WLAN上的多媒体业务质量研究

随着无线网络的迅速发展，网络上的业务流量与日俱增，如何保证无线局城网实时业务服务质量的问题也越来越突出．文中分别介绍了IEEE802．11中的MAC层协议和802．11e标准中所采纳的改进方式，通过对比分析DCF和EDCF的性能特性，具体仿真时延和丢包率两个性能参数，指出了802．11e标准对MAC层所做的改进．     

面向算力网络的多路径时敏优先调度机制

研究了一种面向算力网络的多路径低时延转发调度算法。该算法可以根据网络状态变化动态更新路径价值量生成路径转发决策，并在一定置信概率内以多路冗余发包的方式进行多路备份传输，降低路径传播时延。还提出了一种等级与队列映射算法，利用网络可编程技术改进设备转发逻辑，利用有限数量严格优先队列保障数据包近似按等级出队，降低数据排队时延。仿真实验结果表明，所提出方法可以降低数据传输时延及抖动，为算力网络业务提供稳定吞吐量。     

基于IP突发信源模型数据包的定量计算研究

本文以IP突发信源on／off模型的单IP业务源的数据包生成特性分析为基础，以队列缓冲配置和IP数据包丢失率、排队时延的计算为主要研究对象，通过对多业务源排队系统的IP数据包排队时延进行深入的综合分析，得出了一些新的QoS定量计算解析式，这些解析式可用于计算IP交换路由器QoS参数．     

基于多业务的队列调度算法研究

讨论了几种典型的调度算法,并在WRR基础上提出一种针对多业务的调度算法(MWRR),同时描述了算法的实现过程。该算法根据各队列的延迟时间比来动态调整队列的调度次序。MWRR算法能够降低多业务的端对端时延,为多业务提供更好的QoS保证。最后通过仿真,证明了该算法的优越性。     

基于MR-ARQ协议的多业务QoS保证机制研究

针对无线通信中高误码率、高突发误帧、频谱资源紧张等特点,对多拒绝自动请求重传(MR-ARQ)协议相比于传统ARQ协议在提高系统吞吐量、降低系统平均传输时延和时延抖动等方面的优势性能进行了理论分析。在此基础上,针对不同业务传输时对误码率、传输时延和时延抖动的不同要求,研究了基于MR-ARQ协议的宽带无线接入系统(BWA)中多业务混合传输的服务质量保证(QoS)机制,提出了多速率重传策略、基于业务区分的多队列机制以及上行集中带宽分配等3种系统性能优化方案。最后对系统在采用上面3种方案前后的性能进行了仿真和比较分析,验证了方案的可行性和良好效果。     

具有优先服务机制的嵌套式DRR算法

针对DRR算法在保证业务时延性能上的固有不足,该文提出了具有优先服务策略的嵌套式DRR算法,该算法对需要保证延时的业务类实施专门的服务策略,利用漏桶控制和虚令牌的分配机制,并改善服务队列的调度策略,在不增加算法复杂度的情况下,有效地减小了时延敏感业务队列中包的延迟。文章证明了算法在获得延时保证的同时,选择合适的参数,仍然能够维持调度算法的公平性。仿真结果表明算法对时延性能的改善是明显的。     

无线宽带通信系统的上行带宽资源分配方案

提出了一种适用于宽带无线通信系统的上行无线带宽资源分配方案。在详细描述算法的基础上，建立了对应的仿真系统对算法进行验证。该方案较好地解决了多业务并发时的上行带宽分配问题。兼顾了不同实时业务对时延和带宽的不同需求，与传统技术相比较，提高了带宽利用率，并减少了协议开销和传输时延。     

