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Reliable Distributed Systems

作者： M. Cukier J. Ren C. Sabnis D. Henke J. Pistole W.H. Sanders D.E. Bakken M.E. Berman D.A. Karr R.E. Schantz Center for Reliable and High-Performance Computing Coordinated Science Laboratory and Electrical and Computer Engineering Department University of Illinois Urbana-Champaign Urbana IL USA BBN Technologies Inc. Cambridge MA USA

Dependable distributed systems are difficult to build. This is particularly true if they have dependability requirements that change during the execution of an application, and are built with commercial off-the-shelf hardware. In that case, fault tolerance must be achieved using middleware software, and mechanisms must be provided to communicate the dependability requirements of a distributed application to the system and to adapt the system's configuration to try to achieve the desired dependability. The AQuA architecture allows distributed applications to request a desired level of availability using the Quality Objects (QuO) framework and includes a dependability manager that attempts to meet requested availability levels by configuring the system in response to outside requests and changes in system resources due to faults. The AQuA architecture uses the QuO runtime to process and invoke availability requests, the Proteus dependability manager to configure the system in response to faults and availability requests, and the Ensemble protocol stack to provide group communication services. Furthermore, a CORBA interface is provided to application objects using the AQuA gateway. The gateway provides a mechanism to translate between process-level communication, as supported by Ensemble, and IIOP messages, understood by Object Request Brokers. Both active and passive replication are supported, and the replication type to use is chosen based on the performance and dependability requirements of particular distributed applications.

关键词： Availability Application software computer architecture Hardware Fault tolerant systems Middleware Communication system software Quality management Resource management Runtime

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Statistical real-time channels on multiaccess bus networks

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IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 1997年第8期8卷 769-780页

作者： Chou, CC Shin, KG the Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan

Real-time communication with performance guarantees is expected to become an important and necessary feature of future computer networks. In this paper, we present a scheme which can provide real-time communication services with both absolute and statistical performance guarantees on multiaccess bus networks for given input traffic characteristics and performance requirements. The proposed scheme reserves network bandwidth for real-time connections according to their needs. It also allows for independent addition and deletion of real-time connections while preserving existing guarantees. Our extensive simulation results for motion video communication have shown the proposed scheme to outperform the other well-known schemes.

关键词： real-time communication real-time connection/channel multimedia systems FieldBus (SP50) multiaccess networks digital video transmission

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A fast algorithm for the minimax flow problem with 0/1 weights

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APPLIED MATHEMATICS LETTERS 1997年第1期10卷 11-16页

作者： Han, CC Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan Ann Arbor MI 48109-2122 U.S.A.

In this paper, we define the minimax flow problem and design an O(k . M(n, m)) time optimal algorithm for a special case of the problem in which the weights on arcs are either O or 1, where n is the number of vertices, m is the number of arcs, k (where 1 less than or equal to k less than or equal to m) is the number of arcs with nonzero weights, and M(n;m) is the best time bound for finding a maximum flow in a network.

关键词： design and analysis of algorithms f-saturated critical arcs maximum flow minimax flow residual network

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QoS negotiation in real-time systems and its application to automated flight control

QoS negotiation in real-time systems and its application to ...

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3rd IEEE Real-time Technology and Applications Symposium

作者： Abdelzaher, TF Atkins, EM Shin, KG Real- Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122 United States

ISBN: (纸本)0818680164

We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both predictability and graceful degradation requirements. QoS negotiation is shown to (i) outperform conventional ''binary'' admission control schemes (either guaranteeing the required QoS or rejecting the service request), and (ii) achieve higher application-perceived system utility. We incorporated the proposed QoS-negotiation model into an example realtime middleware service, called RTPOOL, which manages a distributed pool of shared computing resources (processors) to guarantee timeliness QoS for real-time applications. The efficacy and power of QoS negotiation are demonstrated for an automated flight control system implemented on a network of PCs running RTPOOL. This system is used to fly an F-16 fighter aircraft modeled using the Aerial Combat (ACM) F-16 Flight Simulator. Experimental results indicate that QoS negotiation, while maintaining real-time guarantees, enables graceful QoS degradation under conditions in which traditional schedulability analysis and admission control schemes fail.

关键词： Real time systems

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An efficient semaphore implementation scheme for small-memory embedded systems

An efficient semaphore implementation scheme for small-memor...

