无线局域网实时业务优先的调度算法

该文在无线局域网的MAC协议上,基于时分多址技术,提出了分离缓冲器调度控制算法,将业务分为实时性要求的和非实时性要求两类,并给实时性业务以高的优先级.仿真结果表明该算法满足了实时性业务的失效概率要求,一定程度上保证了网络的QoS.     

优先级顶协议的形式化验证

优先级顶协议是一种优先级驱动的抢占式调度协议,它具有无死锁和单阻塞的性质.Dang Van Hung 和Philip Chan在文献[6]中形式地规范和验证了这两个性质.但他们没有对状态函数HiPripcp明确定义,这使得验证的细节较难理解.为了解决这个问题,提出了一种新的方法来验证优先级顶协议单阻塞的性质.通过时段演算的方法,对优先级顶协议进行了规范,并给出了状态函数HiPripcp的明确定义.根据优先级顶协议的规范,形式地验证了该协议的单阻塞性质.采用的验证方法更少地依赖于HiPripcp,这使得验证的细节更易于理解.此外,提出的验证方法可被应用于实时数据库系统中类似协议的形式化验证.     

Performance analysis of priority scheduling mechanisms under heterogeneous network traffic

Priority scheduling principle plays a crucial role in the Differentiated Services (DiffServ) architecture for the provisioning of Quality-of-Service (QoS) of network-based applications. Analytical modelling and performance evaluation of priority queuing systems have received significant attention and research efforts. However, most existing work has primarily focused on the analysis of priority queuing under either Short Range Dependent (SRD) or Long Range Dependent (LRD) traffic only. Recent studies have shown that realistic traffic reveals heterogeneous nature within modern multi-service networks. With the aim of investigating the impact of heterogeneous traffic on the design and performance of network-based systems, this paper proposes a novel analytical model for priority queuing systems subject to heterogeneous LRD self-similar and SRD Poisson traffic. The key contribution of the paper is to extend the application of the generalized Schilder's theorem (originally a large deviation principle for handling Gaussian processes only) to deal with heterogeneous traffic and further develop the analytical upper and lower bounds of the queue length distributions for individual traffic flows. The validity and accuracy of the model demonstrated through extensive comparisons between analytical bounds and simulation results make it a practical and cost-effective evaluation tool for investigating the performance behaviour of priority queuing systems under heterogeneous traffic with various parameter settings.     

End-to-end delay margin balancing approach for routing in multi-class networks

This paper presents Quality of Service (QoS) based routing and priority class assignment algorithms. It introduces an end-to-end delay margin balancing approach to routing, and uses it to formulate a nonlinear optimization problem. In a single-class network, the formulation is shown to be convex; however in a multi-class priority network, it is only convex within specific regions, and is infeasible otherwise. A centralized off-line computation technique is proposed to calculate both the route configuration and end-to-end priority assignment. A gradient-based solution in the convex region and a heuristic to overcome the multi-class discontinuity are derived. An approximation of the optimization problem is developed for on-line distributed processing is then presented. Using the approximation, arriving traffic flows can use vector routing tables to search for routes. Compared with minimum-hop, minimum-delay, and min-interference routing algorithms, the proposed approach enables the single-class network to accommodate more users of different end-to-end delay requirements. In a multi-class priority network, results show that using the objective function to combine route and priority class assignment further increases the supportable network traffic volume. Mohamed Ashour received his B.Sc. (1991) and M.Sc. (1997) in Electrical Engineering from Ain Shams University, Cairo, Egypt. He worked for Hughes and General Dynamics as a Telecommunications Engineer. Currently, he is a Ph.D. Candidate in the Department of Electrical and Computer Engineering of McGill University, Montreal, Quebec, Canada. His current area of research is focused on traffic engineering, routing, and QoS provisioning in DiffServ and MPLS Networks. He is also interested in multi-class queuing analysis of long-range traffic, and QoS provisioning in ad hoc networks and satellite communications. Tho Le-Ngoc obtained his B. Eng. (with Distinction) in Electrical Engineering in 1976, his M.Eng. in Microprocessor Applications in 1978 from McGill University, Montreal, and his Ph.D. in Digital Communications 1983 from the University of Ottawa, Canada. During 1977–1982, he was with Spar Aerospace Limited as a Design Engineer and then a Senior Design Engineer, involved in the development and design of the microprocessor-based controller of Canadarm (of the Space Shuttle), and SCPC/FM, SCPC/PSK, TDMA satellite communications systems. During 1982–1985, he was an Engineering Manager of the Radio Group in the Department of Development Engineering of SRTelecom Inc., developed the new point-to-multipoint DA-TDMA/TDM Subscriber Radio System SR500. He was the System Architect of this first digital point-to-multipoint wireless TDMA system. During 1985–2000, he was a Professor the Department of Electrical and Computer Engineering of Concordia University. Since 2000, he has been with the Department of Electrical and Computer Engineering of McGill University. His research interest is in the area of broadband digital communications with a special emphasis on Modulation, Coding, and Multiple-Access Techniques. He is a Senior Member of the Ordre des Ingénieur du Quebec, a Fellow of the Institute of Electrical and Electronics Engineers (IEEE), a Fellow of the Engineering Institute of Canada (EIC), and a Fellow of the Canadian Academy of Engineering (CAE). He is the recipient of the 2004 Canadian Award in Telecommunications Research, and recipient of the IEEE Canada Fessenden Award 2005.     

