具有大容量缓存器的ATM网络交换节点的接入允许控制

本文讨论了ＡＴＭ网络交换节点的缓存器容量较大时,如何实现实时接入允许控制的问题。我们从大量的计算机模拟的结果中发现,对于符合负指数分布的马尔可夫ＯＮ／ＯＦＦ单一类型或多类型信源,在信元及系统的其它参数保持不变的条件下,信元丢失概率和丢失率,只取决于缓存器容量与信元平均突发长度的比值。本文从“生灭过程”出发加以了证明。     

ATM网络中的ABR业务在不同ONOFF业务背景下的性能研究

本文比较研究了ＡＴＭ网络中的三种不同分布的ＯＮＯＦＦ源对ＡＢＲ业务性能的影响;周期性的ＯＮＯＦＦ源,长度为指数分布的ＯＮＯＦＦ源以及长度为Ｐａｒｅｔｏ分布的ＯＮＯＦＦ源．发现Ｐａｒｅｔｏ分布的ＯＮＯＦＦ源对ＡＢＲ业务的性能影响最大,此时需要更大的缓存器存放在ＶＢＲ业务的ＯＮ期间累积的ＡＢＲ信元．为了改善性能,我们对ＰａｒｅｔｏＯＮＯＦＦ源进行了平滑处理,还在理论上对所得实验结果作了解释．     

ATM网络中的ABR业务在不同ON—OFF业务背景上的性能研究

本文比较研究了ＡＴＭ网络中的三种不同分布的ＯＮ－ＯＦＦ源对ＡＢＲ业务性能的影响;周期性的ＯＮ－ＯＦＦ源,长度为指数分布的ＯＮ－ＯＦＦ源以及长度为Ｐａｒｅｔｏ分布的ＯＮ－ＯＦＦ源,发现Ｐａｒｅｔｏ分布的ＯＮ－ＯＦＦ源对ＡＢＲ业务的性能影响最大,此时需要更大的缓存器存放在ＶＢＲ业务的ＯＮＭ期间累积的ＡＢＲ信元,为了改善性能,我们对ＰｒｅｔｏXＯＮ－ＯＦＦｉｄｒ ｆｊｔｆｂ ｇｕ ｉｍｅ ｔｈｇｊ２,ｇ     

多路ON—OFF信源通过ATM复接器时信元丢失的分析和估计

本文采用类似半导体中“空穴”的思想对离散流体地作了推广，使其适合于两状态ＭＭＤＰ的信源通过ＡＴＭ复接器时的排队分析，然后进一步将它应用于多路ＮＯ－ＯＦＦ信源复接时信元丢失率的分析，经过适当近似以后，得到信元丢失率的闭环表达式。仿真和数值计算表明，该方法准确且适于实时运算，将对ＡＴＭ中呼叫接入控制和资源分配产生积极的影响。     

输入/输出ATM交换机在突发性业务下的性能

本文详尽分析了内部无阻塞输入／输出排队反压型ＡＴＭ交换机在突发性业务下信元丢失、交换机最大吞吐量等性能。输入端口信元的到达过程是ＯＮ－ＯＦＦ突发流，且ＯＮ态以概率ｐ发送信元，ＯＮ－ＯＦＦ长度为Ｐａｒｅｔｏ分布的随机变量；属于同一突发流的信元输往同一个输出端口，不同突发流的信元等概率输往不同的输出端口；输入／输出缓冲器长度有限，交换机加速因子Ｓ任意。本文同时比较了突发长度为周期／几何分布下的交换机性能，其结论对实际设计一输入／输出排队反压型ＡＴＭ交换机具有一定参考意义。     

ATM网络中Pareto分布的ON—OFF业务源对CBR业务时延性能的影响

持续时间长度服从Ｐａｒｅｔｏ分布的ＯＮ－ＯＦＦ源，是比指数分布的ＯＮ－ＯＦＦ源更为接近实际业务统计特性的业务模型。本文研究了背景业务为Ｐａｒｅｔｏ ＯＮ－ＯＦＦ源时，ＣＢＲ业务的时延性能。结果表明，Ｐａｒｅｔｏ分布中的β值决定了ＰａｒｅｔｏＯＮ－ＯＦＦ业务对ＣＢＲ业务性能影响程度的大小。当β值不大于２时，ＯＮ（ＯＦＦ）持续时间方差为无穷大，此时ＣＢＲ业务的时延性能十分差，需要对ＯＮ－ＯＦＦ源进行平     

