ATM网络中基于ABR业务的闭环拥塞控制

论文讨论了ＡＴＭ网络中ＡＢＲ业务的特性及基地ＡＢＲ业务的拥塞控制机制，了拥塞控制技术的最新发展情况，并比较了各种控制机制的优缺点。     

可用比特率业务及其拥塞控制机制

通过ＡＢＲ业务同ＣＢＲ、ＶＢＲ和ＵＢＲ业务比较，描述了它的本质特性，然后分析讨论目前适用于ＡＢＲ业务的几种基于速率控制，闭环反馈形式的拥塞控制机制。     

VBR背景业务下的ABR拥塞特性

ＡＢＲ业务的拥塞控制方案是当前ＡＴＭ研究方面的热点,本文首先分析了存在ＶＢＲ背景业务时,ＡＢＲ拥塞控制方案的动态特性,然后将此分析模型用于研究明确速率反馈交换机的排队性能,并研究了ＴＣＰｏｖｅｒＡＢＲ的拥塞特性。     

ATM网络中ABR业务的开环控制机制

ＡＴＭ网络中ＡＢＲ业务的流量控制是ＡＴＭ论坛的流量管理规范（ＴＭ４．０）中没有完全解决的问题,ＡＢＲ基于速率的闭环控制方案在最大－最小准则下获得了一定进展。但在拥塞发生在信源外或对突发性业务进行控制的情况下,添加开环控制的ＡＢＲ拥塞控制可以获得比闭环控制更佳的作用。研究了ＡＢＲ的开环控制方案,早期的ＵＩＬＩ机制本身存在在一定的问题,在交换机处采用基于计数的ＵＩＬＩ机制能够取得较好的效果。     

ABR和UBR业务模型的TCP接入分析

ＡＢＲ和ＵＢＲ业务是ＡＴＭ中新定义的业务类型，主要面向数据传输服务。ＴＣＰ是目前最为流行的数据输协议，采用基于窗口的拥塞控制机制。本文主要讨论了ＴＣＰ接入ＡＢＲ和ＵＢＲ业务时所呈观的一些特点及ＡＴＭ交换机缓存的大小对ＴＣＰ性能的影响。     

ABR业务流量控制中的是速率反馈

ＡＢＲ（Ａｖａｉｌａｂｌｅ Ｂｉｔ Ｒａｔｅ）业务可以提高ＡＴＭ网络的利用率，能让用户ＬＡＮ通过广域网进行高吞吐量、低丢失率的互通。可以预计，未来ＡＴＭ网上的数据业务将主要用ＡＢＲ连接来传输。ＡＢＲ业务中的首要问题是流量控制。文章在比较了几种流量控制方案后，认为显速率反馈是ＡＢＲ业务流及拥塞控制的一个有效方法，是完善ＡＢＲ业务的一个重要手段，并对显速率算法作了进一步研究。     

ATM宽带网络流量与拥塞控制研究

文章阐明对ＡＴＭ网络进行流量与拥塞控制不仅是由ＡＴＭ网络的分组交换本质所决定，也是实现Ｂ－ＩＳＤＮ的基本要求，文章还对目前ＡＴＭ网络的ＡＢＲ流量与拥塞控制机制进行了评述，提出了ＡＢＲ流量控制尚待解决的一些问题。     

ABR业务特性及业务量管理方法

由ＡＴＭ Ｆｏｒｕｍ提出的ＡＢＲ业务近来颇受各方关注，本文给出了ＡＢＲ业务的背景，ＡＢＲ业务的特点及其流量控制方法，并对在实现ＡＢＲ业务过程中可能碰到的问题进行了讨论。     

ATM网络业务量控制

ＡＴＭ网络的业务量控制是ＡＴＭ网中的关键技术之一。简要介绍了三种业务量控制的方法，即连接接纳控制、业务流警管和ＡＢＲ拥塞控制方法。     

ABR业务流量控制的一种智能机制

本文提出了一种ＡＢＲ业务模糊流量控制机制,仿真结果表明它有效地避免了网络阻塞,在网络的吞吐量上要高于强比例速率控制算法（ＥＰＲＣＡ）。该机制与连接业务的特性无关,且不需要改变有关ＡＢＲ闭环反馈的流量控制结构,这为算法的实际应用提供了前提。     

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.     

