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IEEE Conference on Decision and Control

作者： D.G. Meyer T.L. Piatt A.P. Engelmann J. Hauser Dept. of Electr. & Comput. Eng. Colorado Univ. Boulder CO USA Nonlinear and Real-Time Control Laboratory Electrical & Computer Engineering Department University of Colorado Boulder CO USA University of Colorado Boulder Boulder CO US

Builds on the previous work by the authors (1998) by defining local versions of cross-positivity for vector fields, especially as related to shifted cones. The paper also furthers the development of a stability theory by introducing preliminary concepts of directed stability. The motivation is to apply this theory to analyzing the control of certain directionally constrained models, such as those found in materials processing.

关键词： Materials processing

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Experiments on six commercial TCP implementations using a software fault injection tool†

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Software: Practice and Experience 1999年第12期27卷

作者： Scott Dawson Farnam Jahanian Todd Mitton Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122 USA

TCP, the de facto standard transport protocol in today's operating systems, is a very robust protocol that adapts to various network characteristics, packet loss, link congestion, and even significant differences in vendor implementations. This paper describes a set of experiments performed on six different vendor TCP implementations using ORCHESTRA, a tool for testing and fault injection of communication protocols. These experiments uncovered violations of the TCP protocol specification, and illustrated differences in the philosophies of various vendors in their implementations of TCP. The paper summarizes several lessons learned about the TCP implementations through these experiments. © 1997 John Wiley & Sons, Ltd.

关键词： TCP distributed systems communication protocols fault injection tool protocol testing

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Comparison of connection admission-control schemes in the presence of hand-offs in cellular networks 98

Comparison of connection admission-control schemes in the pr...

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4th Annual ACM/IEEE International Conference on Mobile computing and Networking, MobiCom 1998

作者： Choi, Sunghyun Shin, Kang G. Real-Time Computing Laboratory Department Of Electrical Engineering And Computer Science The University Of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)9781581130355

In this paper, we compare four distributed connection admission control schemes in cellular networks where the first two schemes are to keep the hand-off dropping probability below a target value, the third scheme is to guarantee no hand-off drops through a per-connection bandwidth reservation, and the fourth scheme uses another type of per-connection bandwidth reservation. The first scheme predicts the bandwidth required to handle hand-offs by estimating possible hand-offs from adjacent cells, then performs the admission control for each newly-requested connection. On the other hand, the second scheme predicts the total required bandwidth in the current cell by estimating both incoming and outgoing hand-offs at each cell. The third scheme requires the set of cells which the mobile with a newly-requested connection will traverse, and reserves bandwidth for each connection in each of those cells. The fourth scheme reserves bandwidth for each connection in the predicted next cell of a mobile. We adopt the history-based mobility estimation for the first two schemes. Using extensive simulations, the four schemes are compared quantitatively in terms of (1) important performance measures such as the hand-off dropping probability, connection-blocking probability, and bandwidth utilization, (2) dependency on the de-sign parameters, (3) dependency on the mobility estimation accuracy, and (4) complexity. The simulation results indicate that the first scheme is the most desirable in the sense that it achieves reasonably good performance while requiring much less memory and computation than the other three schemes. © Copyright ACM 1998.

关键词： Bandwidth

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Trajectory morphing for nonlinear systems

Trajectory morphing for nonlinear systems

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1998 American Control Conference, ACC 1998

作者： Hauser, John Meyer, David G. Nonlinear and Real-Time Control Laboratory Electrical and Computer Engineering Department University of Colorado Boulder CO 80309-0425 United States

In this paper nonlinear trajectory morphing is introduced. We show how it can explore the trajectory space of a nonlinear system. A trajectory tracking projection operator is defined for practical implementation of mo... 详细信息

ISBN: (纸本)0780345304

关键词： Nonlinear systems

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Predictive and adaptive bandwidth reservation for hand-offs in QoS-sensitive cellular networks 98

Predictive and adaptive bandwidth reservation for hand-offs ...

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Proceedings of the ACM SIGCOMM '98 conference on Applications, technologies, architectures, and protocols for computer communication

作者： Sunghyun Choi Kang G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan Ann Arbor Michigan

ISBN: (纸本)9781581130034

How to control hand-off drops is a very important Quality-of-Service (QoS) issue in cellular networks. In order to keep the hand-off dropping probability below a pre-specified target value (thus providing a probabilistic QoS guarantee), we design and evaluate predictive and adaptive schemes for the bandwidth reservation for the existing connections' handoffs and the admission control of new *** first develop a method to estimate user mobility based on an aggregate history of hand-offs observed in each cell. This method is then used to predict (probabilistically) mobiles' directions and hand-off times in a cell. For each cell, the bandwidth to be reserved for hand-offs is calculated by estimating the total sum of fractional bandwidths of the expected hand-offs within a mobility-estimation time window. We also develop an algorithm that controls this window for efficient use of bandwidth and effective response to (1) time-varying traffic/mobility and (2) inaccuracy of mobility estimation. Three different admission-control schemes for new connection requests using this bandwidth reservation are proposed. Finally, we evaluate the performance of the proposed schemes to show that they meet our design goal and outperform the static reservation scheme under various scenarios.

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Optimization of a real-time primary-backup replication service

Optimization of a real-time primary-backup replication servi...

