Optical transport networks

The key technologies required for the development of optical transport networks, namely, optical fiber transmission and digital transport, which includes transmission signal multiplexing, transport nodes, and network operation functions, are highlighted. The trends in transport technology, the impact of synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM), the role of telecommunications management networks, and network integrity enhancement techniques are elucidated. It is demonstrated that these technologies have brought about a great change in transport network design and performance. Further innovations are required to fully realize a high-performance computer communication network, a cost-effective nationwide B-ISDN, and local networks for video distribution. These include the realization of an optical access transport network and the extension of trunk network capabilities which will be possible with optical path layer technologies     

ATM和SDH的比较

现代传输网开始向着智能化方向发展,数字传送技术是关键。在支持可变比特率和高突发性业务方面,ＡＴＭ和ＳＤＨ更具优势。采用由高鸿公司开发的基于ＡＴＭ ＡＤＭ的新型传送网／接我设备ＡＰ９００在业务提供、带宽利用、节省投资等方面比采用ＳＤＨ技术更具竞争力。     

Evolution of the Italian Telecommunication Network towards SDH

The digitalization of both transmission and switching facilities as the basis for both a high standard quality of service and the introduction of advanced network features (like intelligent network and integrated services digital network, or ISDN) is described. The development of synchronous digital hierarchy (SDH) systems is discussed, with particular attention given to the add-drop multiplexer and to management issues. The impact of the new SDH transmission equipment on the present plesiochronous network is assessed. The currently envisaged strategy for introducing SDH systems into the Italian transmission network is examined. Deploying SDH systems within large metropolitan areas, both at loop plant and urban junction levels, is discussed     

Implementing a flexible synchronous network

The SYNET project, undertaken by Deutsche Telekom to modernize its transmission network, is discussed. The SYNET technology is based on the synchronous digital hierarchy (SDH), which uses synchronous transport modules of 155 Mbit/s (STM-1). The latter include a maximum usable bit rate of about 50 Mbit/s as well as a variety of additional information intended for network management. Since the transmission network is divided into several network levels characterized by different traffic loads and structures, a range of synchronous components geared to the requirements of the different network levels have been developed. The major differences between the trunk network and the local networks are described. The implementation of SYNET is reviewed     

Broadband transport — the synchronous digital hierarchy

All data networks require a physical transmission medium to convey information between network nodes. Within a local environment this physical medium might, for example, take the form of an Ethernet LAN, but wide area connections are provided using telecommunications constant bit rate transmission equipment. Furthermore, the assumption that data networking is simply the provision of WAN connectivity for large corporate networks is becoming dated. The explosion of interest in the Internet means that, for transport networks, the term data may encompass voice, video and multimedia applications for delivery to both home and office. This places additional requirements on the network infrastructure as each service has specific transport requirements.Network operators are currently in the process of deploying core networks of equipment conforming to the ITU-T Recommendations for a synchronous digital hierarchy (SDH), but many networks also contain a significant proportion of older transmission technologies. This paper provides a review of transmission technology and describes the impact of such networks on the transport of data.     

面向奥运本地传输网优化改造

表文讨论了北京通信本地传输同络现状．描述了为即将到来的奥运会北京通信将进行的有关传输网PDH和SDH的网络改造方案、目标、实现步骤。讨论丁传输网配套网管同、同步网的改造优化原则。     

Multi-wavelength transport networks

Optical networking is attracting a large amount of interest, particularly for local access and increasingly for long-haul, or core, network applications. However, optical networks are essentially analog, and with this return to analog transmission there are a number of issues that need to be understood and overcome if the concept of an optical transport layer is to become a reality. The Multi-Wavelength Transport Network (MWTN) within the European RACE II research program is studying the potential for optical networking in a managed network environment. This article outlines the MWTN networking concept and the comprehensive experimental test bed developed within the project. Communication networks are poised, awaiting the broadband revolution. Telecommunication, computer, and broadcast entertainment market places are converging with multimedia-based future services providing the drive and focus. In such an information-intensive future, customers will demand high-performance service with an agreed and measurable quality at the lowest cost. Furthermore, they will expect a common interface to all services. From a customer's perspective, the role of the network, the terminal equipment and the computer based multimedia application will be virtually indistinguishable. The synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM) techniques are at the forefront of the move toward these future communication networks     

