因特网上视频多点传输算法研究

本文研究因特网上进行视频多点传输的问题.在分析了资源预约协议和智体反馈控制机制的基础上,基于分层编码技术提出一种新的视频传输算法.文中利用ns-2网络模拟器进行了性能评价,结果表明该算法在保证视频基本服务质量的条件下,具有较好的公平性和可扩放性.     

基于最优化的多媒体多播速率控制

传输多媒体流的一种有效方法是采用多速率多播,但多速率多播的速率控制面临许多挑战,如异构性、公平性、实时性及服务质量(QoS)等。提出了一种两阶段优化的策略进行多媒体多播速率控制。把问题公式化为求系统效用最大化的最优化问题,推导出有效的算法。方法综合考虑了服务质量、异构性等,且满足协议间的公平性和多播会晤内各接收者间的公平性。仿真实验表明算法的有效性,与现有的算法相比系统总效用大大提高。     

基于服务公平性感知的弹性光网络动态频谱分配算法

针对弹性光网络中的业务服务公平性问题,从不同粒度、不同跳数业务之间的服务公平性两方面,分别提出了相应的公平性感知动态频谱分配算法.通过引入新的效用函数,使得进行频谱分配时不仅考虑不同粒度、不同跳数业务间的服务公平性,而且还兼顾网络整体的频谱资源利用率,从而大大缓解了网络整体阻塞性能损伤.仿真结果表明,在动态网络环境下,针对不同粒度、不同跳数的业务的公平性问题所提出的方案可以极大地提高弹性光网络中业务之间的服务公平性,并且没有明显的阻塞性能恶化.     

VoIP语音服务质量评测

介绍了VoIP语音服务连接方式、VoIP语音质量的分级、VoIP语音服务质量评测的基本方法、传输性能评价,分析了E-Model作为一个网络传输规划工具在VoIP语音服务质量评测中起的作用及其巨大的局限性。     

基于无线传感器网络的业务流调度算法

实时性要求是无线传感器网络调度算法性能评价的重要内容。对于实时性要求很高的应用场合,调度算法的首要标准是降低数据包的传输时延。针对无线传感器网络的业务流调度问题,结合传统的加权循环调度算法WRR,着眼于解决无线传感器网络中业务流突发引起的时延性能下降问题,提出了新的调度算法-WSWRR。新算法合理分配传感器节点的数据感知和传输时间,使节点在不需要工作时转入低功耗的休眠模式,且能在满足应用要求服务质量的前提下,高效利用节点能量,延长整个传感器网络的生命周期。通过仿真实验,验证了新算法在调度突发数据包时性能得到了很好的改善,且没有增加网络的整体能耗,证明了WSWRR算法的有效性。     

基于IEEE802.16e的多级别业务调度算法研究

在IEEE802.16e标准中,保证QoS的调度算法一直是人们研究的热点,它涉及到从单一业务到多级别业务的调度服务.对多级别业务调度的支持是保证系统性能的重要技术之一.本文针对多级别业务常用的分层调度和联合调度策略,从系统吞吐量、QoS性能和公平性等方面对之进行的仿真分析和性能比较.仿真结果表明联合调度策略综合性能较好.     

基于MPLS的话音传输

因特网的快速发展,促使各种应用及服务不断涌现.多协议标签交换(MPLS)作为一种非常灵活的载体,不仅可以传输数据,而且可以利用其在资源预留协议(RSVP)、服务质量(QoS)方面的优势提供语音及多媒体等方面的服务.文章首先介绍MPLS两种主流语音传输技术,进而与VoIP的传输性能进行了比较分析,最后探讨了VoMPLS存在的技术问题和VoMPLS将来的应用前景.     

区分服务中一种基于聚集流内部公平性的标记算法

在现今异构刚络Internet,区分服务体系结构通过对不同应用和不同要求的数据流部署不同等级的服务,以提供较大粒度的服务质量(Quality of Service,QoS)保证.不同流之间的公平性问题是区分服务中的研究热点,而标记策略是提高公平性的有效方法.目前许多标记算法只考虑了聚集流之间的公平性,而忽略了聚集流内部流之间的公平性.本文针对同一个聚集流中可能包含不同类型的单个流情况(比如存在自适应TCP流和非适应UDP流、不同速率的多媒体UDP流、采用不同TCP协议的数据流、不同分组大小的数据流),提出了一种基于聚集流内部公平性的标记算法(Fair Aggregate Traffic Marker,FATM).论文构造了不同情况下的模拟场景,并给出了实验的相关参数设置.大量模拟实验结果表明:标记算法FATM在保持聚集流之间的公平性和网络吞吐量的基础上,提高聚集流内部单个流之间的公平性.     

