Recovery Block Research Articles

Optimal Component Selection Problem for Cots Based Software System under Consensus Recovery Block Scheme: A Goal Programming Approach

Cost, reliability and time are the three main quality attributes of a software system. Now days much software are designed on COTS component in order to facilitate timely development with reduced cost and improved reliability. Software deigned to handle critical control systems have very high reliability requirements. Fault tolerance is designed in these systems for some or all of the software modules so that execution can be resumed even after failure with minimal loss of data and time. Designing fault tolerance requires extra resources. Even though reliability requirement are very high the developers can’t spend endless resources on any project. This is a trade off problem between reliability and cost. Many such problems have been discussed in literature considering distinct objectives and constraints and have given good results. An effective approach to discuss this problem is to formulate a multi-objective problem with cost minimization and reliability maximization as the two objectives with an upper bound on cost and lower bound on reliability. In this paper we formulate this bi-criteria problem and discuss the solution methodology. The problem is formulated for consensus recovery block fault tolerant scheme. In case a feasible solution for the problem exists, criterion vector approach is used to solve the problem and otherwise if the bounds are contradictory a goal programming approach is used to solve the problem to obtain a compromised solution. Alternative goal solutions are obtained assigning different weights for the objective to facilitate the decision maker with correct decision.

Composite web QoS with workflow conditional pathways using bounded sets

In our previous work (Dillon and Mansour 2009), a stochastic reliability model of atomic web services was proposed. Using the well-known classic two-state bounded set technique, we developed a service-oriented model that dynamically calculates the reliability of composite web services with rollback recovery (Mansour and Dillon in IEEE Trans Serv Comput 4(4), 2011). In order to improve the Quality of Service, fault tolerance techniques have been introduced using recovery block adaptation. Our workflow was based on series-parallel structures that constitute parts of existing structures. It is worth mentioning that major service-oriented systems contain larger and more complex structures than the simple series and parallel ones. This is a limitation in our previous approach. In order to consider more realistic service-oriented systems, other main structures, such as AND, XOR and Loop, should be included into our model. In this article, our previous structures are generalized to include AND, XOR and Loops. In addition to generalized structures, we extended the existing two-state bounded set technique to include three-state systems. This extension was especially motivated by XOR-based structures. A comparative study between bounded set techniques and a new stochastic model is also presented. Our simulation results accurately reflect the performance of the new proposed model and confirm our theoretical studies. Furthermore, Monte Carlos simulations were performed and the results obtained clearly validate our stochastic model.

Dependability and Rollback Recovery for Composite Web Services

In this paper, we propose a service-oriented reliability model that dynamically calculates the reliability of composite web services with rollback recovery based on the real-time reliabilities of the atomic web services of the composition. Our model is a hybrid reliability model based on both path-based and state-based models. Many reliability models assume that failure or error arrival times are exponentially distributed. This is inappropriate for web services as error arrival times are dependent on the operating state including workload of servers where the web service resides. In this manuscript, we modify our previous model (for software based on the Doubly Stochastic Model and Renewal Processes) to evaluate the reliability of atomic web services. In order to fix our idea, we developed the case of one simple web service which contains two states, i.e., idle and active states. In real-world applications, where web services could contain quite a large number of atomic services, the calculus as well as the computing complexity increases greatly. To limit our computing efforts and calculus, we chose the bounded set techniques that we apply using the previously developed stochastic model. As a first type of system combination, we proposed to study a scheme based on combining web services into parallel and serial configurations with centralized coordination. In this case, the broker has an acceptance testing mechanism that examines the results returned from a particular web service. If it was acceptable, then the computation continues to the next web service. Otherwise, it involves rollback and invokes another web service already specified by a checkpoint algorithm. Finally, the acceptance test is conducted using the broker. The broker can be considered as a single point of failure. To increase the reliability of the broker introduced in our systems and mask out errors at the broker level, we suggest a modified general scheme based on Triple modular redundancy and N-version programming. To imitate a real scenario where errors could happen at any stage of our application and improve the quality of Service QoS of the proposed model, we introduce fault-tolerance techniques using an adaption of the recovery block technique.

