Unreliable Service Research Articles

Reliability and sensitivity analysis of the controllable repair system with warm standbys and working breakdown

This paper deals with the reliability and sensitivity analysis of a controllable repair system with M operating units, S warm standby units, and an unreliable service station. Failure times and service times of operating units or standby units are assumed to follow exponential distributions. When the service station normally operates, it is subject to breakdowns; while a breakdown occurs, the service station requires repair at the repair facility. The times to breakdown and repair times of the service station are also assumed to be exponentially distributed. During a breakdown period of the service station, the service station is allowed to provide partial service with lower service rate. A practical justification of the system is also provided. This paper develops the expressions for system reliability, RY(t), as well as the mean time to first failure, MTTFF. The sensitivity and relative sensitivity analyses of RY(t) and MTTFF are performed. Finally, some numerical experiments are designed and performed to demonstrate the effects of system performance measures are affected by the change of each system parameter.

A method for achieving provable data integrity in cloud computing

By storing data files in the cloud, users can make use of cloud computing techniques, thereby reducing hardware investment and simplifying data management. However, ensuring data integrity when using unreliable service providers is a problem. In this paper, we propose a novel method for provable data integrity (PDI) aimed at clients with data stored in untrusted servers in cloud computing environments. An advantage of this model is the low client cost since a constant amount of metadata is generated. Based on a bilinear group, we propose a simple, efficient audit service for public verification of untrusted outsourced storage. Compared with existing PDI methods, we aim to resolve this issue by considering the cost of generating verification metadata at the client. Furthermore, our method supports data dynamics and public verifiability. Finally, the results of extensive experiments conducted to evaluate the performance of our method demonstrate that our method achieves high efficiency.

Application of Bus-Only Lanes in Downtown Washington, D.C.: Concurrent Versus Contraflow Bus Lanes

Buses operating in mixed traffic are subject to congestion and thus experience long delays and unreliable service. The impact of congestion on buses is more pronounced in downtown areas than elsewhere because of heavy vehicular traffic, high transit–pedestrian activity, and friction caused by curbside users. This research explored potential benefits, effects, and costs associated with bus-only lane alternatives, including effects for traffic, transit, and curbside users (e.g., parking and loading). H and I Streets, Northwest, in downtown Washington, D.C., where bus frequency reaches one every minute during peak hours, were modeled through microsimulation. Concurrent-flow lanes and contraflow bus-only lanes were analyzed. A benefit–cost analysis (BCA) was conducted for each scenario of bus-only lanes. Concurrent-flow bus-only lanes (Alternative 1) offered a low-cost solution with good benefits (reduction as high as 5 min/mi in bus travel time). However, sensitivity analysis showed that enforcement of restrictions on right turns and operations would be needed to ensure these benefits. A contraflow bus-only lane on H Street (Alternative 2) provided substantial improvements in auto and transit travel times without right-turn restrictions and with medium costs. As a result, Alternative 2 provided the most monetary benefits, according to the BCA, with a benefit–cost ratio of 28. Benefits associated with contraflow bus lanes were not contingent on enforcement, because they are self-enforcing. Couplet contraflow bus-only lanes on H and I Streets (Alternative 3) represented the highest-cost solution yet resulted in marginal benefits compared with the other scenarios because of its high impact on auto users.

Design and Experimental Demonstration of Software Defined Space Optical Network (SDSON) Architecture Based on Cloud Platform

Space information network is used for real time acquiring, transmitting and processing the space information on the space platform, which provides significant communication services for communication, navigation positioning and science exploration. In this paper, the architecture of Software Defined Space Optical Network (SDSON) based on cloud platform is designed by means of Software Defined Optical Network (SDON) and cloud services. The new architecture combining centralized and distributed management-control mechanism is a multi-layer and multi-domain architecture with powerful computing and storage ability. Moreover, reliable service and unreliable service communication models employed in the space information network are proposed considering the characteristic of Disruption/Delay Tolerant Network (DTN). Finally, the functional verification and demonstration are performed on our optical experimental network platform.

