vehicle for dissemination of research findings and for receipt of feedback before submitting to a peer-reviewed journal. Reception of CPS e-prints by editors of top chemistry journals is very poor. Only 6% of editors responding allow publication of articles that have previously appeared as e-prints. Concerns focus on the lack of peer review and the uncertain permanence of e-print storage. Consequently, it was not surprising to discover that citation analysis yielded no citations to CPS e-prints in the traditional literature of chemistry. Yet data collected and posted by the CPS indicates that the e-prints are valued, read, and discussed to a notable extent within the chemistry community. Thirty-two percent of the most highly rated, viewed, and discussed e-prints eventually appear in the journal literature, indicating the validity of the work submitted to the CPS. This investigation illustrates the ambivalence with which editors and authors view the CPS, but also gives an early sense of the potential free and rapid information dissemination, coupled with open, uninhibited discussion and evaluation, has to expand, enrich, and vitalize the scholarly discourse of chemical scientists. [source] Prediction of new displacive ferroelectrics through systematic pseudosymmetry search.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002Pmc21 symmetry, Results for materials with Pba Polar structures with pseudosymmetry related to a hypothetical non-polar configuration are considered as good candidates for ferroelectrics. Recently, a procedure has been developed for a systematic pseudosymmetry search among structures with a given space-group symmetry. The aim of this paper is the extension of the pseudosymmetry procedure to the case of structures with polar symmetry and its application in the search for new ferroelectrics. The results obtained by the generalized pseudosymmetry search among the compounds with symmetries and listed in the Inorganic Crystal Structure Database are discussed. The calculations have been performed by the program PSEUDO, which forms part of the Bilbao Crystallographic Server (http://www.cryst.ehu.es). In addition, an empirical relation between the atomic displacements necessary to reach the non-polar structure and the transition temperature is proposed and compared with the Abrahams,Kurtz,Jamieson relation. [source] Automated software development with XML and the Java* languageBELL LABS TECHNICAL JOURNAL, Issue 2 2000Glenn R. Bruns In software development with domain-specific languages (DSLs), one defines a requirements language for an application domain and then develops a compiler to generate an implementation from a requirements document. Because DSLs and DSL compilers are expensive to develop, DSLs are seen as cost effective only when many products of the same domain will be developed. In this paper, we show how the cost of DSL design and DSL compiler development can be reduced by defining DSLs as Extensible-Markup-Language (XML) dialects and by developing DSL compilers using commercial XML tools and the Java* language. This approach is illustrated through the Call View Data Language (CDL), a new DSL that generates provisioning support code and database table definitions for Lucent Technologies' 7R/EÔ Network Feature Server. [source] Flexible manufacturing cell SCADA system for educational purposesCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2008Sarah Reynard Abstract This article deals with the development of a Supervisory Control and Data Acquisition SCADA system to be used in a flexible manufacturing cell for educational purposes in different automation engineering fields (SCADA development, PLC programming and industrial communications). When dealing with industrial communications or PLC programming the SCADA is employed as a supervision tool. In the other hand, when teaching SCADA systems the application will be developed by the students and the SCADA presented in this article is employed as a model. The application communicates through Internet with four controllers, by means of an OPC server, visualizes comprehensive information about the elements of the cell, includes the video streaming of an IP camera, and features traceability and report generation capabilities. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 16: 21,30, 2008; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20115 [source] The Dow Chemical Project: Creating a web-based interface to a dynamic simulationCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2005K. Kuriyan Abstract In this study we present a Web-based interface to a dynamic simulation. The simulation is based on an emulsion polymerization process operated by the Dow Chemical Company. We also describe the software architecture that allows simulation updates to be transmitted dynamically across a network, from a server-based simulation to a Web-based client. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 250,256, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20049 [source] Air Products hydrogen liquefaction project: Building a Web-based simulation of an industrial processCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2001K. Kuriyan Abstract In this paper we present a Web-based simulation drawn from a hydrogen liquefaction process operated by Air Products. We describe the software architecture that connects Web-based clients to a simulation server and discuss some implementation issues. © 2001 John Wiley & Sons, Inc. Comput Appl Eng Educ 9: 180,191, 2001 [source] A decentralized and fault-tolerant Desktop Grid system for distributed applications,CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 3 2010Heithem Abbes Abstract This paper proposes a decentralized and fault-tolerant software system for the purpose of managing Desktop Grid resources. Its main design principle is to eliminate the need for a centralized server, therefore to remove the single point of failure and bottleneck of existing Desktop Grids. Instead, each node can play alternatively the role of client or server. Our main contribution is to design the PastryGrid protocol (based on Pastry) for Desktop Grid in order to support a wider class of applications, especially the distributed application with precedence between tasks. Compared with a centralized system, we evaluate our approach over 205 machines executing 2500 tasks. The results we obtain show that our decentralized system outperforms XtremWeb-CH which is configured as a master/slave, with respect to the turnaround time. Copyright © 2009 John Wiley & Sons, Ltd. [source] Efficient and fair scheduling for two-level information broadcasting systemsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 18 2008Byoung-Hoon Lee Abstract In a ubiquitous environment, there are many applications where a server disseminates information of common interest to pervasive clients and devices. For an example, an advertisement server sends information from a broadcast server to display devices. We propose an efficient information scheduling scheme for information broadcast systems to reduce average waiting time for information access while maintaining fairness between information items. Our scheme allocates information items adaptively according to relative popularity for each local server. Simulation results show that our scheme can reduce the waiting time up to 30% compared with the round robin scheme while maintaining cost-effective fairness. Copyright © 2008 John Wiley & Sons, Ltd. [source] Tunable scheduling in a GridRPC frameworkCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 9 2008A. Amar Abstract Among existing grid middleware approaches, one simple, powerful, and flexible approach consists of using servers available in different administrative domains through the classic client,server or remote procedure call paradigm. Network Enabled Servers (NES) implement this model, also called GridRPC. Clients submit computation requests to a scheduler, whose goal is to find a server available on the grid using some performance metric. The aim of this paper is to give an overview of a NES middleware developed in the GRAAL team called distributed interactive engineering toolbox (DIET) and to describe recent developments around plug-in schedulers, workflow management, and tools. DIET is a hierarchical set of components used for the development of applications based on computational servers on the grid. Copyright © 2007 John Wiley & Sons, Ltd. [source] Towards an autonomic approach for edge computingCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 14 2007Mikael Desertot Abstract Nowadays, one of the biggest challenges for companies is to cope with the high cost of their information technologies infrastructure. Edge computing is a new computing paradigm designed to allocate on-demand computing and storage resources. Those resources are Web cache servers scattered over the ISP backbones. We argue that this paradigm could be applied for on-demand full application hosting, helping to reduce costs. In this paper, we present a J2EE (Java Enterprise Edition) dynamic server able to deploy/host J2EE applications on demand and its autonomic manager. For this, we reengineer and experiment with JOnAS, an open-source J2EE static server. Two management policies of the autonomic manager were stressed by a simulation of a worldwide ISP network. Copyright © 2006 John Wiley & Sons, Ltd. [source] CCLRC Portal infrastructure to support research facilitiesCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6 2007Asif Akram Abstract The emergence of portal technology is providing benefits in developing portlet interfaces to applications to meet the current and future requirements of CCLRC facilities support. Portlets can be reused by different projects, e.g. the high-profile Integrative Biology project (with the University of Oxford), and in different Java Specification Request 168 Portlet Specification (JSR 168) compliant portal frameworks. Deployment and maintenance of applications developed as portlets becomes easier and manageable. A community process is already beginning and many portal frameworks come with free-to-use useful portlets. As rendering is carried out in the framework, applications can be easily accessible and internationalized. Portlets are compatible with J2EE, thus providing additional capabilities required in the service-oriented architecture (SOA). We also describe how Web service gateways can be used to provide many of the functionalities encapsulated in a portal server in a way to support Grid applications. Portals used as a rich client can allow users to customize or