A geometric-process repair-model with good-as-new preventive repair

This paper studies a deteriorating simple repairable system. In order to improve the availability or economize the operating costs of the system, the preventive repair is adopted before the system fails. Assume that the preventive repair of the system is as good as new, while the failure repair of the system is not, so that the successive working times form a stochastic decreasing geometric process while the consecutive failure repair times form a stochastic increasing geometric process. Under this assumption and others, by using geometric process we consider a replacement policy N based on the failure number of the system. Our problem is to determine an optimal replacement policy N such that the average cost rate (i.e., the long-run average cost per unit time) is minimized. The explicit expression of the average cost rate is derived, and the corresponding optimal replacement policy can be determined analytically or numerically. And the fixed-length interval time of the preventive repair in the system is also discussed. Finally, an appropriate numerical example is given. It is seen from that both the optimal policies N** and N* are unique. However, the optimal policy N** with preventive repair is better than the optimal policy N* without preventive repair     

Maintenance scheduling and staffing policies in a wafer fabricationfacility

We examine how to reduce the adverse effects of machine down time by prioritizing production equipment for attention by a limited number of maintenance personnel. The maintenance scheduling policies use system information to determine which machines are the most critical at a given time. This information includes repair times, queue lengths, due dates, available capacity, and steady-state utilizations. The effects of different staffing levels are also considered. A discrete-event simulation model of a wafer fabrication facility is used to examine the performance of the different policies. Results indicate that the choice of maintenance scheduling policy can significantly affect system performance under restrictive staffing-levels. Moreover, factory performance is shown to be sensitive to small changes in staffing level     

Optimum policy of one-unit system with two types of maintenance and minimal repair

This paper deals with a one-unit system with minimal repair. Two policies (new Policy IV and Policy IV′) are considered. Under these policies, the Laplace transform of the point-wise availability and the stationary availability of the system are obtained using not the renewal theory but the supplementary variable method. And under new Policy IV, the optimum policy in the sense of the availability is discussed.     

A nonrenewable minimal-repair warranty policy with time-dependentcosts

Estimating warranty costs during the life cycle of a product is important to the manufacturer, who has to plan for creating a fund for warranty reserves. Replacement or repair costs associated with product-failure within the warranty period are drawn from this fund. This paper considers a policy where warranty is not renewed on product failure within the warranty period but the product is minimally repaired by the manufacturer. This implies that, on repair, the failure rate of the item remains the same as just prior to failure. Repair costs are assumed to depend on the product age. Such policies are suitable for complex and expensive products where repair typically involves a small part of the product. s-Expected warranty costs and amount of warranty reserves, based on a selected level of s-confidence, are derived. Applications of the results to various product market situations are considered. The results demonstrate how cost information can be used to decide and determine the warranty length     

Preventive Maintenance Policy Optimization of a Nuclear Reactor High Pressure Injection System Using a Reliability-Cost Model

Previous works have demonstrated that Genetic Algorithms (GA) and Probabilistic Safety Analysis (PSA) can be applied to maintenance policy optimization problems. Here, the flexible scheduling approach proposed in former works has been enhanced. Now, operational costs are considered in the objective function, resulting in a Reliability-Cost model for evaluating industrial systems performance. The GA searches for optimum preventive maintenance policies, which considers factors, such as: probability of needing a repair, costs of related to the repair, outage times, etc. A typical Pressurized Water Reactor High Pressure Injection System has been chosen as a case study. Results ratify the good performance of the method, allowing specific analysis on the weighting factors related to costs and reliability.     

