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1.
This paper quantifies a trade-off existing between cell loss and cell delay in an ATM switch with arbitrary input and output buffer sizes. TheEffective Cell Loss is introduced as a cell loss performance measure which combines both the cell loss due to buffer overflow and the cell loss due to excessive delay. ThisEffective Cell Loss measure allows one to design optimal input and output buffer sizes for a given cell loss requirement. Our analysis is versatile enough to easily study the adverse effect due to nonuniform traffic patterns at a switch. Study shows that the nonuniform traffic may jeopardize ATM switches designed under the uniform traffic assumption. For some examples, we have provided both numerical and computer simulation results to show the validity and usefulness of our analysis.  相似文献   

2.
《Computer Networks》1999,31(18):1927-1933
Efficient and fair use of buffer space in an Asynchronous Transfer Mode (ATM) switch is essential to gain high throughput and low cell loss performance from the network. In this paper a shared buffer architecture associated with threshold-based virtual partition among output ports is proposed. Thresholds are updated based on traffic characteristics on each outgoing link, so as to adapt to traffic loads. The system behavior under varying traffic patterns is investigated via simulation; cell loss rate is the quality of service (QoS) measure used in this study. Our study shows that the threshold based dynamic buffer allocation scheme ensures a fair share of the buffer space even under bursty loading conditions.  相似文献   

3.
Performance of ATM networks depends on switch performance and architecture. This paper presents a simulation study of a new dynamic allocation of input buffer space in ATM switching elements. The switching elements are composed of input and output buffers which are used to store received and forwarded cells, respectively. Efficient and fair use of buffer space in an ATM switch is essential to gain high throughput and low cell loss performance from the network. In this paper, input buffer space of each switching element is allocated dynamically as a function of traffic load. A shared buffer pool is provided with threshold-based virtual partition among input ports, which supplies the necessary input buffer space as required by each input port. The system behaviour under varying traffic loads has investigated using a simulation program. Also, a comparison with a static allocation scheme shows that the threshold based dynamic buffer allocation scheme ensures an increased network throughput and a fair share of the buffer space even under bursty loading conditions.  相似文献   

4.
目前已证明,在同样大小缓冲区的条件下,基于中央排队的交换系统具有较好的性能。文中对在中央排队交换系统中如何实现多址传输及解决多址传输与单址传输冲突的方法进行详细描述,提出了一种称为具有输出缓冲和屏蔽优先级的单写单读方案,实现多址传输并解决多址传输与单址传输的冲突,降低信元丢失率和信元延时,最后给出该方案的仿真建模方法。  相似文献   

5.
A number of recent studies have addressed the use of priority mechanisms in Asynchronous Transfer Mode (ATM) switches. This investigation concerns the performance evaluation and dimensioning of a shared-buffer switching element with a threshold priority mechanism (partial buffer sharing). It assumes that incoming ATM cells are distinguished by a space priority assignment, i.e., loss of high priority cell should be less likely than loss of a low priority cell. The evaluation method is analytic, based on an approximate discrete-time, finite-state Markov model of a switch and its incoming traffic. The development focuse son the formulation of steady-state loss probabilities for each priority class. Evaluation of delay measures for each class is also supported by the model; results concerning the latter are illustrated without development. The analysis of loss probabilities is then used to dimension the buffer capacity and threshold level such that required maximum cell loss probabilities are just satisfied for each cell type. Moreover, when so dimensioned with respect to relatively stringent loss requirements, i.e., probabilities of 10−10 and 10−5 for high and low priority cells, respectively, we find that both loss performance and resource utilization are appreciably improved over a comparable switch without such a mechanism.  相似文献   

6.
Multistage interconnection networks (Banyan networks) are frequently proposed as connections in multiprocessor systems, in ATM switches, or in Gigabit Ethernet switches. There exist several analytical models for evaluating the performance of such networks. Analytical models are much faster for this purpose than simulation. On the other hand, the development of an analytical model is very time-consuming. In this paper, we present a method for the automatic and fast generation of an analytical network model. The generated analysis handles networks of arbitrary size, arbitrary switching element sizes, arbitrary buffer lengths in each network stage, an arbitrary (but uniform) traffic pattern, and an arbitrarily chosen network load. The arbitrary traffic patterns include multicast traffic, which has not been considered by former models.  相似文献   

7.
In this paper, we study the mean delay and maximum buffer requirements at different levels of burstiness for highly bursty data traffic in an ATM node. This performance study is done via an event-driven simulation program which considers both real-time and data traffic. We assume that data traffic is loss-sensitive. A large buffer (fat bucket) is allocated to data traffic to accommodate sudden long burst of cells. Real-time traffic is delay-sensitive. We impose input traffic shaping on real-time traffic using a leaky-bucket based input rate control method. Channel capacity is allocated based on the average arrival rate of each input source to maximize the utilization of channel capacity. Simulation results show that both the maximum buffer requirements and mean node delay for data traffic are directly proportional to the burstiness of its input traffic. Results for mean node delay and cell loss probability of real-time traffic are also analyzed. The simulation program is written in C++ and has been verified using the zero mean statistics concept by comparing simulation results to known theoretical or observed results.  相似文献   

