Design and performance evaluation considerations of a multimediamedical database

Multimedia information management and communications systems for medical applications have been undergoing design and development. The aim of these activities has been the development of distributed computer systems providing storage, processing, and communication services required by the medical community. One of the main critical issues of such systems is the handling of multimedia information (i.e., text, images, graphics, and voice) in a uniform way and the fast access to images through the network. We present the design architecture and concepts used in our multimedia database system, along with its performance evaluation. The evaluation focuses on the response times of a multimedia medical database server, as seen by remote workstations for various retrieval and image transfer requests. For this purpose, a queueing network model was developed and simulated. Communications between the workstations and the database server are governed by the client-server model using TCP/IP and appropriate application protocols on a 10 Mb/s Ethernet LAN     

A survey of QoS architectures

Over the past several years there has been a considerable amount of research within the field of quality-of-service (QoS) support for distributed multimedia systems. To date, most of the work has been within the context of individual architectural layers such as the distributed system platform, operating system, transport subsystem and network layers. Much less progress has been made in addressing the issue of overall end-to-end support for multimedia communications. In recognition of this, a number of research teams have proposed the development of QoS architectures which incorporate QoS-configurable interfaces and QoS driven control and management mechanisms across all architectural layers. This paper examines the state-of-the-art in the development of QoS architectures. The approach taken is to present QoS terminology and a generalized QoS framework for understanding and discussing QoS in the context of distributed multimedia systems. Following this, we evaluate a number of QoS architectures that have emerged in the literature.     

Implementation of a Unix network

A network of over 100 Unix computer systems has been established using the telephone system as its primary communications medium. The system is used primary for software exchange and remote mail, but permits processing with remote resources (files/programs). The authors faced a number of design issues common to distributed processing during its implementation. Several features of the system helped make it successful: low startup cost, no operating-system changes, easy user interface, locally administered security. This paper discusses the design issues and the authors' approach to the problems.     

Ontological Semantics for Distributing Contextual Knowledge in Highly Distributed Autonomic Systems

Much recent research has focused on applying Autonomic Computing principles to achieve constrained self-management in adaptive systems, through self-monitoring and analysis, strategy planning, and self adjustment. However, in a highly distributed system, just monitoring current operation and context is a complex and largely unsolved problem domain. This difficulty is particularly evident in the areas of network management, pervasive computing, and autonomic communications. This paper presents a model for the filtered dissemination of semantically enriched knowledge over a large loosely coupled network of distributed heterogeneous autonomic agents, removing the need to bind explicitly to all of the potential sources of that knowledge. This paper presents an implementation of such a knowledge delivery service, which enables the efficient routing of distributed heterogeneous knowledge to, and only to, nodes that have expressed an interest in that knowledge. This gathered knowledge can then be used as the operational or context information needed to analyze to the system's behavior as part of an autonomic control loop. As a case study this paper focuses on contextual knowledge distribution for autonomic network management. A comparative evaluation of the performance of the knowledge delivery service is also provided. John Keeney holds a BAI degree in Computer Engineering and a PhD in Computer Science from Trinity College Dublin. His primary interests are in controlling autonomic adaptable systems, particularly when those systems are distributed. David Lewis graduated in Electronics Engineering from the University of Southampton and gained his PhD in Computer Science from University College London. His areas of interest include integrated network and service management, distributed system engineering, adaptive and autonomic systems, semantic services and pervasive computing. Declan O’Sullivan was awarded his primary degree, MSc and PhD in Computer Science from Trinity College Dublin. He has a particular interest in the issues of semantic interoperability and heterogeneous information querying within a range of areas, primarily network and service management, autonomic management, and pervasive computing.     

浅析电子商务的安全问题及防范技术

当前电子商务发展非常迅速,这就对电子商务安全问题提出了挑战。电子商务的安全是一个复杂系统工程,需要从技术角度和立法等方面加以保障,以规范电子商务存在的各类安全问题。本文主要讨论电子商务应用中所存在的安全问题,以及防范技术的分析。     

Cognitive process modelling of controllers in en route air traffic control

In recent years, various efforts have been made in air traffic control (ATC) to maintain traffic safety and efficiency in the face of increasing air traffic demands. ATC is a complex process that depends to a large degree on human capabilities, and so understanding how controllers carry out their tasks is an important issue in the design and development of ATC systems. In particular, the human factor is considered to be a serious problem in ATC safety and has been identified as a causal factor in both major and minor incidents. There is, therefore, a need to analyse the mechanisms by which errors occur due to complex factors and to develop systems that can deal with these errors. From the cognitive process perspective, it is essential that system developers have an understanding of the more complex working processes that involve the cooperative work of multiple controllers. Distributed cognition is a methodological framework for analysing cognitive processes that span multiple actors mediated by technology. In this research, we attempt to analyse and model interactions that take place in en route ATC systems based on distributed cognition. We examine the functional problems in an ATC system from a human factors perspective, and conclude by identifying certain measures by which to address these problems. This research focuses on the analysis of air traffic controllers' tasks for en route ATC and modelling controllers' cognitive processes. PRACTITIONER SUMMARY: This research focuses on an experimental study to gain a better understanding of controllers' cognitive processes in air traffic control. We conducted ethnographic observations and then analysed the data to develop a model of controllers' cognitive process. This analysis revealed that strategic routines are applicable to decision making.     

