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     

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     

MSTP应用和发展展望

在概述MSTP演进路线的基础上,文章从运营角度探讨了今后一段时期内MSTP设备应具有的功能和新业务支持能力,如VLAN组网能力、业务分类和服务质量(QoS)控制能力、多业务传送能力等.文章认为多业务传送节点(MSTP)继承了同步数字系列(SDH)的技术优势,同时又能承载以太网、IP和ATM等多种数据业务,并在同一个平台上实现统一的网络控制和管理,将发展成为城域传送网的主流技术.由于具有丰富的接口、灵活的带宽管理和服务质量保证机制,MSTP可很好地将传输技术与数据业务的发展需求结合起来,较好地解决电路和数据业务的综合传送,为电信运营商提供更加广阔的运营空间.     

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。     

Service convergence using MPLS multiservice networks

Enterprises are increasingly using virtual private networks to interconnect remote sites. Traditionally, service providers have used ATM core networks to deliver layer 2 services such as frame relay, ATM, or TDM private lines, which enterprise customers have then used to build their corporate network infrastructure. Such services account for the majority of data service revenues today. However, pressure has increased on service providers to combine increased flexibility with reduced costs in the context of a highly dynamic telecommunications market. Service providers also need to generate new revenues from their IP network infrastructure, through new opportunities such as IP VPNs and virtual private LAN services, while simultaneously achieving operational efficiencies through the convergence of all of their services on a common MPLS backbone. New access and metro network technologies, such as Ethernet, are also emerging that can be used to deliver these new services to enterprise customers alongside ATM and frame relay access. This must be achieved while also supporting existing technologies such as ATM, which continue to deliver highly profitable services. This article discusses the technical challenges in meeting the often conflicting requirements of delivering both traditional layer 2 services and new layer 3 services on a converged MPLS network. We show how both network and service interworking are required, and how these must operate at the user, control, and management planes to enable profitable services to be delivered over the new converged network. The different solutions being defined in the standards bodies are described, and the distinct scenarios they address are explained.     

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     

Overview of implementing ATM based enterprise local area networkfor desktop multimedia computing

The authors discuss important implementation issues in an ATM-based enterprise network, and propose possible migration strategies for the smooth introduction of ATM into the desktop computing environment. They present the ATM traffic service classes and the associated traffic management functions. The authors cover the latest ATM forum standardization efforts on traffic management functions and LAN emulation. Finally, they discuss how to seamlessly support the existing transport control protocol (TCP)/Internet protocol (IP) in an ATM environment     

Traffic management for ATM local area networks

Asynchronous transfer mode (ATM) is the first switching technology to be capable of supporting circuit switching and packet switching within a single integrated switching mechanism. This was one of the research goals that led to the development of ATM. Considerable progress has already been made in implementing constant bit-rate services, similar to conventional circuit switching, over ATM. The authors briefly consider how to support LAN emulation over an ATM network and then explore how to offer the dynamic bandwidth sharing in the local area. Considerable progress has already been made in implementing constant bit-rate services, similar to conventional circuit switching, over ATM. However, the bursty nature of data traffic requires dynamic bandwidth sharing similar to packet switching, and this is still under investigation     

宽带数据通信网的演进

尽管ＩＰ化已成为宽带数据网络的演进方向,但电信运营商在选择融合网络解决方案时比较现实的选择是优化现有传送网基础设施,同时要兼顾公司目前或将要提供的业务。在光联网方案讨论中,文章对ＩＰ ｏｖｅｒ ＳＤＨ和ＩＰ ｏｖｅｒ ＡＴＭ进行了比较,认为集成型ＩＰｏＡ被看好。但由于ＡＴＭ的局限性,未来的联网方案将是基于ＤＷＤＭ的光互联网,而ＡＴＭ将演变为一种边缘技术,网络智能也将随之转移至网络边缘。     

合理构筑宽带IP网的骨干网

在ＩＰ业务的冲击下对下一代ＩＰ网络方案的讨论如火如荼。本文在对各种方案 本介绍的基础上，对ＩＰｏｖｅｒＡＴＭ和ＩＰｏｖｅｒＳＤＨ两种方案进行了比较。前者在ＱｏＳ、多业务支持及带宽管理方面具有优势２，而后者的带宽利用率较高，且组网简单。前者地传统电信运营商的网络，后者则对所新兴的ＩＰ业务运营商更为有利。     

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.     