Improved reliability of public transportation using real-time transfer synchronization

Service reliability of public transportation (PT) systems is a dominant ingredient in what is perceived as the PT image. Unreliable service increases the uncertainties of simultaneous arrivals of vehicles at a transfer point. Implementing proper control actions leads to preventing missed transfers, one of the undesirable features of PT service and a major contributor to a negative image. The present work focuses on performance measurements of a PT system offering direct transfers on multi-legged trips. The method developed evaluates and improves system performance by applying selected operational tactics in real-time scenarios. In order to investigate the efficiency level of the PT system, five types of vehicle positional situations with reference to a transfer point are considered: considerably ahead of schedule, ahead of schedule, on schedule, behind schedule, and considerably behind schedule. Each situation contributes differently to the degree of system performance. The optimization framework developed results in selected operational tactics to attain the maximum number of direct (without waiting) transfers and minimize total passenger travel time. The implementation of the concept is performed in two steps: optimization and simulation. The optimization process searches for the best operational tactics, using the states of the five vehicle-position types, and the simulation serves to validate the optimal results under a stochastic framework using the concept of a multi-agent system. A case study of Auckland, New Zealand, is described for assessing the methodology developed. Results showed a 58% improvement in the system performance index compared to no-tactic operations.

Applied analysis for improving rail-network operations

In times of recession with local authorities being forced to minimize their expenditures and having quite a few budget cuts, it is getting more and more important for public-transport operators to implement an efficient operation in order to be competitive. This work examines the operations of a rail operator in Auckland, New Zealand, and shows options to improve it. It is twofold. First, the crew scheduling component is analyzed by a column generation approach. The results show that efficiency of operations can be improved by more than 9% using different crew schedules. Moreover, this efficiency measure can be further improved by more than 15% when additional driver training is provided to allow for the crew to operate all trains. Second, a detailed reliability analysis is demonstrated to identify and evaluate the sources of unreliable service and develop remedies to resolve observed problems. It is shown that the outcome of the crew-scheduling problem can have a significant impact on the reliability of the rail network. One of the main causes for delays and unreliability problems is heavy passenger load, which increases dwell times. Accurate passenger demand estimation is crucial in resolving these issues and improving the on-time performance of the rail network.

Analysis of an M/G/1 queue with N-policy, single vacation, unreliable service station and replaceable repair facility

This paper considers an M/G/1 repairable queueing system with N-policy and single vacation, in which the service station is subject to random breakdowns. Once the service station breaks down, it is repaired by a repair facility. Moreover, the repair facility may fail during the repair period which results in repair interruptions. Failed repair facility resumes repair after a random period of time. Applying the renewal process theory and the probability decomposition technique, the probability that the service station is broken, the rate of occurrence of breakdowns of the service station, the probability that the repair facility is being replaced, the rate of occurrence of failures of the repair facility and the stochastic decomposition property of the reliability measures are obtained. Following the construction of the long-run expected cost function per unit time, we numerically determined the optimal threshold N ∗ for minimizing the cost function.

Assessment of Solid Waste Management Practices and the Role of Public Participation in Jigjiga Town, Somali Regional State, Ethiopia

Solid waste, which is a consequence of day-to-day activity of human kind, needs to be managed properly. Jigjiga City, like other cities in developing countries, faces problems associated with poorly managed solid waste operation. This study concerns about analysis of the city’s current municipal solid waste management problems, opportunities and existing solid waste management practices and role of community participation. The survey was conducted in 03 and 05 kebeles. Different sampling methods were employed to select the study units including: stratified sampling, systematic random sampling, and purposive sampling. Though the bulk of the data collected were qualitative in nature, it was also supported by quantitative information collected through survey and secondary sources. The study discovered that there is low performance of SWM in the city mainly due to: lack of properly designed collection system and time schedule, inadequate and malfunctioning operation equipment, open burning of refuse, poor condition of the final dumpsite and less awareness creation among community which encouraged illegal dumping are the technical problem identified. Insufficient funds as well as lack of promotion on-waste reduction, recycling, absence of waste recovery, practice of energy option, waste separation and composting are among the management challenges facing the city. Social problems encountered include: lack of public awareness, unwillingness to pay, ill dumping manner (often around residence and any open spaces) and improper outlook for waste workers. Incompetence of organizations in terms of equipment required for operation and man power /staff qualifications, training and human resource developments and/or unreliable service are the institutional challenge that the city encountered in the sector. Finally, the study forwarded some important recommendations towards improving the waste management practices.