基于安全系统工程的铁路运输安全信息系统设计

介绍一种铁路运输安全综合管理信息系统的实现方案。以安全系统工程学作为理论基础,采用先进的计算机信息技术、人工智能、网络通信、智能数据分析等技术,来设计一套基于安全系统工程学的铁路运输安全综合管理信息系统。该系统将实现纵深发展、横向联系的安全信息平台;实现安全风险预控,做到主动预防,达到内激型管理;实现全生命周期管理,使得安全与生产相融合。     

基于通信网络机车分布式系统实时控制的分析与研究

针对基于通信网络的机车控制系统实时性要求及网络传输的可能影响,通过对列车通信网络(TCN)技术特点以及车载分布式控制应用要求的分析,总结了基于网络的实时控制的处理;在分析各个环节的延时成因及影响的基础上,重点对轨道车辆分布式控制系统实时性能进行了分析及研究,得出基于通信网络的实时控制系统必须考虑网络的影响,特别是传输延迟的影响,同时根据应用实践提出了改善基于通信网络的车载分布式控制系统实时性的原理及方法,并进行了测试及验证。     

基于防火墙网络安全技术的探究

伴随网络技术突飞猛进的发展,网络的安全问题频繁发生,网络攻击现象不断涌现,特别是在政府机构、科研研所、金融机构、企业的计算机网络较易遭遇来自黑客的侵袭。黑客攻击者可轻易地攻击未附加任何安全保护措施的网络,例如肆意变更关键的信息数据、进行非授权访问以及传播网络病毒等。这些不良攻击事件一旦出现,将会给相应部门带来较大的经济损失。在已经研制出的众多安全防范方案中,防火墙技术由于较成熟,并具备产品化,相对较早地被不少单位所运用。本文结合网络安全技术发展现状,系统地阐述防火墙的安全技术保障措施及未来发展前景。     

Data communications controls

Computer systems employing data communications networks, such as distributed data processing systems, on line real-time computer systems, and electronic funds transfer systems are expected to significantly increase in the future. These systems require the electronic transmission of messages between a sending station and a receiving station. However, the message transmitted from the sending station may be distorted, modified, or destroyed due to faulty equipment, power fluctuations, cross-talk, and atmospheric conditions. To insure that the receiving end obtains the original message, proper controls must be incorporated into the data communications network. This paper will examine the following data communications controls: integrity controls, privacy and confidentiality measures, and backup and recovery controls.     

Communications Systems Driven by Software Agent Technology

The application of software agent technology to the management of communications' infrastructures is a challenging domain as it requires management on different time scales and has many interacting components. This paper looks at the potential benefits that may be gained from the application of agent technology to communications systems and surveys recent developments. Recent work using distributed network management by adopting co-operating and self-interested agent models of collaboration are described. The paper provides an introduction to the authors' perceptions of agent technology, followed by a discussion of some issues that need to be addressed for agent technology to be of practical use in the communications domain. Following sections describe how agent technology has been used for network management, legacy telecommunications systems, and telecommunications integration. The authors discuss how the emerging standards for agent technology can be used in an applied situation of providing a virtual private network and mobile agent technology used for fully distributed network control.     

Automating financial markets

An electronic financial marketplace can be regarded as a single multiorganizational distributed system with a communications network at the centre and a number of linked peripheral elements. The paper describes the characteristics of electronic marketplaces, the progress being made in automating financial markets, some of the problems that may arise and likely future developments.     

Safety and reliability driven task allocation in distributedsystems

Distributed computer systems are increasingly being employed for critical applications, such as aircraft control, industrial process control, and banking systems. Maximizing performance has been the conventional objective in the allocation of tasks for such systems. Inherently, distributed systems are more complex than centralized systems. The added complexity could increase the potential for system failures. Some work has been done in the past in allocating tasks to distributed systems, considering reliability as the objective function to be maximized. Reliability is defined to be the probability that none of the system components falls while processing. This, however, does not give any guarantees as to the behavior of the system when a failure occurs. A failure, not detected immediately, could lead to a catastrophe. Such systems are unsafe. In this paper, we describe a method to determine an allocation that introduces safety into a heterogeneous distributed system and at the same time attempts to maximize its reliability. First, we devise a new heuristic, based on the concept of clustering, to allocate tasks for maximizing reliability. We show that for task graphs with precedence constraints, our heuristic performs better than previously proposed heuristics. Next, by applying the concept of task-based fault tolerance, which we have previously proposed, we add extra assertion tasks to the system to make it safe. We present a new heuristic that does this in such a way that the decrease in reliability for the added safety is minimized. For the purpose of allocating the extra tasks, this heuristic performs as well as previously known methods and runs an order of magnitude faster. We present a number of simulation results to prove the efficacy of our scheme     

工业网络系统的感知-传输-控制一体化:挑战和进展

工业网络系统是融合工业控制和信息通信的多维动态系统,具有维度高、动态性强、工业通信协议和网络配置嵌入等特性,如何在网络环境下实现信息感知分布性、控制适应性、整体协调性,已成为工业网络系统研究的新挑战.本文简述了工业网络系统的内涵和主要特征,分析了感知-传输-控制一体化面临的挑战和关键问题;综述了分布式状态感知、适变传输、协同控制等关键技术的研究进展;对工业网络系统的未来研究方向和潜在应用前景进行了总结和展望.     