ATM网络中Pareto分布的ON-OFF业务源对CBR业务时延性能的影响

持续时间长度服从Ｐａｒｅｔｏ分布的ＯＮ－ＯＦＦ源，是比指数分布的ＯＮ－ＯＦＦ源更为接近实际业务统计特性的业务模型。本文研究了背景业务为Ｐａｒｅｔｏ ＯＮ－ＯＦＦ源时，ＣＢＲ业务的时延性能。结果表明，Ｐａｒｅｔｏ分布中的β值决定了ＰａｒｅｔｏＯＮ－ＯＦＦ业务对ＣＢＲ业务性能影响程度的大小。当β值不大于２时，ＯＮ（ＯＦＦ）持续时间方差为无穷大，此时ＣＢＲ业务的时延性能十分差，需要对ＯＮ－ＯＦＦ源进行平     

ON－OFF数据源的漏斗算法分析

在高性能综合分组通信网中，提出了漏斗算法作为评价带宽管理的重要元素。本文分析了ＯＮ－ＯＦＦ数据源的漏斗算法。用平均数据速率、峰值数据速率和在一个ＯＮ周期内产生的平均比特数表示ＯＮ－ＯＦＦ数据源的特征。用虚排队说明漏斗算法特性，用二态马尔可夫调制速率过程模仿ＯＮ－ＯＦＦ数据源。分析了有拒绝或扰乱数据标记的缓冲和无缓冲漏斗。推导出关于漏斗参数大小和速率、ＯＮ－ＯＦＦ信源特性与丢失／标记概率和漏斗排队时延的简单闭合表达式。需要的漏斗大小随着在一个ＯＮ周期内产生的平均比特数线性地增加，并随着丢失／标记概率和在漏斗中的平均排队时延的减少成对数关系地增加。     

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．     

Effective bandwidths for multiclass Markov fluids and other ATMsources

The authors show the existence of effective bandwidths for multiclass Markov fluids and other types of sources that are used to model ATM traffic. More precisely, it is shown that when such sources share a buffer with deterministic service rate, a constraint on the tail of the buffer occupancy distribution is a linear constraint on the number of sources. That is, for a small loss probability one can assume that each source transmits at a fixed rate called its effective bandwidth. When traffic parameters are known, effective bandwidths can be calculated and may be used to obtain a circuit-switched style call acceptance and routing algorithm for ATM networks. The important feature of the effective bandwidth of a source is that it is a characteristic of that source and the acceptable loss probability only. Thus, the effective bandwidth of a source does not depend on the number of sources sharing the buffer or the model parameters of other types of sources sharing the buffer     

An efficient method for computing cell loss probability for heterogeneous bursty traffic in ATM networks

In this paper, we present an approximation for the probability of cell loss of heterogeneous bursty traffic in broadband integrated packet networks based on the asynchronous transfer mode. The sources considered here alternate between active and silent periods and are characterized by their peak and average transmission rates. The cell loss probability is obtained by considering only the number of active sources at a given time and computing the amount of traffic that exceeds the link capacity. Since the amount of buffered excess traffic is not considered in this computation, this approximation is actually an upper bound of the cell loss probability. The numerical efficiency of this bound enables it to be used as a measure based on which robust and simple resource allocation strategies can be developed for bursty sources. Comparison of this bound with the simulation results has shown that the bound is close to the actual loss probabilities especially for large burst lengths and high utilizations.     

A connection control strategy for bursty sources in broadband packet networks

This paper proposes an admission strategy for connection-oriented services at the access node of a broadband integrated packet network based on asynchronous transfer mode. Based on an estimate of the probability of cell loss and in the absence of buffering, we determine the number of sources from different classes of bursty traffic which can be accepted. The parameters which are used to describe the traffic sources are average bit rate and peak bit rate. We will evaluate the cell loss estimate for homogeneous and heterogeneous cases. Furthermore, we will examine the variation of this estimate as the average to peak ratio changes. The estimate is an upper bound for the probability of cell loss. Based on this upper bound simple and robust allocation of resources to bursty sources can be developed. The proposed strategy can be implemented using simple computations or via a look-up table to determine admission or denial of an incoming call and therefore allocating the required capacity. The procedure results in efficient use of the bandwidth, ensuring the desired service quality for connection-oriented services and results in proactive control of network congestion.     

Modelling VBR video over networks end-to-end using deterministic smoothing at the source

Video traffic is expected to become increasingly important with the large scale deployment of broadband ISDN. In the literature, it is suggested that smoothing variable bit rate (VBR) video traffic^1,2 before transmitting it onto the network would help reduce the probability of cell loss. In this paper we show why deterministic smoothing at the source approximates the minimum achievable loss over the network end-to-end of all possible smoothing schemes. Furthermore, we develop a powerful yet simple analytical technique that can efficiently calculate the loss probability at any point in a network carrying video traffic. We validate our analytical results using traces of actual video segments. The results can be used for admission control and traffic management. We find that in the case of highly correlated traffic such as motion JPEG video, the way to control loss is to ensure that the fraction of time the arrival process exceeds the service process is small. We also find that for such sources increasing the buffer size only marginally decreases the loss.     