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3rd IEEE Real-time Technology and Applications Symposium

作者： Zuberi, KM Shin, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122 United States

ISBN: (纸本)0818680164

In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time an, object is accessed, and this represents significant run-time overhead. This a's of special concern in cost-conscious, small-size embedded systems such as those used in automotive applications - where costs must be kept to an absolute minimum. Object-oriented programming can be feasible an such applications only if the OS provides efficient, lour-overhead semaphores. We present a new semaphore implementation scheme which saves one context switch per semaphore lod operation in most circumstances and gives performance improvements of 18-25% over traditional semaphore implementation schemes.

关键词： Object oriented programming

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Comment on a pre-run-time scheduling algorithm for hard real-time systems

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IEEE Transactions on Software engineering 1997年第9期23卷 599-600页

作者： Abdelzaher, Tarek F. Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109 United States

In Shepard and Gagne [1], a branch-and-bound implicit enumeration algorithm is described whose purpose is to generate a feasible schedule, if any, for each processor on a multiprocessing node running hard real-time processes. The optimization criterion is to minimize process lateness defined as the difference between the process completion time and deadline. We show in this correspondence that this algorithm does not always succeed in finding a feasible solution, and describe the reason why the algorithm might fail. © 1997 IEEE.

关键词： Branch and bound scheduling algorithm Hard real-time systems Multiprocessors Pre-run-time scheduling Precedence constraints

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Experimental evaluation of failure-detection schemes in real-time communication networks 27

Experimental evaluation of failure-detection schemes in real...

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27th Annual International Symposium on Fault-Tolerant computing, FTCS 1997

作者： Han, Seungjae Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0818678313

An effective failure-detection scheme is essential for reliable communication services. Most computer network rely on behavior-based detection schemes: each node uses heartbeats to detect the failure of its neighbor nodes, and the transport protocol (like TCP) achieves reliable communication by acknowledgment/retransmission. In this paper, we experimentally evaluate the effectiveness of such behavior-based detection schemes in real-time communication. Specifically, we measure and analyze the coverage and latency of two failure-detection schemes-neighbor detection and end-to-end detection-through fault-injection experiments. The experimental results have shown that a significant portion of failures can be detected very quickly by the neighbor detection scheme, while the end-to-end detection scheme uncovers the remaining failures with larger detection latencies. © 1997 IEEE.

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Fast restoration of real-time communication service from component failures in multi-hop networks 97

Fast restoration of real-time communication service from com...

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Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication

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

ISBN: (纸本)9780897919050

For many applications it is important to provide communication services with guaranteed timeliness and fault-tolerance at an acceptable level of overhead. In this paper, we present a scheme for restoring real-time channels, each with guaranteed timeliness, from component failures in multi-hop networks. To ensure fast/guaranteed recovery, backup channels are set up a priori in addition to each primary channel. That is, a dependable real-time connection consists of a primary channel and one or more backup channels. If a primary channel fails, one of its backup channels is activated to become a new primary channel. We describe a protocol which provides an integrated solution to the failure-recovery problem (i.e., channel switching, resource re-allocation, ...). We also present a resource sharing method that significantly reduces the overhead of backup channels. The simulation results show that good coverage (in recovering from failures) can be achieved with about 30% degradation in network utilization under a reasonable failure condition. Moreover, the fault-tolerance level of each dependable connection can be controlled, independently of other connections, to reflect its criticality.

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An efficient semaphore implementation scheme for small-memory embedded systems

An efficient semaphore implementation scheme for small-memor...

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Real-time Technology and Applications Symposium

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

In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time an object is accessed, and this represents significant run-time overhead. This is of special concern in cost-conscious, small-size embedded systems-such as those used in automotive applications-where costs must be kept to an absolute minimum. Object-oriented programming can be feasible in such applications only if the OS provides efficient, low-overhead semaphores. The authors present a new semaphore implementation scheme which saves one context switch per semaphore lock operation in most circumstances and gives performance improvements of 18-25% over traditional semaphore implementation schemes.

关键词： Embedded system Costs Real time systems Object oriented programming Automotive applications Switches Microcontrollers Yarn Embedded computing Laboratories

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Experimental evaluation of failure-detection schemes in real-time communication networks

Experimental evaluation of failure-detection schemes in real...

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International Symposium on Fault-Tolerant computing (FTCS)

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

关键词： Intelligent networks Communication networks computer network reliability Delay Fault detection Telecommunication network reliability Application software Hardware Control systems computer networks

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