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。     

Performance of a nonblocking space-division packet switch withcorrelated input traffic

This work studies the performance of a nonblocking space-division packet switch in a correlated input traffic environment. In constructing the input traffic model, the author considers that each input is a time division multiaccess (TDM) link connecting to multiple sources. Every source on a link supports one call at a time. Each call experiences the alternation of ON and OFF periods, and generates packets periodically while in ON period. The stochastic property of each call does not have to be identical. Packets from each individual call are destined to the same output. The output address of each call is assumed to be uniformly assigned at random. The author derives both upper and lower bounds of the maximum throughput at system saturation. His study indicates that, if the source access rate is substantially lower than the link transmission rate, the effect of input traffic correlation on the output contentions can generally be ignored. Also, the analysis of each input queue becomes separable from the rest of the switch. The same study is carried out with nonuniform call address assignment     

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．     

Estimation of equivalent bandwidth without modeling arrival processes for connection admission control in an ATM multiplexer

The traffic modeling is a key element in analyzing and simulating communications network. Most of the previously studied approaches to the connection admission control (cac) are based on an assumed arrival process model. However, there are some limits to apply the assumed model to the real environment. In this paper, we study a connection admission control (cac) method without assuming arrival processes in an atm multiplexer when homogeneous traffics are multiplexed. To obtain the equivalent bandwidth (eb) without modeling arrival processes, the concept of equivalent bandwidth convergence (ebc) is proposed and implemented by using the upper bound of the first derivative of cell loss rate (clr) for the load. With the ebc concept, one can avoid modeling of the arrival process and implement the cac simply and effectively. We show by numerical examples the convergence process of the average clr and the eb for voice and video traffics, and the robustness of the ebc concept.     

Semi-Markov model for a generalized VBR video in ATM networks

A semi-Markov model describing the performance of an ATM multiplexer with VBR video sources as inputs is presented. The considered system consists of the bit-streams generated by a collection of these sources. The streams which are first separately packetized into fixed size cells, and then, through a statistical multiplexer, join a common queue (assumed to be infinite) where they are served on a FIFO basis by a constant capacity channel. The model to be used is based on the assumption that the video sources operate in two bit-rate modes with unequal average holding times. Each video source is decomposed into an aggregate of two types of ON/OFF mini-sources. Multiplexing a number of such sources leads to a semi-Markov process, which is defined and solved using a phase process with as states the number of active mini-sources of each type. By relating an embedded Markov chain to this phase process, a solution to the resulting queueing system is presented, and the queue length distribution is derived using matrix–geometric techniques. Lastly, results are presented showing that the system performance depends not only on the ratio of the average holding times in the two modes, but also on their magnitudes. This revised version was published online in June 2006 with corrections to the Cover Date.     

DM-CSAT: a LTE-U/Wi-Fi coexistence solution based on reinforcement learning

Recent literature demonstrated promising results of Long-Term Evolution (LTE) deployments over unlicensed bands when coexisting with Wi-Fi networks via the Duty-Cycle (DC) approach. However, it is known that performance in coexistence is strongly dependent on traffic patterns and on the duty-cycle ON–OFF rate of LTE. Most DC solutions rely on static coexistence parameters configuration, hence real-life performance in dynamically varying scenarios might be affected. Advanced reinforcement learning techniques may be used to adjust DC parameters towards efficient coexistence, and we propose a Q-learning Carrier-Sensing Adaptive Transmission mechanism which adapts LTE duty-cycle ON–OFF time ratio to the transmitted data rate, aiming at maximizing the Wi-Fi and LTE-Unlicensed (LTE-U) aggregated throughput. The problem is formulated as a Markov decision process, and the Q-learning solution for finding the best LTE-U ON–OFF time ratio is based on the Bellman’s equation. We evaluate the performance of the proposed solution for different traffic load scenarios using the ns-3 simulator. Results demonstrate the benefits from the adaptability to changing circumstances of the proposed method in terms of Wi-Fi/LTE aggregated throughput, as well as achieving a fair coexistence.

