Experience with PACS in an ATM/Ethernet switched networkenvironment

Legacy local area network (LAN) technologies based on shared media concepts are not adequate for the growth of a large-scale picture archiving and communication system (PACS) in a client-server architecture. First, an asymmetric network load, due to the requests of a large number of PACS clients for only a few main servers, should be compensated by communication links to the servers with a higher bandwidth compared to the clients. Secondly, as the number of PACS nodes increases, the network throughput should not measurably cut production. These requirements can easily be fulfilled using switching technologies. Here asynchronous transfer mode (ATM) is clearly one of the hottest topics in networking because the ATM architecture provides integrated support for a variety of communication services, and it supports virtual networking. On the other hand, most of the imaging modalities are not yet ready for integration into a native ATM network. For a lot of nodes already joining an Ethernet, a cost-effective and pragmatic way to benefit from the switching concept would be a combined ATM/Ethernet switching environment. This incorporates an incremental migration strategy with the immediate benefits of high-speed, high-capacity ATM (for servers and high-sophisticated display workstations), while preserving elements of the existing network technologies. In addition, Ethernet switching instead of shared media Ethernet improves the performance considerably. The LAN emulation (LANE) specification by the ATM forum defines mechanisms that allow ATM networks to coexist with legacy systems using any data networking protocol. This paper points out the suitability of this network architecture in accordance with an appropriate system design     

Wireless ATM network architectures

Emulated LAN technology supports mobile hosts in wireless ATM networks. This paper introduces virtual LAN (VLAN) services using ATM LAN emulation technology which operates on a client/server model. One of the attractive features of the VLAN is the capability to group users into a broadcast domain. The focus of this paper is the issue of supporting quality of service to mobiles in a wireless ATM network. Copyright © 2001 John Wiley & Sons, Ltd.     

在ATM网上实现局域网功能的困难及对策

ＡＴＭ网络作为下一代网络，终将成为网络的主流。但是ＡＴＭ网在目前传统局域网占主导对位的环境条下成为今后的主流和局长的方向，就必须解决二个问题；首先，必须使已有的众多的网络应用软件能在ＡＴＭ工作站上使用；第二，ＡＴＭ网应能很和传统的局 连在一起的工作站一起运作。本文介绍了在ＡＴＭ网上实现局域网功能所面临的困难及一些可能的解决方案。     

Wireless ATM LAN with and without infrastructure

We consider wireless ATM concepts for small LANs, especially for SOHO and future consumer applications. We describe a wireless ATM LAN framework architecture that supports wireless ATM communications in environments with and without fixed ATM infrastructure. For the configuration with an ATM infrastructure, a distributed ATM switched backbone is proposed, which enables a smart ATM switching element to be embedded in every wireless and fixed access point. For bandwidth efficiency and ease of operation (place-and-play), we also propose an ad hoc wireless ATM LAN concept based on the same 5 GHz wireless ATM air interface as is currently under standardization in the ETSI/BRAN and ATM Forum. Unlike CSMA-based ad hoc systems such as HIPERLAN and IEEE802.11, our ad hoc wireless ATM system makes QoS management feasible in an infrastructureless environment by using resource reservation and scheduled medium access protocol. Since cost scalability is essential throughout our system design, we consider forwarding between ad hoc subnets and interworking with the fixed network as important but optional features     

计算机局域网络技术发展综述

对传统计算机局域网络技术进行较为详细的阐述，并针对现有计算机技术、通信技术和多媒体技术的发展对计算机局域网络技术的发展趋势进行详细的综述，如交换式ＬＡＮ、ＡＴＭ ＬＡＮ和交换式互连网络设备。     