8.
《Real》2001,7(3):287-300
This paper describes a framework for the transport of real-time multimedia traffic generated by MPEG-2 applications over ATM networks using an enhanced UBR best effort service (UBR+). Based on the factors affecting the picture quality during transmission, we propose an efficient and cost-effective ATM best effort delivery service. The proposed framework integrates three major components: 1) a dynamic frame-level priority assignment mechanism based on MPEG data structure and feedback from the network (DexPAS), 2) a novel audio-visual AAL5 SSCS with FEC (AV-SSCS), and 3) an intelligent packet video discard scheme named FEC-PSD, which adaptively and selectively adjusts cell drop levels to switch buffer occupancy, video cell payload type and forward error correction capability of the destination. The overall best-effort video delivery framework is evaluated using ATM network simulation and MPEG2 video traces. The ultimate goal of this framework is twofold: First, minimizing loss of critical video data with bounded end-to-end delay for arriving cells and second, reducing the bad throughput crossing the network during congestion. Compared to previous approaches, performance evaluation shows a good protection of Predictive coded (P-) and Bi-directional Predictive coded (B-) frames at the MPEG video slice layer.  相似文献   

9.
ATM论坛将基于速率的流量控制选定为ABR业务的流量控制方法。通过对基于速率的流量控制和基于凭证的流量控制方法的研究,提出了一种信元丢弃流量控制原则,该模型继承了基于凭证方法的记数机制,通过设定高低缓存门限和调节速率升降因数来控制源端速率,仿真结果表明,这种控制机制不仅能够保证缓存的充分利用,而且能够提高其在减少信元丢失等方面的性能。  相似文献   

10.
《Computer Networks》1999,31(6):617-625
On the backbone nodes of enterprise networks which handle data and voice traffic, complicated Quality of Service (QoS) capability, transmission efficiency, and high reliability are required. ATM technology satisfies those requirements. We have developed a large scale enterprise ATM node based on the shared buffer switch architecture. In the node, per-VC traffic control functions are implemented at low cost using centralized control of buffer write and read. In this paper, we explain the detail of the per-VC traffic control functions and show the performance results of ABR control using the node.  相似文献   

11.
In this paper, we analyze the performance characteristics of an ATM switch, where cell arrivals are generated according to a three-state Markovian arrival law. This arrival process is an extension for the two-state ON/OFF source model that has already been extensively treated in the literature, and it allows a much more flexible modeling of a wide variety of VBR sources. As a result, for the finite storage capacity case, the system contents distribution, as well as the cell loss ratio are derived. On the other hand, for the infinite storage capacity case, a method for deriving an expression for the probability generating function of the system contents is presented. Furthermore, an approximation (consisting of multiple geometric terms) for the tail distribution of the system contents is given. The accuracy of this approximation as well as the impact of the traffic parameters on the buffer behavior are discussed via some numerical examples.  相似文献   

12.
In this paper, we present a new, effective connection-oriented congestion control protocol for B-ISDN. The protocol employs the traffic viewpoint hierarchical design approach and is implemented by a two-layer scheme at the call and cell layers. The call layer handles call admission (denial) and provides shortest path connection routing when a call is admitted, while the cell layer allocates switch input buffer space for each traffic type according to each type's cell loss probability grade-of-service requirement. There is a direct interaction between the two layers in processing a connection request. A discrete-time queueing system with geometrically distributed service time and state-dependent Markov modulated Bernoulli process (MMBP) arrivals is established to model heterogeneous networking environments for this protocol and an analytical solution is developed for this queueing system. Numerical results obtained by both analysis and simulation show that the protocol can reduce network congestion as input traffic rates approach switch capacity and, thereby, increase network utilization relative to that possible in the absence of congestion control.  相似文献   

13.
Congestion control based dynamic routing in ATM networks   总被引:2,自引:0,他引:2  
In this paper we describe briefly a dynamic multi-path algorithm that has been considered for connection oriented asynchronous transfer mode (ATM) networks. Our scheme takes advantage of a cell multiplexing capability that has particular advantage in networks supporting variable bit rate (VBR) traffic. The fundamental objective of the scheme is to propose a congestion control based scheme that bridges the gap between routing and congestion control as the network becomes congested. The proposed routing scheme works as a shortest path first algorithm under light traffic conditions. However, as the shortest path becomes congested under unbalanced heavy traffic, the source uses multiple paths when and if available to distribute the calls and reduce cell loss. This mechanism will provide good Quality of Service for clients within the given constraints. We compare the performance of the proposed scheme with other competitive schemes. The throughput and cell loss performance are compared via simulations. These have been carried out concentrating on a five node network, each with varying traffic patterns, with the intention of gaining insight into the strengths and weaknesses of the various schemes.  相似文献   

