Optimal information-dispersal for fault-tolerant communication over a burst-error channel

The (m,n) wireless information dispersal scheme (WIDS) is useful for fault-tolerant parallel wireless communications, where it can be used to tolerate up to n-m path (sub-channel) failures. This paper constructs a performance model of (m,n) WIDS used in wireless communications, and proposes an algorithm to find the optimal set of (m,n) with the highest reliability. This algorithm reduces the complexity of finding the candidate set of (m,n) from O(N/sup 2/) to O(N);N is the maximum number of available sub-channels.     

A heuristic task assignment algorithm to maximize reliability of adistributed system

Distributed systems potentially provide high reliability owing to the program and data-file redundancy possible. In many applications, high reliability is the major consideration for system design. Previous work has shown that the distribution of programs and data-files can affect the system reliability appreciably, and that redundancy in resources such as computers, programs, and data-files can improve the reliability of a distributed system. This work formulates a practical application for a reliability-oriented distributed task assignment problem which is NP-hard. Then, to cope with this challenging problem, a greedy algorithm is proposed, based on some heuristics, to find an approximate solution. The simulation shows that, in most cases tested, the algorithm finds suboptimal solutions efficiently; therefore, it is a desirable approach to solve these problems     

Optimal smoothing for guaranteed service

We consider the transmission of variable bit rate (VBR) video over a network offering a guaranteed service such as ATM VBR or the guaranteed service of the IETF. The guaranteed service requires that the flow accepted by the network has to be conforming with a traffic envelope σ; in return, it receives a service guarantee expressed by a network service curve β. Functions α and β are derived from the parameters used for setting up the reservation, for example, from the T-SPEC and R-SPEC fields used with the resource reservation protocol (RSVP). In order to satisfy the traffic envelope constraint, the output of the encoder is fed to a smoother, possibly with some look-ahead. The resulting stream is transported by the network; at the destination, the decoder waits for an initial playback delay and reads the stream from the receive buffer. We consider the problem of whether there exists one optimal strategy at the smoother which minimizes the playback delay and the receive buffer size, given the traffic envelope α and the service curve β. We show that there does exist such an optimal smoothing, and give an explicit representation for it. We also obtain a simple expression for the smallest playback delay and playback buffer size which can be achieved over all possible smoothing and playback strategies. We show that the computation of optimal smoothing and minimum playback delay do not depend on the past. We show that separate delay equalization is optimal in the constant bit rate (CBR) case, but not otherwise. We also apply the theory to the analysis of which T-SPEC should be requested by a source-destination pair, given some playback delay and buffer constraint, and given the path characteristics advertised in RSVP PATH messages     

基于位置的无线传感器网络可靠性区分服务机制

如何根据不同任务的不同可靠性需求来提供相应的服务是无线传感器网络所面临的最重要问题之一.结合基于位置的路由机制,给出衡量可靠性的量化度量模型,该模型无需全局网络拓扑信息.通过引入虚拟参考点,将数据的转发限制在特定区域从而减少无关传感器节点的能耗.分析了该区域与可靠性的函数关系,得到了可靠性随着参考点与源节点距离的增长而平方级增长的结论.在此基础上给出区分可靠性的服务机制.实验结果表明所提机制有效.     

Optimal design for software reliability and development cost

A process for reliability-related quality programming is developed to fill existing gaps in software design and development so that a quality programming plan can be achieved. The tradeoffs among system reliability improvement, resource consumption, and other relevant constraints through the management phase are investigated. A software reliability-to-cost relation is developed both from a software reliability-related cost model and from software redundancy models with common-cause failures. A generic N-component redundancy model is also developed. The software reliability optimization problems can be formulated into a mixed-integer programming problem     

Ways of increasing the service life of positive photoresists

The change in the functional properties of positive photoresists during their storage is a serious issue in photolithography. The recovery of the functional properties of photoresists, and especially, the quality of the edge of the formed elements and changes in their sizes compared to the sizes in the photostencil, is possible by the introduction of additives into the composition of positive photoresists which form hydrogen bonds with the novolak resins constituting them prior to their usage. Experimental verification of the correlation between the density of the hydrogen bonds and the photoresist resolution has been obtained.     

