Computer networking at the National Computing Centre

The National Computing Centre installed a microcomputer-based local area network in 1981. The paper reviews the operation of this network since its implementation. The configuration of the network and the facilities it provides are described. The justification for such a network is examined, and the objectives of the installation are listed. The criteria on which the network was chosen are discussed, and implementation, training and support are described. The applications of the network are examined, along with user reaction, the impact on work and the benefits achieved. Problems and limitations of the network are also discussed.     

CSMA with collision avoidance

Advances in local area networking have allowed users to run many different applications on one system. Users are now asking for greater access, more functions, more power and greater reliability. This requires that the system tasks should be distributed, and means that the interconnection system used should be highly reliable; ‘passive’, so that no failed component can bring the entire system down; support high through-put; and operate on low-cost cable. This paper describes a broadband transmission system based on a single, passive coaxial cable which detects possible collisions before the data is sent. Examples of two remote stations and two adjacent stations competing for transmission are given, along with performance comparisons of CSMA/CD and CSMA/CA.     

Choosing a local area network

As they employ many different technologies, it is difficult to give a precise definition of a local area network. Most LANs, however, have certain characteristics and these are discussed as are the reasons for using a LAN. Although the technology employed by LANs is not as important to the user as the level of service offered, the technology does have some bearing on this service. The two major types of LANs currently being marketed are described. The applications of LANs and considerations that should be borne in mind when choosing a LAN are discussed and the potential pitfalls pointed out.     

无线局域网技术在开放教育中的应用研究

开放教育条件下的教学在师生关系、时间、地点、资源利用等都发生了变化。教学必须适应开放教育的需要和特点．改变传统教学形式和职能,为了适应现代科技的发展,开放教育对课堂教育提出了更高更新的要求。无线局域网能改变传统的开放教育模式,方便教学,强化教育过程。该文介绍了近年来发展迅速的无线局域网技术,以及如何将无线局域网技术引入开放教育中。     

有效的无线局域网接纳控制机制

针对IEEE802．11e混合协调功能框架没有给出实现接纳控制决策和具体计算接入时间方法的缺陷,提出一种支持实时业务的自适应接纳控制机制AAC。该机制考虑实时业务的突发特性与网络负载等因素,在保证系统现有业务丢包率与时延要求的前提下,通过动态分配发送机会提高系统的吞吐量。仿真实验以及与IEEE802．11e参考接纳控制机制的比较表明,该机制可以有效地降低实时业务的时延与丢包率,提高系统的吞吐量。     

Design of integrated data/voice stations for a CSMA/CD LAN

This paper describes the design and implementation of integrated data/voice stations for a LAN environment. The stations are based on the DB16000 Development Board using a 16-bit CPU. Continuously variable slope delta modulation is selected as the voice encoding technique. Protocols were designed and implemented to handle data and voice separately. Prototypes were built to test the station's performance. The stations communicate with one another at a rate of 1.5 Mbit/s. The voice digitization rate is 16 kbit/s and the terminal speed is 9.6 kbit/s.     

无线局域网吞吐量优化算法

针对无线局域网吞吐量较小且稳定性较差的问题,分析影响无线网络吞吐量性能的因素,提出无线局域网吞吐量优化算法,采用马尔科夫链理论建立吞吐量计算模型,运用动态调整竞争窗口、优化数据帧长度、改进退避时间的策略。NS2仿真结果表明,该算法能有效提高无线局域网的吞吐量。     

面向银行的一种中间件的前后处理过程

银行风险数据处理中间件是一种主要采用数据集市技术来支持银行各种风险监管系统的高层应用中间件。本文首先探讨了提出银行风险数据处理中间件的客观原因和对其进行研究的意义,构建出了中间件系统的体系结构,详细描述了各主要功能模块,并着重设计了面向前端和后端的应用服务接口,最后给出了中间件系统的一个应用实例。中间件系统提炼和封装了共同的银行风险数据处理逻辑,为前端各种风险管理应用提供统一的服务接口和平台,大大缩小了银行风险管理系统的开发周期和开发成本。     

无线局域网路由器ARP攻击故障的排除

随着现在社会信息技术的飞速发展,如今企业网络办公化也正式步入了无线网的领域中。构建无线网最大的好处就是组网无需布线,使用便捷,经济。所以对多数企业来说,无疑是组网方案的最佳选择。由于民航气象客户所处的地理位置分散,不便于使用有线网络。随着无线网络技术的发展,更多的无线网络技术应用到气象信息服务中,使得针对无线网络的故障诊断和安全保障变得与有线网络一样重要。     

An ISDN for the UK

With the advent of new digital technology into public telecommunications networks and given the fact that voice and data are carried in essentially the same way across a digital network, it is realized that the integration of voice and data services is possible and cost effective, and may bring additional benefits. The paper sets out some of the current developments in this area, with an emphasis on British Telecom's pilot Integrated Services Digital Network.     

