共查询到19条相似文献,搜索用时 745 毫秒
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随着网络的发展,网络流量越来越大,拥塞问题越来越严重,各种队列管理算法应运而生,然而这些算法在丢弃数据包时却忽略了数据包的优先级或对优先级队列的处理不够完善。文章先介绍了优先级队列以及一些优先级队列的管理办法,然后提出利用平衡二叉树这种数据结构实现对优先级队列的入队列和出队列操作,最后提出一种对RED(随机提前探测)算法的改进方案。 相似文献
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针对Parlay网关过载控制的需求,提出了一种基于优先级和漏桶算法的Parlay过载控制算法.该算法一方面解决了优先级算法的"饿死"现象;一方面也解决了漏桶算法的网络资源的浪费的问题.仿真试验表明:该算法能有效地解决Parlay网关中过载的问题,且易于实现. 相似文献
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本文在分析RED利用EWMA形式计算平均队列长度的局限性的基础上,提出了一种改进的RED算法。该改进RED算法在计算平均队列长度时考虑了当前队列长度的真实情况,并将两者结合起来进行丢弃决策。仿真结果表明改进RED算法在分组丢弃比例和链路利用率上部优于RED。 相似文献
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一种支持区分服务的模糊公平分组丢弃算法 总被引:2,自引:0,他引:2
随机早期检测(RED)算法是目前Internet中广泛使用的一种缓存管理算法,对RED算法进行改进以提高公平性以及对网络动态变化的适应性一直是主动队列管理的研究重点之一。该文引入新的变量分享指数,取代单个业务流缓存占用量来表征不同业务流对网络资源的占用情况,以克服缓存占用量表征公平性的缺陷。同时,在无线网络中对分享指数的定义进行推广,使其同时兼顾公平性和系统性能(信道条件)。通过对分享指数和队列长度共同制定规则,提出了一种基于模糊逻辑控制的缓存管理算法。算法在根据缓存队列长度计算丢弃概率时,根据不同流对网络资源的占用情况(即分享指数)进一步决定增加或减小相应的丢弃概率,从而可利用不同流之间的差异以加速缓解拥塞,具有更好的自适应性和公平性。仿真表明,采用该算法后,系统性能得到改善。 相似文献
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Floyd提出的随机早丢弃(RED,random carly detection)是基于传统的泊松(Possion)模型,不适应网络流量普遍呈现自相似性的特点。基于此目的,提出了一种新的RED算法——Hurst加权随机早检测算法(HWRED,Hurst weighted random early detection)。新算法能够根据输入流量的自相似系数Hurst,调整RED算法参数。仿真结果表明,新算法提高了队列长度的稳定性,减少了丢包率、排队时延和排队抖动,提高了网络的链路利用率。 相似文献
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A solution algorithm for the image reconstruction problem with three criteria, maximum entropy, minimum nonuniformity and peakedness, and least square error between the original projection data and projection due to reconstruction is presented. Theoretical results of precedence properties which are respected by all noninferior solutions are first derived. These precedence properties are then incorporated into a multiple-criteria optimization framework to improve the computational efficiency. Comparisons of the new algorithm to the MART and MENT algorithms are carried out using computer-generated noise-free and Gaussian noisy projections. Results of the computational experiment and the efficiency of the multiobjective entropy optimization algorithm (MEOA) are reported. 相似文献
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AFPHB的实现机制是区分服务的重要研究课题。文章对区分服务中AFPHB的主动队列管理算法进行了研究,分析了几种算法在平均队长和丢弃概率计算上的差别,探讨了WRED和RIO算法对低丢弃优先级包的保护能力。为了更好地满足AFPHB的要求,结合三色标记器提供的功能,提出了对不同丢弃优先级的包有区别处理的技术思想,并给出了实现算法。 相似文献
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This paper presents a system level approach for the synthesis of hard real-time multitask application specific systems. The algorithm takes into account task precedence constraints among multiple hard real-time tasks and targets a multiprocessor system consisting of a set of heterogeneous off-the-shelf processors. The optimization goal is to select a minimal cost multi-subset of processors while satisfying all the required timing and precedence constraints. There are three design phases: resource allocation, assignment, and scheduling. Since the resource allocation is a search for a minimal cost multi-subset of processors, we adopted an A* search based technique for the first synthesis phase. A variation of the force-directed optimization technique is used to assign a task to an allocated processor. The final scheduling of a hard-real time task is done by the task level scheduler which is based on Earliest Deadline First (EDF) scheduling policy. Our task level scheduler incorporates force-directed scheduling methodology to address the situations where EDF is not optimal. The experimental results on a variety of examples show that the approach is highly effective and efficient. 相似文献
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James Aweya Michel Ouellette Abel Dasylva Delfin Y. Montuno 《International Journal of Network Management》2004,14(6):405-424