树形变化多播技术在蜂窝广播网络中的应用

树形变化多播技术利用层的思想进行数据传播,减轻了网络的传输负载,避免了网络阻塞,从而加强了网络的健壮性和稳定性.本文提出了蜂窝广播网络中基于优先级控制的树形变化多播应用,网络根据优先级进行通讯,减少了通讯冲突,提高了数据传输效率.     

A rule-centric memetic algorithm to minimize the number of tardy jobs in the job shop

This paper addresses the job shop-scheduling problem with minimizing the number of tardy jobs as the objective. This problem is usually treated as a job-sequencing problem, and the permutation-based representation of solutions was commonly used in the existing search-based approaches. In this paper, the flaw of the permutation-based representation is discussed, and a rule-centric concept is proposed to deal with it. A memetic algorithm is then developed to realize the proposed idea by tailored genome encoding/decoding schemes and a local search procedure. Two benchmark approaches, a multi-start hill-climbing approach and a simulated annealing approach, are compared in the experiments. The results show that the proposed approach significantly outperforms the benchmarks.     

Business Continuity Management: A Standards-Based Approach

ABSTRACT

Business enterprises are increasingly realizing the importance of business continuity management (BCM). Availability BS 25999 Standard has facilitated a consistent methodology that organizations can follow in designing their BCM System. This paper intends to provide a conceptual understanding of BCM right from BCM Policy to BCM maturity by describing the steps involved in the implementation of BCM Standard – BS 25999 – to ensure business continuity in the event of an outage. The key BCM tasks have been categorized into three phases of business continuity – Pre-event Preparation, Event Management, and Post-event Continuity. This paper also highlights some of the challenges experienced by the author in carrying out Risk Assessment and Business Impact Analysis. The Business Continuity Maturity Model® of Virtual Corporation is provided (with their permission) as a tool to strengthen business continuity maturity or organizations.     

从化学物质角度介绍美国固体废物和土壤修复管理

通过对美国固体废物和土壤修复的法律基础、管理体系和技术支持的研究,系统地梳理了美国在这两个领域的管理经验,明晰了美国化学物质清单管理制度。根据美国的实施经验,对我国固体废物和土壤修复环境管理提出建议,旨在协同推进我国在这两方面的环保工作。     

云虚拟机资源负载均衡的任务调度研究

针对云计算中现有任务调度模型为追求最短完成时间,而没有从物理资源的负载均衡角度考虑, 提出了基于任务预先分类的调度策略(PCSS)。该策略通过综合考虑任务的最少执行时间和截止时间来设置优先级,根据优先级别将任务批量分配给合适的物理机,实现了任务的最短完成时间和物理机的负载均衡。最后通过Cloudsim 仿真实验分析和比较,该策略能很好地执行用户任务并体现出良好的负载均衡。     

城市景观特色之建筑优先感应倾向研究

在对城市景观特色相关心理学理论的分析和推理基础上,通过对审美主体的调查研究,归纳出审美主体对城市景观特色的感知中,建筑类景观具有更容易被审美主体优先感应的特点,以期为城市景观特色的定位以及城市景观设计提供参考。