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     

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。     

TCP/IPoverATM的性能研究

 本文讨论将传统的TCP拥塞控制机制和CIPOA用于采用ER(FB)算法和EFCI(CCR)算法的ATM网络时可用比特率业务(ABR)和未确定比特率业务(UBR)的性能.仿真结果表明,无论在缓冲区的需求、带宽分配的公平性、吞吐量和链路利用率方面ABR业务的TCP性能均明显优于UBR业务.对于较简单的网络模型ER(FB)算法的TCP性能优于EFCI(CCR)算法,更优于传统的EFCI算法.     

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.     

Dynamics of TCP traffic over ATM networks

Investigates the performance of transport control protocol (TCP) connections over ATM networks without ATM-level congestion control and compares it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from “corrupted” packets, i.e., packets in which at least one cell is dropped by the switch. The authors investigate two packet-discard strategies that alleviate the effects of fragmentation. Partial packet discard, in which remaining cells are discarded after one cell has been dropped from a packet, somewhat improves throughput. They introduce early packet discard, a strategy in which the switch drops whole packets prior to buffer overflow. This mechanism prevents fragmentation and restores throughput to maximal levels     

一种无线ATM网络的MAC协议

主要研究了无线ATM网络对MAC的需求，并介绍了适用于无线ATM的一种新的MAC方案。该协议支持不同类型信息传输，比如恒定比特率（CBR），可变比特率（VBR），可用比特率（ABR），未指定比特率（UBR）。另外此协议还提供了对宽带ATM主干网的无缝连接。同时也支持与ATM相关的QoS级别。对于该协议关注的各种情况的主要原理进行了讨论。     

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.     

Providing rate guarantees for internet application traffic across ATM networks

The TCP⁄IP protocol suite is the standard requirement for all applications that need to communicate over the Internet. As TCP⁄IP applications are unable to specify the QoS parameters needed for most Asynchronous Transfer Mode (ATM) services, they tend to use the unspecified bit rate (UBR) service category when running across ATM networks. The UBR service utilizes any bandwidth that is left unused by the rest of the ATM services. This has led the ATM Forum's Traffic Management Group to define a new service category called guaranteed frame rate (GFR). GFR is intended to provide minimum cell rate guarantees and fair access to excess bandwidth left over from higher-priority services. This article first presents a tutorial overview of GFR and then presents a survey of the research work that has been carried out toward the design and implementation of associated ATM switch mechanisms.     

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。     

The dual flow control problem of TCP over ATM ABR services

In this paper, we investigate the dual control problem—TCP flow control at the TCP layer and ABR flow control at the ATM layer. First, we observe that TCP flow control and ABR flow control cannot co‐operate well. The worst case is that the slow start after packet loss causes high but unused ACR (Allowed Cell Rate) which raises the potential of cell loss and an underflowed switch queue which reduces ABR throughput. We suggest to implement a use‐it‐or‐lose‐it policy for ABR and fast recovery for TCP to avoid these phenomena. Copyright © 1999 John Wiley & Sons, Ltd.     

A Partially-Blocking Queueing System with CBR/VBR and ABR/UBR Arrival Streams

In this paper we consider an ATM transmission link, to which CBR or VBR and ABR or UBR calls arrive according to independent Poisson processes. CBR/VBR calls (characterized by their equivalent bandwidth) are blocked and leave the system if the available link capacity is less than required at the time of arrival. ABR/UBR calls, however, accept partial blocking, meaning that they may enter service even if the available capacity is less than the specified required peak bandwidth, but greater than the so called minimal accepted bandwidth. Partially blocked ABR/UBR calls instead experience longer service time, since smaller given bandwidth entails proportionally longer time spent in the system, as first suggested in [3] and analyzed in details herein. Throughout the life time of an ABR/UBR connection, its bandwidth consumption fluctuates in accordance with the current load on the link but always at the highest possible value up to their peak bandwidth (greedy sources). Additionally, if this minimal accepted bandwidth is unavailable at the time of arrival, ABR/UBR calls are allowed to wait in a finite queue. This system is modeled by a Continuous Time Markov Chain (CTMC) and the CBR/VBR and ABR/UBR blocking probabilities and the mean ABR/UBR waiting- and service times are derived.     

