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real-time Systems Symposium (RTSS)

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

Unlike deterministic real time communication in which excessive resources may be required for absolute performance guarantees, statistical real time communication seeks to achieve both probabilistic performance guarantees and efficient resource sharing. We propose a framework for statistical real time communication in ATM networks that provides delay guaranteed transport of MPEG coded video traffic with a statistically guaranteed cell loss ratio. In order to provide delay guaranteed communication service, we employ a modified version of Traffic-Controlled Rate-Monotonic Priority Scheduling (TCRM). We multiplex a set of statistical real time channels that share: (i) similar traffic characteristics into a common channel called a macro channel, and (ii) the resources of the macro channel. Individual statistical real time channels are given timeliness and probabilistic cell loss guarantees. A macro channel is serviced by the modified TCRM which improves link utilization and makes channel management simpler. Using the analysis of an M/D/1/N queueing system, we propose a procedure for determining the transmission capacity of a macro channel needed to statistically guarantee a cell loss ratio bound. Simulation results have shown our framework to work well as compared to the other approaches. The overall cell loss ratios for multi hop statistical real time channels are shown to be smaller than the pre-determined bounds.

关键词： Intelligent networks Histograms Telecommunication traffic Quality of service Delay Traffic control Laboratories computer science Argon Queueing analysis

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Refined design of random early detection gateways

Refined design of random early detection gateways

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IEEE Conference and Exhibition on Global Telecommunications (GLOBECOM)

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

Random early detection (RED) was proposed as an active gateway queue-management mechanism. This paper proposes to alter the RED design guideline that unconditionally allows transient congestion, and evaluates its impacts. This unconditional allowance of transient congestion is shown to be harmful when the queue is near full, because it causes buffer overflow at a gateway. Buffer overflow at a gateway leads to the global synchronization and oscillation of traffic load on the network. To effectively prevent buffer overflow at a gateway, the RED framework is refined in such a way that the gateway can detect a transient congestion in a timely manner and take actions to quench it when the queue is near full. Based on our simulation results, two enhancements are made in estimating average queue size. Equipped with these enhancements, the refined RED can strike a good balance between the allowance of transient bursty traffic and the avoidance of buffer overflow. Using extensive simulations, the refined RED is comparatively evaluated against and is shown to be superior to the original RED.

关键词： Traffic control Internet Bandwidth Buffer overflow Laboratories Guidelines Telecommunication traffic Explosives Transport protocols Aggregates

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Performance analysis of feedback synchronization for multicast ABR flow control

Performance analysis of feedback synchronization for multica...

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IEEE Conference and Exhibition on Global Telecommunications (GLOBECOM)

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

We present a balanced and unbalanced binary-tree model to explore the delay performance of feedback synchronization algorithms for multicast ABR flow control. Using this model, we analyze the feedback-delay performance scalability of the soft-synchronization protocol (SSP), which derives a single "consolidated" RM (resource management) cell at each multicast branch-point from feedback RM cells of different downstream branches that are not necessarily responses to the same forward RM cell. In contrast with the other existing schemes, SSP is shown to be able to effectively support synchronization of feedback RM cell and make the effective RM cell roundtrip time (RTT) virtually independent of the multicast tree's topology. Also derived is the optimal RM-cell update interval for SSP to minimize RM-cell RTTs for a given multicast tree.

关键词： Performance analysis Feedback Delay Multicast algorithms Scalability Topology Transient response Telecommunication congestion control Laboratories Resource management

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Connector modeling method for component extraction

Connector modeling method for component extraction

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Asia-Pacific Conference on Software Engineering

作者： Young Ran Yu Soo Dong Kim Dong Kwan Kim Department of Computer Science Soongsil University Seoul South Korea Real-time Computing Department ETRI Computer and Software Technology Laboratory Daejeon South Korea

As the component raises a principal factor in software engineering to ensure the productivity and reusability of the software, component extracting and implementation, component-based system construction, verification of component interfaces, and other related techniques raise significant issues in software engineering. As a reflex of this tendency, a connector model as a subsidiary tool is proposed to describe the interactions between components and software architecture. We propose a method that extracts the domain-specific components for a particular business domain using the connector model and specifies formal descriptions that explain the software architecture. The proposed component extraction method ensures the more earlier identification of components in the development cycle and decreases the number of potential modifications by making an estimate of the interfaces of a component. The formal description of software architecture gains a better understanding of architecture and also is used as a tool for verifying software at a higher abstraction level when changes take place.

关键词： Connectors Collaborative work Object oriented modeling Software engineering Software architecture computer architecture Programming Collaboration Protocols Radio access networks

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The use of task graphs for modeling complex system behavior

The use of task graphs for modeling complex system behavior

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International Symposium on Object-Oriented real-time Distributed computing

作者： A. Silberman A.D. Stoyen K. Sundaram Real-Time Computing Laboratory New Jersey Institute of Technology University Heights Newark NJ Center for Management of Information Technology and Department of Computer Science College of Information Science & Technology University of Nebraska at Omaha Nebraska Computer Associates

Task graphs have been used for the specification and analysis of real time systems for some time. We are currently developing a mobile code management system that uses such a representation for specification, analysis, and execution time scheduling, dispatch, and resource allocation decisions. We describe our three level limited hierarchical task graph model. We discuss graph topology, the use of task graphs for both specification and description, and planned software engineering tools that will take advantage of our model. We concentrate on the use of task graphs to model iteration, branching structures, optional execution, and parallelism within a function execution.