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Reliable Distributed Systems

作者： Hengming Zou F. Jahanian Real-time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The primary-backup replication model is one of the commonly adopted approaches to providing fault tolerant data services. Its extension to the real time environment, however, imposes the additional constraint of timing predictability, which requires a bounded overhead for managing redundancy. The paper discusses the trade-off between reducing system overhead and increasing (temporal) consistency between the primary and backup, and explores ways to optimize such a system to minimize either the inconsistency or the system overhead while maintaining the temporal consistency guarantees of the system. An implementation built on top of the existing RTPB model (H. Zou and F. Jahanian, 1998) was developed within the x-kernel architecture on the Mach OSF platform running MK 7.2. Results of an experimental evaluation of the proposed optimization techniques are discussed.

关键词： Fault tolerance Timing Redundancy Fault tolerant systems real time systems Laboratories Environmental management Buildings Protocols Application software

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End-host architecture for QoS-adaptive communication

End-host architecture for QoS-adaptive communication

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real-time Technology and Applications Symposium

作者： T. Abdelzaher K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

Proliferation of communication-intensive real-time applications with "elastic" timeliness constraints such as streaming stored video, requires a new design for end-host communication subsystems. The design should (i) provide per-flow or per-service-class guarantees, (ii) maximize the aggregate utility of the communication service across all clients, (iii) gracefully adapt to transient overload, and (iv) avoid, if possible, starving lower-priority service classes during the period of sustained overload. The authors propose a QoS-optimization algorithm and communication subsystem architecture that satisfy the above requirements. It provides each client its contracted QoS, while adapting gracefully to transient overload and resource shortage. A new concept of flexible QoS contract is introduced, specifying multiple acceptable levels of service (or QoS levels for short) and their corresponding rewards for each client. Allowing clients to specify multiple QoS levels permits the server to perform QoS-optimization and degrade client's QoS under transient overload predictable, as specified in the QoS contract. Clients receive a money-back guarantee if the contracted QoS is violated by the server. The proposed resource-management mechanism maximizes server's total reward under resource constraints. They implemented and evaluated the architecture on a Pentium-based PC platform running under The Open Group (TOG) MK7.2 kernel, demonstrating the capability of the communication subsystem in meeting its design goals.

关键词： Contracts Degradation Aggregates computer architecture Resource management Laboratories Application software Streaming media Kernel Monitoring

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Nonlinear feedback control and observer design for the modern effusion cell

Nonlinear feedback control and observer design for the moder...

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IEEE Conference on Decision and Control

作者： M.K. Tucker D.G. Meyer Nonlinear and Real-Time Control Laboratory Department of Electrical and Computer Engineering University of Colorado Boulder CO USA

In the molecular-beam epitaxy (MBE) process precise control over thickness, composition, and doping profiles are critical for end device performance. This paper addresses the problem of accurately controlling the flux sources (effusion cells) used in MBE. We present a nonlinear compensator based on exact input-output linearization via feedback to control the flux of an effusion cell. The unmeasured states, necessary for implementation of the controller, are estimated by a Kalman-Bucy observer. We present simulations of the composite observer/nonlinear controller system, showing successful flux command following and elimination of shutter induced flux transients.

关键词： Feedback control Molecular beam epitaxial growth Observers Process control Thickness control Doping profiles Linear feedback control systems State estimation Control system synthesis Nonlinear control systems

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Efficient all-to-all personalized exchange in multidimensional torus networks

Efficient all-to-all personalized exchange in multidimension...

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International Conference on Parallel Processing (ICPP)

作者： Young-Joo Suh K.G. Shin Department of Computer Science and Engineering Pohang University of Science and Technology Pohang South Korea Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

This paper presents new algorithms for all-to-all personalized exchange in multidimensional torus-connected multiprocessors. Unlike existing message-combining algorithms in which the number of nodes in each dimension should be power-of-two and square, the proposed algorithms accommodate non-power-of-two tori where the number of nodes in each dimension need not be power-of-two. In addition, destinations remain fixed over a larger number of steps in the proposed algorithms, thus making them amenable to optimizations. Finally, the data structures used are simple, hence making substantial saving of message-rearrangement time.

关键词： Intelligent networks Multidimensional systems Samarium computer science Propagation delay Scattering computer networks Laboratories Communication switching Data structures

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Evaluation of fault-tolerance latency from real-time application's perspectives

Evaluation of fault-tolerance latency from real-time applica...

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IEEE Conference on Aerospace

作者： Hagbae Kim K.G. Shin Department of Electrical Engineering Yonsei University Seoul South Korea Real-Time Computing Laboratory Department of Electrical Engineering and Comput. Sci University of Michigan Ann Arbor MI USA

Information on Fault-Tolerance Latency (FTL), which is defined as the total time required by all sequential steps taken to recover from an error, is important to the design and evaluation of fault-tolerant computers used in safety-critical real-time control systems with deadline information. In this paper we evaluate FTL in terms of several random and deterministic variables accounting for fault behaviors and/or the capability and performance of error-handling mechanisms, while considering various fault-tolerance mechanisms based on the tradeoff between temporal and spatial redundancy, and use the evaluated FTL to check if an error-handling policy can meet the Control System Deadline (CSD) for a given real-time application.

关键词： Fault tolerance Delay Fault tolerant systems Redundancy Fault detection Control systems computer errors real time systems Application software Process control

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