基于Crossbar的可重构网络输入排队分域调度研究

为解决传统网络技术体系中交换结构无法满足大量差异化业务规模化应用的问题,本文基于可重构网络技术体系,采用选择关闭部分Crossbar交叉节点的分域模型,提出了分域调度的思想,分析并推导了承载组内的SDRR调度算法和域内最长队列优先调度算法。最后采用交换性能仿真平台对该调度算法进行了复杂度和时延的仿真比较,结果表明:分域调度的最长队列优先算法比一般最长队列优先算法相对复杂度低,且随着调度域个数增加,相对复杂度降低。在相同业务源输入条件下,Crossbar三分域调度算法的时延小于非分域调度算法的时延,接近公平输出排队调度算法的时延。     

多媒体无线网络中基于WRR的包调度策略研究

研究了多业务无线局域网中的分组调度策略,在WRR-CSDPS(信道状态相关的带权重的循环调度)算法的基础上提出了一种最长队列优先的调度策略。算法的目标是减小最长等待队列的长度。通过理论和仿真验证,在该算法下,系统的吞吐量和时延性能有所提高,该算法能够减小业务对系统缓冲区的容量要求。     

AAL2分组话音复接器缓冲器队列容量的确定方法

该文研究AAL2分组话音复接器缓冲器队列容量的确定方法。提出并从理论上证明用话音分组的最大排队时延为9ms作为确定缓冲器队列容量的标准,可很好地满足分组话音业务服务质量要求的结论,并推导出缓冲器队列容量及门限值的计算公式。仿真结果表明:按作者提出的方法确定缓冲器队列容量及门限值,可获得较低的分组丢弃概率和较小的平均分组排队时延;在满足分组话音业务服务质量要求的前提下,减少了话音分组缓冲器队列的容量,是一种很好的确定缓冲器队列容量和门限值的方法。     

Flow assignment method with traffic characteristics over multiple paths for reducing queuing delay

In traffic engineering (TE), it is vital to take traffic characteristics of the flows into account in appropriately assigning the flows to multiple network paths to achieve better delay performance as a whole in order to effectively distribute traffic flows over the paths. This paper presents a novel traffic characteristic-aware flow assignment method to reduce the queuing delay in a fundamental case where two types of flows with distinct traffic characteristics (e.g., burstiness) are distributed into two paths. First, we extensively analyze the queuing delays in assigning flows in the manner of various combinations of flows in terms of minimizing the worst queuing delay among two paths and show that it is not easy to find the optimal flow assignment when the paths have different bandwidths. Second, we propose an on-line flow assignment method for the different-bandwidth paths and show that the numerical simulation with the method finds a nearly optimal flow assignment and outperforms up to 40% compared with the conventional path-bandwidth-based flow assignment. Our evaluation suggests that considering the traffic characteristics in the flow distribution over multiple paths significantly improves the delay performance when the flows have distinct characteristics.     

Ad Hoc网络中具有QoS保障的同步MAC协议

介绍了Ad Hoc网络中保障实时业务QoS要求的时间同步多址接入协议。该类协议以时分多址为基础,通过资源预留为实时业务预约固定的时隙,赋予实时业务接入信道的优先权,保证了实时业务的接入延时,延时抖动以及吞吐量等QoS指标,为Ad Hoc网络支持多媒体业务的接入奠定了基础。     

DELAY JITTER OF A PERIODIC CELL STREAM THROUGH AN ATM MULTIPLEXER IN A BURSTY TRAFFIC ENVIRONMENT

The periodic cell stream is a very important member among the input traffic sources in ATM networks. In this paper, a finite-buffered ATM multiplexer with traffic sources composed of a periodic cell stream, multiple i.i.d Bernoulli cell streams and bursty two-state Markov Modulated Bernoulli Process (MMBP) cell streams is exactly analyzed. The probability mass function of queuing delay, the autocorrelation and power spectrum of delay jitter for this periodic cell stream are derived. The analysis is used to expose the behavior of delay jitter for a periodic cell stream through an ATM multiplexer in a bursty traffic environment. The simulation results indicate that the analytical results are accurate.     

