具有业务量平滑功能的ATM交换机的性能分析

ATM网络支持大量的突发业务源。突发业务量可用间断Bernoulli过程描述。本文采用一种循环算法,分析了ATM交换机在既有连续比特流业务量又行突发业务量环境下的信元丢失率和平均延迟。数值分析结果和计算机仿真结果一致表明,具有业务量平滑功能的ATM交换机的性能有较大改进。     

On multicast support for shared-memory-based ATM switcharchitecture

Because of its superior performance characteristics in terms of cell loss and throughput for a given memory space, shared-memory ATM switches have gained significant importance in handling bursty traffic in ATM networks. Because of its increased effective load, multicast traffic requires an even greater increase in switching capacity than a shared-memory-based ATM switching system can provide. In order to support multicast operations with a memory-based switching system, the replication and storage methods used for multicast ATM cells for switching purposes become important. Various ways used to support multicast operation with a shared-memory-based ATM switching system have been categorized into several classes. Performance evaluation shows that the class of single-write single-read multicast scheme with output mask (CSWSR-w-OM) implementation overcomes the memory bottleneck involved with replication of multicast cells. It also provides superior performance for a given memory space employed in the shared-memory switching system in comparison to other classes of multicast schemes     

Request rate control for QA services in DQDB/SMDS–ATM gateways

By the advancement of B-ISDN, ATM has been accepted as the future technology to integrate a variety of services as it is a fine comprise between circuit switching technology and packet switching technology. A cost-effective and simple way to realize the global network is to implement a backbone such as DQDB to interconnect the existing LANs and MANs to ATM. The major advantages of DQDB are the complete compatibility of different layers, the capability of handling real-time and non-real-time traffic and little degradation in delay performance with increase in network span and density. However, a major issue of concern in the design of a DQDB/SMDS–ATM gateway is the transparent transfer of non-real-time traffic, as ATM is basically connection-oriented in nature. In the absence of flow control schemes in high-speed networking, some sort of congestion control mechanism becomes an absolute necessity to reduce the cell loss ratio to the minimum and thus wastage in the network resources. In this paper we discuss the transfer of connectionless traffic in a DQDB–ATM interconnection. One of the two congestion control mechanisms for DQDB networks that we have proposed is discussed in detail. In the request rate control mechanism the bandwidth utilization in DQDB is restricted by controlling the request rate from the gateway. DQDB networks interconnected by gateways are modelled and simulated. The request rate congestion control mechanism is evaluated. Simplicity in implementation and effectiveness in performance are the highlights. © 1998 John Wiley & Sons, Ltd.     

Evaluation of congestion control protocols for ABR traffic over ATM networks

Congestion control is very important for effective and stable operation of ATM (Asynchronous Transfer Mode) networks. Owing to the bursty and unpredictable characteristic of data network traffic, its congestion control is particularly a challenge for network researchers and designers. The ATM Forum has recently adopted rate‐based congestion control for ABR (Available Bit‐Rate) traffic which is the service class defined for data network applications. However, there is a number of congestion control schemes prevalent. ATM Forum has decided not to specify switch behaviour for ABR traffic; this has further introduced additional ambiguity. Consequently, an evaluation and comparison of the existing protocols would provide valuable guidance for network designers and engineers; it would also give insight for researchers to explore the essence of different congestion control schemes. In the first part of this paper, we investigate the effectiveness of ABR congestion control in the presence of bursty source traffic and the relationship between the burst time scale and the ABR control time scale. Two ABR congestion control schemes, the ABR Explicit Forward Congestion Indication (EFCI) and ABR Congestion Indication (CI) schemes, are compared with Unspecified Bit Rate (UBR) transport which makes no effort to control congestion. Traffic sources of various burst lengths of 100, 1000, 10000, and an equal mix of 100 and 10000 ATM cells are used in simulations. It is found that ABR congestion control schemes effectively control low frequency, medium to long‐term traffic load transients. This is further supported by the result of integrating TCP over ATM congestion control schemes included in the paper. ABR control schemes do not control high frequency, short‐term load transients well, but ABR control is not necessary in such cases since short‐term transients do not require a large amount of buffering. In the second part of this paper, we evaluate and compare six rate‐based congestion control protocols including Scheme I: EFCI, Scheme II: EFCI with separate RM queues, Scheme III: CI, Scheme IV: CI with separate RM queues, Scheme V: the CAPC2 ER (Explicit Rate), and Scheme VI: the EFCI with utilization‐based congestion indication. Each scheme is simulated and compared in the LAN, WAN, and GFC (General Fairness Configuration) environments specified by the ATM Forum. Effects of varying VC (Virtual Circuits) number and changing endsystem–switch distance has been investigated. Their fairness is also compared using the GFC configuration. We have found that ER control scheme performs significantly better than the other five binary control schemes by its faster response to congestion, smoother regulation of bit‐rates, lower queueing delay, shorter buffer queue length, and fairness. Among the other five schemes, the CI scheme performs better than the EFCI scheme. Providing separate RM queues has significantly improved the EFCI scheme in the WAN environment, but has little effect on the CI scheme. Link utilization‐based congestion detection has suffered from either low utilization or an excess cell loss which is unacceptable in most data applications. Copyright © 2000 John Wiley & Sons, Ltd.     