无线mesh网络中多跳数据流的拥塞控制

提出了一种无线mesh网络的拥塞控制机制LAP(link layer adaptive pacing),利用mesh网关控制有线到无线数据流的发送速率,避免过多数据传输产生跳路间的严重干扰.算法以每个数据流为对象,在改进多跳数据流性能的同时,还很好地保证了网络公平性.此外,控制机制在链路层完成,不需要修改现有传输或路由协议.仿真结果表明LAP控制下的网络性能远远胜过802.11网络,而且较目前主流算法也有明显改善.     

UDP流量对TCP往返延迟的影响

提出一个面向单条链路的TCP综合传输性能测度R,分析其与同一时间粒度内链路的占用带宽和UDP流量比例间的关系,使用中国和美国2条主干信道的实测数据进行了检验。结果表明R测度可表示为以占用带宽和UDP流量比例为参数的正态分布的随机过程。随后进行的CERNET链路R测度正态分布均值参数的拟合分析具有很高的可接受水平,拟合的结果给出的量化关系可用于流量的公平性评价。     

A probabilistic approach for fair-efficient call admission control in wireless multiservice networks

The efficiency of call admission control (CAC) schemes in multiclass wireless networks should be evaluated not only with regard to the call blocking probability (CBP) achieved for every service class (SC) supported but also with regard to quality of service (QoS) and network efficiency criteria. In this article, four CAC schemes offering priority to SCs of advanced QoS requirements, based on guard channel policy, are studied and evaluated taking into account fairness and throughput criteria in addition to CBP. For the performance evaluation of the proposed CAC schemes and to examine fairness issues, two fairness indices are introduced along with a throughput metric. The analytical results, validated through extensive simulations, indicate that by appropriate selection of the CAC parameters satisfactory fairness and throughput are achieved while achieving low CBP.     

An Approach to Scheduling Bursty Traffic

The scheduling scheme in packet switching networks is one of the most critical features that can affect the performance of the network. Hence, many scheduling algorithms have been suggested and some indices, such as fairness and latency, have been proposed for the comparison of their performances. While the nature of Internet traffic is bursty, traditional scheduling algorithms try to smooth the traffic and serve the users based on this smoothed traffic. As a result, the fairness index mainly considers this smoothed traffic and the service rate as the main parameter to differentiate among different sessions or flows. This work uses burstiness as a differentiating factor to evaluate scheduling algorithms proposed in the literature. To achieve this goal, a new index that evaluates the performance of a scheduler with bursty traffic is introduced. Additionally, this paper introduces a new scheduler that not only uses arrival rates but also considers burstiness parameters in its scheduling algorithms.     

QoS guarantee in telecommunication networks: technologies and solutions

The aim of this paper is to show the effect of the presence of specific management functions within a network that offers quality of service (QoS). The objective is not privileging a particular technology but to highlight the importance to know which control functions a solution may use, which performance limits the functions have and what can be a realistic user expectation. The paper focuses on the meaning of QoS and on the applications requiring quality, then describes QoS solutions including transport technologies, QoS‐oriented technologies, parameters and management functions. In more detail, the effect on QoS provision of the following issues is investigated and discussed concerning the possibility (or not) to aggregate and differentiate traffic, the implementation of call admission control and of traffic filtering to limit flows to their committed rates. Again, the conclusions should not be considered a merit mark about technology, but only an investigation about: what users and customers should expect by the technologies using specific control functions evidencing that the real limitations are not imposed by a specific technology, whose features may be changed and extended, but by the application of control functions that can guarantee requirements' matching. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance assessment of AT&T international switched voice services

This paper describes the performance assessment of AT&T international switched voice services. Call availability and call suitability performance issues are emphasized. Field study methods and tools for studying them are discussed. Performance issues addressed include network response times, voice, and voiceband data transmission quality. Two examples of field studies, one an objective study for evaluating the performance of a new service, and the other a subjective study to assess the performance of a new technology are also presented.     