personalize their user interfaces and even their workflow and application access. CCLRC facilities will be able to leverage the work so far carried out on the National Grid Service (NGS) and e-HTPX portals, as they are fully functional and have received detailed user feedback. This demonstrates the usefulness of providing advanced capabilities for e-Research and having the associated business logic in a SOA loosely coupled from the presentation layer for an Integrated e-Science Environment. Copyright © 2006 John Wiley & Sons, Ltd. [source] Measuring and modelling the performance of a parallel ODMG compliant object database serverCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2006Sandra de F. Mendes Sampaio Abstract Object database management systems (ODBMSs) are now established as the database management technology of choice for a range of challenging data intensive applications. Furthermore, the applications associated with object databases typically have stringent performance requirements, and some are associated with very large data sets. An important feature for the performance of object databases is the speed at which relationships can be explored. In queries, this depends on the effectiveness of different join algorithms into which queries that follow relationships can be compiled. This paper presents a performance evaluation of the Polar parallel object database system, focusing in particular on the performance of parallel join algorithms. Polar is a parallel, shared-nothing implementation of the Object Database Management Group (ODMG) standard for object databases. The paper presents an empirical evaluation of queries expressed in the ODMG Query Language (OQL), as well as a cost model for the parallel algebra that is used to evaluate OQL queries. The cost model is validated against the empirical results for a collection of queries using four different join algorithms, one that is value based and three that are pointer based. Copyright © 2005 John Wiley & Sons, Ltd. [source] Feasibility of using the TOSCA telescreening procedures for diabetic retinopathyDIABETIC MEDICINE, Issue 10 2004S. Luzio Abstract Aims The TOSCA project was set up to establish a tele-ophthalmology service to screen for diabetic retinopathy (DR) in Europe. The aim of this study was to determine the feasibility of establishing telemedicine-based digital screening for detecting DR and to evaluate the satisfaction of both patients and healthcare professionals with the screening procedures used within the TOSCA project. Methods The study was a non-randomized, multicentre study carried out in four different countries over a period of 3 months. Patients (n = 390) with diabetes aged > 12 years were included. Two digital retinal images per eye (macular and nasal) were taken and exported to a central server. Patients were asked to complete a questionnaire to assess satisfaction. Accredited graders carried out grading remotely and the results were reported back to the referring centre. Previously graded patient data chosen randomly to represent examples of both DR and no DR were also sent anonymously to the grading centre at a frequency of approximately every 10 patients. Results Most (99%) of the images were assessable enabling a retinopathy grade to be assigned to the patient. Patients found the retinal photography procedures acceptable; only 6% in one centre would not recommend the procedure. Healthcare professionals (photographers and graders) were also satisfied with the overall procedures. The average time taken to grade each patient was approximately 5 min. Conclusions This study demonstrated that it is feasible to electronically transmit and grade retinal images remotely using the TOSCA process. Built-in quality assurance procedures proved acceptable. [source] A new mutual authentication and key exchange protocol with balanced computational power for wireless settingsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2004Chou-Chen Yang Mutual authentication and key exchange protocols (MAKEP) provide two parties in communication with guarantee of true identity. And then the two parties end up sharing a common session key for privacy and data integrity during the session. In MAKEP, public-key-based schemes and symmetric-key-based schemes are often used. However, the former requires high computation complexity and hence, it is not suitable for applications in wireless settings. The latter has to maintain many distinct keys for different parties. Wong et al. proposed the Linear MAKEP to solve these problems. But in term of storage space, it is not optimal. In this paper, we propose a scheme that uses the geometric properties of line to achieve mutual authentication and key exchange. Compared with Wong et al.'s scheme, our scheme is efficient and requires less storage space. It can withstand the replay attack and the unknown key-share attack, and the server does not bear much more computation cost than the client in each session, hence we call it a protocal with balanced computational power. Copyright © 2004 AEI [source] Delay analysis of a probabilistic priority disciplineEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2002Yuming Jiang In computer networks, the Strict Priority (SP) discipline is perhaps the most common and simplest method to schedule