ATM—越来越重要的角色

交互业务以及语音、数据、文本、图象的有效发送依靠两个基本技术:同步数字序列(SDH)和异步转移模式(ATM)。 一个完整的产品系列 现在阿尔卡特的ATM产品是Alcatel 1000系列的一个组成部分。 (1)Alcatel 1000AX/CL是一种用于公用网络的ATM交换系统,配置有具有面向半永久连接和无连接业     

竞争消除;;逻辑组播;;空间组播;;ATM网元

竞争消除(Contention Resolution)ATM 是面向连接的技术,ATM 交换系统内部的 ATM 交换结构通常也采用面向连接的选路方式。与同步数字时分交换不同,ATM 交换在预先建立虚连接后的信元传送阶段仍会发生同抢资源的竞争现象。即使是没有内部竞争的无阻塞 ATM 交换结     

ATM与帧中继的互通

简要回顾与快速分组交换有关的FR和ATM技术及2种技术的结合,讨论了ATM与FR有关网络互通、业务互通的连接复用、参数映射等技术问题.     

我国发展MPLS技术的策略

多协议标签交换（MPLS）是一种在开放的通信网上利用标签引导数据高速、高效传输的新技术。MPLS组网技术是实现IPoverATM的技术方案。采用带有MPLS功能的IP路由器和带有MPLS功能的ATM交换机组建未来宽带综合业务通信网，是业界迫切需要解决的问题。它的价值在于能够在一个无连接的网络中引入连接模式的特性。多协议标签交换技术的主要优点是减少了网络复杂性，兼容现有的各种主流网络技术，使网络的总体成本降低50%，在提供IP业务时能确保QoS和安全性，具有流量工程能力。MPLS的实用价值在于它能够在像IP这样的无连接型网络…     

3种宽带IP技术简介

因特网的高速发展带来了对带宽的巨大需求,原有的主要提供话音业务的电路交换网络已远远不能适应IP(网际协议)业务的需求。为此,各种宽带IP技术应运而生。 1.IP over ATM(异步转移模式) IP是因特网的基础技术,是一个为高级传输协议提供无连接服务的网络协议。它与传输控制协议(TCP)一起构成因特网协议簇的核心单元。IP有相应的地址     

ATM技术在MSTP中的应用

IP技术适应了数据业务的飞速发展,但目前由于IP技术基于协议的收敛速度慢,无法满足语音等高等级业务的服务质量要求,因此现在需要高QoS的业务都推荐采用ATM技术,通过ATM技术良好的面向连接特性,更好地保证业务质量.本文结合新一代多业务传送平台中IMA等ATM新功能,针对网络中大量的ATM应用,提出了相应的解决方案.     

ATM网络向IP业务迁移方案

ATM技术源于SONET和SDH技术,自上世纪80年代以来得到广泛应用,众多网络运营商纷纷投入巨资,建立了覆盖面很广的ATM骨干网络。从理论上说,ATM技术面向连接的交换传输方式和服务质量保证(QoS)使网络能传输音频和视频数据流,也为灵活多样的网络服务提供了技术保证。然而,由于受ATM网络建造和维护成本昂贵、网络管理复杂等因素的限制,该技术至今仍仅限于骨干网的构架,无法推广到终端用户的桌面上。在这一领域,IP技术凭借其良好的开放性及简单方便的特点,占据了牢固的统治地位。随着Internet高速发展及网络服务业竞争日益激烈,网络运营…     

ATM技术及其在校园网中的应用

异步传递模式ATM(Asynchronous Transfer Mode)被ITU—T定为B—ISDN最主要的目标传递模式.传递模式是指电信网中信息传输、复用和交换的方式.ATM利用光纤做为传输媒体,传输速率很高,误码率极低.ATM利用动态统计复用技术,不同的信息被打包成固定长度的53字节信元后进行复用.因而网络带宽的利用率高,网络的通用性好,能够容纳多种不同速率和不同格式的业务.ATM是面向连接的,它综合了分组交换网和电路交换网两者的优点.ATM最初是作为骨干网技术进行研究的,但由于某些标准化不够完善,产品价格过高,传输媒体有限等等技术原因,使ATM技术首先在局域网中得到应用.     

