Availability Of Computer Systems Research Articles

AVAILABILITY ASSESSMENT SIMULATIONS FOR ALLOCATING HUMAN RESOURCES IN AIRSPACE CONTROL CENTERS

Airspace control systems introduced automation into functions previously performed by human operators. This situation increased the dependence on the availability of computer systems, in which degraded operation events can reduce the service level at any controlled airspace. This paper presents a relationship between availability and allocation of human resources in these centers, where maintenance and operations personnel are occasionally asked to repair losses caused by automated functions. A simulation model for the Arena tool is presented, to access availability, and then the operational point of view is explored, focusing on the required availability scenarios. The results presented herein can help determine the size of operations and maintenance teams, considering the reliability and maintainability parameters of airspace control systems.

The normative response to problems of detection and investigation of cyber crime

Certain aspects of cyber crime represent the essence of the problems that authorities prosecuting crimes committed by abuse of information technology face everyday. All these specific features of cyber crime must be taken into consideration in order to understand and overcome difficulties in investigation and prosecution of crimes and trial of perpetrators. Given all the above and in order to respond to the specific nature of criminal activities committed using computer networks and systems, it is understandable that countries strive to adapt or complement the existing criminal law provisions. To create an appropriate legal framework for fighting this type of crime by means of criminal law, rules of substantive criminal law should incriminate certain behaviors and predict offenses against the confidentiality, integrity and availability of computer data and computer systems and rules of criminal procedure law should determine the appropriate powers of the authorities in order to identify sources of illicit actions and collect information on the committed offense and the offender which could be used as evidence in criminal proceedings.

Design and reliability, availability, maintainability, and safety analysis of a high availability quadruple vital computer system

With the development of high-speed railways in China, more than 2000 high-speed trains will be put into use. Safety and efficiency of railway transportation is increasingly important. We have designed a high availability quadruple vital computer (HAQVC) system based on the analysis of the architecture of the traditional double 2-out-of-2 system and 2-out-of-3 system. The HAQVC system is a system with high availability and safety, with prominent characteristics such as fire-new internal architecture, high efficiency, reliable data interaction mechanism, and operation state change mechanism. The hardware of the vital CPU is based on ARM7 with the real-time embedded safe operation system (ES-OS). The Markov modeling method is designed to evaluate the reliability, availability, maintainability, and safety (RAMS) of the system. In this paper, we demonstrate that the HAQVC system is more reliable than the all voting triple modular redundancy (AVTMR) system and double 2-out-of-2 system. Thus, the design can be used for a specific application system, such as an airplane or high-speed railway system.

Data Theft? Cybercrime and the Increasing Criminalization of Access to Data

The use of computers in the commission of crime, so-called ‘cybercrime’, presents a considerable challenge to law enforcement. Central to the prosecution of cybercrime is the offence of unauthorised access to a computer, or ‘hacking’. Originally conceived of as analogous to trespass, the trend in some jurisdictions has been toward punishing access to computer data per se. This issue also arises under the Council of Europe Convention on Cybercrime which criminalizes ‘offences against the confidentiality, integrity and availability of computer data and systems’. As the criminal law traditionally provides protection only to limited forms of information, the increasing use of the criminal law to protect computer data therefore confers on it a status not enjoyed by information stored in other forms. Drawing upon the laws of Australia, the United Kingdom and the United States, this article explores the increasing criminalization of access to computer data. It describes the evolution of cybercrime laws and considers ways in which problems of over breadth may be avoided. Questions will also be raised as to the appropriate role of the criminal law in protecting information.

Nutrition Informatics

Nutrition experts have used computers and electronic media since the early introduction of computer systems 4 decades ago ( 1 Youngwirth J. The evolution of computers in dietetics A review. J Am Diet Assoc. 1983; 82: 62-67 Google Scholar , 2 Hoover L.W. Computers in dietetics State of the art, 1976. J Am Diet Assoc. 1976; 68: 39-41 Google Scholar ). Once the availability of computer systems became widespread in the 1960s, dietetics professionals looked to the new tools to help decrease costs, eliminate task redundancy, and increase efficiency. The use of the “digital electronic computer” for nutrition tasks, although not widespread, was seen in almost every aspect of nutrition care before 1990 ( 3 Tullis I.F. Lawson V. Williams R. The digital computer in calculating dietary data. J Am Diet Assoc. 1965; 65: 384-386 Google Scholar ). L. B. Hoggle is a project management consultant, Health Pathways, Inc, Gaithersburg, MD. M. A. Michael is chief, Clinical Nutrition Services S. M. Houston is a senior project manager and nurse informaticist E. J. Ayres is assistant director for Ethics and Technology Development, all with the NIH Clinical Center, National Institutes of Health, Bethesda, MD.

