管理在ATM上传输的TCP/IP业务

管理在ATM上传输的TCP/IP局域网业务 当企业重新确定经营方法以满足用户需求时,它们不断要求增加局域网互连应用带宽。ATM论坛最近制订了业务可用比特率(ABR类)标准,以更有效地支持在ATM上应用TCP/IP等局域网互连。象不确定比特率(UBR)这种业务,有可能接入网络的备用带宽,在其应用方面有不可预测的业务需求(如TCP/IP)。然而,ABR和UBR业务有各种可供选用的方法。为了选择支持TCP/IP通过ATM传输的正确方法,需要做认真的评价。     

一种考察CCR的ABR业务二值法流量控制方案

 本文提出了一种考察CCR的有关ATM网络中ABR业务的流量控制方案EFCI(CCR)算法,具有二值法算法简单的特点,并能保证带宽分配的公平性,能有效地控制交换节点队列的长度,且该算法在拓扑结构较为复杂的网络中性能良好.     

ATM通信量管理技术及其在视频点播中的应用

ATM现有的5种通信量业务类型,即：恒定比特率（CBR）、可变比特率（VBR）、可用比特率（ABR）、不定比特率（UBR）和可保证帧速率（GFR）业务,在应用中各有所长。阐述了将ATM ABR业务运用于视频点播系统时,客户端和服务器端的缓存尺寸设置方法,为ABR业务在视频点播系统中的实际应用提供了有力的理论基础。     

电信业务及其传输技术

9904833一种增强的 EFCI 拥塞控制算法的研究[刊]/康智斌//西安电子科技大学学报.—1998,25(5).—642～645(DC)基于明显前向拥塞指示(EFCI)的拥塞控制是一种简单的可用比特率(Available Bit Rate:ABR)拥塞控     

按队长周期性设置EFCI的ABR流量控制算法

本文提出了一种新的基于EFCI的ABR流量控制算法,它的基本思想是扩展EFCI的功能,使其不仅反映网络阻塞状况,而且还反映网络排队状况,在交换机中通过周期性设置EFCI来传递网络的排队信息。仿真结果表明,本文提出的算法比基本EFCI算法具有更好的控制行为,减小了ACR和排队长度的振荡幅度,提高了链路利用率,并具有较高的性能价格比。     

基于EFCI的ABR业务拥塞检测算法特性分析

ABR业务是ATM提供的一种重要的数据传输服务,该文介绍了两种基于EFCI的ABR业务拥塞检测算法,并通过仿真结果分析了它们的速率调节特性和队列利用律。     

携带虚拟队列长度信息的ABR业务流量控制算法

本文提出了一种新的基于速率检测拥塞的ABR流量控制算法--E-EFCI，它的基本思想是在基于速率检测拥塞的基础上扩展EFCI的功能，使其不仅反映网络阻塞状况，而且还反映网络排队状况。在交换机中通过虚拟队列的长度设置EFCI来传递网络的排队信息。仿真结果表明，本文提出的算法比基本EFCI算法具有更好的控制行为，减小了ACR和排队长度的振荡幅度，提高了链路、缓存利用率，加快拥塞解除，并具有较高的性能价格比。     

网络流量控制技术的进展与面临的挑战

一、ATM 网络流量控制(flow control)或通信量拥塞控制(traffic congestion control),是ATM论坛在近两年来倾力谋求解决的棘手问题.已纳入用户一网络接口规范UNI3.0的用以告警通带即将饱和的“明确转发拥塞指示(EFCI)”协议,以及令ATM交换机得以合理地管理并疏通业务量的“用途参数控制(UPC)”协议(含漏桶算法)、“连接允许控制(CAC)”协议、“优先权处置算法(PFA)”、“类属(数据)流控制(GFC)字段”、“信元包丢弃顺序(CLP)字段”等都是其早期成果.由于这些技术只能参与网络的开环控制,而同.多数只适于交换机自身应用,远不能适应ATM论坛精心定义的CBR、VBR、UBR、ABR四种速率行为各不相同的业务作交换型虚电路(SVC)连接与控制的需要;作WAN连接、特别是作LAN—WAN连接时尤为如此.因为在这样的应用环境下必须采用能令拥塞消息立即返馈回去的闭环控制技术,对于旨在充分利用网络带宽资源的ABR接续更是非此不可.     

The DDTCI switch algorithm for ABR traffic control in ATM networks

For the issue of flow control for Available Bit Rate (ABR) traffic in ATM network,a new improved Explicit Rate (ER) algorithm named Dynamic Double Threshold Congestion Indication (DDTCI) algorithm is presented based on the Explicit Forward Congestion Indication (EFCI) Current Cell Rate (CCR) algorithm and Relative Rate (RR) algorithm. Different from the early ER algorithm, both the high-level and the low-level threshold is dynamically changing according to the state of the bottleneck node. We determinate the congestion state with the information of the two dynamic threshold, and control the cell rate of the source by feed back mechanism. Except for the well performance in both link utilization and fairness in distribution of available bandwidth, the improved algorithm can alleviate the fluctuation of sending rate dramatically. The mechanism is modeled by a fluid model, and the useful expressions are derived.Simulation results show up our conclusion.     