Optimal redundancies for reliability and availability of series systems

Five different series system configurations with standby units are compared based on their overall reliability and availability. The time-to-failure of a component and its repair time are assumed to have the negative exponential distribution. The mean time-to-failure, MTTF, and the steady-state availability, A_T(∞), are obtained for the first three simple configurations and comparisons are performed. For all five configurations, comparisons are made based on assumed numerical values given to the distribution parameters, as well as to the cost of the components. The configurations are ranked based on: MTTF, A_T(∞), cost and cost-benefit where benefit is either MTTF or A_T(∞).     

Optimal computation of k-to-l-out-of-n system reliability

An expansion theorem for the success of a k-to-l-out-of-n:G system is presented. Consequently, an optimal algorithm for computing the reliability of a k-to-l-out-of-n:G system with non-identical components is developed. This algorithm is implemented for the special case {(n+k) < 2(l+1)}, and its computation time is shown to compare favorably with those of existing algorithms. Charts of system reliability versus component reliability or other parameters are computer plotted and then utilized in a study of system performance.     

A methodology for predicting service life and design of reliability experiments

This paper summarizes a methodology for reliability prediction of new products where field data are sparse, and the allowed number & length of experiments are limited. The methodology relies on estimating a set where the unknown parameters are most likely to be found, calculation of an upper bound for the reliability metric of interest conditioned that the parameters reside in the estimated set, and tightening the bounds via design of experiments. Models of failure propagation, failure acceleration, system operations, and time/cycle to failure at various levels of fidelity & expert elicited information may be incorporated to enhance the accuracy of the predictions. The application of the model is illustrated through numerical studies.     

A new learning automata based approach for increasing utility of service providers

Utility is an important factor for serviceproviders, and they try to increase their utilities through adopting different policies and strategies. Because of unpredictable failures in systems, there are many scenarios in which the failures may cause random losses for service providers. Loss sharing can decrease negative effects of unexpected random losses. Because of capabilities of learning automata in random and stochastic environments, in this paper, a new learning automaton based method is presented for loss sharing purpose. It is illustrated that the loss sharing can be useful for service providers and helps them to decrease negative effect of the random losses. The presented method can be used especially in collaborative environments such as federated clouds. Results of the conducted experiments show the usefulness of the presented approach to improve utility of service providers.     

VoIP reliability: a service provider's perspective

Voice over IP services offer important revenue-generating opportunities, as well as many technical challenges in providing high-quality services. Users have come to expect highly available telecommunications services with high-quality voice. Service providers need reliable high-performance networks to meet user expectations, and must be able to guarantee performance and reliability to their customers. In converged voice and data networks, the network infrastructure must deliver very high quality and availability for some customer needs, while also providing low-cost high-capacity bandwidth for other needs. The use of quality of service mechanisms to provide prioritization for various traffic types is a key element needed for voice and data network convergence. However, it is not sufficient if the underlying networks are unreliable. The focus of this article is to address the reliability aspects of VoIP services, including the underlying IP networks.     

IPRAN承载网LTE业务的可靠性部署

随着LTE(Long Term Evolution)网络的大规模部署及多业务发展战略的推进,无线宽带化趋势越来越明显,IP化业务的承载需求成为主导。承载网的建设需要满足高质量承载、高可靠性、可维护可管理、低代价演进的LTE承载特性。本文以中国联通承载网IPRAN（IP Radio Access Network）方案为例,阐述下IPRAN承载网LTE业务的可靠性部署。     

Optimal design improving a communication network reliability

Improvement of the reliability of a communication network is an optimal problem that finds some links to add to the network such that the reliability of the network reaches a given level and the total cost of these links is minimized. A decomposition method based on branch and bound is used for solving the problem. In order to speed up the solution procedure, an upper bound on system reliability in terms of node degrees is applied. Specially, when the threshold P_o is large enough, a new algorithm, the cut tree algorithm, can more effectively give the optimal solution.     