There is current interest in differentiated service architectures where packets with different priorities can share the same queue. In the case of congestion, packets marked with higher drop probability are preferentially dropped in order to make buffer room for packets marked with lower drop probability. Active queue management (AQM) based on randomized packet dropping has become a key component of this packet forwarding model. This paper extends our previously developed AQM algorithm called DRED with multiple packet drop precedence to allow for priority treatment of traffic in a network. The main advantage of using the DRED algorithm is the lower parameter configuration complexity it offers and the ease of configuration for a wide range of network conditions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Chaudhuri S. Walker R.A. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1996,4(2):273-279
The authors present a new polynomial-time algorithm for computing lower bounds on the number of functional units (FUs) of each type required to schedule a data flow graph in a specified number of control steps. A formal approach is presented that is guaranteed to find the tightest possible bounds that can be found by relaxing either the precedence constraints or integrality constraints on the scheduling problem. This tight, yet fairly efficient, bounding method can be used to estimate FU area, to generate resource constraints for reducing the search space, or in conjunction with exact techniques for efficient optimal design space exploration 相似文献
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通过分析IEEE 802.16关于VoIP(voice over IP)的传输规范和服务质量保证机制,指出了区分VoIP的优先级和VoIP要求弹性QoS的性质对VoIP接纳控制有着极其重要的意义,提出了VoIP接纳控制的弹性准则和优先级准则。在运用有效带宽理论确定了VoIP传输所需最小带宽的基础上,提出了基于优先级的弹性接纳控制算法,并以概率强度因子对算法进行了优化。该算法能够根据剩余资源动态地调整接纳强度和策略,对不同优先级的VoIP表现出不同的接纳特性,资源紧张时合理限制低优先级VoIP的接纳。为评价算法性能,通过Markov模型对建议算法的拒绝率进行分析,并在PMP(point-to-multipoint)模式下与新呼叫限制算法进行了对比仿真,结果表明本算法在表现出更高接纳能力的同时具有更低的新连接阻塞率和切换连接掉线率。 相似文献
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Reliability and Performance of Star Topology Grid Service With Precedence Constraints on Subtask Execution 总被引:1,自引:0,他引:1
《Reliability, IEEE Transactions on》2006,55(3):507-515
The paper considers grid computing systems with star architectures in which the resource management system (RMS) divides service tasks into subtasks, and sends the subtasks to different specialized resources for execution. To provide the desired level of service reliability, the RMS can assign the same subtasks to several independent resources for parallel execution. Some subtasks cannot be executed until they have received input data, which can be the result of other subtasks. This imposes precedence constraints on the order of subtask execution. The service reliability & performance indices are introduced, and a fast numerical algorithm for their evaluation given any subtask distribution is suggested. Illustrative examples are presented. 相似文献
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Finite automata decomposition for flexible manufacturing systems control and scheduling 总被引:1,自引:0,他引:1
H. Darabi M.A. Jafari S.S. Manapure 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2003,33(2):168-175
Despite the efforts in scheduling and control of flexible manufacturing systems (FMSs) with resource constraints, the current pool of scheduling techniques faces two major drawbacks: modeling and complexity. Modeling is the task of converting the FMS data to a set of information, ready to be processed by a scheduling algorithm. Complexity has a direct relation with the amount of effort required to execute a scheduling algorithm successfully on the information set generated in the modeling phase. In this paper, we use finite automata (FA) theory to develop a modeling formalism and its accompanying scheduling algorithm for control and scheduling of FMS with resource constraints. While the FA-based modeling is completely automatic and does not need any human-designer interference, its related algorithm is both effective and efficient. We use IDEF3 standard to capture the FMS activities and resource data. We propose a three-step procedure. In the first step, the IDEF3 data set is converted to a finite automaton, preserving the activity precedence relationships. In the second step, the resulted finite automaton is decomposed to smaller (in size) scheduling problems that can be independently optimized. In the third step, a heuristic scheduling algorithm is used to handle each problem separately. We applied the developed procedure to 100 problems. The results are satisfactory and promising. 相似文献