     

A histogram-based model for video traffic behavior in an ATMmultiplexer

The authors introduce a model based on arrival rate histograms for characterizing the behavior of an ATM buffer when it is carrying variable bit rate video traffic. Traffic smoothing on a frame-by-frame basis allows a quasistatic approximation that accurately predicts results such as buffer occupancy distributions and cell loss rates to be made. Convolving individual source histograms allow prediction of the queueing performance of a multiplexed stream. The approximation is investigated in more detail by modeling video as a Markov modulated Poisson process. It is shown that the multiplexer system is nearly completely decomposable (NCD). NCD systems have a well-known approximate solution, which is identical to the histogram approximation. Error bounds for the NCD approximation are also known and are reasonably tight. Results indicate that while the presence of strong correlations is an important characteristic of video traffic, the actual form of that correlation is not     

Design rules and equivalent capacity for buffering of Pareto source

Formulae are developed that act as design rules when buffering an ON-OFF source with long range dependent (LRD) characteristics. These can be used to predict the buffer overflow probability, or the equivalent capacity required to ensure a specified buffer overflow probability. The traffic source has Pareto distributed ON and OFF periods, and therefore this analysis can be seen as an extension of earlier results for exponential ON and OFF periods     

BOUNDS FOR MULTIPLEXING LEAKY-BUCKET ENFORCED SOURCES IN ATM NETWORKS

Leaky-bucket (LB) based traffic parameters are widely used for traffic declaration and monitoring (enforcing) in asynchronous transfer mode (ATM) networks. For such a system, every traffic source is policed by an LB enforcer before entering the access node at the edge of the network. In this article, we investigate the characteristics of the model that such traffic sources are multiplexed together by a multiplexer in the edge node. Based on the worst case performance, we derive the upper bound and the lower bound of queue length at the multiplexer as functions of the LB parameters and number of connections. In particular, we also take the peak cell rate, which is an important parameter, into consideration. We also modify the well-known Little’s formula which is derived based on long-term average, to be suitable for a complete busy period. It helps us to derive bounds on average waiting time by way of average queue length.     

An analysis of statistical multiplexing in an ATM transport network

The traffic characteristics of an asynchronous transfer mode (ATM) network are analyzed by theoretical methods. A new method is proposed to express the burstiness of the cell arrival process. Both statistical multiplexing and statistical bandwidth allocation are quantitatively evaluated. When packetized video traffic and voice traffic are multiplexed, the number of multiplexable sources strongly depends on the peak bit rate of the multiplexed video sources, and statistical bandwidth allocation is ineffective without control. On the other hand, lowering the peak bit rate of video traffic effectively improves bandwidth utilization     

Evaluating the limit behavior of the ATM traffic within a network

This paper is concerned with the ATM traffic characterization within the network. Most of the work performed up to now has studied the effects of traffic on the access multiplexer and the first switch of an ATM network. Various source models were assumed to generate the ATM traffic. So, while the performance of a single switch node has been exhaustively examined, the statistical behavior of the traffic modified as it crosses the network has not been thoroughly analyzed yet. This paper, through an analysis of a network of cascaded queues, indicates that limit distributions exist in the statistical behavior of the traffic streams and in the queue performance, although a formal proof is believed to be very hard to obtain. The first modelling step consists of deriving the exact interdeparture time distribution for the cells of a reference-connection arriving to the output queue of a switch node with a general interarrival time distribution and multiplexed with a background traffic stream. The analysis is iterated through a long sequence of cascaded output queues, until the interdeparture time distribution converges. Simulations show that the analytical results are accurate at each stage of the network under the hypothesis of independent queues, and are also good approximations in the case of correlated queues. This study shows that the queue performance at the limit point is always better than the M/D/1 case. The distributions found in this way depend only on the connection bandwidth and on the background traffic behavior. The initial characteristics of a connection (burst length distributions and burst interarrival time distributions) only influence the convergence speed, not the limit distribution     

A Scalable Call Admission Control Algorithm

In this paper, we propose a scalable algorithm for connection admission control (CAC). The algorithm applies to a multiprotocol label switching (MPLS) ATM switch with a FIFO buffer. The switch carries data from statistically independent variable bit rate (VBR) sources that asynchronously alternate between ON and OFF states with exponentially distributed periods. The sources may be heterogeneous both in terms of their statistical characteristics (peak cell rate, sustained cell rate, and burst size attributes) as well as their quality of service (QoS) requirements. The performance of the proposed CAC scheme is evaluated using known performance bounds and simulation results. For the purpose of comparison, we also present scalability analyses for some of the previously proposed CAC schemes. Our results show that the proposed CAC scheme consistently performs better and operates the link close to the highest possible utilization level. Furthermore, the scheme scales well with increasing amount of resources (link capacity and buffer size) and accommodates intelligently the mix of traffic offered by sources of diversed burstiness characteristics.     

Simulation study on ATM multiplexing of MPEG video sources

In this paper we study the performance of ATM multiplexing of homogeneous MPEG video sources. A source scheduling method is developed to improve the performance of ATM multiplexer for MPEG video sources. Simulation results show that the level of burstiness for the aggregated MPEG traffic is reduced and the network performance is enhanced. Based on the rationale of the source scheduling method, a simple but efficient bandwidth allocation algorithm is also derived for connection admission of MPEG video in an ATM multiplexer. Copyright © 2001 John Wiley & Sons, Ltd.     