MSTP技术及其应用

MSTP（Multi-ServiceTransportPlatform）是基于SDH的多业务传送平台.MSTP是指基于SDH平台同时实现TDM,ATM和以太网等业务的接入处理和传送,并提供统一网管的多业务综合传送设备.MSTP设备是对传统SDH设备的继承和发展,是传送技术演进的重要阶段.MSTP的引入不但可以充分利用现有的丰富的SDH网络资源,借鉴SDH传输系统多年的网络运维和管理经验,完全兼容目前大量应用的TDM业务,还可以实现以太网、ATM等多种业务的综合传送和接入,满足日益增长的数据业务需求.文章主要介绍了MSTP技术的特点及新一代MSTP的产生背景,并在最后对其在几项业务中的应用做了较为详尽的论述.     

Carriage of SDH over satellite systems

This paper examines the potential of satellite systems to carry synchronous digital hierarchy (SDH) transmissions and proposes a possible earth-station architecture capitalizing on the benefits that SDH equipment offers. It is shown that a range of SDH multiplexing rates are viable over satellite and that multi-destination operation of satellite systems is facilitated by using the inherent features of the SDH. The use of STM-1 (155 Mbit/s) and sub-STM-1 transmission rates as transmission sections along with appropriate integration of the multiplexing and modem equipment would:. (a) enable SDH path continuity between earth-stations, allowing the satellite network to be integrated with managed terrestrial networks to form global managed transmission platforms. (b) provide bandwidth and equipment savings at earth-stations. Several technical issues relating to SDH operation over satellite systems are considered and SDH pointer corruption is examined in some detail.     

Emergent Properties of the BT SDH Network

When planning an SDH network, explicit structure, such as rings or a network hierarchy, is often imposed to allow for easier network protection and management. Decisions on node connectivity are also heavily dependent on available transmission capacity and network geography, as well as the demands placed on the SDH transport layer. The strictly imposed structure therefore makes it unlikely for unplanned properties to appear but here we describe how the BT SDH network exhibits emergent power-law properties in a range of metrics. These properties are similar to those previously found in the Internet, but the Internet in contrast is not globally planned, has adaptive elements such as dynamic routing and peering agreements, lacks explicit imposed structure, and is less coupled to transmission topologies.This paper shows that even with a wide range of restrictions and controls the BT SDH network topology follows power-laws and we offer possible sources for them, concentrating on the possible effect of adjacent network layers. The existence of these properties has wide implications in network modelling, as well as network scaling, growth, and robustness analysis.     

自动交换传送网(ASTN)技术研究与开发

相比较第一代静态传送网(PDH/SDH/ATM/OTN)技术,自动交换传送网(ASTN)是带有交换功能的第二代智能传送网,它是目前传送网技术的最新研究成果。首先分析了ASTN技术对比传统传送网技术的优势;给出了ASTN的节点结构;研究和分析了ASTN的转发平面、管理平面的关键技术,尤其是对ASTN的核心技术-基于GM-PLS协议栈的控制平面做了详尽的技术分析;最后对未来的传送网技术进行了展望。     

Service-specific resource allocation in WDM networks with quality constraints

The need to establish wavelength-routed connections in a service-differentiated fashion is becoming increasingly important due to a variety of candidate client networks (e.g., IP, SDH, ATM) and the requirements for QoS-delivery within transport layers. The multiservice operation changes the way we deal with wavelength-routed paths, as they are now being characterized by manifold properties, such as transmission quality, restoration, network management, and policies. We propose a generic approach to service-differentiated connection accommodation in wavelength-routed networks where, for the network state representation, the supplementary network graphs are defined and referred to as service-specific wavelength-resource graphs. These graphs are used for the appropriate allocation of wavelengths on concatenated physical resources building a wavelength route, along which the necessary transmission quality is achieved and the required management and surveillance functions are provided. By considering twofold wavelength routing metrics, i.e., QoS metrics (service requirements) and resource metrics (quality constraints), these graphs can yield the solution to the QoS-routing problem, i.e., the provision of service-specific guarantees under quality constraints-a feature that is still missing from the existing architectures. The numerical analysis of dynamically reconfigurable multiservice WDM networks is presented for regular network operation as well as for optical network service restoration.     