packets from different classes of applications, each with diverse performance requirements. With this discipline, however, packets at higher priority levels can starve packets at lower priority levels. To resolve this starvation problem, we propose to assign a parameter to each priority queue in the SP discipline. The assigned parameter determines the probability or extent by which its corresponding queue is served when the queue is polled by the server. We thus form a new packet service discipline, referred to as the Probabilistic Priority (PP) discipline. By properly adjusting the assigned parameters, not only is the performance of higher priority classes satisfied, but also the performance of lower priority classes can be improved. This paper analyzes the delay performance of the PP discipline. A decomposition approach is proposed for calculating the average waiting times and their bounds are studied. Two approximation approaches are proposed to estimate the waiting times. Simulation results that validate the numerical analysis are presented and examined. A numerical example which demonstrates the use of the PP discipline to achieve service differentiation is presented. This example also shows how the assigned parameters can be determined from the results of analysis mentioned above. [source] Basic Surveying of the Koralm TunnelGEOMECHANICS AND TUNNELLING, Issue 4 2008Arnold Eder The "Koralm tunnel basic network" had to be prepared for the design, construction, and construction supervision of the ÖBB railway project "Koralmbahn Graz-Klagenfurt" with the 32.8 km long Koralm tunnel as its core piece. This network is based on the "primary network" which is integrated into a network of GPS permanent stations and was or will be complemented as required. Since the project area covers two meridian zones of the national system, it was necessary to create a projection in a separate meridian zone for planar calculations. The paper describes the preparation, surveying and calculation of this network. In addition, it includes procedure instructions for the use of the network by planners and construction companies. Since the network has to be adapted to each construction phase, it has to be continuously developed. This will be described too. All data are managed by means of an ArcGIS server. Grundvermessung des Koralmtunnels Das Koralmtunnel-Grundlagennetz wurde für die Planung, den Bau und die Bauüberwachung des Koralmtunnels erstellt. Der 32,8 km lange Koralmtunnel bildet das Schlüsselbauwerk im Rahmen der neuen Eisenbahnverbindung Koralmbahn zwischen Graz und Klagenfurt. Das Netz baut auf einem Grundnetz, das in einem permanenten GPS-Stationsrahmen integriert ist, und wird je nach Projektfortschritt und -anforderungen erweitert. Durch die Lage des Projekts über zwei Meridianstreifen des öffentlichen Systems war es außerdem erforderlich, eine neue, ebene Projektion zu entwerfen. Der Beitrag beschreibt die Vorbereitungen für dieses System, die erforderlichen Vermessungs- und Berechnungstätigkeiten sowie die Hinweise für den Gebrauch dieses Netzes durch Planer oder bauausführende Firmen. Da in jeder Projektphase eine ständige Adaptierung des Netzes unabdingbar ist, werden auch Hinweise zu diesen Tätigkeiten gegeben. Alle Daten werden mithilfe eines ArcGIS-Servers verwaltet. [source] On-line Monitoring of Nocturnal Home HemodialysisHEMODIALYSIS INTERNATIONAL, Issue 1 2003SJA Stokvis Background. Nocturnal home hemodialysis (NHD, 6,7 times weekly 6,8 hours) is a promising dialysis modality. On-line distant monitoring is complicated and expensive, and its usefulness should be evaluated. Methods. Since December 2001, 15 patients were included in a Dutch NHD project (,Nocturne'). So far, 3 patients received a renal transplant. Patients are assisted by their spouses. The dialysis machine is connected through the public telephone network by a bedside node and routers to the server in a call center. All patients received a dedicated ISDN-connection. Alarms produced by the machine are detected in the call center. For each type of alarm, a period is defined during which the patient can solve the problem. When the alarm continues after this period, the call center will notify the patient. Results. During 4 months, approximately 900 alarms in 1300 dialysis treatments were produced. In only 11 of 900 cases, the partner had to wake up the patient because he/she did not hear the alarm. The call center had to call 13 times, always because the patient resumed sleeping after the end of the treatment. No intervention because of serious problems was required. A majority of patients and personnel consider on-line monitoring nevertheless important as it gives a sense of safety. Additionally, nurses use the real-time connection frequently to check running dialysis treatments. Also, the system enables automatic saving of important treatment data in an electronic patient file. The experience so far is used to design a so-called ,secure bitpipe' for homecare applications, with emphasis on privacy, safety, security and effectivity. Conclusion. On-line monitoring of NHD may not be crucial, but enables good coaching of patients and gives a sense of safety. [source] LOVD: Easy creation of a locus-specific sequence variation database using an "LSDB-in-a-box" approach,HUMAN MUTATION, Issue 