SIGTRAN中的QoS保障措施

下一代网络是基于分组交换的网络。SIGTRAN作为下一代网络中专门用于传输信令的传输层协议,对信令传输的可靠性、时延等问题起着至关重要的作用。QoS问题是IP网络中的关键问题,也是下一代网络中需要重点考虑的问题。SIGTRAN协议在设计的时候就考虑到了许多保证QoS的措施,从而保证了下一代网络中信令消息的传输性能。文中简要介绍了SIGTRAN协议的体系结构,给出了SIGTRAN中的QoS定义,分析了SIGTRAN中的各种QoS保障措施,最后对这些QoS保障措施进行了总结。     

VxWorks操作系统中SCTP协议栈的研究与实现

随着IP网向多业务网的发展,尤其是近年来VoIP技术的发展,需要在IP网络上传输有严格时间要求的信令。IETF的信令传输工作组(SIGTRAN)定义了一种新的传输层协议：SCTP(流控制传输协议),用于在IP网上提供可靠的报文传输。本文实现了BSD的SCTP协议栈源代码到VxWorks上的移植。同时分析了VxWorks中SCTP协议栈的实际运行性能。     

SCTP性能的仿真分析

SCTP是下一代网络(NGN)的一种重要传输协议,融合TCP与UDP协议的优点,提供端到端的可靠业务传输,用来在IP网络上可信地传输SS7信令.立足SCTP一些新特性(比如多流性、多宿性),通过仿真软件NS2,在网络时延、抖动、丢包率、吞吐量几个典型的QoS参数方面,对比分析了SCTP协议与不同版本的TCP协议;仿真结果表明,使用SCTP协议的网络综合性能优于传统的TCP协议,从而进一步提高了网络的QoS,同时用户QoE也得到了提升.将SCTP性能与不同的TCP协议进行对比,基于这些网络QoS参数进行对比分析,为以后的SCTP特性进一步研究工作起到了铺垫的作用.     

下一代网络多媒体流自适应QoS研究

下一代网络是一个支持话音、数据和视频的多媒体网络。随着网络的发展,如何保障下一代网络多媒体流QoS是一个重要的研究课题。为保证多媒体流QoS,系统必须分配足够的CPU、I/O、网络带宽资源,在多媒体传输过程中,这些资源是动态变化的。论文提出一种带优先级的自适应节调节方法,采用AIMD调节技术调节数据帧长度,自适应调节QoS,实验表明,该方法保证了NGN多媒体流的QoS,也使得网络资源得到充分利用。     

基于IP的H.248协议可靠传输方案

以软交换为代表的下一代网络主要采用H.248协议对网关进行控制。该文介绍了H.248协议,提出基于IP传输协议存在的不可靠性,分析了可靠传输机制,设置3个定时器,给出一种基于IP的H.248协议可靠传输方案。初步实现结果表明,该方案可以保证事务的可靠传输,提高信令处理效率,是完全可行的。     

移动网络的通信性能保障技术研究

探究了移动网络数据业务的服务保障机制，结合ATM网络自身的特点分析了为保证商定的QoS协议网络各层所需要提供的功能，设计出QoS的协商、修改，以及用户切换网络后的重协商过程。对系统信令流程和各种数据业务的QoS特性进行了测试，证明了方法的有效性。     

层次化移动IPv6环境中的QoS机制

本文针对层次化移动IPv6的网络提出了一种QoS信令,为移动节点提供服务质量的保障。在分析了RSVP信令的特点及其由于对多播的支持而增加的复杂性的基础上,设计了一个简化的RSVP信令,然后把此RSVP信令和层次化的移动协议相结合提出了一个综合的QoS切换方案,并在层次化的移动环境下,对此QoS信令和其它几种QoS机制在资源预留时间和信令负荷方面进行了性能比较。     

融合的多业务立体网络

责任编辑/仝培杰 tpj@ccu.com.cn 美术编辑/陈静本期关注 立体网络(下转A12页)来主要为七大技术领域。IP信令技术IP本来是一个没有信令的网络,也是一个没有连接的网络,自然也是一个无法根据业务需求来调度网络资源的网络。MPLS做为IP网络的信令技术的入门协议,结束了IP网络无信令网络的历史,开始了IP信令网的发展与进步。QoS技术QoS是需要设备、网络、信令和应用系统共同来保障的。从硬QoS保障到软QoS保障,人们从应用的角度有了越来越深刻的理解。网络安全技术IP是一个追求开放性的网络,因此它存在着太多的安全漏洞。安全涉及到…     

软交换信令网关软件模型设计与实现

下一代网络是一个以业务为中心,开放的融合型的新型网络,它把业务的控制平面和传输平面相分离。软交换体系结构则是其中各种网络和核心IP网络互通融合的一个解决方案。信令网关在软交换体系结构中占有重要的地位,它负责对在异构网络之间传输的信令消息进行转换,承担着业务的控制平面功能。探讨和分析了信令网关的软件体系结构模型,还简要的分析了下一代网络的概念,以及信令网关在软交换体系结构中的应用模型。     

IMS中SIP会话建立时延的研究

为了在3G核心网中支持多媒体会话,3GPP在R5中引入了IP多媒体子系统(IMS),并选择SIP作为IMS中的呼叫/会话的控制信令.IMS可以提供多媒体业务和语音业务,对QoS提出了更高的要求.主要讨论IMS QoS的一个重要参数-SIP会话建立时延.分析了SIP会话建立时延模型和相关因素并从3方面提出了优化措施,SIP的传输协议选择,信令重传机制的改进以及对SIP信令的压缩,最后进行了性能仿真.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.