• Journal of KIISE:Computer Systems and Theory
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• v.28 no.11
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• pp.573-580
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• 2001

When tasks access shared resources in real-time systems, the unbounded priority inversion may occur. In such cases it is impossible to guarantee the schedulability of real-time tasks. Several resource access protocols have been proposed to bound the duration of priority inversion and sufficient conditions are given to guarantee the schedulability of periodic task set. In this paper, we show an improved sufficient condition for schedulability when the dynamic priority ceiling protocol is used. Our approach exploits the fact that a lower priority task can continue to execute as far as the higher priority tasks do not miss their deadlines. This permitting execution time of the higher priority tasks for a lower priority task can be excluded from the worst-case blocking time of the higher priority tasks. Since the worst-case blocking time of tasks can be reduced, the sufficient condition for schedulability of dynamic priority ceiling protocol becomes further tight.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.5
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• pp.453-461
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• 1989

Mean waiting time for each priority packet of each node in packet based priority token ring local area networks(LAN) was approximately analyzed using Bux's token ring LAN results which have not considered priority and Cohbam's head of line(HOL) priority results. In this paper, priority reservation method suggested in the IEEE 802.5 standard was not used. Relative error between numerical results which was presented in this paper and simulation results was identified by +-5%. For traffic intenity, number of node, packet length, transmission speed, line length, token latency, number of priority class and traffic percentage to some heavy trafficd node, mean waiting time of each priority was analyzed.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.793-805
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• 2001

In the recent priority system, high-priority packet will be served first and low-priority packet will be served when there isn\`t any high-priority packet in the system. By the way, even high-priority packet can be blocked by HOL (Head of Line) contention in the input queueing System. Therefore, the whole switching performance can be improved by serving low-priority packet even though high-priority packet is blocked. In this paper, we study the performance of preemptive priority in an input queueing switch for high speed switch system. The analysis of this switching system is taken into account of the influence of priority scheduling and the window scheme for head-of-line contention. We derive queue length distribution, delay and maximum throughput for the switching system based on these control schemes. Because of the service dependencies between inputs, an exact analysis of this switching system is intractable. Consequently, we provide an approximate analysis based on some independence assumption and the flow conservation rule. We use an equivalent queueing system to estimate the service capability seen by each input. In case of the preemptive priority policy without considering a window scheme, we extend the approximation technique used by Chen and Guerin [1] to obtain more accurate results. Moreover, we also propose newly a window scheme that is appropriate for the preemptive priority switching system in view of implementation and operation. It can improve the total system throughput and delay performance of low priority packets. We also analyze this window scheme using an equivalent queueing system and compare the performance results with that without the window scheme. Numerical results are compared with simulations.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2000.10a
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• pp.259-262
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• 2000

The Cross-impact Hierarchy Process (CHP), an extended model of the Analytic Hierarchy Process(AHP) which is linked to Cross Impact Analysis(CIA), is a powerful decision making tool to assist in the ranking of large number of dependent technological alternatives. In this paper, we will describe an application of the CHP to the aerospace industry. We here conducted a questionnaire survey for S company that is one of the representative aerospace companies in Korea. A questionnaire was designed to obtain both the priority with dependence (the CHP priority) and the priority with independence (the AHP priority) in order to compare the priority derived by each of two methods. The hierarchy in this case study is concerned with priority setting for R&D area to ensure dependent aerospace design technology of the company, The result shows that there exists the difference hard to neglect between the final priorities gained by two methods.

• Journal of the Korean Institute of Landscape Architecture
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• v.24 no.1
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• pp.42-54
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• 1996

Many of urban parks which have been designated for urban planning regulation are not well developed because the priority of investment is inferior to that of other public facilities. Park development is an urgent urban policy and it is hard to decide priority among parks. Therefore, it is necessary to evaluate the priority of park development. Thus the Analytic Hierarchy Process has been introduced because it is suitable for achieving objectivity by collecting the professional opinions. The goals of park development are evaluated by AHP method and the priorities among goals are conservation of natural environment, satisfying the residents' residents' needs, population density, regional pollution, land acquisition cost, ratio of greeneries and facilities within park areas. Priority of park development is decided by the standardization of each individual inventory data and considering of the professional opinions. Among the multi-attribute judgement methods, AHP method may be the most widely used. Despite the critical evaluations of the AHP, such as limitation of the nine-point scale and the rank reversal problem, application of AHP to decide the priority of park development is suitable for actual circumstances.