Evaluation of Bus Reliability Measures and Development of a New Composite Indicator

Reliability is cited as a key aspect of service quality, but many of the indicators in use today do not measure reliability from the user's perspective. A review of earlier work on transit user behavior concluded that the traveler's perspective of reliability was driven by punctuality in arriving at the destination, short waiting times at the origin stop, and consistent wait and travel times. Twenty indicators were assessed, but none were well suited to capturing all of these elements of reliability. A new measure, journey time buffer index (JTBI), was therefore proposed; the index used estimates of wait times at bus stops while capturing variability in wait and travel times that tended to increase the disutility of transit travel. Alternative formulations were developed for short and long headway service, and the new indicator was applied to the London Transit Commission's bus network in London, Ontario, Canada. This procedure demonstrated that the JTBI was better suited to identifying the factors contributing to unreliable service than metrics that focused on a single component of reliability. A linear regression analysis also highlighted that route length, stop spacing, time of day, route orientation relative to the city center, and passenger load all influenced reliability although the low adjusted R2 value of .298 showed that some major causes of reliability were not captured by the model.

An efficient method for checking the integrity of data in the Cloud

Cloud computing and storage services allow clients to move their data center and applications to centralized large data centers and thus avoid the burden of local data storage and maintenance. However, this poses new challenges related to creating secure and reliable data storage over unreliable service providers. In this study, we address the problem of ensuring the integrity of data storage in cloud computing. In particular, we consider methods for reducing the burden of generating a constant amount of metadata at the client side. By exploiting some good attributes of the bilinear group, we can devise a simple and efficient audit service for public verification of untrusted and outsourced storage, which can be important for achieving widespread deployment of cloud computing. Whereas many prior studies on ensuring remote data integrity did not consider the burden of generating verification metadata at the client side, the objective of this study is to resolve this issue. Moreover, our scheme also supports data dynamics and public verifiability. Extensive security and performance analysis shows that the proposed scheme is highly efficient and provably secure.

An Assessment of the Impact of Total Quality Management Practices at Parkview Premier Clinical Laboratories

Stiff competition in a tough economic environment was a key driver for Parkview Clinical Laboratories to introduce total quality management (TQM) as an integrated management approach to continuously improve performance of products, processes and services ultimately yielding and surpassing customers’ expectations. This study sought to assess the impact of TQM practices in improving healthcare service delivery at Parkview Clinical Laboratories against the Stepwise Laboratory Improvement Process towards Accreditation (SLIPTA) framework. Other drivers for TQM included but not limited to: increased customer complaints as a result of delayed turnaround times, unreliable service delivery and erroneous laboratory results. Literature on total quality management principles such as Kaizen stepwise continuous improvement, Lean management and six sigma principles and the WHO-AFRO SLIPTA model provided a framework for the study. The study conducted a baseline study against the SLIPTA constructs to measure service quality at three intervals. A customer survey was done to obtain quantitative data pertaining to customer needs and satisfaction whose constructs were guided by the gap model. Research elements were stratified according to profession to ensure representation of various services. To assess customer satisfaction whose constructs were guided by the gap model, and also to capture customer needs and complaints, the quantitative approach was also adopted. This enabled responses to be statistically analysed to determine their significant levels and to classify the need and complaints of gap analysis. The quantitative research approach was also chosen after considering the large sample size, in order to provide accurate and valid data representative of the target population using structured instruments like questionnaires. Customer surveys sought to identify and group the customer needs decision making. Hence quantitative analysis of the complaints was very important to measure the gravity of service gaps.

TFCWS: Testing Framework for composite web services.