A preliminary model of end user sophistication for insider threat prediction in IT systems

The dangers that originate from acts of IT system misuse by legitimate users constitute a separate category of threats with well documented consequences for the integrity, privacy and availability of computer systems and networks. Amongst the various properties of malicious legitimate users one of the most notable ones is the level of his/her sophistication. Various studies indicate that user sophistication and the potential to misuse IT systems are properties that are strongly related. This paper presents a methodology that automates the process of gauging end user sophistication. The establishment of suitable metrics to characterize end user sophistication is discussed followed by an experimental verification of the metrics on a sample of 60 legitimate users, using the UNIX Operating System. The results indicate that a combination of application execution audits and computational resource utilization metrics could be used to characterize the level of IT sophistication of an end user. Although additional testing in a greater variety of computational environments is required in order to validate the derived preliminary scheme, it is considered that the derived methodology could serve as a component of experimental insider threat prediction processes, or any other model that requires a procedure to measure the level of IT knowledge of a legitimate user base.

Micro-FE analyses of bone: state of the art.

The ability to provide a complete characterization of elastic properties of bone has vastly improved our understanding of trabecular bone mechanical properties. Based on this information, it was possible to validate several mechanical concepts related to the elastic behavior of trabecular bone that could not be validated earlier. With recently developed micro-CT scanners and the availability of large parallel computer systems, this technique has also enabled the determination of physiological bone tissue loading conditions from very large microFE models that can represent whole human bones in detail. Such analyses can provide the data needed for a better understanding of bone failure processes or cell mediated load adaptive remodeling processes. Computational demands for whole bone analyses, however, are still excessive. Unlike linear stress and strain analyses, the application of PFE to study non-linear processes, in particular bone failure mechanisms, is still in an early phase Results of recent studies, however, are promising and indicate that an accurate prediction of bone failure with these techniques is possible. Compelling features of such analyses are that they enable multi-axial failure criteria at the apparent level to be developed using primarily computational methods as well as that they can provide a basis for detailed analysis of micro-mechanics associated with trabecular failure at the apparent level. The application of microFE techniques to analyze bone in vivo is in an early stage as well. First results have indicated that, although the resolution of presently available in vivo imaging techniques (i.e. pQCT and MR) is much less than that of images used so far for uFE analyses, the technique can provide meaningful elastic properties of trabecular bone in vivo in most cases. It is expected that the remaining uncertainties in the microFE results can be eliminated as soon as the resolution of in vivo images is improved. With the fast developments in pQCT(47) and MR scanning, this will probably be in the near future.

Quantitative risk assessment of computer virus attacks on computer networks

This paper discusses the various types of malicious software, particularly computer viruses, which threaten computer network dependability, including such attributes as reliability, availability, safety and security of computer systems. Quantitative risk assessment of computer virus attacks on computer networks is investigated. To this end, an analytical model to study computer virus propagation in a typical network is developed and the results are presented. The model developed in this paper theoretically supports what is commonly performed in network management, where particular network resources are to be protected or preserved under hostile conditions. Some strategic controls are discussed.

Computing bounds on steady state availability of repairable computer systems

One of the most important performance measures for computer system designers is system availability. Most often, Markov models are used in representing systems for dependability/availability analysis. Due to complex interactions between components and complex repair policies, the Markov model often has an irregular structure, and closed-form solutions are extremely difficult to obtain. Also, a realistic system model often has an unmanageably large state space and it quickly becomes impractical to even generate the entire transition rate matrix. In this paper, we present a methodology that can (i) bound the system steady state availability and at the same time, (ii) drastically reduce the state space of the model that must be solved. The bounding algorithm is iterative and generates a part of the transition matrix at each step. At each step, tighter bounds on system availability are obtained. The algorithm also allows the size of the submodel, to be solved at each step, to be chosen so as to accommodate memory limitations. This general bounding methodology provides an efficient way to evaluate dependability models with very large state spaces without ever generating the entire transition rate matrix.

THE EFFECTIVENESS OF COMPUTER - ASSISTED INSTRUCTION IN A HORTICULTURE PLANT IDENTIFICATION CLASS

Plant identification is a prerequisite to many, if not all, horticulturally related classes. It typically has been taught through the use of live specimens, slides, and text books. Recently, computers have entered the picture as a possible tool to teach plant identification. Increased availability and sophistication of computer systems in the college setting have led to the increased use of computers in instruction. The objective of this study was to determine if there was a relationship between a student's learning style and academic achievement following computer assisted instruction. Undergraduate students enrolled in a plant identification class were involved in the study. Students learned plant identification either by: 1) viewing live specimens, 2) utilizing a computer instruction database system, or 3) combining live specimens with computer instruction. The students' cognitive knowledge was evaluated with pre and post tests. Learning style and attitude toward computer assisted instruction were also obtained.

Prophylaxis for “virus” propagation and general computer security policy

Viruses propagate easily with economic consequences that are difficult to estimate. Appropriate means of prevention, detection and protection are needed to preserve integrity and availability of computer systems. Prophylaxis effects first have to be reasearched to provide data for choice of appropriate measures according to the general security policy. Several models for virus propagations borrowed from biology have been developed in the continuous case to indicate that segregation controls imposed by file value increase the population density of virus. This confirm previous experimental results obtained by F. Cohen on personal computers and mainframes. Uniform virus prevention is highly recommended rather than segregation by file value which is basically the principle of most of centralized packages. Also, security measures offered by most of the resource access security systems are not effective for virus infections which can pass high security levels when they are introduced by trusted users. It is suggested to apply a flexible management prevention program adapted to environment, men and virus changes in relation with a normal use of information systems which have to play their economic and strategic roles without losses.Two perspectives are suggested. The first makes reference to the SRI's real-time Inrusion-Detection Expert System ( IDES ) based on statistical tests for abnormality, considering deviations from an expected behavior. It works for individual as well as group users or remote hosts. The second proposes the use of neural networks as another technical solution actually available. It should work for such an anomaly detection based on behavior segregation rather than value.