MPLS VPN在多分支企业组网中的研究与应用

MPLS(Multiprotocol Label Switch)是多协议标签交换的简称,因其具有面向连接和开放结构而得到广泛应用,MPLS将两层交换和IP路由控制能够更好地集成,与此同时,也使得IP技术以及异步传输模式能够更好地结合,从而在不改变现有的用户网络的条件下,也能够提供更加安全、高速、业务高度多层统一的网络平台;并且,在下一代网络平台的分组转发、交换、选路等层面中担当着十分重要的角色,从而满足企业中组网的多方位需求,成为和传统的ATM、SDH、MSTP等相提并论的企业广域网组网技术。     

智能交换光网络技术

传统的电路交换电话网和分组交换数据网都是为各自的业务专门设计的。而且网络呈现多种接入方式并存的状况,语音用TDM网络、IP用以太网或ATM、视频用HFC网络。在这种情况下,针对某一种业务的通信连接在逻辑上就构成了一种独立的网络结构,任何一种网络都不能很好地同时适用于其它的业务类型,于是就形成了分别面向单一业务的多种业务网络相互重叠的结构形式,从而导致整体通信网络架构呈现业务专门化、结构重叠和功能重复等特点。原先只为语音业务而设计的骨干通信网络由于功能重叠、网络层次结构复杂、缺乏互通性,极大地降低了网络…     

A guide to data communications: B-ISDN and how it works

The capabilities of the emerging broadband integrated services digital network (B-ISDN) are examined. Fundamental differences between broadband and narrowband ISDN are identified. The basics of asynchronous transfer mode (ATM), the switching technique used by BISDN networks, are discussed. Channel identification, generic flow control, using ATM, and connectionless service are considered. The first services expected to make use of ATM are briefly described     

A pipelined, multiprocessor architecture for a connectionlessserver for broadband ISDN

The direct provision of connectionless service in BISDN calls for servers that are connected to or are part of an ATM network to provide the routing function at input speeds up to 622 Mb/s. Routing is achieved in such a server by changing the VCI/VPI headers in the ATM cells; actual switching is done by existing switches in the ATM network. The paper presents an architecture capable of executing all the functions of a server at input speeds up to 622 Mb/s, scalable to multiple inputs at that speed, making use of processors and special hardware that are available today. To avoid storing large quantities of data, the architecture routes data packets by examining routing information in the initial cell of the packet and routing subsequent cells as they arrive rather than waiting until the complete packet has arrived. It is capable of handling packets that have been multiplexed at the SAR sublayer using AAL Type 3/4 and, with minor modifications, could also handle Type 5 traffic. Arguments are also presented for the use of AAL Type 5 for the direct connectionless service     

Architectural issues of ATM based connectionless overlay network

Connectionless service such as SMDS, or its European equivalent CBDS, can be provided by an ATM network by building a separate connectionless overlay network (CLON) on top of the ATM bearer service. A CLON is composed of a number of connectionless servers, CLSs, which provide the routing function, connected by semipermanent virtual paths (VPs). In this paper, architectural issues related to the design of a CLON are studied. In particular, we address the question of the optimal number of CLSs and their interconnection topology, assuming the underlying ATM network and the mean connectionless traffic load are known. The objective of the design process is to meet given design criteria with minimum costs. The QoS requirements of the SMDS/CBDS service are briefly reviewed and a simple cost model for the CLON network is given. The dimensioning of the logical links is also considered. Then the design process to find the optimal solution for the whole network is outlined. A simplified procedure was applied in numerical studies of the topological optimization. In order to find the general dependence of the optimal number of CLSs on the size of the network and other network parameters, the optimization procedure was applied to a large number of sample ATM networks, generated by an algorithm which is briefly described. Results from these studies are presented and discussed.     

Connectionless service for public ATM networks

The interconnection of connectionless LANs and MANs over a connection-oriented B-ISDN presents a dilemma with regard to efficient interoperability. In order to provide solutions to this dilemma, there have been many techniques proposed. We describe and evaluate the architectural and conceptual alternatives available for the implementation of a connectionless service for public ATM networks. We also suggest a scheme through which best-effort connectionless service may be provided in public ATM networks using connectionless servers and hop-by-hop flow control. There is as yet no consensus on issues such as bandwidth management, address resolution, connectionless server forwarding modes, or connectionless server topology, and therefore much of the area remains open for research. These research issues must be addressed, however, in order to realize the interoperability, and thereby the acceptance, of ATM     

Data communications using ATM: architectures, protocols, andresource management

The introduction of ATM is being propelled by the need for fast data communications in public and private networks. What is needed is a clear picture of protocol architectures and traffic characteristics of the various applications to be supported both now and in the future. The authors discuss ATM network architectures with special focus on the support of connectionless LAN interconnection and show which benefits can be obtained from the introduction of a connectionless server in an ATM network. They outline issues related to the use of existing protocols when ATM networks are introduced and show which protocol complexities have to be handled by gateways and servers, again using the example of connectionless LAN interconnection. Having presented network and protocol architectures the issue of data communication in ATM, resource allocation, is treated     

