以太网业务接入网分析

　　Packet-Optical Ethernet Business Access Networks

　　Services without boundaries

　　Ethernet has rapidly become the technology of choice for service providers supporting enterprise networks and services. But business customers are demanding increased band-width with more flexibility and differentiated service quality at lower costs. As a result， service providers are faced with many overlapping and conflicting challenges when trying to meet the demands of their business customers. This paper explains how Packet-Optical Ethernet business networks have evolved and how new solutions are able to overcome the limitations of Ethernet access in the last mile， in terms of physical delivery infrastruc-ture， manageability， operations， administration and maintenance （OAM） and intelligent demarcation.

　　Table of contents

　　1 Introduction

　　1 Market drivers and challenges

　　3 Packet-Optical Transport and Ethernet business networks

　　4 Carrier Ethernet and the MEF

　　5 The evolution of Packet-Optical Ethernet business access services

　　6 Alcatel-Lucent Next-generation Packet-Optical Ethernet business access solutions

　　8 Conclusion

　　8 Acronyms

　　Introduction

　　Enterprises have growing bandwidth， reach and reliability requirements for their voice， data and video traffic. They are also deploying new applications to meet crucial business objectives， such as increasing efficiency and reducing costs. The challenges for service providers are to deliver higher speed access for business services， provide connectivity to more enterprise sites — wherever they are located — and to do this without significant increases in cost and complexity.

　　Ethernet has rapidly become the technology of choice for service providers supporting enterprise networks and services. It offers the ability to provide a single ubiquitous technology for multiple service types， and it is the technology of choice for transporting IP-based applications. Ethernet also provides the bandwidth， flexibility， service transparency and low cost requirements needed for today’s packet-orientated business services.

　　Thanks to the efforts of the International Telecommunication Union Telecommunication Stan-dardization Sector （ITU-T）， the Institute of Electrical and Electronics Engineers （IEEE）， and the Metro Ethernet Forum （MEF）， the limitations of traditional LAN-based Ethernet in terms of scal-ability， reliability， Quality of Service （QoS） and manageability have been solved. This has allowed the widespread deployment of network solutions using Ethernet， or “Carrier Ethernet” as the MEF defines this new， more robust Ethernet.

　　Market drivers and challenges

　　Service providers have many overlapping and conflicting challenges when trying to meet the demands of their business customers. Business customers are demanding increased bandwidth with more flexibility and differentiated service quality at lower costs：

　　• Higher bandwidth services with far better granularity than those provided by traditional private line （E1/T1 or E3/T3） or frame relay

　　• Ubiquitous connectivity and capabilities to all of their sites， regardless of existing infrastructure

　　（copper， fiber）

　　• Service quality at least as good as today’s networks in terms of security， availability， latency and latency variation

　　• Ability to pay for differentiated service quality and to monitor and confirm， in real time， that service level agreements （SLAs） for their services are being met （pay for extremely low latency and latency variation for some services and best effort for other services）

　　• Consolidation of data and centralization of switching to move the switching capability from the customer to the service provider （customers want their hub sites provided with a single trunk that consolidates and routes all traffic to/from remote sites， rather than a link per site as required with traditional solutions）

　　• Near instantaneous service turn-up for new services to existing sites

　　• Connectivity to new sites extremely rapidly （days rather than weeks）

　　• Overall service package costs that are less than with traditional private line services

　　At the same time service providers have to deal with：

　　• Cannibalization of revenue streams from their existing service products， while trying to migrate to new service products

　　• Maximizing return on investment （ROI） on the evolution of their network from circuit to packet， while continuing to maximize the ROI from their embedded networks

　　Packet-Optical Ethernet Business Access Networks | Technology White Paper 1

　　• Potential escalation in operating expenditures （OPEX） due to the increased complexity of the technology for new services types and the increased complexity of the management require-ments demanded by customers

　　• An unpredictable growth model because it is becoming increasingly difficult to predict when and where customers will want new or higher bandwidth services

　　Ethernet is designed to transport IP. It also provides the ability to address flexible bandwidth needs with a cheap， ubiquitous customer interface. Carrier Ethernet， as defined by the MEF， extends Eth-ernet with the service quality capabilities demanded by business customers.

　　Fiber is the natural technology of choice to deliver Carrier Ethernet business services. However， fiber is not widely available in many last mile access networks where copper continues to dominate. According to Vertical Systems， in 2007 the vast majority of business sites in the U.S. and Europe had no access to fiber， with small and medium business sites disproportionately underserved com-pared to large business sites.1

　　Businesses in the same buildings within major metropolitan areas are most likely to have access to fiber， whereas businesses in smaller buildings and in less populated areas are the least likely to have access to fiber. Where business sites are not fiber-connected， service providers may opt to build fiber out to the building， if this makes sense commercially. Alternatively they would like the option to deliver Ethernet business services over existing copper infrastructures. This has prompted an increased interest in dedicated platforms that deliver Ethernet business access over copper， such

　　as Ethernet over bonded copper and Ethernet over TDM access circuits.