2.5-Gb/s low-jitter low-power monolithically integrated optical receiver

A high-scale integrated optical receiver including a preamplifier, a limiting amplifier, a clock and data recovery (CDR) block, and a 1:4 demultiplexer (DEMUX) has been realized in a 0.25 μm CMOS technology. Using the loop parameter optimization method and the low-jitter circuit design technique, the rms and peak-to-peak jitter of the recovered 625-MHz clock are 9.4 and 46.3 ps, respectively, which meet the jitter specifications stipulated in ITU-T recommendation G.958. The recovered and frequency divided 625 MHz clock has a phase noise of ?83.8 dBc/Hz at 20 kHz offset in response to 2.5 Gb/s PRBS input data (223---1), and the 2.5 Gb/s PRBS data has been demultiplexed into four 625 Mb/s data. The power dissipation is only 0.3 W under a single 3.3 V supply (excluding output buffers).

A low-jitter low-power monolithically integrated optical receiver for SDH STM-16

A high-scale integrated optical receiver including a preamplifier, a limiting amplifier, a clock and data recovery (CDR) block, and a 1:4 demultiplexer (DEMUX) has been realized in a 0.25 μm CMOS technology. Using the loop parameter optimization method and the low-jitter circuit design technique, the rms and peak-to-peak jitter of the recovered 625 MHz clock are 9.4 and 46.3 ps, respectively, which meet the jitter specifications stipulated in ITU-T recommendation G.958. In response to 2.5 Gb/s PRBS input data (223−1), the recovered and frequency divided 625 MHz clock has a phase noise of −83.8 dBc/Hz at 20 kHz offset and the 2.5 Gb/s PRBS data has been demultiplexed into four 625 Mb/s data. The power dissipation is only 0.3 W under a single 3.3 V supply (excluding output buffers).

A Fuzzy Approach for Component Selection amongst Different Versions of Alternatives for a Fault Tolerant Modular Software System under Recovery Block Scheme Incorporating Build-or-Buy Strategy

Software projects generally have to deal with producing and managing large and complex software products. As the functionality of computer operations become more essential and yet more critical, there is a great need for the development of modular software system. Component-Based Software Engineering concerned with composing, selecting and designing components to satisfy a set of requirements while minimizing cost and maximizing reliability of the software system. This paper discusses the fuzzy approach for component selection using “Build-or-Buy” strategy in designing a software structure. We introduce a framework that helps developers to decide whether to buy or build components. In case a commercial off-the-shelf (COTS) component is selected then different versions are available for each alternative of a module and only one version will be selected. If a component is an in-house built component, then the alternative of a module is selected. Numerical illustrations are provided to demonstrate the model developed.

Parsonage-Turner Syndrome

Parsonage-Turner Syndrome (PTS), also referred to as idiopathic brachial plexopathy or neuralgic amyotrophy, is a rare disorder consisting of a complex constellation of symptoms with abrupt onset of shoulder pain, usually unilaterally, followed by progressive neurologic deficits of motor weakness, dysesthesias, and numbness. Although the etiology of the syndrome is unclear, it is reported in various clinical situations, including postoperatively, postinfectious, posttraumatic, and postvaccination. The identification of the syndrome in the postoperative patient remains a challenge as symptoms may easily be attributed to sequelae of surgical positioning, postoperative recovery, or postanesthetic block pain. The purpose of this review is to bring forth salient, identifiable factors which may assist the surgical clinician in identifying the condition sooner. An early and proper diagnosis affords the opportunity to treat the patient accordingly and to the satisfaction of both surgeon and patient.

OPTIMAL COMPONENT SELECTION OF COTS BASED SOFTWARE SYSTEM UNDER CONSENSUS RECOVERY BLOCK SCHEME INCORPORATING EXECUTION TIME

Computer based systems have increased dramatically in scope, complexity, pervasiveness. Most industries are highly dependent on computers for their basic day to day functioning. Safe & reliable software operations are an essential requirement for many systems across different industries. The number of functions to be included in a software system is decided during the software development. Any software system must be constructed in such a way that execution can resume even after the occurrence of failure with minimal loss of data and time. Such software systems which can continue execution even in presence of faults are called fault tolerant software. When failure occurs one of the redundant software modules get executed and prevent system failure. The fault tolerant software systems are usually developed by integrating COTS (commercial off-the-shelf) software components. The motivation for using COTS components is that they will reduce overall system development costs and reduce development time. In this paper, reliability models for fault tolerant consensus recovery blocks are analyzed. In first optimization model, we formulate joint optimization problem in which reliability maximization of software system and execution time minimization for each function of software system are considered under budgetary constraint. In the second model the issue of compatibility among alternatives available for different modules, is discussed. Numerical illustrations are provided to demonstrate the developed models.

