Lotka-Volterra-like approach to large-scale systems stability

A new aggregation form of large-scale systems is proposed in this paper. It is of the ‘Lotka-Volterra’ type and appears natural for the generalized Lotka-Volterra large-scale (possibly time-varying) systems, which is shown in the paper. The Lotka-Volterra aggregation form yields a comparison system of the generalized Lotka-Volterra type, which is composed of a linear and a non-linear part. In addition this aggregation form leads to new stability conditions for time-varying large-scale systems, and enables an extension of Weissenberger's results on exponential stability domain estimates to the asymptotic stability domain estimate of time-varying systems. An advantageous feature of the system aggregation and stability analysis developed in the paper is the omission of requirements for (any particular, e.g. exponential) stability of disconnected subsystems.     

Dynamic distributed systems

This paper introduces a new methodology for building flexible and programmable multiprocessor systems. It is based on a distributed implementation of monitors which is supported by a system-wide address relocation mechanism. This provides the dynamic reallocation of processes and monitors within the system. Methods of implementing the communications subsystem based on a number of common network architectures are presented. An algorithm which effects dynamic resource allocation is presented. Its effect is that groups of processes which are interacting through a monitor will tend to accumulate at various sites in the system in a manner reflecting the dynamic interaction patterns of the program. This is accomplished without there being any centralized control, or even knowledge of the overall program interactions. The feasibility of the system has been investigated using a model system running on a loosely connected dual processor system.     

Independent recovery in large-scale distributed systems

In large systems, replication can become important means to improve data access times and availability. Existing recovery protocols, on the other hand, were proposed for small-scale distributed systems. Such protocols typically update stale, newly-recovered sites with replicated data and resolve the commit uncertainty of recovering sites. Thus, given that in large systems failures are more frequent and that data access times are costlier, such protocols can potentially introduce large overheads in large systems and must be avoided, if possible. We call these protocols dependent recovery protocols since they require a recovering site to consult with other sites. Independent recovery has been studied in the context of one-copy systems and has been proven unattainable. This paper offers independent recovery protocols for large-scale systems with replicated data. It shows how the protocols can be incorporated into several well-known replication protocols and proves that these protocols continue to ensure data consistency. The paper then addresses the issue of nonblocking atomic commitment. It presents mechanisms which can reduce the overhead of termination protocols and the probability of blocking. Finally, the performance impact of the proposed recovery protocols is studied through the use of simulation and analytical studies. The results of these studies show that the significant benefits of independent recovery can be enjoyed with a very small loss in data availability and a very small increase in the number of transaction abortions     

Object-based approach to programming distributed systems

Two kinds of parallel computers exist: those with shared memory and those without. The former are difficult to build but easy to program. The latter are easy to build but difficult to program. In this paper we present a hybrid model that combines the best properties of each by simulating a restricted object-based shared memory on machines that do not share physical memory. In this model, objects can be replicated on multiple machines. An operation that does not change an object can then be done locally, without any network traffic. Update operations can be done using the reliable broadcast protocol described in the paper. We have constructed a prototype system, designed and implemented a new programming language for it, and programmed various applications using it. The model, algorithms, language, applications and performance will be discussed.     

Adaptive diagnosis in distributed systems

Real-time problem diagnosis in large distributed computer systems and networks is a challenging task that requires fast and accurate inferences from potentially huge data volumes. In this paper, we propose a cost-efficient, adaptive diagnostic technique called active probing . Probes are end-to-end test transactions that collect information about the performance of a distributed system. Active probing uses probabilistic reasoning techniques combined with information-theoretic approach, and allows a fast online inference about the current system state via active selection of only a small number of most-informative tests. We demonstrate empirically that the active probing scheme greatly reduces both the number of probes (from 60% to 75% in most of our real-life applications), and the time needed for localizing the problem when compared with nonadaptive (preplanned) probing schemes. We also provide some theoretical results on the complexity of probe selection, and the effect of "noisy" probes on the accuracy of diagnosis. Finally, we discuss how to model the system's dynamics using dynamic Bayesian networks (DBNs), and an efficient approximate approach called sequential multifault; empirical results demonstrate clear advantage of such approaches over "static" techniques that do not handle system's changes.     