　　At the same time as placing demands on the access network， the change in the service provider product mix from traditional E1/T1-based business services to Ethernet-based business services makes it increasingly commercially viable to move to an all packet or hybrid packet/optical trans-port infrastructure. In making the move to a packet-based transport infrastructure for business ser-vices， business customers are still demanding the same transport capabilities. Therefore， the packet transport solution must provide security， availability， manageability， low latency and resiliency that， at a minimum， matches what is provided today by SDH/SONET options.

　　Multi-Protocol Label Switching （MPLS） is the technology of choice for packet transport. MPLS Transport Profile （MPLS-TP） and its ITU-T standard counterpart Transport-MPLS （T-MPLS） extend MPLS to provide connection-oriented transport that is suitable for transporting packet and

　　TDM services over optical networks. Key attributes of T-MPLS/MPLS-TP are OAM and resiliency features that ensure the capabilities needed for today’s service environment — scalable operations， high availability， performance monitoring and multi-domain support.

　　In addition to the OAM and resiliency capabilities provided by T-MPLS/MPLS-TP， business custom-ers and service providers alike are starting to demand a clear demarcation device — an Ethernet Demarcation Device （EDD） — between the customer’s network and the service provider network.

　　The EDD provides strong OAM and SLA management capabilities that allow the service provider to test， monitor and assure services all the way to the customer’s premises. It creates a clear network and service demarcation point between the service provider’s and the customer’s networks， and helps to provide end-to-end visibility all the way to the customer’s premises. It also ensures that the service provider can isolate the customer’s network when testing and monitoring the end-to-end network connection and service to eliminate diagnostic errors caused by customer activities.

　　1 ”Got Business Fiber？，” Vertical Systems Group STATFlash， 2008.

　　2 Packet-Optical Ethernet Business Access Networks | Technology White Paper

　　Packet-Optical Transport and Ethernet business networks

　　Ethernet business networks are built with two components that must integrate together seamlessly： the Ethernet transport network and the Ethernet business access network.

　　In the Ethernet transport network， Packet-Optical Transport plays a key role. It allows service pro-

　　viders to evolve their core networks to provide transport solutions for the new packet based services.

　　Packet-Optical Transport solutions simultaneously support SDH/SONET and Carrier Ethernet transport. This simultaneous support allows service providers to evolve their networks from circuit to packet at the rate that they want， only moving to pure packet when the business model is right （Figure 1）。

　　Figure 1. Packet-Optical Transport

　　

　　Three separate platforms

　　Purpose-built

　　convergence platform

　　Packet

　　TDM

　　WDM Packet-optical transport

　　In the Ethernet business access network， Packet-Optical Transport allows service providers to sup-port a mix of traditional private line services and Ethernet business services， with both SDH/SON-ET and Ethernet used to provide business services. This approach allows service providers to evolve their business services product portfolio from E1/T1-based services to Ethernet-based services at the rate that suites them. It also allows them to select the best transport solution for their product mix：

　　SDH/SONET， Ethernet or a hybrid approach. In addition， in the last mile （the physical connection between the customer premises equipment （CPE） and the transport network） Packet-Optical Trans-port solutions give service providers the flexibility to embrace all physical access technologies： fiber， copper （using Ethernet over Plesiochronous Digital Hierarchy （PDH））， or integration with packet microwave devices where neither fiber or copper is available.

　　End-to-end across the Ethernet business network， Packet-Optical Transport provides the QoS， OAM， and manageability to guarantee end-to-end service delivery at the appropriate quality levels.

　　At the Ethernet layer， Ethernet OAM provides end-to-end service monitoring and service as-surance. Standards-based OAM， such as IEEE 802.3ah Link OAM， 802.1ag Connectivity Fault Management， and ITU-T Y.1731 Ethernet Service OAM performance and monitoring， provide the capabilities to fulfill these requirements.

　　At the transport layer， transport OAM is essential to provide and guarantee a highly available， resil-ient， manageable transport network. For Ethernet over SDH/SONET （EoS）， the transport layer uses the trusted SDH/SONET mechanisms. As service providers evolve to Packet-Optical networks us-ing T-MPLS/MPLS-TP as the transport layer， OAM capabilities are required for T-MPLS/MPLS-TP that allow the network to be managed consistently with SDH/SONET， Optical Transport Network （OTN） and Wave Division Multiplexing （WDM）.