Optimal component selection of COTS based software system under recovery block scheme incorporating execution time

For the effective development of the faulttolerant software system, cost, reliability and time are the important aspects to be considered. Ideally, any software system must be constructed in such a way that execution can resume even after failure without the loss of data and time. Such software systems which can continue execution even after the occurrence of faults are called fault tolerant software. Software is developed to perform a pre-decided number of functions that can be executed by the software system. When fault occurs, one of the redundant components get executed and prevents system failure. Advancement of technology and increasing software development cost has made the use of commercial off-the-shelf (COTS) software which builds system with reduced risk, cost and development time while increasing functionality and capability of the system. In this paper, two reliability models for fault tolerant recovery blocks are discussed. In the first optimization model, we formulate a joint optimization problem in which reliability maximization of software system and execution time minimization for each function of software system are considered under budgetary constraint. In the second model the issue of compatibility among alternatives available for different modules, is discussed. Numerical illustrations are provided to demonstrate the models developed in this paper.

Potential Role of PP2A in Regulating Ca2+‐Activated Cl− Channels in Pulmonary Artery Smooth Muscle Cells

Ca2+‐activated Cl− currents (IClCa) represent a major excitatory mechanism in vascular smooth muscle cells (SMCs). Our group previously showed that CaMKII and Calcineurin (CaN) exert opposed regulatory effects on IClCa in arterial SMCs. In this study, we determined whether other phosphatases also modulate IClCa in rabbit pulmonary artery (PA) myocytes. In a previous study, our group (Ayon et al., Faseb J. 22: 937.16, 2008) detected significant mRNA and protein expression of multiple isoforms for PP1, PP2A and PP2B in rabbit PA tissue homogenates. Recently, we have extended our studies to show significant cytoplasmic immunolabeling of PP1α, PP1β/d, PP1γ, and PP2A in isolated PASMCs. Results from previous patch clamp experiments on freshly isolated PA myocytes (Ayon et al., Faseb J. 22: 937.16, 2008) showed differential responses when manipulating endogenous PP1 and PP2A as opposed to supplying these phosphatases exogenously. To address this issue we examined the effects of Fostriecin (FOS), a highly specific inhibitor of PP2A, on an exogenous application of PP2A in the presence of ATP. Cells dialyzed with 150 nM FOS produced a delayed but pronounced block of exogenous PP2A‐induced recovery of IClCa which contrasted with the inability of FOS to alter the recovery of IClCa evoked by endogenous phosphatase(s). These results suggest that endogenous PP1 and CaN, not PP2A, are involved in IClCa regulation in PASMCs.

Blockade of NMDA receptor channels by 9-aminoacridine and its derivatives

9-Aminoacridine is known as “foot-in-the-door” NMDA receptor channel blocker because its binding prevents channel closure. Structural determinants of this mechanism of block were studied using a series of 9-aminoacridine derivatives. Experiments were performed on native NMDA receptors of hippocampal pyramidal neurons, isolated from rat brain slices. The use-dependence of block and kinetics of recovery from block were used to characterize mechanism of block produced by the compounds. Modifications, which preserve the flat structure of the tricyclic 9-aminoacridine moiety, affect blocking activity and kinetics but not the foot-in-the-door mechanism. On the contrary, disruption of the flat structure changes the mechanism of block to trapping. It is concluded that flat aromatic structure is one of the critical determinants of the action mechanism of 9-aminoacridine.

Exact Fault-Sensitive Feasibility Analysis of Real-Time Tasks

In this paper, we consider the problem of checking the feasibility of a set of n real-time tasks while provisioning for timely recovery from (at most) k transient faults. We extend the well-known processor demand approach to take into account the extra overhead that may be induced by potential recovery operations under earliest-deadline-first scheduling. We develop a necessary and sufficient test using a dynamic programming technique. An improvement upon the previous solutions is to address and efficiently solve the case where the recovery blocks associated with a given task do not necessarily have the same execution time. We also provide an online version of the algorithm that does not require a priori knowledge of release times. The online algorithm runs in O(m ldr k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) time, where m is the number of ready tasks. We extend the framework to periodic execution settings: We derive a sufficient condition that can be checked efficiently for the feasibility of periodic tasks in the presence of faults. Finally, we analyze the case where the recovery blocks are to be executed nonpreemptively and we formally show that the problem becomes intractable under that assumption.

