Impact of QOS requirements on video coding for ATM networks

The broadband integrated services digital networks (B-ISDN) based on asynchronous transfer mode (ATM) technology can support a wide range of applications such as voice, video, still images, and data. Compression techniques increase the effective bandwidth utilization, but the bursty and asynchronous nature of the traffic can still lead to congestion in the network, and degradation of image quality and quality of service (QOS). Some of the features to provide better coding schemes for ATM networks are layered coding, resynchronization, buffering, interleaved schemes, constrained bit rate due to buffers, encapsulation with the RTP or AAL1 for clock recovery, lapped transforms, motion compensation, and optimal bit allocation for coders based on wavelet transforms. We review various techniques forimage and video coding such as transforms, motion compensation, vector quantization, and subband coding. We outline the impact of the cell loss ratio (CLR), delay and cell delay variation (CDV) on video coding: blocking effects, loss of frame synchronization, motion vectors, and vector quantization codewords. The open problems include tuning coding parameters to the available QOS provided by the network.     

Synchronous optical network and broadband ISDN protocols

High-level technical information on Sonet (synchronous optical network) B-ISDN (broadband integrated services digital network) protocols, and interface structures is provided. Since the B-ISDN protocol standards to be used in the Broadband Reference Model are currently being discussed in the CCITT, most of the standards are not yet available. Therefore, some of the protocols described here are not based on agreements reached in national and international standards bodies. The discussion covers B-ISDN architecture and the ISO model. Sonet protocols and architecture, B-ISDN configuration, and the ATM (asynchronous transfer model) architecture     

Protocol wrappers for layered network packet processing inreconfigurable hardware

A library of layered protocol wrappers processes Internet packets in reconfigurable hardware. Collectively, the wrappers simplify and streamline the implementation of high-level networking functions by abstracting the operation of lower-level packet processing functions. The library synthesizes into field-programmable gate array (FPGA) logic and is utilized in a network platform called the field-programmable port extender (FPX). The library processes asynchronous transfer mode (ATM) cells, ATM adaptation layer 5 (AAL5) frames, Internet protocol (IP) messages, and user datagrarn protocol (UDP) packets directly in hardware. Applications can process data at several layers of the protocol stack using the library of wrappers discussed in this article. Layers are important for networks because they let applications abstract from above and below details of the network protocols. At the lowest layer, networks modify raw data passing between interfaces. At higher levels, the applications process variable length frames or IP packets.A network platform called the field-programmable port extender (FPX) streamlines and simplifies network transmission processing directly in hardware     

基于OAM性能监测的ATM QoS管理

监视网络性能参数的变化是实现ATM网络QoS管理的一个关键，但是ITU－T定义的OAM性能管理功能只简单地监视网络性能，产生报告信息，而不能对QoS的管理提供足够的支持，本文为此在讨论QoS和网络性能参数的基础上，设计了一个ATM网络的QoS管理模型，其中，对OAM性能管理功能进行了改进，一些满足QoS管理需求的ATM网络性能监测功能在OAM信元的保留字段中得以实现。     

基于ATM交换结构的Hopfield神经网络调度算法

针对ATM交换结构,采用输入缓冲和每条入线在同一个时隙内可传送多于一个信元的策略,利用神经网络具有的实时性、高度并行处理能力和易于电路或光电技术实现等特点,提出了一种Hopfield神经网络调度算法。实验仿真比较表明,该方法不但大大提高了吞吐率,消除了队头阻塞造成的性能恶化,而且降低了信元丢失率和较大程度地降低了平均信元时延,提高了ATM交换结构的性能,实现了信元的优化调度。     

Modeling and distributed simulation of a broadband-ISDN network

A distributed approach to communication network simulation using a network of workstations configured as a loosely coupled parallel processor to model and simulate the broadband integrated services digital network (B-ISDN) is proposed. In a loosely coupled parallel processor system, a number of concurrently executable processors communicate asynchronously using explicit messages over high-speed links. Since this architecture is similar to that of B-ISDN networks, it constitutes a realistic testbed for their modeling and simulation. The authors describe an implementation of this approach on 50 Sun workstations at Brown University. Performance results, based on representative B-ISDN networks and realistic traffic models, indicate that the distributed approach is efficient and accurate     