Performance of in-call buffer/window allocation schemes for short intermittent file transfers over broadband packet networks

While static open loop rate controls may be adequate for handling continuous bit rate (CBR) traffic, relatively smooth data traffic, and relatively low speed bursty data traffic over broadband integrated networks, high speed bursty data sources need more dynamic controls. Burst level resource allocation is one such dynamic control. Potential benefits and other issues for burst level resource parameter negotiations for bursty data traffic over high speed wide area packet networks have been discussed earlier.^1–6 A detailed analysis of an adaptive buffer/window negotiation scheme for long file transfers using these concepts is presented in Reference 1. In this paper we discuss two burst level buffer/window negotiation schemes for short intermittent file transfers, focusing on the specific needs of such traffic streams. We develop closed network of queues models to reflect the behaviour of the proposed schemes. These models, while being simple, capture essential details of the control schemes. Under fairly general assumptions, the resulting network of queues is of product form and can be analysed using the mean value analysis. We use such an analysis to compare the proposed schemes and to determine appropriate sizes of trunk buffers to achieve the desired balance between bandwidth utilization and file transfer delay. The effects of other parameters on the performance of these schemes as well as on the buffer sizing rules are also discussed. Burst level (in-call) parameter negotiation may be carried out by the end system with the network elements or by an interface system (access controller) with the broadband network elements. We discuss implications of this location as well as the needed protocol features. Finally, the service discrimination capabilities desired at the trunk controllers in switching nodes are briefly discussed.     

Analysis of interdeparture processes for bursty traffic in ATMnetworks

Admission control in asynchronous transfer mode (ATM) networks is considered. An ATM switch is modeled as a discrete-time single-server queue at which the following three different kinds of arrival processes are allowed to join together: arrivals of cells with a general interarrival time distribution; Bernoulli arrivals of cells in batches; and interrupted Poisson processes. An exact analysis is given to derive the waiting-time distributions and interdeparture-time distributions for arriving cells subject to admission control in ATM networks. The model is extended to approximately obtain the end-to-end delay distributions for the designated traffic stream. Such an analysis is important for voice or coded video because they require a playout mechanism at the destination. Since the analysis is approximate, the simulation results needed to assess its accuracy are provided. Numerical examples show how the traffic characteristics of the designated traffic stream are affected by the total traffic load at the switching node, the number of other bursty traffic sources, and the degree of burstiness of the traffic source itself     

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.     

Measured average cell rate‐based congestion avoidance scheme

Techniques for congestion control of available bit‐rate (ABR) traffic in ATM (asynchronous transfer mode) networks remain an important issue. Several congestion control schemes have been proposed to adjust the cell rates of sources with a modified or mean allowed cell rate. To make these schemes work effectively in practice, the modified or mean allowed cell rate must converge under all conditions. However, it is not easy to obtain an accurate value, and an inaccurate value could result in network performance degradation such as severe oscillations and considerable unfairness. Therefore, we propose a measured average cell rate‐based congestion avoidance for ABR traffic in ATM networks. The scheme has high throughput and achieves shorter queue lengths without congestion. With measured average cell rate, the scheme provides fast convergence to a start‐up virtual connection (VC) and rate of equalization from different initial conditions of the sources. Thus, this scheme provides better fairness among connections. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