基于拥塞估计的TCP窗口在线学习方法

针对传统TCP拥塞窗口更新、控制机制所导致的Ad Hoc网络吞吐量下降的问题,利用机器学习算法来改善TCP在Ad Hoc网络中的性能。该方法利用确认帧的时间间隔,通过连续动作集(CALA)算法快速学习并估计当前网络链路中的拥塞状况,从而能够迅速调整TCP拥塞窗口。仿真实验表明:当Ad Hoc网络环境较好时,学习型TCP的吞吐量略优于TCP-Few、TCP-Reno协议,但在环境较差的情况下,学习型TCP的吞吐量远远优于TCP-Few和TCP-Reno协议。     

Performance and buffering requirements of Internet protocols overATM ABR and UBR services

ATM networks are quickly being adopted as backbones over various parts of the Internet. This article studies the dynamics and performance of the TCP/IP protocol over the ABR and UBR services of ATM networks. Specifically the buffering requirements in the ATM switches as well as the ATM edge devices. It is shown that with a good switch algorithm, ABR pushes congestion to the edges of the ATM network while UBR leaves it inside the ATM portion. As a result, the switch ABR buffer requirement for zero-packet-loss high-throughput TCP transmission is a sublinear function of the number of TCP connections     

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.     

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。     

Traffic management for TCP/IP over satellite ATM networks

Several Ka-band satellite systems have been proposed that will use ATM technology to seamlessly transport Internet traffic. The ATM UBR, GFR, and ABR service categories have been designed for data. However, several studies have reported poor TCP performance over satellite ATM networks. We describe techniques to improve TCP performance over satellite ATM networks. We first discuss the various design options available for TCP end systems, IP-ATM edge devices, as well as ATM switches for long-latency connections. We discuss buffer management policies, guaranteed rate services, and the virtual source/virtual destination option in ATM. We present a comparison of ATM service categories for TCP transport over satellite links. The main goal of this article is to discuss design and performance issues for the transport of TCP over UBR, GFR, and ABR services for satellite ATM networks     

A detailed experimental performance evaluation on TCP over UBR

The ATM service category UBR is intended for non-real-time applications that do not require guaranteed QoS commitments. With additional, relatively inexpensive control functions such as packet discard schemes, UBR could become a cost-effective alternative for the transmission of data traffic, offering a straightforward and flexible solution as opposed to nrt-VBR and GFR that applies stricter traffic specifications as well as ABR with its sophisticated and complex rate-control protocol. This paper presents the results obtained from a comprehensive set of experiments with TCP over UBR, comprising measurements taken on different protocol layers. The goal is to experimentally investigate the performance of UBR to carry TCP traffic, to evaluate the performance gain achievable by packet discard schemes and TCP parameter tuning, to study the influence of the TCP implementation, and in a final step, to relate the measurements to simulation results. This revised version was published online in August 2006 with corrections to the Cover Date.     

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。     

Interoperability of EFCI and ER switches for ABR services in ATMnetworks

With the advances in switching technologies, explicit rate (ER) switches are becoming popular since they perform better than explicit forward congestion indication (EFCI) switches. In the transitional period, EFCI and ER switches may coexist in the same ATM network. Hence, the efficiency of various ER schemes should be reevaluated in the mixed EFCI-ER environment, not only in the homogeneous ER environment. Also, some important implications are observed in the heterogeneous environments. Because the location of an ER switch in the topology is critical to its performance, some placement rules, which describe how to place the ER switches for network operators, are developed in order to achieve a better performance of the network. The results presented should serve as an operational reference for service providers     

ATM网中ABR业务及其反馈流量控制

ABR（AvailableBitRate）业务是近年来为了充分利用ATM网络的剩余带宽而提出的一种新型业务类型，自从1993年被ATM论坛正式提出以来得到了很快的发展。文章对该业务的特点和发展过程作了较全面的介绍，对该类型业务的流量控制方法作了比较深入的分析和研究，对流量控制中关键因素的改进提出了自己的见解。     

Fluid analysis of a TCP connection over ABR

This paper reports on an analytical study of the performances of the ATM‐ABR service category in transporting TCP/IP flows over an ATM network. We explore the behavior of a TCP connection over an ATM‐ABR VC, in presence of exogenous non‐controlled traffic. This fluid analysis of the system allows the study of the interaction between the window‐based end‐to‐end flow control TCP protocol and the rate‐based flow control ABR mechanism, which is restricted to the ATM part of the network. The main aim of this study is to give performance evaluation formulae to model the behavior of such a TCP over ABR connection. This revised version was published online in June 2006 with corrections to the Cover Date.