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real-time Technology and Applications Symposium

作者： S.-W. Moon K.G. Shin J. Rexford Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA Network Mathematics Research Networking and Distributed Systems AT and T Research Laboratories Murray Hill NJ USA

In packet-switched networks, queueing of packets at the switches can result when multiple connections share the same physical link. To accommodate a large number of connections, a switch can employ link-scheduling algorithms to prioritize the transmission of the queued packets. Due to the high-speed links and small packet sizes, a hardware solution is needed for the priority queue in order to make the link schedulers effective. But for good performance, the switch should also support a large number of priority levels (P) and be able to buffer a large number of packets (N). So a hardware priority queue design must be both fast and scalable (with respect to N and P) in order to be implemented effectively. In this paper we first compare four existing hardware priority queue architectures, and identify scalability limitations on implementing these existing architectures for large N and P. Based on our findings, we propose two new priority queue architectures, and evaluate them using simulation results from Verilog HDL and Epoch implementations.

关键词： Packet switching Switches Traffic control Scheduling algorithm Asynchronous transfer mode Hardware design languages Communication system traffic control computer architecture Moon real time systems

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Task assignment and scheduling for open real-time control systems

Task assignment and scheduling for open real-time control sy...

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American Control Conference (ACC)

作者： Byung Kook Kim K.G. Shin Department of Electrical Engineering Korea Advanced Institute of Science and Technology Taejon South Korea Department of Elec. Engineering Comp. Sci Real-Time Computing Laboratory University of Michigan Ann Arbor MI USA

A problem for task assignment and scheduling on a network of processors is formulated and solved for open real-time control systems. In order to ensure smooth operation and good performance of open real-time control systems, one must analyze the problem of task assignment and scheduling during the conceptual system design stage. For this type of applications, we propose use of a performance index called the control latency, a weighted sum of feedback, command, and monitoring latencies. Given a set of tasks for a specific control application, the execution time of each task, and intra/inter-processor communication latencies, we have developed an optimal task assignment and scheduling algorithm by minimizing this performance index. Since this problem is NP-hard, we have employed a branch-and-bound algorithm to efficiently search for an optimal task assignment while maintaining task schedulability. A prototypical example of open-architecture control for CNC machines is presented to illustrate the good performance of the proposed algorithm.

关键词： real time systems Control systems Processor scheduling Performance analysis Communication system control Delay Scheduling algorithm Weight control Feedback Monitoring

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PRIAM: Polite rescheduler for intelligent automated manufacturing

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IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION 1996年第2期12卷 235-245页

作者： Tsukada, TK Shin, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

This paper considers the problem of rescheduling in a decentralized manufacturing system, Flexible manufacturing systems must be able to respond to unexpected disruptions, including schedule disruptions, However, when a cell controller in a decentralized system responds to a disruption, it may disrupt some other cell, because the actions taken at one cell may have some consequence at another cell, In the approach we propose, a controller at a disrupted cell tries to respond in a way which is likely to be least disruptive to other cells, through negotiation with controllers at other cells, This approach, which we call ''polite replanning,'' has the advantage of retaining much of any original distributed plan, while avoiding wide propagation of the disruption through the rest of the system, We apply this concept to the domain of distributed factory rescheduling, and describe PRIAM (polite rescheduler for intelligent automated manufacturing), a ''polite'' rescheduling architecture which is currently under development, Simulation results show that the use of negotiation in ''polite'' rescheduling prevents the wide propagation of disruption from an initial local disruption.

关键词： Manufacturing automation Job shop scheduling Manufacturing systems Control systems Production facilities Flexible manufacturing systems Pulp manufacturing Automatic control computer architecture Computational modeling

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Centralized wireless MAC protocols using slotted ALOHA and dynamic TDD transmission

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PERFORMANCE EVALUATION 1996年 27-8卷 331-346页

作者： Choi, SY Shin, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan Ann Arbor MI 48109-2122 USA

ALOHA scheme with dynamic time Division Duplexed (TDD) transmission is designed and analyzed. A centralized (i.e., star) network is adopted as the topology of a cell which consists of a base station and a number of mobile clients. In dynamic TDD transmission mode, a channel is time-shared for downlink and uplink transmissions under the dynamic access control of the base station. We first propose two MAC protocols (called TDD1 and TDD2) depending on how downlink and uplink transmissions are multiplexed. We then analyze throughput and average delay of TDD1 and an alternative ALOHA scheme using Frequency Division Duplexed (FDD) transmission. Finally, we evaluate the performance of these schemes, and compare TDD1 (calculations), TDD2 (simulations), and FDD (calculations). TDD schemes are found to always work as good as, or better than, FDD. TDD2 is observed to outperform TDD1 with respect to the downlink delay in the presence of light uplink and heavy downlink traffic loads while they work almost the same in other cases.