2 2005Ivo F.A.C. Fokkema Abstract The completion of the human genome project has initiated, as well as provided the basis for, the collection and study of all sequence variation between individuals. Direct access to up-to-date information on sequence variation is currently provided most efficiently through web-based, gene-centered, locus-specific databases (LSDBs). We have developed the Leiden Open (source) Variation Database (LOVD) software approaching the "LSDB-in-a-Box" idea for the easy creation and maintenance of a fully web-based gene sequence variation database. LOVD is platform-independent and uses PHP and MySQL open source software only. The basic gene-centered and modular design of the database follows the recommendations of the Human Genome Variation Society (HGVS) and focuses on the collection and display of DNA sequence variations. With minimal effort, the LOVD platform is extendable with clinical data. The open set-up should both facilitate and promote functional extension with scripts written by the community. The LOVD software is freely available from the Leiden Muscular Dystrophy pages (www.DMD.nl/LOVD/). To promote the use of LOVD, we currently offer curators the possibility to set up an LSDB on our Leiden server. Hum Mutat 26(2), 1,6, 2005. © 2005 Wiley-Liss, Inc. [source] Proxy-assisted P2P and multicast transmission schemes for layered-video streaming over wireless networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9-10 2010Yung-Cheng Kao Abstract This work describes the process of efficiently streaming a set of layered-videos from a remote server via proxy of the base station to multiple heterogeneous and asynchronous clients in wireless networks, such as the WiMAX network, which are devices that request different layers of the video according to their profiles. The process focuses on that the transmission cost savings for caching X layers of a video are not only from requests on X layers, but also from requests on layers that are lower than X layers. A set of proxy-assisted transmission schemes are proposed for layered-video streaming by integrating the proxy caching with reactive transmission schemes, peer-to-peer mesh networks and base station multicast capability. The optimal proxy prefix cache allocation is calculated for each transmission scheme to identify the cache layer and cache length of each video to minimize the aggregate transmission cost. Experimental results demonstrate that an adaptive proxy-assisted transmission scheme can lead to significant transmission cost savings. Copyright © 2009 John Wiley & Sons, Ltd. [source] Mobile-initiated network-executed SIP-based handover in IMS over heterogeneous accessesINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9-10 2010Wei-Kuo Chiang Abstract The services of next generation networks are envisioned to be potentially capable of seamless mobility in spite of the heterogeneity in underlying access technologies. It is undoubted that to accomplish seamless services across heterogeneous networking environments gets harder in case of simultaneous mobility. In this article, we propose a mobile-initiated network-executed (MINE) session initial protocol (SIP)-based handover mechanism to facilitate simultaneous mobility in IP multimedia subsystem over heterogeneous accesses. The novelty of the proposed approach is that no changes are required to the existing network infrastructure since handover decision is fully made by the mobile host (MH) and handover execution is performed by a new-added application server called mobility server (MS). When the MH decides to initiate a handover and obtains a new IP address, it will send a SIP Publish message to trigger the MS to carry out the handover execution. With the network-executed design of the MINE, the MS can perform third-party registration for security re-association and third-party call control for session re-establishment in parallel. Moreover, the Master,Slave Determination procedures derived from H.245 are used in the MS to handle fairly the racing conditions resulting from simultaneous mobility such that redundant message flows are eliminated. Mathematical analyses present that the MINE can shorten the handover latency and reduce power consumption, as observed from a comparison with the integrated solution of an optimized macro-mobility mechanism and a receiver-side simultaneous mobility approach. Copyright © 2010 John Wiley & Sons, Ltd. [source] Secure fast WLAN handoff using time-bound delegated authenticationINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2009Hung-Yu Chien Abstract To support multimedia applications with good quality of services for roaming wireless local area network users, it is imperative to reduce the long re-authentication latency that users experience during handoff among access points (APs). Athough a great deal of research resources have been put into the reduction of the re-authentication latency, these schemes developed so far seem to either suffer from heavy overhead problems or have weak security. In this paper, we propose a novel approach to reducing the re-authentication latency. With the authentication server (AS) periodically delegating its authentication authority to the authenticated APs, the APs can authenticate the roaming users on behalf of the AS. As