Approximation analysis of multi-class closed queueing maintenance networks with a parts inventory system and two-phase Coxian time distributions

We consider a maintenance network where a set of bases is supported by a replacement parts inventory system and a centrally located repair depot. The ordering policy for the parts is the (S, Q) inventory policy. We extended the previous results to the network, where processing times at each node follow a two-phase Coxian distribution. The proposed network was modeled as a multi-class closed queueing network with a synchronization station. To make the analysis of the network computationally tractable, we developed a two-phase approximation method. In the first phase of the method, the proposed network was analyzed with the previous algorithm based on a product-form approximation. In the second phase, a sub-network was again analyzed with the procedure of a product-form approximation method such that the state space of the sub-network was reduced. In the analysis of a sub-network, a recursive method was also used to solve balance equations by exploiting the special structure of the Markov chain. The new algorithm provided a good estimation of the performance measures of interest. In addition to being accurate, the new algorithm is simple and converges rapidly.     

Building human agency: a timely manifesto

The 2009 Passive and Low Energy Architecture Conference (PLEA), held in Québec City, Canada, was themed ‘Architecture, Energy and the Occupant's Perspective’, with the ambition of positioning building inhabitants as key ‘active’ determinants of energy performance in ‘passive’ design through adaptive opportunities. Conference delegates committed to a Manifesto that embodied both the key longstanding priorities of PLEA and explicitly conveyed the priorities of the conference hosts. The Manifesto is examined in terms of how it captures and represents a shift in thinking that has occurred over the past few years, away from technological and technocratic solutions to comfort provisioning and towards reframing building energy consumption as a social and ethical challenge in which comfort plays a key role.

La Conférence 2009 sur l'Architecture Passive et Basse Energie (PLEA), qui s'est tenue à Québec, au Canada, avait pour thème « Architecture, Energie et la Perspective de l'Occupant », avec pour ambition de positionner les habitants d'immeubles comme principaux déterminants « actifs » de la performance énergétique dans un design « passif » par des opportunités d'adaptation. Les délégués de la conférence se sont engagés en faveur d'un Manifeste qui, tout à la fois, incarne les principales priorités qui sont depuis longtemps celles des Conférences PLEA et traduit explicitement les priorités des hôtes de la conférence. Cet article examine le Manifeste quant à la manière dont il appréhende et reflète le changement intervenu au cours de ces dernières années dans la manière de voir les choses, consistant à se détourner d'un confort fourni par des solutions technologiques et technocratiques et à aller dans le sens d'un recadrage de la consommation énergétique des immeubles considérée comme un défi social et éthique dans lequel le confort joue un rôle clé.

Mots clés: comportement adaptatif, agence, confort, fourniture du confort, qualité environnementale intérieure, habitants, manifeste, Conférence sur l'Architecture Passive et Basse Energie (PLEA)     

Energy-saving self-configuring networked data centers

In this paper, we develop the optimal minimum-energy scheduler for the dynamic online joint allocation of the task sizes, computing rates, communication rates and communication powers in virtualized Networked Data Centers (NetDCs) that operates under hard per-job delay-constraints. The referred NetDC’s infrastructure is composed by multiple frequency-scalable Virtual Machines (VMs), that are interconnected by a bandwidth and power-limited switched Local Area Network (LAN). Due to the nonlinear power-vs.-communication rate relationship, the resulting Computing-Communication Optimization Problem (CCOP) is inherently nonconvex. In order to analytically compute the exact solution of the CCOP, we develop a solving approach that relies on the following two main steps: (i) we prove that the CCOP retains a loosely coupled structure, that allows us to perform the lossless decomposition of the CCOP into the cascade of two simpler sub-problems; and, (ii) we prove that the coupling between the aforementioned sub-problems is provided by a (scalar) constraint, that is linear in the offered workload. The resulting optimal scheduler is amenable of scalable and distributed online implementation and its analytical characterization is in closed-form. After numerically testing its actual performance under randomly time-varying synthetically generated and real-world measured workload traces, we compare the obtained performance with the corresponding ones of some state-of-the-art static and sequential schedulers.     

基于IAR EW430开发环境的FRAM应用研究

本文基于TI的MSP-EXP430FR5739 LaunchPad硬件评估套件和IAR EW430 IDE开发环境,研究了MSP430FR5739型MCU的FRAM分区配置方法,分别采用程序代码关键字声明法及面对复杂应用满足更高定制要求时修改XLINK配置文件法共两种方法实现了分区调配,编写了相应测试程序进行实验,验证结果达到了预期.同时对实际应用中FRAM分区后应进行MPU保护做出阐述,本文提出的方法可用于MSP430FR系列其他型号MCU器件的FRAM调配.     