关键词： wireless LANs and MAC protocol star topology slotted ALOHA dynamic time Division Duplexing (TDD)

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EMERALDS: A microkernel for embedded real-time systems

EMERALDS: A microkernel for embedded real-time systems

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1996 IEEE real-time Technology and Applications Symposium, RTAS 1996

作者： Zuberi, Khawar M. Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122 United States

EMERALDS (Extensible Microkernel for Embedded real time Distributed Systems) is a real time microkernel designed for cost conscious small to medium size embedded systems. It not only offers standard OS services like multi threaded processes, real time scheduling, protected address spaces, message passing, semaphores, and timers, but does so in an efficient manner while keeping the kernel size to just tens of kilobytes. For efficiency, EMERALDS uses the novel approach of mapping the kernel into each user level address space, so even with full memory protection, system calls do not need context switches unless a user level server is involved. EMERALDS also provides the flexibility for users to add communication protocol stacks and device drivers as user level servers without modifying the kernel. We have completed a uniprocessor version of EMERALDS for the Motorola 68040 processor whose size is under 13 KBytes. Context switch takes under 12 /spl mu/s and system calls have overhead just 1.8 /spl mu/s more than that of simple subroutine calls. © 1996 IEEE.

关键词： Message passing

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A router architecture for real-time point-to-point networks 96

A router architecture for real-time point-to-point networks

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Proceedings of the 23rd annual international symposium on computer architecture

作者： Jennifer Rexford John Hall Kang G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI

ISBN: (纸本)9780897917865

Parallel machines have the potential to satisfy the large computational demands of emerging real-time applications. These applications require a predictable communication network, where time-constrained traffic requires bounds on latency or throughput while good average performance suffices for best-effort packets. This paper presents a router architecture that tailors low-level routing, switching, arbitration and flow-control policies to the conflicting demands of each traffic class. The router implements deadline-based scheduling, with packet switching and table-driven multicast routing, to bound end-to-end delay for time-constrained traffic, while allowing best-effort traffic to capitalize on the low-latency routing and switching schemes common in modern parallel machines. To limit the cost of servicing time-constrained traffic, the router shares packet buffers and link-scheduling logic between the multiple output ports. Verilog simulations demonstrate that the design meets the performance goals of both traffic classes in a single-chip solution.

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A causal message ordering scheme for distributed embedded real-time systems

A causal message ordering scheme for distributed embedded re...

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Reliable Distributed Systems

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 any distributed system, messages must be ordered according to their cause-and-effect relation to ensure correct behavior of the system. Causal ordering is also essential for services like atomic multicast and replication. In distributed real-time systems, not only must proper causal ordering be ensured, but message deadlines must be met as well. Previous algorithms which ensure such behavior include the /spl Delta/-protocol family and the MARS approach. However, both these algorithms give large response times by delaying all messages for a fixed period of time. In this paper we show that for small- to medium-sized real-time systems (consisting of a few tens of nodes) as are commonly used for embedded applications, it becomes feasible to extend the h-protocol so that instead of delaying all messages for a fixed period, each message is delayed according to its deadline. Our algorithm requires certain message deadlines to be adjusted by the application designer and we show that for small-scale applications such as those used in embedded systems, this adjustment is feasible and can be automated by the use of proper CAD tools.

关键词： real time systems Temperature sensors Multicast algorithms Delay effects Distributed computing Laboratories Mars Algorithm design and analysis Embedded system Design automation

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EMERALDS: a microkernel for embedded real-time systems

EMERALDS: a microkernel for embedded real-time systems

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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

关键词： real time systems Kernel Switches Protection Context Communication switching Costs Embedded system Message passing Protocols

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Resource management for real-time communication: making theory meet practice

Resource management for real-time communication: making theo...

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real-time Technology and Applications Symposium

作者： A. Mehra A. Indiresan K.G. Shin Real-time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

This paper focuses on bridging the gap between theory and practice in the management of host CPU and link resources for real-time communication. Using our implementation of real-time channels, a paradigm for real-time communication in packet-switched networks, we illustrate the tradeoff between resource capacity and channel admissibility, which determines the number and type of real-time channels that can be accepted for service and the performance delivered to best-effort traffic. We demonstrate that this tradeoff is affected significantly by the choice of implementation paradigms and the grain at which CPU and link resources are multiplexed amongst active channels. To account for this effect we extend the admission control procedure for real-time channels originally proposed using idealized resource models. Our results show that practical considerations significantly reduce channel admissibility compared to idealized resource models. Further, the optimum choice of multiplexing grain depends on several factors such as resource preemption overheads, the relationship between CPU and link bandwidth, and the interaction between link bandwidth allocation and CPU bandwidth allocation.

关键词： Resource management Bandwidth Channel capacity Channel allocation Delay Laboratories engineering management High-speed networks Quality of service Jitter

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Structuring communication software for quality-of-service guarantees

Structuring communication software for quality-of-service gu...

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real-time Systems Symposium (RTSS)

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

We propose architectural mechanisms for structuring host communication software to provide QoS guarantees. In particular, we present and evaluate a QoS sensitive communication subsystems architecture for end hosts that provides real time communication support for generic network hardware. This architecture provides services for managing communication resources for guaranteed QoS (real time) connections, such as admission control, traffic enforcement, buffer management, and CPU and link scheduling. The design of the architecture is based on three key goals: maintenance of QoS guarantees on a per connection basis, overload protection between established connections, and fairness in delivered performance to best effort traffic. Using this architecture we implement real time channels, a paradigm for real time communication services in packet switched networks. We evaluate the implementation to demonstrate the efficacy with which the architecture maintains QoS guarantees while adhering to the stated design goals. The evaluation also demonstrates the need for specific features and policies provided in the architecture.

关键词： Software quality Quality of service computer architecture Resource management Communication system traffic control Hardware Admission control Protection Packet switching Communication switching

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