Reliability growth modeling and optimal release policy under fuzzy environment of an N-version programming system incorporating the effect of fault removal efficiency

Failure of a safety critical system can lead to big losses. Very high software reliability is required for automating the working of systems such as aircraft controller and nuclear reactor controller software systems. Fault-tolerant softwares are used to increase the overall reliability of software systems. Fault tolerance is achieved using the fault-tolerant schemes such as fault recovery (recovery block scheme), fault masking (N-version programming (NVP)) or a combination of both (Hybrid scheme). These softwares incorporate the ability of system survival even on a failure. Many researchers in the field of software engineering have done excellent work to study the reliability of fault-tolerant systems. Most of them consider the stable system reliability. Few attempts have been made in reliability modeling to study the reliability growth for an NVP system. Recently, a model was proposed to analyze the reliability growth of an NVP system incorporating the effect of fault removal efficiency. In this model, a proportion of the number of failures is assumed to be a measure of fault generation while an appropriate measure of fault generation should be the proportion of faults removed. In this paper, we first propose a testing efficiency model incorporating the effect of imperfect fault debugging and error generation. Using this model, a software reliability growth model (SRGM) is developed to model the reliability growth of an NVP system. The proposed model is useful for practical applications and can provide the measures of debugging effectiveness and additional workload or skilled professional required. It is very important for a developer to determine the optimal release time of the software to improve its performance in terms of competition and cost. In this paper, we also formulate the optimal software release time problem for a 3VP system under fuzzy environment and discuss a the fuzzy optimization technique for solving the problem with a numerical illustration.

A Single-Version Algorithmic Approach to Fault Tolerant Computing Using Static Redundancy

&#x0D; &#x0D; &#x0D; This paper describes a single-version algorithmic approach to design in fault tolerant computing in various computing systems by using static redundancy in order to mask transient bit errors in processor-memory and registers. This low-cost single-version scheme relies on a time redundancy approach. This software scheme does not intend to tolerate software design bugs. Instead of using multiple and independent versions of an application program, this single-version approach uses multiple copies of an application program. This low-cost approach is useful to tolerate various malicious code modifications and transient-faults during the run time of a computing application system without incurring any additional cost for extra hardware and extra software versions as an N-version programming scheme (NVP) or a Recovery block scheme (RBS). This proposed model is a practical and usable one that demands an affordable redundancy in time and space. The proposed scheme is capable of tolerating various operational faults that might occur during the execution time of an application.&#x0D; &#x0D; &#x0D;

Quasi-atomic recovery for distributed agents

Distributed multi-agent systems are usually large-scale, involving a large number of agents and messages. Existing checkpoint and recovery strategies are not quite favorable to such systems due to either global recovery spread or runtime logging overhead associated with these strategies. This paper presents our work on the design of correct and efficient checkpoint and recovery strategies for distributed agent systems. The initial part of the paper introduces a formal model to capture the correctness of recovery that is applicable in general, including those used by existing techniques such as deterministic as well as non-deterministic, and single as well as simultaneous recoveries. In particular, notions of atomic and quasi-atomic recovery blocks are introduced to capture the subset of events nullified in a single recovery. It is proved that the correctness of multiple recoveries is guaranteed if a recovery technique ensures well-ordering of corresponding recovery blocks. The rest of the paper utilizes the features of agent communication protocols towards the design of a simple and efficient checkpoint protocol. In particular, agents interact with each other via well-defined agent communication protocols. Agent protocol sessions are group-based and all message interactions are localized inside such groups. A group checkpoint strategy is proposed that uses these features of locality and well-structured-ness for the purpose of both reducing runtime overhead and minimizing recovery spread. The resulted protocol creates strong and asynchronous group checkpoints, i.e., without any explicit kernel message or runtime message logging. An accompanying recovery protocol uses a notion of a protocol dependency graph to identify the minimal quasi-atomic recovery block corresponding to single or simultaneous agent crashes. Correctness of the recovery protocol is proved under the formal model. The paper concludes with a discussion on the significance and contrast of our research with other related works, followed by future research directions.