Data communication in ATM networks

An increasing number of customers require LAN access with high bandwidth and low delay over long distances. To satisfy these needs, several high-speed network techniques have been developed. Asynchronous transfer mode (ATM) is superior compared to other networking technologies, as it offers high bandwidth and is scalable in the sense that the bandwidth capacity of an ATM system is not fundamentally limited to the technology itself. Initial ATM installations will operate as subnetworks of existing networks and MAC layer protocols. One of the main challenges in ATM is the transparent support of existing connectionless LAN services. Several activities have been launched within international standard bodies and forums to specify ways of providing data communication services over ATM. Most notable examples are Switched Multimegabit Data Service (SMDS) and the similar Connectionless Broadband Data Service (CBDS) supported mostly by public network service providers. But also other approaches such as IP over ATM, and LAN emulation that show more adherence to the existing local and campus area networking paradigms. The article presents the requirements and architecture of the LAN emulation service. It describes the alternative methods for carrying IP packets over ATM, a public broadband service architecture and CBDS. The traffic management aspects of the data communication services are also discussed     

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     

Next generation local area networks

Many people now consider the local area network (LAN) to which their desktop personal computer (PC) is attached to be more important to them than the telephone network, resulting in a drive to increase both the performance and the reliability of LANs. This paper examines the key drivers for new LAN technologies, summarising LAN developments over previous years. It then looks at possible options for future LANs, which will need to evolve to meet changing traffic patterns brought about by widespread use of intranets and multimedia applications. This encompasses both new technologies such as Gigabit Ethernet, and new architectures such as virtual LANs (VLANs), multi-protocol over ATM (MPOA) and multi-protocol over LANs (MPOL).     

A shared-memory virtual channel queue for ATM broadband terminal adaptors

In order to take advantage of the low entry cost of the future public ATM (asynchronous transfer mode) network with shared facilities, it is highly desirable to interconnect different hosts and local area networks (LANs) to the ATM network. The interface between the computer hosts or LANs and the ATM network, commonly called a broadband terminal adaptor (BTA), provides the necessary format conversion for the data packets and the ATM cells. It is conceivable that multiple packets from different virtual channels are interleaved as they arrive at the receive-end BTA. The BTA must have a sufficiently large buffer, called a virtual channel queue (VCQ), to temporarily store the partially received packets. Once a complete packet has been received, it is forwarded to the host or LAN. Whenever the buffer fills with all incomplete packets, a packet must be discarded to make room for others. In this paper, we first study, through computer simulations, the buffer size requirement of a shared-memory VCQ for different numbers of virtual channels at various packet loss probabilities. We then present two different implementation architectures for the shared-memory VCQ, and compare their hardware complexity. The second architecture with linked-queue approach, adopted in our work, requires less buffer and has better scalability to accommodate a large number of virtual channels. Various possible error conditions, such as cell losses in the ATM network and the VCQ buffer overflow, are considered. Corresponding solutions are proposed and included in the VCQ designs.     

A nonpreemptive priority-based access control scheme for broadbandad hoc wireless ATM local area networks

The DQRUMA (distributed-queueing request update multiple access) protocol has been considered as an access protocol for the BAHAMA (broadband ad hoc wireless ATM local area network). However, it cannot support the service discipline of integrated multimedia traffic since it does not include any priority and access control policy. In this paper, we propose a nonpreemptive priority-based access control scheme for the DQRUMA protocol. Under such a scheme, modifying the CSMA/CA protocol in the contention period supports many levels of priorities such that user mobility (handoff) can be supported in BAHAMA. Besides, the proposed transmit-permission policy and adaptive bandwidth allocation scheme provide various QoS (quality-of-service) guarantees while maintaining high bandwidth utilization. Simulations show that it provides a good performance in ad hoc wireless ATM LAN environments     

ATM local area networks

LAN emulation offers a best-effort, connectionless, packet transfer service at the MAC sublayer, implemented on top of a connection-oriented ATM network LAN emulation using switched virtual connections requires address resolution to locate the destination end station followed by connection establishment to the resulting ATM address. Address resolution may be implemented by a broadcast technique or by an address server. The broadcast method is the simplest for small networks but a combination of both is probably better. The use of the MAC address to identify an end station, with dynamic binding to its current physical location in the ATM network, allows the ATM LAN segment to be viewed as a virtual LAN. The virtual LAN model permits end stations to move and change physical location while maintaining connection to the same ATM LAN segment. This greatly simplifies the management of large data networks     