ATM网络中突发业务的漏桶算法分析

统计复用可以使突发业务获得较高的频带利用率，但必须对输入的业务量进行恰当的控制，否则会造成严重的网络拥塞，漏桶法是ＡＴＭ网络基于速率调节进行业务量控制的一种重要的方法，本文对突发业务的漏桶算法进行了分析，得出了突发业务的漏桶性能与输入业务统计参数和漏桶参数之间关系的解析式，计算机模拟结果表明它与理论分析的一致性。     

Design and evaluation of an efficient traffic control scheme for integrated voice,video, and data over asynchronous transfer mode networks: Explicit allowed rate algorithm

Asychronous transfer mode (ATM) networks are high‐speed networks with guaranteed quality of service. The main cause of congestion in ATM networks is over utilization of physical bandwidth. Unlike constant bit‐rate (CBR) traffic, the bandwidth reserved by variable bit‐rate (VBR) traffic is not fully utilized at all instances. Hence, this unused bandwidth is allocated to available bit‐rate (ABR) traffic. As the bandwidth used by VBR traffic changes, available bandwidth for ABR traffic varies; i.e., available bandwidth for ABR traffic is inversely proportional to the bandwidth used by the VBR traffic. Based on this fact, a rate‐based congestion control algorithm, Explicit Allowed Rate Algorithm (EARA), is presented in this paper. EARA is compared with Proportional Rate Control Algorithm (PRCA) and Explicit Rate Indication Congestion Avoidance Algorithm (ERICA), in both LAN and WAN environments. Simulations of all three algorithms are conducted under both congestion and fairness configurations with simultaneous generation of CBR, rt‐VBR, nrt‐VBR and ABR traffic. The results show that, with very small over‐head on the switch, EARA significantly decreases the required buffer space and improves the network throughput. Copyright © 1999 John Wiley & Sons, Ltd.     

Multirate scheduling of VBR video traffic in ATM networks

One of the major attractions of asynchronous transfer mode (ATM) networks for transporting bursty video traffic is its ability to exploit the multiplexing gains of packet switching while providing quality of service guarantees. Unfortunately, most of the multiplexing mechanisms proposed in the literature fail to exploit the multiplexing gains of ATM. We propose a multirate service mechanism that allows a session to be served at different rates at different times. Applications generating bursty data, such as variable bit-rate (VBR) video, can take advantage of multirate service by requesting a high rate of service for brief periods of bursty arrivals and a much lower rate of service for all other times. Consequently, the applications can improve their delay performance without reserving a high bandwidth for the entire duration of the sessions. Furthermore, the scheduler can multiplex the peaks and the lulls in service rates of different sessions and improve the utilization of the system. Using MPEG video traces from a number of applications, we show that multirate servers outperform single-rate PGPS (packet-by-packet generalized processor sharing) servers and CBR (constant bit-rate) servers in terms of number of connections admitted, while providing the same level of service guarantees. We also investigate the performance of multirate service when service quality need not be guaranteed. We refer to this as predictive service. We propose a measurement-based admission control procedure for predictive service, and show that it helps increase the size of the admissible region even further     

Performance analysis of reactive congestion control for ATMnetworks

In ATM networks, preventive congestion control is widely recognized for efficiently avoiding congestion, and it is implemented by a conjunction of connection admission control and usage parameter control. However, congestion may still occur because of unpredictable statistical fluctuation of traffic sources even when preventive control is performed in the network. The authors study another kind of congestion control, i.e., reactive congestion control, in which each source changes its cell emitting rate adaptively to the traffic load at the switching node (or at the multiplexer). The intention is that, by incorporating such a congestion control method in ATM networks, more efficient congestion control is established. They develop an analytical model, and carry out an approximate analysis of reactive congestion control algorithm. Numerical results show that the reactive congestion control algorithms are very effective in avoiding congestion and in achieving the statistical gain. Furthermore, the binary congestion control algorithm with push-out mechanism is shown to provide the best performance among the reactive congestion control algorithms treated     

Dynamic multithreshold rate control mechanisms for supporting ABRtraffic in ATM networks