In every business domain Web Services are more popular solutions to implement the software. Composite web service can be created by combining basic web services. Many unreliable web services are deployed on the internet. Hence, testing is required to ensure reliability. Software testers have great challenges to test web services. Source code of web services is unavailable. The Testing Framework is used to test web services without knowledge of its internal structure. In this paper, we have proposed a Testing Framework for Composite Web Services (TFCWS). It generates report which shows the total number of test cases executed for each web service with pass or fail status of each test case. It calculates the throughput of web service and response time of each test case. We have used web services response times for analysis of TFCWS, Soap UI and Storm.

Can Private Water Vendors Help Meet the Millennium Development Goals? - A Study of Karachi City Urban Water Market

This working paper examines the role of Private Water Vendors (PWV) in supplying water to urban dwellers in city of Karachi, Pakistan. The increasing gap in the water supply-demand in Karachi has meant that communities especially the urban poor have had to rely on alternate suppliers i.e. informal PWV to meet their water needs. It is estimated that 60% of the piped consumers in Karachi also supplement their water needs from PWV due to interrupted official. PWV are often viewed as temporary rent seekers taking advantage of unreliable public services so as to exploit customers with overpriced low quality water supply. Both governments and international agencies often ignore PWV as they reflect a failure on part of the government to supply clean piped water to its citizens. However, PWV role should not be ignored as they fill a critical market gap of ensuring water access to communities that otherwise are underserved. Often operating in competitive environments, PWV buy (and illegally extract) bulk water from local water utilities and supply through tankers, kiosks and carts mostly to urban poor in localities that do not have piped connections. Only recently are these PWV being increasingly recognized as providing complimentary services. They are seen as "gap fillers" in countries with high coverage areas and low service quality and are pioneering operations in areas where there is no public service. Global statistics, unfortunately, do not recognize the contributions of PWV towards the targets of Millennium Development Goals (MDG), yet PWV are the difference between water and no water in many urban communities. Using the specific case study of Karachi, Pakistan, this paper explores the wider debate that PWV contribute (at least in spirit if not statistically) towards achieving the MDG.

Trust Management in Peer-to-Peer Networks

In recent years, various applications of Peer-to-Peer (P2P) computing have been widely used because of its unique advantages, which have play ed an important role in commerce, communications and other fields. The P2P system is essentially a distributed system, without central servers. Each peer is both client and server, who have the same status. However, some features of P2P networks, such as autonomy, dynamic, and heterogeneity lead to an important problem, namely unreliable quality of service. Unreliable quality of service is usually presented as providing false or unreliable service, impacting customer satisfaction. The establishment of trust models which evaluate s capabilities of peers can measure the service capacity of a peer, and identify malicious behavior, thereby reducing the risk of interaction and being an effective technique to ensure the overall availability of P2P networks. A trust model named METrust in P2P networks based on the recommendation is proposed. In METrust, a peer selects recommendation peers whose evaluation criteria are similar, and evaluation criteria of peers are determined through the AHP method (Analytic Hierarchy Process). Each peer in the network has a unique credibility of recommendation, and two trust parameters for updating the credibility of recommendation are introduced, namely updating range and updating strength. METrust proposes algorithms to compute the trust of peers. Simulations show that, the trust model METrust can identify malicious peers, and improve the quality of service in P2P networks effectively.

An Enhanced Erasure Code-Based Security Mechanism for Cloud Storage

Cloud computing offers a wide range of luxuries, such as high performance, rapid elasticity, on-demand self-service, and low cost. However, data security continues to be a significant impediment in the promotion and popularization of cloud computing. To address the problem of data leakage caused by unreliable service providers and external cyber attacks, an enhanced erasure code-based security mechanism is proposed and elaborated in terms of four aspects: data encoding, data transmission, data placement, and data reconstruction, which ensure data security throughout the whole traversing into cloud storage. Based on the mechanism, we implement a secure cloud storage system (SCSS). The key design issues, including data division, construction of generator matrix, data encoding, fragment naming, and data decoding, are also described in detail. Finally, we conduct an analysis of data availability and security and performance evaluation. Experimental results and analysis demonstrate that SCSS achieves high availability, strong security, and excellent performance.