建设穗深SDH 622Mbit/s光缆传输系统试验网的设想

本文叙述利用穗深地区现有光缆路由(粤港、榕穗光缆路由)建设穗深同步数字系列(SDH)622Mbit/s传输系统环形网的设想。对PDH、SDH设备进行了比较,对线形传输、环形传输方式进行了比较并用曲线图对环形网两点间最长传输距离的经济性进行了估算。列出了设备的主要技术指标。     

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.     

Implementing the Orwell protocol over a fibre-based high-speed ATMnetwork

Asynchronous transfer mode (ATM) has emerged as a possible contender for the next generation switching system and fundamental transport basis for the broadband integrated services digital network (B-ISDN) and telecommunications in the future. It is widely thought of as the network to accommodate the uncertain requirements of future public communications because of its high degree of flexibility and service independency. The Orwell protocol developed by British Telecom can provide a communication base to meet the requirements of such a network. Orwell is used as a slotted ring protocol designed to carry a mixture of services which form the basis of an ATM network. The authors describe the realisation of a 155.52 Mbit/s fibre-optic physical layer from the Orwell protocol based on an ATM technology, and also discuss how the Orwell protocol can offer broadband transport capabilities and can provide access to and interwork with existing networks, such as telephone networks and 64 kbit/s based ISDNs     

MPLS在基于SDH的3G接入网中的应用

以WCDMA为例,目前可商用的R99和R4版本都采用ATM承载技术,很多以SDH传输网作为传送平台的大型移动通信运营商采用基于SDH透传的MSTP技术从TDM向ATM平滑过渡,而未来的3G网络将发展成为从接入网到核心网全面采用IP承载的网络,考虑到IP网络在流量控制、QoS等方面的局限性,基于MPLS技术的IP承载将得到广泛的应用.但对于基础传输网络为SDH网络的运营商而言,不可能新建一个全新的纯MPLS网络来究成接入网向IP承载的过渡,必须以现有的SDH网络或MPLS网络为基础进行平滑过渡.讨论了3G接入网的IP演进进程中,MPLS在SDH传输网中的应用方案.     

Single-chip 622-Mb/s SDH/SONET framer, digital cross-connect andadd/drop multiplexer solution

This paper presents a single-chip all-CMOS solution for 4×OC-3c, OC-12, and OC-12c synchronous digital hierarchy/synchronous optical network (SDH/SONET) framing with integrated serial line interfaces. Outstanding features of this chip are clock and data recovery and fulfillment of ITU-T and Bellcore jitter requirements for SDH/SONET systems, as well as the large range of functions offered. These functions include asynchronous transfer mode (ATM) and point-to-point protocol (PPP) support, as well as built-in native SDH/SONET functions such as digital cross-connect, add/drop multiplexing, and automatic protection switching. In addition, the chip is based on a new scalable modular architecture     

MSTP在城域网中应用探讨

在SDH技术的基础上,MSTP(多业务传送平台)吸收了以太网、ATM、MPLS、RPR(弹性分组环)等技术的优点,对业务接口进行了丰富,成为城域网的热点技术.本文主要从应用角度出发,分析了MSTP在承载大客户以太网专线、软交换、3G等业务方面的应用模式,为城域网的进一步发展开拓思路.     

Future transport network architectures

The architecture of today's long distance transmission networks, which we call the baseline architecture, is a complex and multilayered hierarchy of TDM circuits. One premise of the baseline architecture is that restoration from network failures is provided mostly by SONET/SDH rings. This article presents an alternative architecture that uses ATM and optical layer cross-connect technology for TDM services. Using a sophisticated set of network design tools developed at AT&T Labs-Research, we show that the alternative architecture offers dramatic capital savings and improved network efficiency over the baseline architecture. Most of this savings can be attributed to use of OLXC mesh network restoration, which makes more efficient use of capacity than SONET/SDH rings, and use of ATM switching for transport of TDM circuits, which consolidates the numerous TDM equipment layers inherent to the baseline architecture. In addition, motivated by the rapid growth of IP services, we analyze in the alternative architecture whether to provide restoration for IP services in the IP layer itself, by rerouting packets over precalculated restoration paths with MPLS, or to alternatively provide restoration of failed IP layer links in the OLXC layer. One potential advantage of IP layer restoration is that network operators may choose to only restore a fraction of the services, in particular the “priority” services, affected by a network failure. This article gives some methodology of how to determine this fraction at which IP layer restoration is cost-competitive with OLXC restoration