关键词： Electrical capacitance tomography computer science computer languages Java information retrieval Spatial databases Data engineering Relational databases Flow graphs Data analysis

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A fixed-priority-driven open environment for real-time applications

A fixed-priority-driven open environment for real-time appli...

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real-time Systems Symposium (RTSS)

作者： Tei-Wei Kuo Ching-Hui Li Real-Time and Embedded System Laboratory Department of Computer Science and Information Engineering National Chung Cheng University Chiayi Taiwan

This paper extends the useful concept of open systems proposed by W.S. Liu, et al. (1997) in scheduling real-time applications and non-real-time applications, where the schedulability of each real-time application can be validated independently of other applications in the system. We replace the underlying earliest-deadline-first OS scheduler of the open system architecture by W.S. Liu, et al. (1997) with a rate-monotonic OS scheduler. The motivation behind this work is that many existing operating systems may not support the earliest deadline first scheduling very well. We propose to use the idea of sporadic servers to preserve CPU cycles for applications. We also develop schedulability tests for real-time applications which adopt the rate monotonic scheduling algorithm, the earliest deadline first scheduling algorithm, the priority ceiling protocol, and the stack resource policy. We allow tasks in each application to share local and global non-preemptable resources. A global resource synchronization mechanism is proposed. This paper provides a fixed-priority-based alternative for the important open system architecture.

关键词： Processor scheduling Application software Open systems real time systems Testing Scheduling algorithm Operating systems Protocols Embedded system computer science

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Task graphs for mobile code-an introduction to ITGS

Task graphs for mobile code-an introduction to ITGS

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International Workshop on Object Orientation in Operating Systems

作者： Silberman Stoyen Real-Time Computing Laboratory New Jersey Institute of Technology Newark NJ USA Center for Management of Information Technology and Department of Computer Science College of Information Science & Technology University of Nebraska Omaha NE USA

We present ITGS, the Integrated Task Graph System. ITGS is a combined specification and analysis system for the design of complex real-time system, in particular those involving mobile code. ITGS data structures and analysis algorithms will be used throughout a systems design cycle. In addition, ITGS will either contain or interface with CASE tools and a run-time system or systems in order to provide "cradle-to-grave" support based upon the task-graph model.

关键词： Software requirements and specifications

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QoS provisioning with qContracts in web and multimedia servers

QoS provisioning with qContracts in web and multimedia serve...

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real-time Systems Symposium (RTSS)

作者： T.F. Abdelzaher K.G. Shin Department of Computer Science University of Virginia Charlottesville VA USA Department of Elec Engineering and Computer Science Real-Time Computing Laboratory University슠of슠Michigan Ann Arbor MI USA

The advent of performance-critical services such as online brokerage and e-commerce, as well as QoS-sensitive services such as streaming multimedia, makes existing FIFO servers incapable of meeting application QoS requirements. Re-designing server code to support QoS provisioning, on the other hand, is costly and time-consuming. To remedy this problem, we propose a new QoS-provisioning approach that does not require modification of server and QoS code. We develop a middleware, called qContracts, that can be transparently interposed between the server process and the operating system to achieve performance differentiation and soft QoS guarantees. The middleware enables reuse of existing legacy software in QoS-sensitive contexts, and off-loads QoS management concerns from future real-time service programmers. As an example, we show how the Apache web server is endowed with QoS support using qContracts on UNIX. Experimental results show the efficacy of the middleware in achieving the contracted QoS, while imposing less than 1% overhead.

关键词： Middleware Sockets Operating systems Programming profession Contracts computer science Laboratories Argon Business Context-aware services

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Configurable complete exchanges in 2D torus-connected networks

Configurable complete exchanges in 2D torus-connected networ...

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International Conference on Parallel Processing (ICPP)

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

Complete exchange communications are found necessary in many important parallel algorithms. This paper presents algorithms for complete exchange for 2D torus-connected multiprocessors. The proposed algorithms are unique in that they are configurable while trading the time for message startups against larger message sizes. At one extreme, the algorithm minimizes the number of message startups at the expense of increased message-transmission time. At the other extreme, the message-transmission time is reduced at the expense of increased number of message startups. The algorithms are structured such that intermediate solutions are feasible, i.e., the number of message startups can be increased slightly and the message-transmission time is correspondingly reduced. The ability to configure these algorithms makes the proposed algorithms distinct from others and leads to efficient portable implementation of complete exchange algorithms.

关键词： Intelligent networks computer networks computer science Laboratories Partitioning algorithms

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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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