• The KIPS Transactions:PartA
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• v.16A no.3
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• pp.189-198
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• 2009

The traditional interrupt-based protocol processing at end hosts has two priority-inversion problems. First, low-priority packets may interrupt and delay high-priority process executionssince interrupts have the highest priority in most operating systems. Second, low-priority packet may delay high priority packets when they arrive almost simultaneously since interrupt processing is performed in a FCFS (first come, first served) order. These problems can be solved by a priority-based protocol processing policy and implementation. However, general priority-based schemes commonly have the problem of starvation and cannot support the each network flow requiring the mutually exclusive QoS since the packets are processed in the FCFS order. Therefore, the priority-based schemes are not appropriate for different QoS-demanding applications. In this paper, we present a bottom-half-based approach that relies on priority- and budget-based processing. The proposed approach allows us to solve both the starvation and priority-inversion problems, and further enables effective QoS isolation between different network connections. This feature also enables bounding the protocol processing time at an end host. We finally show through experiments that the proposed approach achieves QoS isolation and control.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.35 no.4
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• pp.162-170
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• 2012

We propose a new priority discipline called the strict T-preemptive priority discipline, and derive the waiting time distributions of each class in the strict T-preemptive priority M/G/1 queue. Using this queueing analysis, we evaluate the performance of an opportunistic spectrum access in cognitive radio networks, where a communication channel is divided into time slots, a licensed primary user is assigned to one channel, and multiple unlicensed secondary users may opportunistically exploit time slots unused by the primary user. We also present a numerical example of the analysis of the opportunistic spectrum access where the arrival rates and service times distributions of each users are identical.

• Industrial Engineering and Management Systems
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• v.3 no.1
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• pp.12-21
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• 2004

This paper investigates the design of a priority rule in a multi-product disassembly environment. Specifically, it is concerned with product scheduling by which the inventory control of disassembled parts can be incorporated into a priority rule to reduce part lead times. The part lead time consists of two components: flow time and supply delay. The primary focus of the paper is on the development of a disassembly priority rule that aims to reduce the supply delay. We propose a priority rule, called Minimum Distance (MD) rule, to improve the supply delay performance. Finally, we provide a comparative analysis on the performance of traditional rules and the new rule proposed in this paper via a simulation model.

• IEMEK Journal of Embedded Systems and Applications
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• v.15 no.2
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• pp.95-101
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• 2020

In situations where mobile robots are operated either by autonomous systems or human operators, such as smart factories, priority-based teleoperation is crucial for the multiple operators with different priority to take over the right of the robot control without conflict. This paper proposes a priority-based teleoperation system for multiple operators to control the robots. This paper also introduces an efficient joystick-based robot control command generation algorithm for differential-drive mobile robots. The proposed system is implemented with ROS (Robot Operating System) and embedded control boards, and is applied to Pioneer 3AT mobile robot platform. The experimental results demonstrate the effectiveness of the proposed joystick control command algorithm and the priority-based control input selection.

• Journal of the Korea Society for Simulation
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• v.2 no.1
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• pp.13-22
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• 1993

In a multiple-bus multiprocessor system in which processors and memory modulus are interconnected through system buses, time delay due to bus contention degrades system performance. In order to reduce such a problem , and optimal bus arbitration scheme and its hardware are neccessary. In this study, performaces of four arbitration schemes are analyzed and compared : fixed-priority, equal-priority, rotating-priority and round-robin priority schemes. For the study, the software simulator of a multiple-bus multiprocessor system is developed by using SLAM II. Simulation results show that, when memory sccesses are evenly distributed to all memory modulus, round-robin priority scheme provides the best performance. But when a hot spot exists, the use of the fixed priority scheme results in the shortest access time.