A method for call admission control in ATM networks with heterogeneous sources

We present a procedure for call admission control for ATM networks. The procedure can be applied to deciding if an additional Virtual Channel (user, source) can be assigned to an end-to-end Virtual Path, or if a link connecting two ATM switches can carry an additional VC. Each source is characterized by its peak rate, mean rate, and cycle length. The objective is to admit as many sources as possible, while meeting a desirable level of cell loss probability. We adapt an effective bandwidth technique to the case where sources do not have to belong to a small number of classes. We do this by suggesting an upper bound for the cell-loss-probability for the case of heterogeneous Markovian on-off sources, and by showing that its computation can be performed in real time by the sending switch, with a reasonable amount of computational and storage resources. We show by simulation that the proposed procedure is effective even for highly bursty source mixes, where it achieves more than 80% of the theoretically possible multiplexing gain.     

Adaptive scalar quantization without side information

In this paper, we introduce a novel technique for adaptive scalar quantization. Adaptivity is useful in applications, including image compression, where the statistics of the source are either not known a priori or will change over time. Our algorithm uses previously quantized samples to estimate the distribution of the source, and does not require that side information be sent in order to adapt to changing source statistics. Our quantization scheme is thus backward adaptive. We propose that an adaptive quantizer can be separated into two building blocks, namely, model estimation and quantizer design. The model estimation produces an estimate of the changing source probability density function, which is then used to redesign the quantizer using standard techniques. We introduce nonparametric estimation techniques that only assume smoothness of the input distribution. We discuss the various sources of error in our estimation and argue that, for a wide class of sources with a smooth probability density function (pdf), we provide a good approximation to a "universal" quantizer, with the approximation becoming better as the rate increases. We study the performance of our scheme and show how the loss due to adaptivity is minimal in typical scenarios. In particular, we provide examples and show how our technique can achieve signal-to-noise ratios within 0.05 dB of the optimal Lloyd-Max quantizer for a memoryless source, while achieving over 1.5 dB gain over a fixed quantizer for a bimodal source.     

Multichannel Convolution Blind Separation Algorithm for MIMO DSSS/CDMA System

Direct-sequence spread-spectrum (DSSS)/code division multiple access (CDMA) transmissions are now widely used for secure communications and multiple access. They can be transmitted at a low signal-to-noise ratio, and have a low probability of interception and capture. How to obtain the original users' signal in a noncooperative context or estimate the spreading sequence in blind conditions is a very difficult problem. Most of the signal sources are assumed to be instantaneous mixtures. In fact, the received CDMA signals are linearly convoluted. A more complicated blind source separation (BSS) algorithm is required to achieve better source separation. In this paper, a new BSS algorithm is proposed for separating linearly convolved signals in CDMA systems when the mixture coefficients of the signal and channel response are totally unknown, but some knowledge about the temporal model does exist. This algorithm is based on minimizing the squared cross-output-channel-correlation criterion. The simulation results show the effectiveness of the algorithm in the blind detection of DS-CDMA signals.     

Performance evaluation of forward error correction in an ATMenvironment

The loss behavior of a cell multiplexer and the performance of forward error correction (FEC) for two homogeneous and one heterogeneous traffic scenarios are discussed. The loss behavior depends on the statistics of the source and on the traffic scenario. Simulation results indicate that the percentage of cells lost in a block is geometrically distributed. Using these results a mathematical model for the performance of FEC is developed, and the effectiveness of FEC for the three traffic scenarios is computed. It is shown that FEC is not effective for the two homogeneous scenarios. However, FEC reduces the loss rate for the video sources by several orders of magnitude for a heterogeneous scenario consisting of video and burst sources     

An analytical paradigm to compare routing strategies in an ATMmultimedia environment

We propose an analytical model for the study of two different routing strategies in an ATM network supporting multimedia traffic flow: the multimedia virtual circuit (MVC) and the independent virtual circuit (IVC). The first strategy consists of assigning a single virtual channel to all of the monomedia streams which make up the multimedia flows; the second strategy consists of multiplexing homogeneous monomedia streams belonging to different multimedia sources on the same virtual channel. With this aim, a multimedia source is modeled as an arrival process defined as the superposition of heterogeneous correlated arrival processes, each of which models one monomedia source. In order to take into account the intermedia relationships which exist in a multimedia stream, each monomedia source is modeled as an interrupted Bernoulli process in which the transition and the arrival probabilities are functions of the states of the other monomedia sources. A finite-buffer discrete-time approach is used in order to compare MVC and IVC performance when an aggregate of N heterogeneous multimedia sources loads the network. Performance is evaluated for each monomedia source in terms of loss probability and jitter probability density function. To assess the proposed paradigm, a case study is shown     

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.