无线ATM网介质访问控制协议的研究

近年来无线ATM网络得到广泛研究,扩展ATM网络的宽带业务至无线环境面临许多方面的问题。介质访问控制(MAC)方法是无线ATM网的关键技术之一。MAC层协议的好坏直接影响系统性能和移动终端的复杂性。文中综合分析目前已有的无线ATM介质访问控制协议及方法,指出设计无线ATM网MAC层协议的三条原则,提出下一步研究方向。     

B-ISDN中的拥塞控制技术

B-ISDN是现代通信网的发展方向,而其中的拥塞控制技术则是一个重要方面。由于B-ISDN中采用新的传递方式—ATM,使传统的网络拥塞控制方法不再适用。本文参照ITUT有关建议的最新内容对B-ISDN中网络拥塞控制的基本思想、工作机制以及各项功能做了较为详细的分析讨论,并提出了一些B-ISDN拥塞控制技术中尚需进一步研究的问题。     

基于ATM技术的无线PCS网

文中介绍了无线ATM的网络结构、协议参考模型和PCS支持的固定ATM网的信令协议,它是对目前的ATM和PCS规范的最小修改。     

基于自相似模型的网络性能测试

网络性能测试是保证信息网络高性能、高可靠和高可用性的重要和基本手段。该文给出了网络性能测试的基本概念和方法;介绍了基于IP的网络性能参数;分析了IPoverATM网络流量的自相似性,建立了网络流量的自相似模型;基于自相似模型开发了网络性能测试工具并对实际网络进行了测量和分析。     

Multicasting VP design methodology using simulated annealing in an ATM network

Multicast routing over semi-permanent VP (virtual path)s in an ATM (asynchronous transfer mode)-based B-ISDN (broadband integrated services digital network) determines a set of VPs connecting from a source node to destination nodes. The problem of finding the optimal constrained multicasting tree over the semi-permanent VPs in an ATM network is known to be NP (nondeterministic polynomial time)-complete. We develop an optimization methodology for searching a constrained multicast routing tree with minimum cost, using simulated annealing technique. We define the problem-dependent components such as state space and cost function, and refine the implementation-dependent factors including initial temperature and cooling schedule. The simulation results show that our optimization methodology demonstrates good behavior in terms of performance on a variety of graphs modeling the sample ATM networks.     

Impact of wireless access on traffic management in ATM networks

Traffic management plays an important role in providing differentiated quality of service and supporting the integration of a variety of broadband services within a common ATM network. Wireless ATM access networks are under definition in standards bodies as well as subject of various research activities and first field trials. The nature of the wireless medium requires new protocols that are able to cope with multiple access, error prone wireless channels, and user mobility. When attaching a wireless ATM network to a fixed ATM network proper interaction of traffic and resource management functions throughout both networks is necessary to achieve stringent QoS objectives. In this paper the relation between mobile specific protocols and traffic management functions as well as their mutual impacts are discussed. Three key areas to enable seamless traffic management integration are identified and possible solutions are outlined.     

Improved WWW multimedia transmission performance in HTTP/TCP overATM networks

Transmission control protocol/Internet protocol (TCP/IP) is the de facto standard of the networking world. It dynamically adjusts routing of packets to accommodate failures in channels and allows construction of very large networks with little central management. But IP packets are based on the datagram model and are not really suited to real-time traffic. In order to overcome the drawbacks, a new network technology, ATM, is proposed. ATM provides quality of service (QOS) guarantees for various classes of applications and in-order delivery of packets via connection oriented virtual circuits. Unfortunately, when ATM is to be internetworked with the existing network infrastructure, some special signaling, addressing and routing protocols are needed. IP over ATM is one of the methods proposed by IETF. It allows existing TCP/IP applications to run on ATM end-stations and ATM networks to interconnect with legacy LAN/WAN technologies. But the performance of TCP/IP over ATM leaves something to be desired. Partial packet discard (PPD) and early packet discard (EPD) are two schemes to improve its performance. This paper proposes a “selective packet retransmission” scheme for improving HTTP/TCP performance when transmitting through ATM networks. In selective packet retransmission, we take advantage of the property of humans' perception tolerance for errors to determine whether to retransmit a corrupted TCP segment or not. For lossable data, such as images, when an error occurs because of cell losses, it will not be retransmitted. The simulations show that, for the same buffer size and traffic load, selective packet retransmission performs better than PPD, EPD, and plain TCP over ATM     