Network management for the NCIH

The North Carolina Information Highway (NCIH) will support many applications, including distance learning, LAN interconnection, video conferencing, law enforcement, and health care. Initially, the NCIH is supporting distance learning and local area network (LAN) interconnection applications for the North Carolina State Government. The operations plan for the NCIH was driven by end-user service requirements, network operator requirements, and the network architecture. The NCIH is a multi-vendor, multi-carrier ATM network offering a 155-Mb/s OC-3c SONET/ATM customer access interface to support many applications. BellSouth, along with Bellcore, Fujitsu, NTI, and other carriers, has developed and implemented an operations plan for managing the NCIH     

B-ISDN中的无连接业务

以ATM交换为基础的B-ISDN提供高速、面向连接、分组长度固定的信元交换.当代PC和高速LAN的发展需要面向连接的ATM网络传输无连接业务.本文重点介绍ATM网络中无连接业务的分类、协议结构和具体实现形式.     

在ATM网上实现局域网功能的困难及对策

ＡＴＭ网络作为下一代网络，终装成为网络的主流。但量ＡＴＭ网要在目前传统局域网点主导地位的环境下成为今后的主流和发展的方向，就必须解决二个问题；首先必须使已有的众多的网络应用软件能在ＡＴＭ工作站上使用；第二，ＡＴＭ网应能很容易和传统的局域网连在一起的工作站一起动作。     

ATM local area networks: a survey of requirements, architectures,and standards

There is increasing interest in deploying ATM technology in local or campus networks. ATM is an ideal technology to overcome many of the limitations of today's LAN technologies. This article focuses on the application of ATM in the LAN environment to interconnect high-end host computers, and on the interworking of ATM-based LANs with legacy LANs. The authors introduce ATM LAN requirements, followed by a discussion of possible ATM LAN architectures to support these requirements. The article then covers current standards and their relation to the possible architectures, and concludes with a discussion of current ATM LAN issues and directions     

Design alternatives for wireless local area networks

In this paper an overview of the wireless local area network (LAN) area is provided. The two types of wireless LAN topologies used today, infrastructure and ad hoc, are presented. The requirements that a wireless LAN is expected to meet are discussed. These requirements impact on the implementation of both the Physical and MAC layer of a wireless LAN. The unique characteristics of wireless physical layers are discussed and the five technology alternatives used today are presented. MAC layer issues are discussed and the two existing standards, IEEE 802.11 and HIPERLAN 1, are examined. Polling‐based MAC protocols (RAP, GRAP) are also reviewed. Finally, an introduction is made to wireless technologies that interact with WLANs, such as personal area networking (PAN) and wireless ATM and an overview of HIPERLAN 2, a WLAN using ATM technology, is provided. Copyright © 2001 John Wiley & Sons, Ltd.     

LAN emulation on an ATM network

The authors evaluate architecture alternatives relating to the provision of a LAN emulation service over a connection-oriented ATM network, and present the LAN emulation architecture as actually adopted by the ATM Forum LANE SWG. The role of servers is discussed as is the provision of broadcast/multicast services     

Cells-In-Frames: a system overview

Cells-In-Frames provides an efficient mechanism for integrating both voice and data traffic on an existing campus network that is currently supporting legacy LAN workstations. The solution suggested by this article is to export ATM services within standard LAN frames. Each frame will carry the traffic from one or more ATM cells, but any given LAN frame is associated with only one ATM virtual circuit. The widely different qualities of service required for voice and data traffic is achieved rough the use of AAL1 and AAL5 services. The AAL functions are split appropriately between the workstation and the LAN switch that interfaces to an ATM backbone network. With the use of the Q.2931 signalling protocols defined for ATM, Cells-in-Frames achieves a long-sought-after goal of providing switched networking services to LAN-attached workstations     

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)     

ATM网络抗毁和自恢复技术研究

基于ATM/MPLS技术的通信网络是承载宽带多媒体业务的综合平台。为了对承载业务进行抗毁保护,对ATM的最基本的1+1、1∶1、m∶n抗毁保护结构进行了研究和总结。同时结合网络传输层,如:PDH、SDH、WDM、MPLS的保护和应用层业务,如:IP、电路交换、以太网和帧中继的抗毁迂回策略,提出了ATM的多层次抗毁自恢复组网结构,为ATM的应用研究提供了借鉴。