Adaptive event-triggered state estimation for large-scale systems subject to deception attacks

This paper addresses state estimation issues of large-scale systems with measurements subject to deception attacks,where the communication topology among sub-es...     

Adaptive rational Krylov subspaces for large-scale dynamical systems

The rational Krylov space is recognized as a powerful tool within model order reduction techniques for linear dynamical systems. However, its success has been hindered by the lack of a parameter-free procedure, which would effectively generate the sequence of shifts used to build the space. In this paper we propose an adaptive computation of these shifts. The whole procedure only requires us to inject some initial rough estimate of the spectral region of the matrix, while further information is automatically generated during the process. The approach is a full generalization to the nonsymmetric case of the idea first proposed in Druskin et al. (2010) [18] and it is used for two important problems in control: the approximation of the transfer function and the numerical solution of large Lyapunov equations. The procedure can be naturally extended to other related problems, such as the solution of the Sylvester equation, and parametric or higher order systems. Several numerical experiments are proposed to assess the quality of the rational projection space over its most natural competitors.     

A codesign approach for distributed systems

Distributed systems have become prevalent in response to the rapidly expanding Internet's demands. Their design presents new challenges because it involves the interaction of hardware and software. Continual marketplace innovation drives computing toward heterogeneity in both hardware and software and generates a complexity that goes beyond the earlier codesign approaches, which were developed for more homogeneous systems executing in non-distributed environments. Codesign of heterogeneous systems requires the support of a powerful modeling and simulation environment because analysis alone cannot deal with all the challenges such complex systems pose. We believe that modeling and simulation, using the discrete-event system specification modeling and simulation framework, are the most suitable vehicles to study the complexities associated with developing distributed-object computing systems     

Risk modeling in distributed, large-scale systems

Risk is inherent in distributed, large-scale systems. The paper explores the challenges of risk modeling in such systems, and suggests a risk modeling approach that is responsive to the requirements of complex, distributed, large-scale systems. An example of the use of the approach in the marine transportation system is given. The paper concludes with a discussion of limitations of the approach and of future work     

An approach to efficient distributed transactions

Most distributed systems proposed on the basis of the concept of atomic action or transaction strongly limit parallelism, thus reducing their level of efficiency. In this paper, features of efficiency in a distributed transaction system are investigated. Two mechanisms are proposed in order to enhance potential concurrency both among different transactions and within a single transaction during the commit phase:

- a synchronization mechanism has been designed which suggests an approach to concurrency control by allowing the release of acquired locks before transaction completion. The possibility of exploiting this mechanism to implement nested transactions is also discussed.

- a distributed commit protocol is developed which enhances concurrency among the participants in an atomic action, thus achieving quick execution with high modularity.

     

An integrated approach for simulation of mechatronic systems applied to a hexapod robot

Mechatronics is the integration of mechanism, electronics and computer control to produce a functional system. The design process involves application of many engineering areas and various approaches are possible. Computer programs are available in different engineering areas. Engineers define systems and inputs, and user-friendly programs establish mathematical models, solve them and give simulation outputs. In this study, SolidWorks is used for solid modeling and assembly, CosmosMotion is used for rigid body dynamics, CosmosWorks is used for finite element vibration and strength analyses, and Adlink module is used for actuator control. The integration of the design process is achieved with a main program developed in Visual Basic, which uses the application programming interface (API) capabilities. The procedure is applied to a hexapod robot. The robot has been produced to develop and test the procedure. CosmosMotion results are verified by the analytical results obtained from the dynamic equations of the hexapod. Besides known kinematic workspace definition of robots, kinetic and rigidity workspace concepts are introduced. Mechatronic systems can be designed and evaluated easily and effectively by using the design process developed in this work.     

Portable virtual cycle accounting for large-scale distributed cycle sharing systems