一种新的高性能网络——异步传输模式局域网

本文论述了把异步传输模式（ＡＴＭ）引入到局域网（ＬＡＮ）的必要性和应用前景，提出了如何构成ＡＴＭＬＡＮ和用软硬件来设计ＡＴＭＬＡＮ的机理与方法，对ＡＴＭＬＡＮ的基本概念，协议模型，互连技术，体系结构和网络样式进行了探讨，其目的是推动ＡＴＭＬＡＮ在我国的研究发展和应用。     

Generating Systems of Equations for Performance Evaluation of Multistage Interconnection Networks

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.     

Methodologies for bandwidth allocation,transmission scheduling,and congestion avoidance in broadband ATM networks

The call types supported in high-speed packet networks vary widely in their bandwidth requirements and tolerance to message delay and loss. In this paper, we classify various traffic sources which are likely to be integrated in broadband ATM networks, and suggest schemes for bandwidth allocation and transmission scheduling to meet the quality and performance objectives. We propose ATM cell-multiplexing using a Dynamic Time-Slice (DTS) scheme which guarantees a required bandwidth for each traffic class and/or virtual circuit (VC), and is dynamic in that it allows the different traffic classes or VCs to share the bandwidth with a soft boundary. Any bandwidth momentarily unused by a class or a VC is made available to the other traffic present in the multiplexer. The scheme guarantees a desired bandwidth to connections which require a fixed wide bandwidth. Thus, it facilitates setting up circuit-like connections in a network using the ATM protocol for transport. The DTS scheme is an efficient way of combining constant bit-rate (CBR) services with variable bit-rate (VBR) stastically multiplexed services. We also described methodologies to schedule delivery of delay-tolerant data traffic within the framework of the DTS scheme. Important issues such as buffer allocations, guarantee of service quality, and ease of implementation are also discussed.     

ATM communications network control by neural networks

A learning method that uses neural networks for service quality control in the asynchronous transfer mode (ATM) communications network is described. Because the precise characteristics of the source traffic are not known and the service quality requirements change over time, building an efficient network controller which can control the network traffic is a difficult task. The proposed ATM network controller uses backpropagation neural networks for learning the relations between the offered traffic and service quality. The neural network is adaptive and easy to implement. A training data selection method called the leaky pattern table method is proposed to learn precise relations. The performance of the proposed controller is evaluated by simulation of basic call admission models.     

Analysis of an access node multiplexer in a system serving CBR and VBR traffic

This paper considers a multiplexer at the access node of a system serving both CBR and VBR services in a B-ISDN environment. The CBR traffic component represents fixed bit rate services in an ATM network. Such services need to be allocated a fixed number of time slots in each output frame. The VBR traffic here represents connectionless and connection oriented variable bit rate services that are loss sensitive but delay insensitive. A mathematical model is developed for such a system and performance parameters are evaluated. These results are verified by simulation.     

基于模糊神经网络的ATM网络业务量智能预测

文章尝试将模糊神经网络方法引入ATM网络的业务量预测中。ATM网络业务源一般是随机产生的时变信号,其模型一般很难描述。文章充分考虑了模糊神经网络的学习功能,通过对相关模型的仿真,能够很好地描述ATM网络中的业务流特性,对多媒体的业务量做出了准确的预测。与传统的神经网络方法比较,具有更好的逼近效果。     

基于测量的接纳控制算法研究综述

介绍了计算机网络QoS研究中基本网络模型、服务模型以及在接纳控制研究中常用的流量描述模型.重点综述了在连接接纳控制研究中占重要地位的基于测量的接纳控制算法,详尽描述和分析了各主要算法的思想、数学模型、应用环境及优缺点,并对各主要算法进行了比较,同时介绍了当前接纳控制研究的一些新进展,包括集成服务网络,区分服务网络及ATM QoS的基于测量的接纳控制研究,并对未来接纳控制研究进行了展望.