Validating complex computer system availability models

The authors report on experiences in validating complex computer-system availability models. A validation process, the availability models, and the data-collection process are described. An iteration of the model validation process emphasizing discrepancies between observed system behavior from data and from the model assumptions is presented. Analysis of data from five sites revealed that interruption dependencies on a device and across devices within a system exist. Furthermore, the frequency of, dependencies between, and downtime of device interruptions constitute differentiating characteristics of the causes of device interruptions. Data on partially available machine states, nonexponentially distributed machine downtimes, and nonstationarity of the machine interruption process are included. Validating the model assumptions is essential to model interpretation. Model accuracy is assessed. Exponentially distributed times between interruptions on a device and exponentially distributed device downtimes are not significant with respect to average measures of availability. The benefits of and issues for availability-model validation are summarized. >

Microcomputers and the Visually Impaired (Low‐vision to No‐vision)

Considers the need for and availability of computer systems (hardware and software) for the visually disabled. Describes image enlargement systems, speech synthesisers, Braille devices, and keyboard modifications. Lists relevant organisations and products which can help the visually impaired.

Bounding availability of repairable computer systems

Markov models are widely used for the analysis of availability of computer/communication systems. Realistic models often involve state space cardinalities that are so large that it is impractical to generate the transition rate matrix let alone solve for availability measures. Various state space reduction methods have been developed, particularly for transient analysis. In this paper we present an approximation technique for determining steady state availability. Of particular interest is that the method also provides bounds on the error. Examples are given to illustrate the method.

Office-based system for voice analysis.

There has been recent growing interest in the analysis of various electronically recorded signals as potential tools for objective assessment of vocal dysfunction. In the past, analysis of such signals required an expensive multitrack FM recorder, mainframe computer system, customized software, and significant time commitment. This report describes an adaptation of commercially available components that allow digital recording of multiple electronic signals, storage of data, and subsequent signal analysis using an inexpensive personal microcomputer system. Commercially available software for manipulation and examination signals is discussed as adapted for examination of glottographic and acoustic signals. The relatively inexpensive availability of similar computer systems will, hopefully, encourage assessment of the clinical applications of objective techniques of voice quality.

Calculating availability and performability measures of repairable computer systems using randomization

Repairable computer systems are considered, the availability behavior of which can be modeled as a homogeneous Markov process. The randomization method is used to calculate various measures over a finite observation period related to availability modeling of these systems. These measures include the distribution of the number of events of a certain type, the distribution of the length of time in a set of states, and the probability of a near-coincident fault. The method is then extended to calculate performability distributions. The method relies on coloring subintervals of the finite observation period based on the particular application, and then calculating the measure of interest using these colored intervals.

Reliability And Availability Modelling Of Complex Behavior Of Computer Systems

AbstractIncreased system complexity, changes in technology, complex interaction between reliability and performance of systems, and complex system behavior require a systematic approach to provide accurate analysis and prediction of system reliability and availability. The paper presents basic concepts, approaches, and features of the modelling for complex availability and reliability processes of computer systems utilizing Markov Models. Among the basic items of discussion are combinations of different types of failures, coverage, transition-reconfiguration processes, and repair dependencies. The paper focuses on the practical aspects of modelling and the interpretation of the results of analysis, which can be applied to a large class of fault-tolerant systems and local area networks.

Reliability modelling of redundant computer systems with common-cause failures

This paper presents a common-cause failure analysis of redundant computer systems. Three mathematical models representing a two-unit redundant computer system are developed. Computer system reliability, steady-state availability, mean time to failure and variance of time to failure formulas are developed. In addition, a general formula for redundant computer system steady-state availability is derived when the failed computer system repair times are described by Erlangian distribution. The computer system reliability, availability and mean time to failure plots are shown.

Probabilistic modeling of computer system availability

System availability is becoming an increasingly important factor in evaluating the behavior of commercial computer systems. This is due to the increased dependence of enterprises on continuously operating computer systems and to the emphasis on fault-tolerant designs. Thus, we expect availability modeling to be of increasing interest to computer system analysts and for performance models and availability models to be used to evaluate combined performance/availability (performability) measures. Since commercial computer systems are repairable, availability measures are of greater interest than reliability measures. Reliability measures are typically used to evaluate nonrepairable systems such as occur in military and aerospace applications. We will discuss system aspects which should be represented in an availability model; however, our main focus is a state of the art summary of analytical and numerical methods used to solve computer system availability models. We will consider both transient and steady-state availability measures and for transient measures, both expected values and distributions. We are developing a program package for system availability modeling and intend to incorporate the best solution methods.

Modeling and analysis of computer system availability

Modeling and analysis of computer system availability