伦敦中心区“交通拥挤收费”的运作效果、最新进展与相关思考

在对伦敦交通拥挤收费计划的实施背景进行简要回顾的基础之上,综合诸多研究跟踪报告资料,从交通流量、拥挤水平、经济影响、绕行交通等关键侧面,分析和介绍该政策的实际运作效果及其最新进展;进一步证明城市公共政策的制定具有复杂性和系统性,维护公众利益是城市公共政策的首要法则;应注意交通拥挤收费政策的适用性,需要因地制宜,切忌照搬。     

Effectiveness and issues of congestion control in 802.11g wireless LANs

The current paper presents a collection of experimental data portraying the performance achieved in the wireless setting by several TCP-friendly congestion controls recently proposed in literature. This work is partly motivated by the consideration that the majority of the analytical results in this area are validated by simulation, rather than by field tests. Examining these algorithms in real environments can help verify their actual effectiveness over the wireless Internet. To reach such goal, two representative controls among the so-called window-based TCP-friendly schemes have been implemented, namely, the General Additive Increase Multiplicative Decrease (GAIMD) strategy, and the SQuare RooT (SQRT) binomial control; the most representative algorithm among rate-based controls, the TCP Friendly Rate Control (TFRC), has also been considered. Their TCP-fairness and smoothness have been comprehensively evaluated in an IEEE 802.11g Wireless Local Area Network (WLAN). The obtained results show that the GAIMD and SQRT strategies reveal non-negligible scalability and smoothness problems, that markedly limit their performance. It is empirically demonstrated that their “optimal” increase/decrease rules, based on TCP-Reno analytical model, cannot guarantee an adequate performance when GAIMD and SQRT compete with TCP-Sack, a de facto standard for current TCP implementations. TFRC is demonstrated to occasionally behave bewildering: properly tuning one of its congestion control parameters and enhancing the algorithm with a flow-control mechanism result in a definitely fairer share of bandwidth with concurrent TCP flows. Michele Borri received the M.Sc. degree in Computer Engineering from the University of Modena and Reggio Emilia in the academic year 2001–2002 and took a specialisation in Telecommunication Engineering in 2002. His professional activity is currently balanced between researching at the University of Modena and Reggio Emilia, and consulting as a system engineer and network architect. His research interests focus on congestion control and multimedia services in next generation Internet. Michele Borri has been participating to national research projects promoted by the Italian National Research Council (CNR). Maurizio Casoni is Associate Professor in Telecommunications at the University of Modena and Reggio Emilia. He graduated with honors in Electrical Engineering at the University of Bologna in 1991, with a grant by Telecom Italia and received the Ph.D. degree also in Electrical Engineering from the University of Bologna, in 1995. In 1995 he was with the Computer Science Department at Washington University in St. Louis, MO, as a research fellow where he worked on ATM broadband switching architectures. He has studied ATM broadband switching architectures and Clos architectures for the design of large photonic switches in the framework of the European Projects ATMOS and KEOPS. He has also investigated the performance of 3rd generation UMTS systems. His current research interests deal with Optical Networking, mainly focusing on Optical Burst Switching, and Satellite Networks. He currently holds the course of Interconnection Systems for undergraduate students and the course of Switching Systems for graduate students of Telecommunications Engineering. Maria Luisa Merani is currently an associate professor of Telecommunication Networks at the University of Modena and Reggio Emilia, Department of Information Engineering. She is an IEEE Senior member and has served on the Technical Program Committees of several major communication conferences (IEEE ICC, IEEE Globecom, IEEE VTC, APCC). In 2005 she has been technical program cochair of the second IEEE International Symposium in Wireless Communication Systems. In 2007 she will be the Wireless Symposium chair of IEEE Globecom. At present she is involved in research on congestion control for next generation Internet and on multicast video streaming. Her most recent research interests are related to the area of radio communications, with emphasis on performance evaluation of mobile radio systems, 3G data networking and transport solutions for optical networks. Maria Luisa Merani received both her M.Sc. (summa cum laude) and Ph.D. in electrical engineering from the University of Bologna, Italy, in the academic years 1985/86 and 1991/92, respectively. In 1992 she spent one year at the Computer Science Department of the University of California in Los Angeles, CA, USA.     

Information Security Management: An Approach to Combine Process Certification And Product Evaluation

Information Security (IS) is the key to the effective management of any organisation in today’s commercial and industrial sectors. Line managers’ performance, for instance, is rated according to the extent to which their operations conform to the IS policies of their respective organizations. In the same way, senior management’s performance is judged by how well the organization performs in terms of internationally accepted codes of IS practice. IS management, however, is not always a quantifiable entity and its evaluation is complicated by the fact that it can be viewed either from an electronic perspective, in which case the focus will fall solely on product and/or systems evaluation, or from a procedural and management perspective, in which case the focus will, instead, fall on the certification of the IS management process. This article will, therefore, be devoted to providing a consolidated approach to the evaluation of IS management, in terms of which full cognisance will be taken of both these perspectives.     