重尾ON/OFF源模型生成自相似业务流研究

因为传统模型没有考虑网络业务流量各种时间尺度都具有突发性,因此是不完善的,一系列的测量结果表明,网络业务流量显示自相似性,重尾分布ON／OFF模型能比较好地解释自相似业务流的产生原因,可以把LAN上的业务分解为多个活动（active)主机对之间的业务流,本文通过系统的仿真实验研究了重尾ON／OFF源模型生成自相似流的机理,并与理论结果进行了对比,而且补充了理论结果。     

Loss performance analysis of an ATM multiplexer loaded withhigh-speed on-off sources

The performance of an asynchronous transfer mode (ATM) multiplexer whose input consists of the superposition of a multiplicity of homogeneous on-off sources modeled by a two-state Markovian process is studied. The approach is based on the approximation of the actual input process by means of a suitably chosen two-state Markov modulated Poisson process (MMPP), as a simple and effective choice for the representation of superposition arrival streams. To evaluate the cell loss performance, a new matching procedure that leads to accurate results compared to simulation is developed. The application limits of the proposed method are also discussed. The outstanding physical meaning of this procedure permits a deep insight into the multiplexer performance behavior as the source parameters and the multiplexer buffer size are varied     

Characterization of Arrival Statistics of Multiplexed Voice Packets

An assumption that voice packets arrive by a Poisson arrival (or an exponential interarrival) distribution has not widely been accepted by analysts from an obvious observation that voice packets are generated at regular intervals in a talkspurt. Through a simulation, supported by an approximate analysis, this paper claims that when a sufficiently large number of voice sources are multiplexed, packets observe an exponential or hypoexponential interarrival distribution. When the number of packets arriving during a single or a multiple slot is considered instead, a more liberal claim is made that regardless of the number of voice sources multiplexed, a Poisson process can be assumed with reasonable accuracy.     

Performance Analysis of an ATM Multiplexer with Multiple QoS VBR Traffic

In this paper, we propose a new queuing model, MMDP/MMDP/1/K, for an asynchronous transfer mode (ATM) multiplexer with multiple quality of service (QoS) variable bit rate (VBR) traffic in broad band-integrated services digital network (B-ISDN). We use the Markov Modulated Deterministic Process (MMDP) to approximate the actual arrival process and another MMDP for service process. Using queuing analysis, we derive a formula for the cell loss probability of the ATM multiplexer in terms of the limiting probabilities of a Markov chain. The cell loss probability can be used for connection admission control in ATM multiplexer and the calculation of equivalent bandwidth for arrival traffic. The major advantages of this approach are simplicity in analysis, accuracy of analysis by comparison of simulation, and numerical stability.     

Assessing the accuracy of using aggregated traffic traces in network engineering

Aggregated traffic traces are commonly used in network engineering for QoS or performance parameters evaluation. Many performance models come from such aggregated traces. However, real traffic is a marked point process combining two processes: one for the arrival times of packets and the other for their size in bytes. This paper deals with assessing whether aggregated traces are a good representation of real traffic. Based on the analysis of many traffic traces, and focusing only on loss probability, it is shown that the packet drop probability obtained for the aggregated traffic traces can significantly differ from the real packet drop probability obtained for the real traffic traces. Then, a solution which enables one to obtain correct loss probability based on aggregated traffic traces is proposed by determining the correct aggregation scale and traffic parameters to be applied.     

Performance of a finite capacity asynchronous multiplexer with modulated input

In this paper, a finite capacity multiplexer in ATM environments with modulated deterministic input sources is investigated. We consider three cases of input traffic: (1) a fixed number of deterministic cell-generating sources, (2) a fixed number of sources where each source is modulated by an ON-OFF process, and (3) a variable number of ON-OFF sources, modulated by a call arrival process in conjunction with a connection admission control scheme. The main performance measures in this study are the cell and call blocking probabilities. For case (1), we give a tight upper bound for the transient phase of the state process to reach stationary conditions. The state probabilities and the corresponding cell blocking probability are determined by means of an exact analysis. For cases (2) and (3), where we deal with more complex input traffic, the compound state process and the overall cell blocking probability are analyzed using a quasi-stationary approximation technique. This approximation is validated by means of simulations. The analysis presented is shown to be able to give reasonably accurate approximate results for ATM-multiplexer performance for cases in which conventional simulation and analytic methods already approach computing time and complexity boundaries.