Comparison of failure dependent protection strategies in optical networks

The criticality of survivable network design and operation increases with increasing transmission speed. Path protection strategies achieve better network utilization compared to link protection strategies; however, the recovery time of connections in path protection strategies are higher than that in link protection strategies. This paper evaluates and compares the performance of three failure dependent strategies: (1) failure dependent path protection; (2) link protection; and (3) Diversion—a variant of the segmented path protection approach. In addition, a framework for evaluating the connection recovery time is also developed. The protection strategies are compared for their recovery time and blocking performance using extensive simluations.

Performance distribution of a fault-tolerant system in the presence of failure correlation

This paper considers software systems consisting of fault-tolerant components built from functionally equivalent but independently developed modules (versions) characterized by different reliability and execution times. The components are designed using either the N-version programming method or the recovery block scheme. In our general model, we also allow the number of versions that can run simultaneously to be limited because of hardware or computation time constraints. An analytical algorithm and a numerical procedure to evaluate system execution-time distributions are presented. This algorithm takes into account the positive correlation among failures in different versions by introducing common-cause failures (mutually exclusive and independent common causes are considered). Illustrative examples are presented.

Fault-tolerant embedded system design and optimization considering reliability estimation uncertainty

In this paper, we model embedded system design and optimization, considering component redundancy and uncertainty in the component reliability estimates. The systems being studied consist of software embedded in associated hardware components. Very often, component reliability values are not known exactly. Therefore, for reliability analysis studies and system optimization, it is meaningful to consider component reliability estimates as random variables with associated estimation uncertainty. In this new research, the system design process is formulated as a multiple-objective optimization problem to maximize an estimate of system reliability, and also, to minimize the variance of the reliability estimate. The two objectives are combined by penalizing the variance for prospective solutions. The two most common fault-tolerant embedded system architectures, N-Version Programming and Recovery Block, are considered as strategies to improve system reliability by providing system redundancy. Four distinct models are presented to demonstrate the proposed optimization techniques with or without redundancy. For many design problems, multiple functionally equivalent software versions have failure correlation even if they have been independently developed. The failure correlation may result from faults in the software specification, faults from a voting algorithm, and/or related faults from any two software versions. Our approach considers this correlation in formulating practical optimization models. Genetic algorithms with a dynamic penalty function are applied in solving this optimization problem, and reasonable and interesting results are obtained and discussed.

Clonidine effects on pain evoked SII activity in humans

We investigated pain evoked activity in the human secondary sensory cortex (SII) following clonidine administration in six healthy volunteers using multi-channel magnetoencephalography (MEG). Pain was elicited by electrical shocks applied intracutaneously to the fingertip. Subjects rated pain intensity and perceptions of tiredness and passiveness by numerical ranking scales. Each subject underwent two investigations, one week apart from each other, with clonidine doses of 1.5 or 3.0 μg/kg, administered intravenously in a random order and double-blinded. We applied a total number of seven blocks, each consisting of 60 painful stimuli, with one adaptation block, one pre-medication block, four post-medication blocks and one recovery block at the end of the session. MEG data were analysed by dipole reconstruction using CURRY R (Neuroscan, Hamburg) software package. Cortical activity in the contralateral SII cortex appeared with peak latencies of 118.5 ± 10 ms. This activity was significantly reduced by clonidine, in parallel with a reduction of pain intensity and enhancement of subjective tiredness and passiveness. There was, however, no significant correlation between MEG and subjective effects. Although both clonidine doses had similar effects, the higher dose induced longer changes. Results indicate that intravenous clonidine is able to relieve pain, but the exact mechanism of clonidine at the level of the SII cortex remains unclear. It is possible that clonidine interacts with the brainstem ascending system regulating vigilance and arousal which would explain the observed decrement of pain induced activity in SII. An additional more specific analgesic action at spinal level cannot be excluded.

OPTIMAL VERSION SEQUENCING IN FAULT-TOLERANT PROGRAMS

This paper considers software systems consisting of fault-tolerant components. These components are built from functionally equivalent but independently developed versions characterized by different reliability and execution times. Because of resource constraints, the number of versions that can run simultaneously is limited. The expected system execution time and its reliability (defined as probability of obtaining the correct output within a specified time) strictly depends on the sequence of versions execution. Different sequences can provide either maximal system reliability or minimal expected execution time. An optimization procedure is suggested for finding such sequences. The procedure is based on an algorithm for determining system execution time distribution that uses the moment generating function approach and on the genetic algorithm. Both N-version programming and the recovery block scheme are considered within a universal model. An illustrated example is presented.