Network policy languages: a survey and a new approach

A survey of current network policy languages is presented. Next, a summary of the techniques for detecting policy conflicts is given. Finally, a new language, path-based policy language, which offers improvements to these is introduced. Previous network policy languages vary from the very specific, using packet filters at the bit level, to the more abstract where concepts are represented, with implementation details left up to individual network devices. As background information a policy framework model and policy-based routing protocols are discussed. The PPL's path-based approach for representing network policies is advantageous in that quality of service and security policies can be associated with an explicit path through the network. This assignment of policies to network flows aids in new initiatives such as integrated services. The more stringent requirement of supporting path-based policies can easily be relaxed with the use of wild card characters to also support differentiated services and best-effort service, which is provided by the Internet today     

Satellite network management in a crowded spectral environment

The domestic satellite industry has grown from the start-up phase to a position of relative maturity under a variety of flexible regulatory policies. This article focuses on two areas of policy which are critical to future growth in the industry. First, the existing policy governing orbital assignments is reviewed and recommendations presented for future policy changes. Second, the article stresses the need for policies to insure that all participants can operate in an environment free of undue frequency interference. The article concludes that the public interest motivation behind these policies is best served by a balance between regulatory oversight and industry self-help.     

An Empirical Study of Consumer Perceptions and Comprehension of Web Site Privacy Policies

The U.S. legislation at both the federal and state levels mandates certain organizations to inform customers about information uses and disclosures. Such disclosures are typically accomplished through privacy policies, both online and offline. Unfortunately, the policies are not easy to comprehend, and, as a result, online consumers frequently do not read the policies provided at healthcare Web sites. Because these policies are often required by law, they should be clear so that consumers are likely to read them and to ensure that consumers can comprehend these policies. This, in turn, may increase consumer trust and encourage consumers to feel more comfortable when interacting with online organizations. In this paper, we present results of an empirical study, involving 993 Internet users, which compared various ways to present privacy policy information to online consumers. Our findings suggest that users perceive typical, paragraph-form policies to be more secure than other forms of policy representation, yet user comprehension of such paragraph-form policies is poor as compared to other policy representations. The results of this study can help managers create more trustworthy policies, aid compliance officers in detecting deceptive organizations, and serve legislative bodies by providing tangible evidence as to the ineffectiveness of current privacy policies.      

Paging and Registration in Cellular Networks: Jointly Optimal Policies and an Iterative Algorithm

This paper explores optimization of paging and registration policies in cellular networks. Motion is modeled as a discrete-time Markov process, and minimization of the discounted, infinite-horizon average cost is addressed. The structure of jointly optimal paging and registration policies is investigated through the use of dynamic programming for partially observed Markov processes. It is shown that there exist policies with a certain simple form that are jointly optimal. An iterative algorithm for policies with the simple form is proposed and investigated. The algorithm alternates between paging policy optimization, and registration policy optimization. It finds a pair of individually optimal policies. Majorization theory and Riesz's rearrangement inequality are used to show that jointly optimal paging and registration policies are given for symmetric or Gaussian random walk models by the nearest-location-first paging policy and distance threshold registration policies.     

Domains and policies in third generation mobile network managementsystems

The efficiency and manageability of network management architectures, are based largely upon structuring principles, which make intensive use of concepts such as management domains and management policies. The paper discusses architectural aspects of management for the universal mobile telecommunication system (UMTS), and suggests a model for the structuring of the managed system into management domains, and the subsequent control of it through policies. Explicit statements are made concerning the representation of the policy structure. Furthermore, the assistance that standardized support managed objects can provide in policy implementation is examined. Finally, a schema for capturing the interrelations between policy objects is provided, assisting in this way the effective management of the policy structure     

Optimal and Structured Call Admission Control Policies for Resource-Sharing Systems

Many communication and networking systems can be modeled as resource-sharing systems with multiple classes of calls. Call admission control (CAC) is an essential component of such systems. Markov decision process (MDP) tools can be applied to analyze and compute the optimal CAC policy that optimizes certain performance metrics of the system. But for most practical systems, it is prohibitively difficult to compute the optimal CAC policy using any MDP algorithm because of the "curse of dimensionality". We are, therefore, motivated to consider two families of structured CAC policies: reservation and threshold policies. These policies are easy to implement and have good performance in practice. However, since the number of structured policies grows exponentially with the number of call classes and the capacity of the system, finding the optimal structured policy is a complex unsolved problem. In this paper, we develop fast and efficient search algorithms to determine the parameters of the structured policies. We prove the convergence of the algorithms. Through extensive numerical experiments, we show that the search algorithms converge quickly and work for systems with large capacity and many call classes. In addition, the returned structured policies have optimal or near-optimal performance, and outperform those structured policies with parameters chosen based on simple heuristics     