A novel Markov analytical model for the TCP/AQM systems

A novel closed-loop feedback TCP/AQM(Transfer Control Protocol/Active Queue Management) model is proposed in this paper using a discrete-time Markov chain,and a way to calculate the equilibrium distribution of this model is given.In the model,system time is divided into time slots,the bottleneck router queue model and TCP window size model in each slot are analyzed.Finally,by combining adjacent slots,an integrated TCP/AQM analytical model is developed.By this model,the average values of packets dropping rat...     

Integrated evolutionary neural network approach with distributed computing for congestion management

Electric supply industry is facing deregulation all over the world. Under deregulated power supply scenario, power transmission congestion has become more intensified and recurrent, as compared to conventional regulated power system. Congestion may lead to violation of voltage or transmission capacity limits, thus threatens the power system security and reliability. Also the growing congestion may lead to unanticipated divergent electricity pricing. Owing to these facts congestion management has become a crucial issue in the deregulated power system scenario.Fast and precise prediction of nodal congestion prices in real time deregulated/spot power market may enable market participants and system operators to keep pace with the congestion by taking preventive measures like transaction rescheduling, bids (both for supplying and consuming electricity) modification, regulated dispatch of electric power, etc. This paper proposes an integrated evolutionary neural network (ENN) approach to predict nodal congestion prices (NCPs) for congestion management in spot power market. Distributed computing is employed to tackle the heterogeneity of the data in the prediction of NCP values. Developed ENNs have been trained and tested under distributed computing environment, using a message passing paradigm. Proposed hybrid approach for NCP prediction is demonstrated on a 6-bus test power system with and without distributed computing. The proposed approach not only demonstrated the computing efficiency of the developed ENN model over the conventional optimal power flow method but also shows the time saving aspect of distributed computing.     

光分组交换节点技术

文章首先介绍了光分组交换网络的分类和光分组交换节点的基本结构,接着详细讨论了全光分组交换节点设计和实现中的关键问题:交换结构的设计、光存储的实现以及分组拥塞问题的解决方案。     

Statistical multiplexing gain for variable bit rate video codecs in ATM networks

Asynchronous transfer mode (ATM) broadband networks will support variable bit rate video codecs, which are capable of maintaining a constant picture quality. To demonstrate this capability, a prototype hardware video coder has been developed in the Siemens Central Communications Laboratories. The prototype uses interframe coding, combined with a discrete cosine transform, and is able to reproduce the original picture quality, independent of signal sources or picture material used. A gain in transmission efficiency is expected when several video sources share a common ATM channel (‘statistical multiplexing’). This paper reports on a series of measurements that have been performed using this coder for a large variety of video sources to determine the possible gain in transmission efficiency. The main results are: for realistic video phone scenes, up to about three times the number of signals can be transmitted compared to transmision with constant rate and the same picture quality, if the output signal of the coder has been smoothed over a period of one frame. Smoothing over shorter periods reduces the potential gain substantially. The statistical multiplexing gain increases with the duration of the picture sequences due to the criterion of constant picture quality. It varies very little with the acceptable packet loss rate.     

废水制酸装置净化单元堵塞的治理

介绍了吉林石化公司丙烯腈厂废水制酸装置在生产过程中由于以液硫作为补充能源及制酸原料而出现的硫在焚烧炉中不完全燃烧和残余的硫升华而造成的净化系统堵塞等问题。通过改进焚烧炉系统以及净化单元采用二级逆喷洗涤系统等方法,原料硫得到了充分燃烧,在解决了净化单元系统堵塞问题的同时产生良好的社会效益。     

国产首套刨煤机组控制系统在晓明矿的应用

文章介绍了由三一重型装备有限公司自主生产的全自动刨煤机BH38/2×400的控制系统,该控制系统的硬件系统由防爆工控机、主控制器、支架控制器等设备组成,其通信系统采用可靠性高,传输距离远的CAN总线通信方式.通过全自动刨煤机组BH38/2×400在铁法晓明矿北二419工作面的应用,标志着我国已经取得了薄煤层开采的关键核...     

OFEX Controller to Improve Queueing and User Performance in Multi‐bottleneck Networks

We have designed and investigated a new congestion control scheme, called optimal and fully explicit (OFEX) controller. Different from existing relatively explicit controllers, this new scheme can provide not only optimal bandwidth allocation but also a fully explicit congestion signal to sources. It uses the congestion signal from the most congested link instead of the cumulative signal from the flow path. In this way, it overcomes the drawback of relatively explicit controllers exhibiting bias toward multi‐bottlenecked users and significantly improves their convergence speed and source throughput performance. Furthermore, our OFEX‐controller design considers a dynamic model by proposing a remedial measure against the unpredictable bandwidth changes in contention‐based multi‐access networks. Compared with former works/controllers, this remedy also effectively reduces the instantaneous queue size in a router and thus significantly improves queuing delay and packet loss performance. We have evaluated the effectiveness of the OFEX controller in OPNET. The experimental comparison with the existing relatively explicit controllers verifies the superiority of our new scheme.