Existing feedback-based rate control schemes supporting the available bit rate (ABR) service in ATM networks mostly employ a single static buffer threshold at each switching node as the forewarning of congestion. We first propose a continuous-based adaptive rate control mechanism, which employs, logically, an infinite number of thresholds. Each node periodically determines the precise permitted rate of immediate upstream nodes based on a simple fluid model aimed at satisfying both loss-free and starvation-free criteria. The scheme achieves high utilization and low (zero) cell-loss probability under highly bursty (deterministic) traffic, but at the expense of a drastic increase in signalling overhead due to frequent adjustment of permitted rates. To reduce overhead, we further propose a so-called stepwise-based rate control mechanism adopting a limited number of movable thresholds, referred to as the threshold set. The threshold set shifts up (down) reflecting the increase (decrease) in departure rates. Compared to continuous-based control via simulation, stepwise-based control is shown to be efficient and accurate using a reasonably low number of thresholds. Moreover, we also display simulation results, which demonstrate that the stepwise-based mechanism outperforms existing single-static-threshold-based schemes in terms of cell-loss probability and link utilization     

具有突发业务量成形的ATM复接器的性能分析

分析了综合业务环境下，具有突业务量成形的ＡＴＭ复接器的性能，提出了用间断贝努利过程可近似描述突发源经成形器后的输出过程。用改进的迭代算法，求出了ＡＴＭ复接器的信元丢失率和平均延迟。     

Engineering ATM networks for congestion avoidance

With the combination of telecommunication, entertainment and computer industries, computer networking is adopting a new method called Asynchronous Transfer Mode (ATM) networking. Congestion control plays an important role in the effective and stable operation of ATM networks. Traffic management concerns with the design of a set of mechanisms which ensure that the network bandwidth, buffer and computational resources are efficiently utilized while meeting the various Quality of Service (QoS) guarantees given to sources as part of a traffic contract. In this paper, the most widely recognized congestion control schemes for ABR service are investigated. Some of these schemes show either lack of scalability or fairness while other well‐behaved schemes may require a highly complex switch algorithm that is unsuitable for implementation in cell‐switching high‐speed ATM networks. A new and improved congestion control scheme is proposed to support the best‐effort ABR traffic. This algorithm provides the congestion avoidance ability with high throughput and low delay, in addition to achieving the max–min fairness allocation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Picture quality optimization in ABR video services

In transmission of bursty traffic such as video and data, a network with a fixed capacity may have some unused bandwidth. The available bit-rate (ABR) scheme in ATM networks can make use of this spare channel capacity as a lower priority service. ABR has been developed initially for delay-tolerant services such as data. In this paper we demonstrate how with the help of a video transcoder delay-sensitive services such as video may be transmitted over ABR networks. The transcoder further compresses the video bit stream according to the rates dictated by the network with minimum degradation to the picture quality. We have optimised the video quality by combining the classical minimum cell rate (MCR) with the subjectively acceptable minimum quality (SAMQ). The performance of two different coding formats for ABR sources, namely the constant bit-rate (CBR) and variable bit-rate (VBR) video input to the transcoder are compared. We also present techniques for further reduction of congestion at the multiplexing switches to improve video quality and report on the impact of the forward and backward link delays on the ABR performance with a video transcoder.     

Comparison of admission control schemes in ATM networks

Asynchronous transfer mode (ATM) offers an efficient means of carrying a wide spectrum of BISDN traffic provided that network congestion is prevented. Unfortunately, efficient congestion control is difficult to achieve in integrated broadband networks, owing to the wide range of traffic characteristics and quality of service (QOS) requirements. We have implemented a network simulator that allows us to evaluate many proposed admission control schemes using many different traffic models. We present the results of several simulation studies, including one study of the performance of the admission control schemes in the presence of traffic sources that exhibit long-term dependence.     

突发业务环境下CBR业务性能的实验分析

CBR业务是一类极为重要的实时业务,能否有效地传递这类业务关系到从现有网络向ATM的过渡,因此CBR业务的服务质量是一个值得研究的重要课题。本文利用计算机仿真的方法,全面地分析了突发业务环境下,影响CBR业务服务质量的各种因素,指出复接器占有率、缓冲区容量、背景强度、背景流的自相关特征对CBR业务的时延及时延抖动有很大的影响,尤其是背景流具有长时相关性时,CBR业务的服务质量将严重恶化,必须设法加以控制。