IP on ATM local area networks

ATM offers increased bandwidth and greater flexibility and manageability. However, ATM's success as a LAN technology depends on its ability to provide LAN-like services compatible with existing protocols and applications. The authors address the various issues in the design and implementation of the Internet Protocol (IP) in the evolving ATM LANs     

Hybrid transport solutions for TDM/data networking services

There is a growing demand for native data transport services for enterprises and corporations across public transport networks. Equipment vendors have begun to incorporate a variety of LAN and storage area network interfaces, notably Ethernet, Fibre Channel/FICON, and ESCON, on traditional metro and long-haul transport equipment. Embracing Ethernet and SAN technology enables the introduction of flexible high-capacity transport services optimized for data networking. Transport operators may thus offer both enterprise-centric connectivity services, such as transparent LAN connectivity and virtual LAN services, as well as traditional bandwidth services, such as private lines, while preserving the operations and management infrastructure of the existing public networks. We discuss the benefits of a hybrid Ethernet/TDM transport solution     

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)     

Programming telecommunication networks

The move toward market deregulation and open competition has sparked a wave of serious introspection in the telecommunications service industry. Telecom providers and operators are now required to open up their primary revenue channels to competing industries. The competition for product differentiation increasingly depends on the level of sophistication, degree of flexibility, and speed of deployment of services that a future provider can offer. These factors in turn depend heavily on the flexibility of the software architecture in place in a provider's operational infrastructure. Within this context, we examine the service architecture of two major global communication networks-the telephone network and the Internet and explore their weaknesses and strengths. We discuss the realization of an open programmable networking environment based on a new service architecture for advanced telecommunication services that overcomes the limitations of the existing networks. Our approach to network programmability stems from two angles-one conceptual, the other implementational. In the first, we attempt to develop a service model that is open and reflects the economic market structure of the future telecommunications service industry. Furthermore, we introduce an extended reference model for realizing the service marketplace and present it as a vehicle for creating multimedia services with QoS guarantees. In the second, we investigate the feasibility of engineering the reference model from an implementation standpoint. We describe a realization of the open programmable networking environment as a broadband kernel. Called xbind, the broadband kernel incorporates IP and CORBA technologies for signaling, management, and service creation, and ATM for transport. We also address some of the important QoS, performance, scalability, and implementation issues     

Multicast forwarding over ATM: Native approaches

Multicasting is growing in importance as new multimedia applications are devised. Throughout this article, multicasting is understood as the efficient multipoint-to-multipoint transmission of information (in terms of network resource consumption) between the members of a group. Most multicast services have been designed up to now to work over connectionless environments. The approach adopted by connection-oriented networks has been to try to imitate these connectionless multicast schemes with the aim of supporting IP multicast or network-layer broadcast. However, these solutions present drawbacks in terms of delay or signaling overhead. The goal of native ATM multicasting is to provide multicast communications support by taking into account the characteristics of ATM. Therefore, the design philosophy of multicast must be rethought by making it more suitable for connection-oriented networks. Native ATM multicasting is based on mechanisms implemented at the switches to allow the correct ATM-layer multicast forwarding of information. These mechanisms seek to avoid the delay and signaling problems of current solutions, e.g., LAN emulation and IP multicast over ATM. This article provides a survey of the literature on the strategies that offer multicast communications in ATM environments, with special stress on native ATM multicast forwarding mechanisms. Other aspects, such as signaling, quality of service, traffic control, and routing, are not addressed in detail in this article.     

3.5 GHz固定无线接入市场令人关注

3.5GHz是国际电联推荐的用于固定无线接入的频段，系统构成一般包括基站、远端站和网管系统三大部分。3．5GHz固定无线接入可基于电路方式、IP方式、ATM方式等，提供的业务包括中高速因特网接入、局域网互连、VPN、租用线、IP电话／IP传真、视频会议、PSTN／ISDN等。中国2001年在5个城市首次进行了3.5GHz固定接入业务的招标，目前中标公司大都在提供业务。2002年年底信息产业部在32个城市再次进行3．5GHz频段的招标，激发了新一轮的竞争。     

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     

Compensating for moderate effective throughput at the desktop

This article presents the design and development of a networking system architecture targeted to support high-speed TCP/IP communication over ATM. The discussed architecture has been developed in the form of an integrated system which incorporates state-of-the-art software and hardware subsystems, and an OC-12c ATM adapter (622 Mb/s). Moreover, the design of this embedded system has been based on the Chorus real-time operating system, which, in turn, hosts an accelerated TCP/IP protocol stack over ATM. Furthermore, the embedded system board has been developed according to the PCI specification to easily be plugged into a host platform. In addition, the OC-12c ATM adapter subsystem has been designed and developed in order to also be plugged into the same host. The developed architecture has proven very efficient and reliable, providing high-throughput and low-latency bulk data communications. The measured performance on an OC-3c-based (155 Mb/s) testbed has shown that an optimally implemented TCP/IP stack, hosted by a real-time kernel and coupled with an ATM adapter, offers a robust desktop platform for high-speed end-to-end communications. The main feature of the accelerated TCP/IP protocol stack is the out-of-band processing of control and data information. The protocol accelerator embedded system processes the TCP/IP headers and accomplishes checksum computations, while data is transferred from the host's user memory space directly to the network. Finally, for validation purposes, the prototype system has been incorporated in an existing networking infrastructure targeted to support mass storage applications