On max-min fair congestion control for multicast ABR service in ATM

In the ATM Forum activities, considerable efforts have focused on the congestion control of point-to-point available bit rate (ABR) service. We present a novel approach that extends existing point-to-point (unicast) congestion control protocols to a point-to-multipoint (multicast) environment. In particular, we establish a unified framework to derive a multicast congestion control protocol for an ABR service from a given rate-based unicast protocol. We generalize a known necessary and sufficient condition on the max-min fairness of unicast rate allocation for a multicast service. Using this condition, we show that the resulting multicast protocol derived using our framework preserves the fairness characteristics of the underlying unicast protocol. The practical significance of our approach is illustrated by extending a standard congestion control mechanism for an ABR service to a multicast environment. The performance of the resulting multicast protocol is examined using benchmark network configurations suggested by the traffic management subworking group at the ATM Forum, and simulation results are presented to substantiate our claims     

ATM宽带网络流量与拥塞控制研究

文章阐明对 ATM 网络进行流量与拥塞控制不仅是由 ATM网络的分组交换本质所决定,也是实现 B-ISDN 的基本要求。文章还对目前 ATM 网络的 ABR流量与拥塞控制机制进行了评述,提出了 ABR 流量控制尚待解决的一些问题。     

Fair packet discarding for controlling ABR traffic in ATM networks

The asynchronous transfer mode (ATM) Forum has chosen rate-based control as the flow control scheme for the available bit-rate (ABR) service. However, rate-based schemes can achieve congestion control only if all users act in a cooperative manner. Even a limited number of uncooperative users can cause congestion collapse. We propose a mechanism called fair packet discarding to provide incentives to users to participate in network congestion control so that the network can operate in a more efficient manner     

Parameter tuning of rate-based congestion control algorithm for ABR service class in ATM networks

A rate-based congestion control algorithm has been developed and standardized in the ATM forum for ABR service class. In the standard the behaviour of source and destination end systems is specified by several control parameters such as RIF (rate increase factor) and RDF (rate decrease factor). In spite of the fact that the performance of the rate-based congestion control algorithm depends heavily on the selection of these control parameters, no selection method of parameters is shown in the standard. In this paper, by extending our previous work, appropriate settings of rate-control parameters in the various circumstances are investigated. We first analyse the dynamical behaviour of the rate-based congestion control for multiple groups of ABR connections with different propagation delays. Next we evaluate the effect of CBR traffic on ABR connections. Simulation results for a multihop network configuration are also presented to exhibit the trade-off relationship among cell loss probability, link utilization and fairness. Finally, a selection method of control parameters in the multihop network is proposed based on our analytic methods and simulation results © 1998 John Wiley & Sons, Ltd.     

TCP window control scheme using ER value in TCP over ABR services

A window control theme in TCP over ABR service is proposed. In this scheme, the TCP congestion window size is determined by explicit rate (ER) values, representing the degree of network congestion. Simulation results show an improvement in TCP throughput, reducing the transmissions as well as effectively utilising the bandwidth available to a given TCP connection     

基于星上处理的卫星ATM中ABR 业务拥塞控制算法研究

卫星ATM是近年来通信领域的研究热点,拥塞控制是其中很关键的一个问题.本文主要研究基于星上处理的卫星ATM网的ABR流量控制,它通过对流量的长时预测来达到控制目的.由于卫星信道的大延时,无法实现精确的长时预测,因而将预测结果直接用于ABR的拥塞控制效果不甚理想.将长时预测同动态利用因子控制的方法结合之后,在链路效率、信元丢失率、不同连接数目和暂态响应等方面都取得很好的结果.     

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.