The sink tree paradigm: connectionless traffic support on ATM LAN's

Asynchronous transfer mode (ATM) is a connection-oriented technology in which all communication is based on virtual connections established prior to the transfer of data. It is expected that the bulk of traffic carried by the ATM network will be data traffic, e.g., local area network (LAN) internetwork traffic. Hence, a major issue regarding ATM is the support for connectionless (datagram) traffic. A scheme for the efficient support for connectionless traffic in ATM LANs based on trees of virtual connections is proposed. In this scheme, a sink tree is built for every switch in the LAN. Each tree provides an efficient means of routing connectionless traffic from any switch in the network to the sink switch (root) of the tree. The sink tree solution may also be used to broadcast connectionless messages in the reverse direction. The trees can easily be updated to adapt to topological changes or congestion in the network. A protocol for refreshing the tree structure using the ATM switch routing tables is described. An adaptive rate control solution, in conjunction with fast back pressure at the ATM layer, is presented. It is shown that this scheme achieves high utilization of available bandwidth for connectionless traffic, has low cell loss probability, and small overhead     

Comparison of ATM switching architectures

Clear examination of work currently done within CCITT indicates the importance of a broadband telecommunication network. As this network should be capable of integrating all services in an efficient way—in order to reduce cost—the asynchronous transfer mode (ATM) was selected by CCITT as the target transfer mode for implementing the broadband integrated services digital network (BISDN). This selection implies that the switching nodes in the BISDN network are capable of supporting this high-speed packet and connection-orientated technique. Within the literature different switching node architectures based upon ATM have been proposed. All of these architectures should meet the high-speed and high-throughput requirements so as to cope with the delay and jitter performance objectives. In a first step this paper describes alternative switching techniques for the basic building block (switching element) of a switching node. A common model architecture of the switching element is drafted. A classification of switching elements described in the literature is derived and the influence on the complexity and performance is weighted. In a second step the switching node architecture is further elaborated according to the control and flexibility requirements. Core (switching) and edge (switching related) functions are listed, and possible functional partitionings are discussed. Finally, these ATM switching architectures are compared according to a background frame consisting of several straightforward comparison points such as the buffering strategy, the internal routeing method, the switching overhead, the connection-orientated or connectionless operation, etc.     

B-ISDN and the OSI protocol reference model

The evolution of public telecommunication networks toward broadband integrated services digital networks (B-ISDNs) is presented. The asynchronous transfer mode (ATM), which supports B-ISDNs, and the B-ISDN protocol reference model are discussed. It is shown that the service offered by the ATM layer in the B-ISDN protocol reference model is equivalent to the service offered by the OSI physical layer. It is also shown that the service offered by the ATM adaptation layer (AAL) type 3/4 is similar to an OSI data link service. The emergence of the metropolitan area network (MAN) standard as an intermediate support for broadband services and the similarities between the DQDB MAC and the AAL type 3/4 in its connectionless mode are discussed     

Performance management issues of currently operated ATM enterprisenetworks

The author proposes a solution for the allocation and balancing of resources to maximize available bandwidth shared among corporate users. Currently established broadband virtual private networks (BVPNs) based on asynchronous transfer mode (ATM) technology comprise ATM cross-connects (ATM-CCs) and a lot of intelligent customer premises equipment (CPE). The CPE, an intelligent ATM service switcher or ATM multiplexer, enables the corporate user to connect routers, private branch exchanges (PBXs), or codecs onto the ATM network. One fundamental characteristic of CPE is that it is capable of accumulating asynchronous and synchronous traffic which may belong to different corporate users' sites. A typical example given of a BVPN configuration serving two corporate network users with four user sites each. In general, each user site needs to exchange asynchronous (connectionless) data streams for the inter-local area network (LAN) communication and synchronous (connection-oriented) data streams with constant bit rates for video/voice communication. The configuration and the performance aspects of inter-LAN communications employing a connectionless server (CLS) are discussed. The bandwidth allocation aspects of the BVPN having to convey synchronous and asynchronous traffic in an ATM environment without a CLS are discussed, including the bandwidth allocation algorithm. The important characteristics of the proposed algorithm is also summarised     

Designing a practical ATM LAN

The adaptor cards and driver software for workstations and local asynchronous transfer mode (ATM) switches and switch control software used in an ATM local area network (LAN) system are discussed. It is shown that the ATM hardware and software components together provide services that are essential for ATM to be considered a realistic alternative to current shared-media LANs. These services include: completely transparent support for the TCP/IP protocol suite, an application programming interface for full access to the underlying ATM capabilities, support for AAL5, AAL3/4, and the null AAL, both connection-oriented and connectionless service, dynamic connection establishment or switched virtual circuits, resource reservation of guaranteed bandwidth and quality of service, full-bandwidth multicast and broadcast, virtual path and channel routing among multiple switches, automatic configuration and failure recovery, dynamic address assignment and internetwork address resolution, and network management via the simple network management protocol (SNMP)