基于信息物理系统的面向方面中间件特征模型

信息物理系统（Cyber-physical Systems,CPS）是集计算、通信和控制能力于一体的多维复杂的分布式系统,这就要求系统必须通过专门的定制。实时中间件可以有效地解决分布式系统的异构性和互操作性等问题。信息物理系统中间件存在着分布性、容错性、性能分析、实时性、日志记录等非功能的横切关注点,基于面向方面的中间件构建技术,能够把这些横切关注从中间件中分离出来,形成独立于中间件的核心功能的方面。文中提出一个面向方面的中间件,能够处理分布式信息物理系统的动态问题,在文中,将重点放在特征模型定义,并且概述了其映射到一个动态的面向方面的中间件平台。     

HARNESS fault tolerant MPI design, usage and performance issues

Initial versions of MPI were designed to work efficiently on multi-processors which had very little job control and thus static process models. Subsequently forcing them to support a dynamic process model suitable for use on clusters or distributed systems would have reduced their performance. As current HPC collaborative applications increase in size and distribution the potential levels of node and network failures increase. This is especially true when MPI implementations are used as the communication media for GRID applications where the GRID architectures themselves are inherently unreliable thus requiring new fault tolerant MPI systems to be developed. Here we present a new implementation of MPI called FT-MPI that allows the semantics and associated modes of failures to be explicitly controlled by an application via a modified MPI API. Given is an overview of the FT-MPI semantics, design, example applications and some performance issues such as efficient group communications and complex data handling. Also briefly described is the HARNESS g_hcore system that handles low-level system operations on behalf of the MPI implementation. This includes details of plug-in services developed and their interaction with the FT-MPI runtime library.     

An architecture for attacking the communication bottleneck in P systems

The distributed implementation of P systems on a cluster of processors has met with a bottleneck communications problem. When the number of membranes grows in the system, the network gets congested and the time taken to execute an evolution step degrades. In this article, we suggest a software architecture denominated “partially parallel evolution with partially parallel communication”, where some membranes are located in each processor, proxies are used to communicate with membranes located in different processors, and a policy of access control to the communications network is mandatory. With all this, we get a certain parallelism in the system and an acceptable functioning in communications. In addition to this, it establishes a series of equations that allows us to determine in the architecture the optimum number of processors needed, the time required to execute an evolution step, the number of membranes to be located in each processor, and the conditions to determine when it is best to use the distributed solution or the sequential one. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Distributed embedded smart cameras for surveillance applications

Recent advances in computing, communication, and sensor technology are pushing the development of many new applications. This trend is especially evident in pervasive computing, sensor networks, and embedded systems. Smart cameras, one example of this innovation, are equipped with a high-performance onboard computing and communication infrastructure, combining video sensing, processing, and communications in a single embedded device. By providing access to many views through cooperation among individual cameras, networks of embedded cameras can potentially support more complex and challenging applications - including smart rooms, surveillance, tracking, and motion analysis - than a single camera. We designed our smart camera as a fully embedded system, focusing on power consumption, QoS management, and limited resources. The camera is a scalable, embedded, high-performance, multiprocessor platform consisting of a network processor and a variable number of digital signal processors (DSPs). Using the implemented software framework, our embedded cameras offer system-level services such as dynamic load distribution and task reconfiguration. In addition, we combined several smart cameras to form a distributed embedded surveillance system that supports cooperation and communication among cameras.     

一种简单的嵌入式IPSec的研究与实现

随着越来越多的嵌入式系统需要接入Internet以进行全球性的信息通信,这就日益要求解决嵌入式系统的网络通信安全问题.本文阐述了IPSec的体系结构,分析了一种简单的嵌入式IPSec的工作原理、结构、各模块的功能实现和一些简单的安全测试.     

Adaptive Allocation of Independent Tasks to Maximize Throughput

In this paper, we consider the task allocation problem for computing a large set of equal-sized independent tasks on a heterogeneous computing system where the tasks initially reside on a single computer (the root) in the system. This problem represents the computation paradigm for a wide range of applications such as SETI@home and Monte Carlo simulations. We consider the scenario where the systems have a general graph-structured topology and the computers are capable of concurrent communications and overlapping communications with computation. We show that the maximization of system throughput reduces to a standard network flow problem. We then develop a decentralized adaptive algorithm that solves a relaxed form of the standard network flow problem and maximizes the system throughput. This algorithm is then approximated by a simple decentralized protocol to coordinate the resources adaptively. Simulations are conducted to verify the effectiveness of the proposed approach. For both uniformly distributed and power law distributed systems, a close-to-optimal throughput is achieved, and improved performance over a bandwidth-centric heuristic is observed. The adaptivity of the proposed approach is also verified through simulations.