Optimal reliability of systems subject to imperfect fault-coverage

This paper maximizes the reliability of systems subjected to imperfect fault-coverage. The results include the effect of common-cause failures and `maximum allowable spare limit'. The generalized results are presented and then the policies for some specific systems are given. The systems considered include parallel, parallel-series, series parallel, k-out-of-n, and NMR (k-out-of-(2k-1)) systems. The results are generalized for the non s-identical component case     

Web服务组合可靠性测试分析系统的设计与实现

由于Web服务组合复杂多样,传统的Web服务组合可靠性测试分析系统无法对其进行有效测试,测试分析的准确性较低。因此,提出基于Petri网的Web服务组合可靠性测试分析系统,Petri网能够构建高质量且可靠的Web服务组合分析系统,所构建的系统中各个模块能够同步运转且独立进行工作,细致描述了Petri网Web服务组合中的原子操作模块、顺序操作模块、选择操作模块和共同操作模块的工作流程,并给出Web服务的可靠性分析函数表达式,以及Web服务本体扩展流程的关键代码。实验结果表明,所设计的系统是有效的,并且具有较高的可靠性测试准确性。     

Optimal use of partial redundancy and the system reliability which results

Partial system triplication with a single majority vote is analysed to find (a) the region of superiority of partial triplication over total triplication and (b) over no redundancy, (c) the degree of partial triplication which maximises reliability, (d) the maximum system reliability produced by partial redundancy. Only approximate or numerical solutions to (a) and (c) have appeared previously. (b) and (d) are entirely new.     

Optimal real-time admission control algorithms for thevideo-on-demand (VOD) service

In order to meet the quality-of-service (QOS) requirements of the VOD (video-on-demand) service, and, on the other hand, to maximize the system throughput (revenue), it is essential that the admission control algorithm be carefully designed. Two new types of admission control schemes for the VOD service are proposed. They are the enhanced strict admission control (ESAC) and the probabilistic admission control (PAC). In the ESAC schemes, we propose to use more statistics (of small amount and easily pre-calculated) than the peak frame size of the stored video information to strictly guarantee the QOS requirement and to achieve potentially much higher throughput. In the PAC schemes, we propose to use similar statistics as used in the ESAC schemes to achieve even higher throughput at the cost of some small and controllable likelihood of lost/overdue data. The admission control problems are formulated as feasibility problems where different systems of simultaneous equations are considered. For each admission control scheme, if the corresponding system of simultaneous equations has a feasible solution, then admit the call request; otherwise, reject the call. Special structures of the systems are identified so as to facilitate the development of optimal real-time admission control algorithms. Efficient optimal algorithms are also proposed to calculate the minimal buffer requirement for a given performance objective     

Optimal media service selection scheme for mobile users in mobile cloud

Wireless Networks - Media cloud environments can provide a large number of multimedia services to mobile clients due to its flexibility and agility. However, a number of challenges need to be...     

Frequency-domain detection of superluminal group velocity in adistributed Bragg reflector

Using a free-space configuration and a frequency-domain detection setup, group velocities of electromagnetic waves in a distributed Bragg reflector are investigated. Experimental data indicate that, near the regions of minimal transmission in our configuration, the group velocity is 2.1 times faster than the speed of light in vacuum. A transmission model based on diagonalization of the transfer matrix is used to compare the experimental data and the theoretical calculations, and good agreement is obtained. An overview of the experimental uncertainties and their effects on the measured quantities is provided     

云存储系统中数据副本服务的可靠性保障研究

以数据节点与网络链路的可靠性因素分析为基础,提出了云存储系统的数据副本服务可靠性模型。根据访问可靠性与数据副本数量、用户访问量之间的关系,设计数据服务可靠性、副本生成时机、存储节点选择的确定方法,实现了副本分布、删除算法,并在云存储系统ERS-Cloud上进行一系列实验,结果表明该方法能够有效保障数据服务的可靠性,进一步降低副本的冗余存储数量。