突发性业务环境下周期性信元流通过ATM复接器的时延抖动

在输入ATM网络的业务源中,周期性信元流是很重要的一种.本文精确地分析了一个有限缓存的ATM复接器,其输入业务源由一路周期性信元流、多路随机性贝努利(Bernoulli)信元流和突发性两状态马尔科夫调制贝努利(MMBP)信元流构成.得出了该路周期性信元流的排队时延分布、时延抖动的自相关函数和功率谱.揭示了突发性业务环境下周期性信元流通过ATM复接器的时延抖动行为.计算机模拟验证了分析结果的正确性.     

Scheduling nonuniform traffic in a packet switching system withlarge propagation delay

Transmission algorithms are introduced for use in a single-hop packet switching system with nonuniform traffic and with propagation delay that Is large relative to the packet transmission time. The traffic model allows arbitrary traffic streams subject only to a constraint on the number of data packets which can arrive at any individual source in the system or for any individual destination in the system over time periods of specified length. The algorithms are based primarily on sending transmission schedules to the receivers immediately before transmitting each data packet multiple times so that the receiver can maximize the number of packets it captures. An algorithm based on matchings in a random graph is shown to provide mean total delay divided by mean propagation delay arbitrarily close to one, as the propagation delay tends to infinity     

Analysis of a delay-dependent priority discipline in an integratedmulticlass traffic fast packet switch

A dynamic packet transmission priority discipline, head-of-the-line with priority jumps, is proposed and analyzed for a packet switch serving multiple classes of delay-sensitive traffic. It is shown that, under realistic traffic conditions, the discipline can make the tail probabilities of the delay distributions for the different classes of traffic, in excess of their respective delay requirements, approximately the same, thus resulting in fairness of service and minimization of the maximum tail probability among the different classes. Implementation of the discipline is considered to be relatively simple, and involved processing overhead is minimal     

ARCMA—adaptive request channel multiple access protocol for wireless ATM networks

We propose a new multiple access protocol based on demand assignment. This protocol is designed to reduce contention in the request phase while minimizing transmission delay under various network (ATM) environments. Our protocol uses an adaptive scheme that changes under heavy traffic conditions, and also provides priority to certain delay‐sensitive traffic. Copyright © 2001 John Wiley & Sons, Ltd.     

Multipath routing in mobile ad hoc network with probabilistic splitting of traffic

Multipath routing is a burning issue in mobile ad hoc network due to its various advantages over single path routing. Some of these advantages are load balancing, bandwidth aggregation, and fault tolerance. Multipath routing means multiple paths exist between source and destination pair. Many works discussed in section 2 addressed queuing delays, but none of them suggested queuing delay for multiple path deliveries of data in mobile ad hoc network context. In this paper, we have designed a mathematical model to compute delay and throughput for multipath. Our model follow the network of M/M/1 queues, and we have applied Burke’s theorem to calculate the queuing delay of the packet in mobile network scenario. This model can be used to estimate delay and throughput of an individual path. Further, through the analysis the best path for data delivery out of available multiple paths as well as the multipath path can be used simultaneously for data delivery to the destination. Simulation result shows that splitted traffic multiple paths outperform splitted traffic. Therefore, our model is useful for design and analysis of ad hoc network. The simulation work has been carried out in Qualnet simulator.     

Analytical model of busy channel multiple access (BCMA) for packetradio networks in a local environment

The performance obtainable with busy-channel multiple access (BCMA) techniques is analytically defined in the context of multichannel local radio networks. Network behavior is characterized in terms of throughput and transmission delay when a single radiofrequency channel is shared among many users, thought to be within the range of a central station, suitably located in the local area. The analytical model is based on a suitable Markov model for the generic terminal, and it is assumed that the traffic presented to the common channel conforms to a Poisson distribution. An analytical evaluation of throughput as a function of offered traffic and average transmission delay is presented. The numerical results obtained are for a particular case of BCMA, the well-known busy-tone multiple access (BTMA). In this example, the analytical model proposed allows fast performance evaluation and suitable comparison with CSMA and ALOHA protocol techniques and evaluation of the capture effect