卫星TCP/ATM传输中的明确窗口指示拥塞控制策略研究

卫星ATM是近年来卫星通信领域的一个研究热点,TCP业务在卫星ATM中的传输是其中一个重要的研究课题.由于在TCP协议中主要是通过对窗口的控制来实现拥塞控制,而卫星信道传输的长延时特性大大降低了TCP层拥塞控制的效率.本文提出一种基于UBR传输的明确窗口指示拥塞控制策略,仿真结果表明在效率、公平性、VBR背景传输下的性能等各方面,取得了比目前广泛使用的Reno TCP更好的结果.并且该算法实现简单,交换机实现零信元丢失的缓冲区很小并且与TCP源连接的数目无关.     

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.     

Modelling and analysis of routing and resource allocation techniques in multi‐service networks

In this paper a novel call level model based on the extension of the classical Erlang multi‐rate model for broadband integrated services networks is proposed. We use the model to study routing strategies in multi‐service networks where service classes with/without QoS guarantees coexist. Examples for such networks include ATM and IP‐based integrated networks. In ATM, the CBR and VBR service classes provide QoS guarantees, while the ABR and UBR service classes are of the best effort type. In IP, traditional TCP/IP traffic is of the best effort type, while new protocols like the RSVP or the differentiated services with central resource handling attempt to support QoS parameters. The coexistence of guaranteed and best effort traffic gives rise to new challenging problems since for a given elastic (best effort) connection the bottleneck link determines the available bandwidth and thereby puts constraints on the bandwidth at the other links along the connection's path. Since the available bandwidth fluctuates in time following the load on the links, routing and link allocation in this environment together with blocking probability calculations and fairness issues need to be studied. By means of our proposed model we are able to conduct a survey of various routing and link allocation techniques as well as to develop a modified shortest path routing algorithm which, according to the numerical examples, performs well in this environment. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance issues in public ABR service

The available bit rate (ABR) service attracted much attention during the negotiations leading to Traffic Management Specification Version 4.0, finalized by the ATM Forum. In thr ABR service, feedback flow control of the source rate is provided in response to the changing asynchronous transfer mode (ATM)-layer transfer characteristics. The reference behavior of the source end system, the destination end system, and the switch, as detailed in the specification, allows cooperative control among these systems. The performance of the public ABR service is discussed in connection with the evolution of ATM switches. Public networks with first-generation switches provide an ABR service with a limited peak cell rate (PCR), while those with second-generation switches can provide an ABR service with any PCR. In such networks, TCP-over-ABR works well. Point-to-multipoint ABR will be provided in advanced switches. A method is proposed for maintaining the throughput of point-to-multipoint ABR when the number of leaves is increased     

串行网络中ABR业务的流量控制和缓存设计

本文提出一种ABR业务速率在优化率和请求率之间的切换控制方法。在上述控制算法基础上,研究了保证信元在交换节点处无丢弃,同时输出带宽得到充分利用的交换节点的缓存和阈值设计问题。新的流量控制机制实现了源节点发送率和交换节点缓存的小抖动控制。     

基于ATM的无源光网络媒质接入控制协议的设计

针对基于ＡＴＭ的无源光网络（ＡＴＭ－ＰＯＮ）设计了一种媒质接入控制（ＭＡＣ）协议。该协议的设计遵照ＩＴＵ－Ｔ有关ＡＴＭ－ＰＯＮ的建议Ｇ．９８３．１（１９９８年１０月）中所定义的帧结构。该协议能够支持ＣＢＲ／ＶＢＲ、ＡＢＲ和ＵＢＲ等多种业务,并能够保证用户公平地接入和充分地利用网络的资源。其中ＣＢＲ／ＶＢＲ业务的优先级最高,同时也确保ＡＢＲ业务至少能以最小信元通信。系统的剩余带宽资源被分配给ＵＢＲ业     

A new ATM adaptation layer for TCP/IP over wireless ATM networks

This paper describes the design and performance of a new ATM adaptation layer protocol (AAL‐T) for improving TCP performance over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber links for which ATM was introduced in the beginning. Since the low performance of TCP over wireless ATM networks is mainly due to the fact that TCP always responds to all packet losses by congestion control, the key idea in the design is to push the error control portion of TCP to the AAL layer so that TCP is only responsible for congestion control. The AAL‐T is based on a novel and reliable ARQ mechanism to support quality‐critical TCP traffic over wireless ATM networks. The proposed AAL protocol has been validated using the OPNET tool with the simulated wireless ATM network. The simulation results show that the AAL‐T provides higher throughput for TCP over wireless ATM networks compared to the existing approach of TCP with AAL 5. This revised version was published online in July 2006 with corrections to the Cover Date.     

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。