our performance analysis and simulation results demonstrate, our new approach is capable of greatly reducing the latency and overhead while achieving a high security level. Furthermore, it does not increase the complexity on the AP side because only the already existing four-way handshake with new keying mechanism is required. Copyright © 2008 John Wiley & Sons, Ltd. [source] A new traffic model for backbone networks and its application to performance analysisINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2008Ming Yu Abstract In this paper, we present a new traffic model constructed from a random number of shifting level processes (SLP) aggregated over time, in which the lengths of the active periods of the SLP are of Pareto or truncated Pareto distribution. For both cases, the model has been proved to be asymptotically second-order self-similar. However, based on extensive traffic data we collected from a backbone network, we find that the active periods of the constructing SLPs can be approximated better by a truncated Pareto distribution, instead of the Pareto distribution as assumed in existing traffic model constructions. The queueing problem of a single server fed with a traffic described by the model is equivalently converted to a problem with a traffic described by Norros' model. For the tail probability of the queue length distribution, an approximate expression and upper bound have been found in terms of large deviation estimates and are mathematically more tractable than existing results. The effectiveness of the traffic model and performance results are demonstrated by our simulations and experimental studies on a backbone network. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigating the performance of a middleware protocol architecture for tele-measurementINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2008Luca Berruti Abstract The rapid growth of network infrastructures and the large availability of instrumentation supporting remote control have encouraged the deployment of complex and sophisticated laboratories and the design of software platforms for accessing the resources present there. Although the market offers several solutions to remotely manage equipment, little attention has been paid to the hardware and software architectures devoted to control distance learning experimental environments and to manage laboratories consisting of heterogeneous devices. The paper illustrates the architectural approach adopted within the LABNET project and describes in detail the main software components of the devised platform, which allows to exploit the instrumentation via a common Web user interface, thus making the system available independent of any specific (commercial) environment or application. Specifically, attention is focused on the LABNET server (LNS), which represents the supervising central unit and, therefore, a very critical element of the system. The paper mainly points out the architecture and protocols at the basis of the LNS and discusses a set of performance tests aimed at proving the effectiveness of the system and comparing it with a well-known commercial solution. Copyright © 2007 John Wiley & Sons, Ltd. [source] A zone co-operation approach for efficient caching in mobile ad hoc networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2006Narottam Chand Abstract Mobile Ad hoc NETwork (MANET) presents a constrained communication environment due to fundamental limitations of client resources, insufficient wireless bandwidth and users' frequent mobility. Caching of frequently accessed data in such environment is a potential technique that can improve the data access performance and availability. Co-operative caching, which allows the sharing and co-ordination of cached data among clients, can further explore the potential of the caching techniques. In this paper, we propose a novel scheme, called zone co-operative (ZC) for caching in MANETs. In ZC scheme, one-hop neighbours of a mobile client form a co-operative cache zone. For a data miss in the local cache, each client first searches the data in its zone before forwarding the request to the next client that lies along routing path towards server. As a part of cache management, cache admission control and value -based replacement policy are developed to improve the data accessibility and reduce the local cache miss ratio. An analytical study of ZC based on data popularity, node density and transmission range is also performed. Simulation experiments show that the ZC caching mechanism achieves significant improvements in cache hit ratio and average query latency in comparison with other caching strategies. Copyright © 2006 John Wiley & Sons, Ltd. [source] Estimating and eliminating redundant data transfers over the web: a fragment based approachINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2005Christos Bouras Abstract Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ,Web Components' but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd. [source] The distribution of file transmission duration in the webINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2004R. Nossenson Abstract It is well known that the distribution of files transmission duration in the Web is heavy-tailed (A practical guide to Heavy Tails: Statistical