14.
We consider an ATM switch consisting of a number of output-buffered ATM switch elements operating in parallel. Such an architecture may lead to uneven distribution of cells over the parallel switch element buffers, if no modifications to the design is made. With this motivation, we propose a threshold based load balancing method to evenly distribute the cells over the parallel switch element buffers. We present the details of how the load balancing method can be implemented. Our computer simulations show that the proposed load balancing method significantly reduces the cell loss probability. The study is done with two input traffic models: random traffic and bursty traffic.  相似文献   

15.
iLQF调度算法及其参数的仿真   总被引:1,自引:0,他引:1  
文章介绍一种无内部阻塞ATM交换结构的输入缓存模型及其缓存信元的iLQF调度算法(即迭代的最长队列优先调度算法),并具体给出该算法的实现方案。通过仿真,分析和确定了交换结构的输入缓存长度和iLQF调度算法的迭代次数对信元丢失率的影响。  相似文献   

16.
17.
The problem of end-to-end connection performance in Asynchronous Transfer Mode (ATM) networks is extremely important because its solution provides the information (such as end-to-end delay distribution and cell loss ratio) necessary for the definition of the Quality of Service (QoS) guarantees for real-time connections. Due to the analytical complexities inherent in this problem, we are seeking to develop an efficient simulation technique for the fast production of results. The presented approach is a combination of an earlier time-parallel technique and probabilistic routing. An implementation of this technique on a multiprocessor with modest capabilities shows promising speed-up. Using the developed simulator, several experiments are conducted for the end-to-end behavior of ATM connections using bursty traffic models, including ones with active periods derived from heavy tailed distributions. An important feature of the study is that the interfering traffic is of the same type as the end-to-end traffic. Thus, no assumptions are made about traffic smoothing or approximations of the aggregate interference process by Poisson arrivals. The presented end-to-end performance results include the Cell Loss Ratio (CLR) and the delay distribution at the multiplexers and at each intermediate switch of the connection path. Among the presented findings, it is illustrated that if only few sources with heavy tailed active periods are multiplexed and if the utilizations are low, then the end result is not necessarily a worse performance as one would anticipate when larger aggregations of such sources asymptotically approximate a self-similar process.  相似文献   

18.
In this paper we describe a network modelingapproach intended to assist in the performancemanagement, design, and optimization of broadbandtraffic networks. Switch and source models, as well asrouting optimization and decision support algorithmshave been integrated in a prototype software tool,called DATANMOT (Data Network Modeling and OptimizationTool). The switch models developed are based on standard Frame Relay and ATM switch implementations.Specifically, an analytical model of the Fujitsu FETEX150 ATM switch is described here in detail. Fluid-flowapproximation methods were used for performance evaluation, with computational complexity lowenough for near-real time applications. As a result,given the network configuration and input traffic, anevaluation of the quality of service can be derived and used in optimal routing, admission controland network planning. These techniques have beenincorporated in our modeling tool to demonstrate themodel-based approach to network management. In addition, all configuration, modeling, and managementfunctions of the software tool are supported by agraphical user interface, and a databasesystem.  相似文献   

19.
ATM网络的一种实时传输调度和信元丢失控制的综合方案   总被引:9,自引:2,他引:9  
林闯 《计算机学报》1998,21(4):333-340
本文提出了ATM网络的一种实时传输调度和信元丢失控制的综合方案。  相似文献   

20.
Pipelined Circuit Switching (PCS) has been suggested as an efficient switching method for supporting interprocessor communication in multicomputer networks due to its ability to preserve both communication performance and fault-tolerant demands in these networks. A number of studies have demonstrated that PCS can exhibit superior performance characteristics over Wormhole Switching (WS) under uniform traffic. However, the performance properties of PCS have not yet been thoroughly investigated in the presence of non-uniform traffic. Analytical model of PCS for common networks (e.g., hypercube) under the uniform traffic pattern has been reported in the literature. A non-uniform traffic model that has attracted much attention is the hot spot model which leads to extreme network congestion resulting in serious performance degradation due to the tree saturation phenomenon in the network. An analytical model for WS with hot spot traffic has been reported in the literature. However, to the best of our knowledge, there has not been reported any analytical model for PCS augmented with virtual channels in the presence of hot spot traffic. This paper proposes a model for this switching mechanism using new methods to calculate the probability of message header blocking and hot spot rates on channels. The model makes latency predictions that are in good agreement with those obtained through simulation experiments. An extensive performance comparison using the new analytical model reveals that PCS performs the same or in some occasions worse than WS in the presence of hot spot traffic.  相似文献   

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