CPU cycle sharing among distributed heterogeneous computers is the key function in large-scale volunteer computing and desktop grid applications. One important problem in large-scale distributed cycle sharing system is how to account for the amount of computation work performed by a CPU cycle provider, in a uniform and portable fashion across heterogeneous hardware and operating system platforms. Such an accounting mechanism is especially desirable when CPU resources are traded and a lack of uniform workload accounting will hinder the enforcement of market-driven CPU pricing/trading policies in distributed cycle sharing systems. Java Virtual Machine (JVM) has proved to be a good match for distributed cycle sharing because of its abilities to run applications on a wide variety of platforms without modification (portability) and to host untrusted applications (safety). In this paper, we present the design, implementation, and evaluation of an efficient, application-transparent virtual cycle accounting scheme integrated into JVM. Our scheme achieves portable workload accounting across heterogeneous computing platforms by accounting for JVM virtual instructions instead of real processor cycles. Different from the existing JVM CPU accounting mechanisms that involve bytecode rewriting, our scheme is transparent to applications and does not require visible changes to application and library code interfaces which would break applications that use Reflection API. Moreover, our scheme is efficient via the use of processor registers for accounting. Our experimental results demonstrate both high accounting accuracy and low runtime overhead of virtual cycle accounting.     

A macroeconomic model for resource allocation in large-scale distributed systems

In this paper we discuss an economic model for resource sharing in large-scale distributed systems. The model captures traditional concepts such as consumer satisfaction and provider revenues and enables us to analyze the effect of different pricing strategies upon measures of performance important for the consumers and the providers. We show that given a particular set of model parameters the satisfaction reaches an optimum; this value represents the perfect balance between the utility and the price paid for resources. Our results confirm that brokers play a very important role and can influence positively the market. We also show that consumer satisfaction does not track the consumer utility; these two important performance measures for consumers behave differently under different pricing strategies. Pricing strategies also affect the revenues obtained by providers, as well as, the ability to satisfy a larger population of users.     

Adaptive channel allocation for large-scale streaming content delivery systems

Scheduling algorithms are used in content delivery systems to control the resource allocation rate. They not only improve system efficiency, but also increase user satisfaction. Lower renege rate and less waiting time for users are the main goals for a scheduling algorithm. Among existing algorithms, On-Demand strategy does not perform well, while rate control channel allocation policies performs much better. Pure-Rate-Control (PRC) and Multiple-Service-Class (MSC) belong to the rate control algorithms. MSC performs well, but a drawback is that it uses the Hot Index, which is hard to decide and has significant effects on the performance. In order to solve this problem and to improve the overall system performance, two new algorithms, Modified MSC(MMSC) and Adaptive Algorithm (AA), are proposed in this paper. Both of them solved the problem of MSC very well and improved the overall performance. For example, the renege rate of AA is about 5.4% less than that of MMSC, and about 9.8% less than that of MSC.

An integrated approach of designing functionality with security for distributed cyber-physical systems

The Journal of Supercomputing - In this work, we propose a multi-tier architectural model to separate functionality and security concerns for distributed cyber-physical systems. On the line of...     

A temporal approach for testing distributed systems

This paper deals with testing distributed software systems. In the past, two important problems have been determined for executing tests using a distributed test architecture: controllability and observability problems. A coordinated test method has subsequently been proposed to solve these two problems. In the present article: 1) we show that controllability and observability are indeed resolved if and only if the test system respects timing constraints, even when the system under test is non-real-time; 2) we determine these timing constraints; 3) we determine other timing constraints which optimize the duration of test execution; 4) we show that the communication medium used by the test system does not necessarily have to be FIFO; and 5) we show that the centralized test method can be considered just as a particular case of the proposed coordinated test method.     

An efficient TDMA start-up and restart synchronization approach for distributed embedded systems

A desired attribute in safety-critical embedded real-time systems is a system time and event synchronization capability on which predictable communication can be established. Focusing on bus-based communication protocols, we present a novel, efficient, and low-cost start-up and restart synchronization approach for TDMA environments. This approach utilizes information about a node's message length that forms a unique sequence to achieve synchronization such that communication overhead can be avoided. We present a fault-tolerant initial synchronization protocol with a bounded start-up time. The protocol avoids start-up collisions by deterministically postponing retries after a collision. We also present a resynchronization strategy that incorporates recovering nodes into synchronization.     

An approach for decomposition and reduction of dynamical models of large-scale power systems

This paper describes an approach for decomposition and reduction of dynamical models of largo scale power systems. In this approach the system is decomposed into two subsystems, the first one is described by a linear model while the second is described by a non-linear model. This decomposition is based on a derived criteria for linearization by which we can know the two subsystems a priori. Further, the linear subsystem model is reduced by aggregation and hence the order of the system is reduced. The results of the validity of this approach as applied to two different largo power systems are indicated.