Measurement‐based admission control scheme with priority and service classes for application in wireless IP networks

Wireless IP networks will provide voice and data services using IP protocols over the wireless channel. But current IP is unsuitable to provide delay or loss bounds and insufficient to support diverse quality of service, both required by real‐time applications. In order to support real‐time applications in wireless IP networks, in this paper a measurement‐based admission control (MBAC) with priority criteria and service classes is considered. First we have shown the suitability of MBAC in wireless IP networks by comparing its performance with a parameter‐based scheme. Next, we have investigated the performance of strictly policy‐based MBAC and policy plus traffic characteristic‐based MBAC schemes in terms of (1) increasing the user mobility, (2) changing traffic parameters and (3) the presence of greedy users. The efficiency and fairness of each scheme are measured in terms of lower class new and handoff traffic performance. Copyright © 2003 John Wiley & Sons, Ltd.     

Manual and Automatic Design for UMTS Networks

This paper describes manual and automatic design strategies of UMTS networks. The design aims at adjusting antenna parameters: antenna pattern, tilt and azimuth angles, as well as the common channels' transmitted power to improve the network performance in terms of coverage, capacity, quality of service and service continuity. The manual design strategy is based on an expert system that analyzes different quality criteria of the network and suggests the designer the most effective parameter modifications. The automatic design strategy is based on a Genetic Algorithm that orchestrates the design process. Two optimisation models are considered: the first one uses constant load hypotheses in the network evaluation; the second one takes into account inhomogeneous traffic distribution and utilizes accurate modelling of basic UMTS quantities such as power, load and interference. Detailed examples of network optimization illustrate the effectiveness of the design strategies.     

ATM网中ABR业务及其反馈流量控制

ABR（AvailableBitRate）业务是近年来为了充分利用ATM网络的剩余带宽而提出的一种新型业务类型，自从1993年被ATM论坛正式提出以来得到了很快的发展。文章对该业务的特点和发展过程作了较全面的介绍，对该类型业务的流量控制方法作了比较深入的分析和研究，对流量控制中关键因素的改进提出了自己的见解。     

Resource allocation for statistical quality of service provision in buffered crossbar switches

The buffered crossbar switch is a promising switching architecture that plays a crucial role for providing quality of service (QoS) in computer networks. Sufficient amount of resources—bandwidth and buffer space—must be allocated in buffered crossbar switches for QoS provision. Resource allocation based on deterministic QoS objectives might be too conservative in practical network operations. To improve resource utilization in buffered crossbar switches, we study the problem of resource allocation for statistical QoS provision in this paper. First, we develop a model and techniques for analyzing the probabilistic delay performance of buffered crossbar switches, which is described by the delay upper bound with a prescribed violation probability. Then, we determine the required amounts of bandwidth and buffer space to achieve the probabilistic delay objectives for different traffic classes in buffered crossbar switches. In our analysis, we apply the effective arrival envelope to specify traffic load in a statistical manner and characterize switch service capacity by using the service curve technique. Instead of just focusing on one specific type of scheduler, the model and techniques developed in this paper are very flexible and can be used for analyzing buffered crossbar switches with a wide variety of scheduling algorithms. Copyright © 2007 John Wiley & Sons, Ltd.     

A NEW ABR CONGESTION CONTROL ALGORITHM ACHIEVING FAIRNESS UNDER SEVERAL CRITERIA

All ABR congestion control algorithms reported are designed to achieve max-min fairness. In this paper, a new algorithm named dynamic bandwidth allocation algorithm is presented. Under the same framework, the algorithm can achieve fairness under several given criteria. Simulation result shows that the new algorithm works well under various network configurations, various traffic classes, and scale well to LANs or WANs.     

Enhanced distributed explicit rate allocation for ABR services inATM networks

Rate allocation for available bit-rate (ABR) services in ATM networks has received a considerable amount of attention, but important issues such as bandwidth fairness, MCR rate guarantees, and queue control still require further investigation. In light of these concerns, an enhanced rate allocation algorithm is proposed for congestion management using explicit rate feedback control. The algorithm uses fast, exact rate computations and is capable of achieving a variety of MCR-related fairness criteria. The scheme handles transient effects and can function in heterogeneous networks carrying higher priority real-time traffic. Simulation results for a wide range of network scenarios demonstrate that the algorithm effectively controls queue buildups and achieves good fairness. Performance scalability to large networks under challenging conditions is also shown for a given control parameter set