On processor sharing and its applications to cellular data network provisioning

To develop simple traffic engineering rules for the downlink of a cellular system using Proportional Fairness (PF) scheduling, we study the “strict” and “approximate” insensitivity of a Processor Sharing (PS) system, specifically for the Egalitarian (EPS) and Discriminatory (DPS) variants of PS. Assuming homogeneous channel conditions, all concurrent flows are allocated an equal share of downlink transmission slots regardless of flow types and locations. The cell system is modeled as an EPS queue. We prove the performance insensitivity of EPS in a relevant new case that has not been studied in the literature. Considering heterogenous channel conditions, the system is modeled as the DPS queue in which each traffic type is divided into subclasses with different assigned weights. Asymmetric weights among the subclasses model the unequal channel sharing that occurs with PF scheduling. Our results show that the first-order performance of the DPS is largely insensitive to the input traffic characteristics, as long as the weights among subclasses are not highly skewed. Our findings, confirmed by the simulation of a cellular system, imply reduced complexity for traffic provisioning procedures. However, our study also shows that the first-order performance is sensitive to the traffic details when there is discrimination among different traffic types. This observation implies that the introduction of differentiated services may pose a great challenge to network provisioning in future cellular systems.     

Optimizing utilization of resource pools in web application servers

Among the web application server resources, the most critical for their performance are those that are held exclusively by a service request for the duration of its execution (or some significant part of it). Such exclusively held server resources become performance bottleneck points, with failures to obtain such a resource constituting a major portion of request rejections under server overload conditions. In this paper, we propose a methodology that computes the optimal pool sizes for two such critical resources: web server threads and database connections. Our methodology uses information about incoming request flow and about fine‐grained server resource utilization by service requests of different types, obtained through offline and online request profiling. In our methodology, we advocate (and show its benefits) the use of a database connection pooling mechanism that caches database connections for the duration of a service request execution (so‐called request‐wide database connection caching). We evaluate our methodology by testing it on the TPC‐W web application. Our method is able to accurately compute the optimal number of server threads and database connections, and the value of sustainable request throughput computed by the method always lies within a 5% margin of the actual value determined experimentally. Copyright © 2010 John Wiley & Sons, Ltd.     

ANSWER: AutoNomouS netWorked sEnsoR system

Sensor networks are expected to evolve into long-lived, open, ubiquitous, multi-purpose networked systems. We propose a new concept called AutoNomouS netWorked sEnsoR system (ANSWER) whose mission is to provide in situ users with real-time, secure information that enhances their situational and location awareness. To the best of our knowledge, solutions that accomplish this goal do not yet exist. ANSWER finds immediate applications to both overt and covert operations ranging from tactical battlefield surveillance to crisis management and homeland security. The architectural model of ANSWER is composed of a large number of sensors and of a set of (mobile) aggregation-and-forwarding nodes that organize and manage the sensors in their vicinity. In this paper we present the main features that enable ANSWER to effectively and efficiently provide secure, QoS-aware information services to in situ mobile users; namely, secure dynamic task-based networking and in-network storage to support application-level tasks and queries (each specified with desired QoS and security attributes), while hiding network-level details; and a model-based methodology exploiting QoS and security trade-offs for smart AFN mobility subject to application and network requirements and constraints. This new concept is in sharp departure from the prevalent view in NSS design that networking is independent of the task(s) at hand and information processing and storage are, primarily, the responsibility of remote entities.     

基于势能导向多下一跳路由的服务承载网构建方法

服务承载网络是基于服务构建的以满足服务端到端QoS保障为出发点的覆盖网络,是满足可重构柔性网络对业务需求支撑的有效的网络架构。基于可重构柔性网络体系框架,分析服务承载网构建的主要问题,提出了可重构柔性网络下服务承载网的构建原则,在此基础上给出了基于势能导向多下一跳路由的服务承载网构建算法,并对其进行了性能分析及仿真。仿真结果表明,该算法具有较高的构建成功率。     

云计算下基于CRP算法的资源提供策略

云计算资源管理系统是用于接收来自云计算用户的资源请求,并且把特定的资源封装为服务提供给资源请求者。在云计算环境下,如何为资源请求者选择合适的资源是一个值得研究的课题。文中通过对云计算下现有的资源提供策略的分析,同时根据不同云提供者提供的计算资源的成本不同的特点,综合考虑资源的计算能力、可靠性和单位成本三点因素,提出了云计算下基于CRP算法的资源提供策略。这种资源提供策略既能提供满足用户资源请求的服务,也能降低云服务提供者的运营成本,从而获得更大收益。