Markovian queue optimisation analysis with an unreliable server subject to working breakdowns and impatient customers

This study investigates an infinite capacity Markovian queue with a single unreliable service station, in which the customers may balk (do not enter) and renege (leave the queue after entering). The unreliable service station can be working breakdowns even if no customers are in the system. The matrix-analytic method is used to compute the steady-state probabilities for the number of customers, rate matrix and stability condition in the system. The single-objective model for cost and bi-objective model for cost and expected waiting time are derived in the system to fit in with practical applications. The particle swarm optimisation algorithm is implemented to find the optimal combinations of parameters in the pursuit of minimum cost. Two different approaches are used to identify the Pareto optimal set and compared: the epsilon-constraint method and non-dominate sorting genetic algorithm. Compared results allow using the traditional optimisation approach epsilon-constraint method, which is computationally faster and permits a direct sensitivity analysis of the solution under constraint or parameter perturbation. The Pareto front and non-dominated solutions set are obtained and illustrated. The decision makers can use these to improve their decision-making quality.

Reliability indices of discrete-time Geox/G/1 queueing system with unreliable service station and multiple adaptive delayed vacations

This paper considers the discrete-time GeoX/G/1 queueing model with unreliable service station and multiple adaptive delayed vacations from the perspective of reliability research. Following problems will be discussed: 1) The probability that the server is in a “generalized busy period” at time n; 2) The probability that the service station is in failure at time n, i.e., the transient unavailability of the service station, and the steady state unavailability of the service station; 3) The expected number of service station failures during the time interval (0, n], and the steady state failure frequency of the service station; 4) The expected number of service station breakdowns in a server’s “generalized busy period”. Finally, the authors demonstrate that some common discrete-time queueing models with unreliable service station are special cases of the model discussed in this paper.

Customer Satisfaction With Complaint Resolution in the Power Sector in a Developing Economy

Public services play a critical role in helping nations evolve into modern societies. The power sector is especially vital because of its profound influence on other sectors of the economy. Unfortunately, the power sector in Bangladesh has played almost a reverse role, being associated with rampant corruption, mismanagement, and unreliable service provision, thus depriving the clientele from needed services. About 80% of the subscribers have complained about service failures in the sector. This study examines the elements of postcomplaint satisfaction with customer service. Descriptive statistics reveal the “low quality” perception that subscribers harbor about the particular utility service. Multiple regression analysis suggests that providers' empathy had the greatest effect on customer satisfaction followed by assurance. Using the metrics suggested by this study, the article concludes how social control mechanisms can restore “service justice” to the legitimate customers and enhance their welfare by making the provider more effective as a customer-responsive organization.

Reliability-based measures for a system with an uncertain parameter environment

This article proposes a procedure to construct membership functions of the system characteristics of a repairable system with one primary machine, one standby machine and an unreliable service station. Failure and repair times of both the operating and standby machines are assumed to follow fuzzified exponential distributions. In addition, the failure and repair times of the service station also follow fuzzified exponential distributions. The α-cut approach is used to extract a family of conventional crisp intervals for the desired system characteristics from the fuzzy repairable system, determined with a set of parametric nonlinear programs using their membership functions. A numerical example successfully illustrates the practicality of the proposed approach. Because system characteristics are governed by the membership functions, more information is provided for use by designers and practitioners. The successful extension of the parameter spaces to fuzzy environments permits the repairable system to have wider practical applications.

Three m-failure group maintenance models for M/M/N unreliable queuing service systems

This paper considers group maintenance problems for an unreliable service system with N independent operating servers and a Markovian queue. A specific class of group maintenance policies is developed where the repair is started as soon as the number of failed servers reaches a predetermined threshold. This is actually a Quasi Birth-and-Death Process with two dimensions, the level for the arrival/service process and the phase for the failure/repair process. Two models with positive repair time and another with instantaneous repair are considered. The matrix geometric approach is applied to calculate the steady state distribution and the expected average cost for all three models. For the theoretical analysis, this paper proves that there exists an optimal group maintenance parameter m*, which can find the minimal average cost for all three models. Additionally, some mathematical properties and sensitivity analyses are numerically demonstrated based on various parameters. Finally, the comparisons of these three proposed models in many aspects are also discussed.