基于本地差分隐私的众包隐私保护方法

在移动互联网发展的今天,基于位置服务（LBS）技术在移动互联上取得显著进展。针对个人用户进行精确定位时,数据信息隐私存在着泄露风险的问题,本文提出一种基于本地化差分隐私的地理不可区分性的扰动方法。在用户的真实位置数据信息流出客户端前采用地理不可区分性位置扰动方式,作用于真实位置以得到近似位置数据,服务器端收到后制成二级区域网格图,之后采用差分隐私对该图的工人计数进行扰动,最后在空间范围查询下进行实验验证,并与满足ε-本地化差分隐私扰动算法进行对比,精确度提高2.7%,同时与平均划分隐私预算分配方式进行实验对比,提高区域计数精确度4.57%。     

Protocol implementation for Universe

The communications protocols used on the Universe network and the implementor's experiences with them are described. By examining ‘lightweight’ and ‘heavyweight’ protocols, the paper examines the problems of protocols for mixed networks.     

Monitoring tool for the Cambridge Ring LAN

A Cambridge Ring monitor station can detect breaks in a LAN, as well as pinpoint nodes which are causing data corruption. However, no facility exists for inspecting the data actually being transmitted by a corrupting node. A design for a Cambridge Ring probe is described which enables such data capture. Moreover, this probe can be used in conjunction with an oscilloscope for low-level fault finding, or together with a logic state analyser for high-level fault finding and/or performance measurement. Preliminary results are presented which demonstrate the usefulness of the probe for the former. A discussion of how the probe can be used for the latter is also included.     

Cryptographic key exchange based on locationing information

This paper addresses the cryptographic key exchange problem in a wireless network. An infrastructure-based wireless network such as a Wireless LAN is considered. An indoor wireless locationing system, based on a collection of beacon nodes, is assumed to be present. The proposed technique makes use of ranging information between nodes to establish a shared secret key between security principals. The key exchange technique is based on the notion of symmetric ranging combined with Merkle’s puzzles. This technique is independent of any underlying encryption algorithm. The system’s security properties, in terms of the time to obtain the secret key and the time for an adversary to break the key, are analyzed using empirical implementations. The results show that the secret key can be established in five seconds between the principals, while it requires the adversary two orders of magnitude more time in some cases to substantially more than an hour (when the implementation times out) in most cases.     

浅谈无线局域网安全解决方案

在无线通信技术的不断发展的新时代,无线局域网已经变成计算机互联网行业的一个热点话题。但是,无线局域网的安全性不够强的缺点,却对它的进一步发展产生了一定的阻碍,始终影响着它的发展。在无线局域网逐步得到广泛的应用的过程中,对其安全性也提出了更高的要求。无线局域网突破了传统的有线网络的限制,但是,也存在着诸多的安全问题,因此,必须增强无线局域网安全防范意识,并且积极探索无线局域网安全解决方案,从而切实保证无线局域网业务的顺利开展。本文结合现阶段无线局域网的发展形势,重点阐述了无线局域网安全解决方案。     

浅析虚拟局域网

虚拟局域网VLAN是局域网LAN交换技术中迅速发展的组网技术。该技术的核心是通过路由和交换设备在网络的物理拓扑结构基础上建立一个逻辑网络,以使网络中任意局域网LAN段或站点能够组合成逻辑上的局域网。本文就虚拟局域网(VLAN)技术进行了介绍,同时对其不同的划分方法进行了分析并指出其优缺点。     

Distributed systems and their protocols

Several models have been developed to assist with the design and understanding of distributed systems. The client-server model is used here to develop a set of requirements to be met by protocol sets used within a distributed system. An architecture within which protocols may be implemented to meet the requirements developed is proposed. A number of key requirements are reviewed and areas requiring further development identified.     

Data communications: IFIP's international ‘network’ of experts

Data communications are essential for any advances in the implementation and operation of distributed systems. A substantial research and development effort is now being directed at the interconnection of the various elements of complete systems. Individuals and groups from a variety of backgrounds are involved in the development of new systems, and communication between them is essential. One of the aims of the International Federation for Information Processing is to promote the exchange of information about data communications — both within and between the developed and developing countries. The structure of IFIP's Technical Committee 6: data communications, and the ways in which it achieves its aims are discussed in detail.