A Model for Static Conflict Analysis of Management Policies

Management of today's distributed systems is becoming increasingly complex. There is an obvious requirement for a flexible mechanism to help manage such systems. Rule-based management is one such mechanism. However, in order for rule-based management to become widely usable a method is required by which conflicts between management policies (defined as rules) can be identified and resolved. This paper creates a set theoretic model for rules as a trituple of the relationship between the subject, action and target of a policy. It also identifies two classes of policy set — 'syntactically easy policy set' (SEPS) and 'syntactically non-easy policy set' (SNEPS). SEPSs are policies which are sets of all the Cartesian products of its subjects, actions and targets, whereas SNEPSs are only a subset of that Cartesian product. Conflict analysis of SEPSs has been handled in other papers; this paper addresses conflict analysis of SNEPSs. A method for resolving conflict is suggested. The paper also raises some issues that arise when considering a database of policies.     

Maintenance strategies following the expiration of warranty

The authors study two types of replacement policies, following the expiration of warranty, for a unit with an IFR failure-time distribution: (1) the user applies minimal repair for a fixed length of time and replaces the unit by a new one at the end of this period; and (2) the unit is replaced by the user at first failure following the minimal repair period. In addition to stationary strategies that minimize the long-run mean cost to the user, the authors also consider nonstationary strategies that arise following the expiration of a nonrenewing warranty. Following renewing warranties, they prove that the cost rate function is pseudo-convex under a fixed maintenance period policy. The same result holds under nonrenewing repair warranties, and nonrenewing replacement warranties when the optimal maintenance period of each cycle is determined as a function of the age of the item in use at the end of the warranty period     

Distributed policy processing in active‐service based infrastructures

More and more applications in the Internet are requiring an intelligent service infrastructure to provide customized services. In this paper, we present an infrastructure, which can transparently and effectively provide customized active‐services to end users and dynamically adapt to changing customized policies in large distributed heterogeneous environments. The infrastructure consists of two components: the policy agent and middleware box. Particularly, our technologies include: (1) Generic active‐service based infrastructure, where the policy agent can integrate policies requested by applications, and middleware boxes can transparently execute services and (2) Distributed policy processing in the middleware box. We study two policy partitioning schemes to achieve conflict‐free policies for distributed policy processing and guarantee the correctness of the policy execution. We conduct extensive performance evaluations on different schemes proposed. Our experimental results demonstrate that our policy partitioning schemes can effectively generate partition‐capable and conflict‐free policy sets. The evaluation results also show that distributed policy processing can achieve over 70% increase in performance/price ratio with proper assignment of the policy distribution degree compared to a purely centralized approach. Copyright © 2005 John Wiley & Sons, Ltd.     

保护协商证书隐私的策略签名方案

信任协商过程中主体间通过交互披露信任证和访问控制策略逐渐建立信任关系,策略和信任证都可以是隐私信息,需在建立信任的协商过程中得以保护。该文提出了一种基于策略签名方案(PBSS),它采用基于身份的环签名实现对符合协商策略的证书集匿名性以保护,以信任委托断言作为策略认证的身份信息,在符合协商策略的多组证书子集中用满足策略的一组证书签名消息,验证方能证明签名方提供符合策略的证书集,但不能获得签名方提供证书的真实信息。该文在随机预言模型中给出了PBSS方案的安全性证明,在BDH问题是困难的假设下,该方案被证明是安全的。本方案只需要2个配对运算,算法中配对计算量与策略的表达式和证书集大小无关,计算量上比Bagga(2006)提出的PCPC方案低。     