Techniques and Application. Birkhauser: Boston, 1998; 3,26). This paper attempts to understand the reasons for this phenomenon by isolating the three major factors influencing the transmission duration: file size, network conditions and server load. We present evidence that the transmission-duration distribution (TDD) of the same file from the same server to the same client in the Web is Pareto and therefore heavy tailed. Furthermore, text files transmission delay for a specific client/server pair is not significantly affected by the file sizes: all files transmitted from the same server to the same client have very similar transmission duration distributions, regardless of their size. We use simulations to estimate the impact of network conditions and server load on the TDD. When the server and the client are on the same local network, the TDD of each file is usually Pareto as well (for server files and client requests that are distributed in a realistic way). By examining a wide-area network situation, we conclude that the network conditions do not have a major influence on the heavy-tailed behaviour of TDD. In contrast, the server load is shown to have a significant impact on the high variability of this distribution. Copyright © 2004 John Wiley & Sons, Ltd. [source] The effects of correlated arrivals at a server with credit-based traffic policingINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2001K. Mitchell Abstract In this paper we observe the steady state and transient behaviour of correlated cell arrivals into a server with credit-based traffic policing. We derive expressions for the lag- k correlations of the departure process from the traffic policing mechanism, and observe how dependencies in the departure stream affect cell loss at the server. The results illustrate the impact of the second-order statistics and the higher moments of the cell arrival processes on the traffic policing mechanism performance. Copyright © 2001 John Wiley & Sons, Ltd. [source] Block-based fine granularity scalable video coding with optimized rate allocation for content-aware streamingINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 6 2003Yuwen He Abstract This article proposes a novel block-based fine granularity scalable (FGS) video coding structure with optimized rate allocation for content-aware streaming, which is more flexible than MPEG-4 FGS specified in the streaming profile of MPEG-4 standard (IS-14496). In MPEG-4 FGS streaming, rate allocation can only be based on frame because MBs' compressed data are interlaced between bit-planes. However in the proposed coding structure, every MB's data are independent; therefore, streaming server can allocate bits according to content's importance, and the quality of those regions of interest is enhanced selectively with more bits allocated. In this way, the streaming server can have a differentiated delivery strategy to support a personalized streaming service considering user's preference. But the uniform rate allocation of proposed block-based FGS coding will result in a greater loss of coding efficiency than that of MPEG-4 FGS within a quite wide bit-rate range. An optimized and fast rate allocation method according to block's rate-distortion is proposed to solve this critical issue. And the coding efficiency is improved successfully, which can be comparable with MPEG-4 FGS coding and is even better up to 0.5 dB, with some sequences at medium bit-rates. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 322,330, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10066 [source] Video compression for multicast environments using spatial scalability and simulcast codingINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 6 2003Wade K. Wan Abstract A common problem with many video transmission applications is the wide range of available bandwidths between the server and different clients. These environments require efficient multicast video service, the capability to transmit and receive the same video sequence at different resolutions. Two approaches to achieve multicast service are scalable coding (dependent bitstream coding) and simulcast coding (independent bitstream coding). One would expect scalable coding to have higher coding efficiency because a scalable coded bitstream can exploit similar information in another bitstream. This reasoning would suggest that multicast implementations should only use scalable coding for maximum coding efficiency. However, this article shows results where simulcast coding has been found to outperform spatial scalability (one type of scalable coding). In this article, methods are described to select between simulcast coding and spatial scalability for multicast video transmission. These techniques can be used to determine the proper multicast coding approach for providing service to clients with different communication links. The methodology described can also be used to construct decision regions to guide more general scenarios or adaptively switch between the two coding approaches. A number of important results were obtained that may be directly applicable to commercial multicast systems. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 331,340, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10065 [source] | |||||||||||||||||||||||||||||||