Optimal allocation of minimal & perfect repairs under resource constraints

The effect of a repair of a complex system can usually be approximated by the following two types: minimal repair for which the system is restored to its functioning state with minimum effort, or perfect repair for which the system is replaced or repaired to a good-as-new state. When both types of repair are possible, an important problem is to determine the repair policy; that is, the type of repair which should be carried out after a failure. In this paper, an optimal allocation problem is studied for a monotonic failure rate repairable system under some resource constraints. In the first model, the numbers of minimal & perfect repairs are fixed, and the optimal repair policy maximizing the expected system lifetime is studied. In the second model, the total amount of repair resource is fixed, and the costs of each minimal & perfect repair are assumed to be known. The optimal allocation algorithm is derived in this case. Two numerical examples are shown to illustrate the procedures.     

A Comparison of Allocation Policies in Wavelength Routing Networks*

We consider wavelength routing networks with and without wavelength converters, and several wavelength allocation policies. Through numerical and simulation results we obtain upper and lower bounds on the blocking probabilities for two wavelength allocation policies that are most likely to be used in practice, namely, most-used and first-fit allocation. These bounds are the blocking probabilities obtained by the random wavelength allocation policy with either no converters or with converters at all nodes of the network. Furthermore, we demonstrate that using the most-used or first-fit policies gives an improvement on call blocking probabilities that is equivalent to employing converters at a number of nodes in a network with the random allocation policy. These results have been obtained for a wide range of loads for both single-path and general mesh topology networks. The main conclusion of our work is that the gains obtained by employing specialized and expensive hardware (namely, wavelength converters) can be realized cost-effectively by making more intelligent choices in software (namely, the wavelength allocation policy).     

QoS provisioning and tracking fluid policies in input queueingswitches

The concept of tracking fluid policies by packetized policies is extended to input queueing switches. It is considered that the speedup of the switch is one. One of the interesting applications of the tracking policy in TDMA satellite switches is elaborated. For the special case of 2×2 switches, it is shown that a tracking nonanticipative policy always exists. It is found that, in general, nonanticipative policies do not exist for switches with more than two input and output ports. For the general case of N×N switches, a heuristic tracking policy is provided. The heuristic algorithm is based on two notions: port tracking and critical links. These notions can be employed in the derivation of other heuristic tracking policies as well. Simulation results show the usefulness of the heuristic algorithm and the two basic concepts it relies on     

解决IPsec/VPN安全策略问题的新方法

提出了一种解决IPsec／VPN安全策略问题的新方法。根据安全策略来决定对所有进入或外出的通信量进行安全操作，因此正确地指定与配置安全策略显得非常重要。目前针对单个安全网关是通过手工配置IPsec安全策略，这样效率非常低且易出错。在该方法中根据给定的要求，通过把整个通信量流分成互不相关的束，找出满足每束要求的子集，然后生成每束要求操作的策略。这样不仅减少了管理员的大量工作，而且还保证了策略的正确。     

The technical and legal dangers of code-based fair use enforcement

Digital rights management (DRM) mechanisms, built upon trusted computing platforms, promise to give content providers the ability to impose rules reliably and deterministically on end-user experiences with information resources ranging from literary works and scholarly publications to a vast array of entertainment content. DRM represents just the first wave of a class of technologies that aspire not only to implement copyright-protecting usage controls on computing devices, but increasingly to take on the enforcement of a broader set of organizational and public policies. The paper focuses on policy enforcement in the specific context of content use. It reviews the concepts and architecture of policy specification and enforcement, citing examples from the special case of DRM, and provides a detailed discussion of how usage control policies are evaluated in DRM systems. Since the expression and interpretation of policies is only one "layer" of the general problem of persistent policy enforcement, we consider the role that trusted computing systems can play in ensuring that computing agents interpret policies in reliable and deterministic ways. Finally, we consider the challenges inherent in the construction of technical mechanisms that mimic social policies.