MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 / Chapter 2Chapter2Carrier Ethernetby Abdul KasimIn order to leverage the potential of Ethernet beyond the LAN, it had to be augmentedwith additional “carrier-class” characteristics; identifying and formalizing these detailed characteristics was, therefore, essential to enabling this role for Ethernet. Thischapter focuses specifically on standardization and other efforts underway to developa foundation for transforming LAN Ethernet into a Service Provider—based offering,henceforth referred to as Carrier Ethernet (services). Carrier Ethernet delivered overService Provider networks across the MAN and WAN optimally enables next-generationpacket applications.The first fundamental step is defining Carrier Ethernet, what it precisely means andunderstanding the rationale for this definition. Also as fundamental, is an establishedreference framework—the context in which this definition applies, and the necessaryelements that make up this context. In so doing, a common and consistent understanding as well as a “language” to describe Carrier Ethernet services is provided; with thisas the basis, the attributes are discussed in greater detail (note: in the context of thisbook, only a sufficient overview can be reasonably provided), with selective discussionsin a few areas that are deemed especially critical to enabling Carrier Ethernet.Most of the standardization effort, especially at the service-level, has been carriedon by the Metro Ethernet Forum (MEF) and so expectedly, this chapter devotes asignificant part to the MEF-initiated development; but efforts by other standardsbodies are also identified. This chapter also attempts to incorporate some commercialdevelopments enabling Carrier Ethernet. Often, forward-looking entities—whetherService Providers or equipment manufacturers—are ahead of the standards bodiesin terms of recognizing and addressing the practical issues that usually emerge whenoffering new services. A look at these issues and their respective solutions in themarketplace serves, therefore, to provide a better understanding of the actual statusquo in the field.45ch02.indd 4510/1/07 10:31:48 PM
MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 /Chapter 246Chapter 2Defining Carrier EthernetAlthough numerous efforts, both informal and formal (standards-based), have beenundertaken to make Ethernet more viable as a technology and service beyond theLAN, the MEF has been instrumental in initiating a substantial formal effort to define Carrier Ethernet services (delivered by Service Providers). This definition was aprerequisite to developing a common understanding and a common objective in thedelivery of such services.Among the first steps undertaken was to define more precisely what such Ethernetservices would entail, since, as noted in the previous chapter and repeated in Table 2.1,there are fundamental differences in providing Ethernet in the Service Provider network(broadly referred to as Carrier Ethernet) as opposed to providing Ethernet in the LAN.The context in which Carrier Ethernet services are defined is, therefore, the ServiceProvider networks and the several types of services already being delivered over theseTABLE 2.1Ethernet in the LAN Versus Ethernet in a Service Provide Network (Spanning the MAN and WAN)DimensionLocal Area NetworkService Provider NetworkGeography/ReachUsually less than 1–2 km; deployed inbuilding(s) and small campuses10–100 km and longer; deployed ina metro area or even across distantmetro areasService ProviderEnterprise (IT group); implemented by Service Provider (Carrier typically);internal IT group.services offered commercially for aninitial and recurring costUser of serviceEnterpriseEnterpriseNumber of end users/points (Scale)In the tens/hundredsThousands or tens/hundreds ofthousandsBandwidth10M/100M/1000M1M and greater—up to 10,000M;usually in granular increments of 1MAggregation requiredServices offered (scope)Enterprise data applicationsVoice / TDM and data connectivityapplications such as Internet Access,intra-metro connectivityDelivery of Ethernet servicesOver coax (CAT 5) and ﬁber;Best effortOver a host of media, incumbenttransport technologies, and with anassociated service-level agreement(SLA)Tolerance to failures (resiliency)Generally reasonable because network Very low tolerance because failuresis usually intra-enterprise and over a usually have a larger impact—oftensmaller physical area so failures canon revenues and competitivenessbe addressed relatively quicklyManageabilityManageability possible with fairlysimple tools given fewer numberof users and applications within asmaller physical area (typically abuilding or campus) and the relativelyhigher tolerance to failure issuesch02.indd 46Scale and scope of the ServiceProvider network in terms of thenumber of users and the geographicalfootprint introduces signiﬁcantcomplexity necessitating sophisticatedmanagement tools and capabilities10/1/07 10:31:48 PM
MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 /Chapter 2Carrier Ethernet47networks. In fact, Carrier Ethernet essentially encompasses the deterministic and otherservice delivery aspects for standardized Ethernet services. This point is key because ithighlights the focus on standardized Ethernet services and the specific characteristicsof such services and not necessarily the underlying transport infrastructure itself. Sowhat is Carrier Ethernet?Carrier Ethernet: A Formal DefinitionThe MEF1 has defined Carrier Ethernet as the “ubiquitous, standardized, Carrier-classservice defined by five attributes that distinguish Carrier Ethernet from the familiarLAN based Ethernet.” As depicted in Figure 2.1, these five attributes, in no particularorder, are1. Standardized services2. Scalability3. Reliability4. Quality of Service (QoS)5. Service managementCarrier Ethernet essentially augments traditional Ethernet, optimized for LAN deployment, with Carrier-class capabilities which make it optimal for deployment in ServiceProvider Access/Metro Area Networks and beyond, to the Wide Area Network. And conversely, from an end-user (enterprise) standpoint, Carrier Ethernet is a service that notonly provides a standard Ethernet (or for that matter, a standardized non-Ethernet2)handoff but also provides the robustness, deterministic performance, management, andflexibility expected of Carrier-class services.Fundamental to both Carrier Ethernet and LAN Ethernet is the fact that data iscarried in an Ethernet frame. What this means is, in effect, an Ethernet frame originating at a device in the LAN, now continues to traverse across one or more ServiceProvider networks,3 largely unaltered, and terminates at a device in a remote LAN.One way to look at this transformation is that it essentially creates one larger Ethernet,spanning LANs, MANs, and may be even the WAN, albeit delivered as a service to thecustomer. This transformation is shown in Figure 2.2, courtesy of the MEF, and illustrates the remarkable potential of Carrier Ethernet. The terms UNI and NNI in thefigure denote standardized interface hand-offs between the enterprise customer and1MEF is the preeminent nonprofit industry body focused solely on enabling Carrier Ethernet. The “Metro”reference in MEF is now a misnomer, however, and does not accurately reflect its charter and focus, whichhas long extended beyond the metro.2Because it can, as will be seen later, also support non-Ethernet services (albeit over an Ethernet layer).3The Service Provider networks could encompass both the MAN and the WAN.ch02.indd 4710/1/07 10:31:49 PM
MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 /Chapter 248Chapter 2StandardizedServicesScalabilityQuality tyFigure 2.1 Attributes of Carrier Ethernet (Source: rEthernetAccessCarrierEthernetInternetEthernet Services “Eth” LayerUNISubscriberSiteSubscriberSiteService Provider 1Metro EthernetNetworkE-NNIService Provider 2Metro re 2.2 Carrier Ethernet spanning Access, Metro, and Wide Area Networks (Source: MEF)ch02.indd 4810/1/07 10:31:50 PM
MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 /Chapter 2Carrier Ethernet49the Service Provider network and between Service Providers (or Network Operators4),whose infrastructure is used to deliver the service, respectively, and are explained inmore detail later in this chapter.The Ethernet frame(s) may be transported as is, either natively and directly over aphysical media or encapsulated and delivered over a variety of overlay networks builtusing different technologies. Each of these very different networking technology solutions, however, delivers5 Carrier Ethernet services. It is critical to understand that theCarrier Ethernet attributes often manifest only partially in commercial solutions todaybecause they exist at the network/transport/physical layers as opposed to the servicelayer6. This will become clear in rest of the Part II when the various commercial solutions currently employed to deliver Carrier Ethernet are discussed.The focus in this book is primarily on delivering Carrier Ethernet services;the network and transport delivery infrastructure—the Carrier Ethernet solutions,provide the carrier-class attributes that enable commercial Carrier Ethernet services.Often, the term ‘Carrier Ethernet’ is interchangeably used to refer to both the Ethernetservices and the underpinning enabling solution infrastructure.NOTEThe Carrier-class attributes are delivered differently by the various network solutions(for example, how reliability is offered in one solution versus another). This is largely aresult of their respective geneses and subsequent evolution. It is important to also notethat some of the Carrier Ethernet attributes in a solution existed pre-Carrier Ethernet(albeit at the transport layer and not at the service layer) and were, in fact, initial drivers for the use of respective solution. For example, SONET offered impressive resiliencyto any failures in the fiber and/or equipment deployed in a ring topology, so it was adopted to support mission-critical voice services that required stringent SLAs.Each of the Carrier Ethernet solutions and its respective evolution toward optimizing delivery in Service Provider networks is discussed in a fair amount of detail inPart II of the book.Carrier Ethernet: The AttributesThe five attributes that define Carrier Ethernet essentially provide the additional capabilities necessary to use Ethernet in much the same way as the other precedingservice provider technologies such as ATM and Frame Relay.7 Each of these attributesis elaborated upon and its rationale highlighted in the sections that follow.4A Network Operator is distinguished from a Service Provider by the fact that the former’s infrastructureis employed in the delivery of Carrier Ethernet services; however, the service itself is commercially offeredto the customers (usually on a subscription basis) by the Service Provider. Service Provider often leaseinfrastructure from network operators to deliver services.5More accurately, as will be evident in Part II, the solutions strive to offer the attributes of Carrier Ethernet.6Because at these lower layers inherently address only a subset of the higher-level service.7Especially helpful today because Ethernet is largely being used as a substitute for Frame Relay and ATM.ch02.indd 4910/1/07 10:31:50 PM
MH Technical title / Delivering Carrier Ethernet: Extending Ethernet Beyond the LAN / Kasim / 747-6 /Chapter 250Chapter 2This attribute essentially enables a Service Provider to delivera host of both Packet and traditional TDM (see chapter 10 for more information onTDM) multi-point services in an efficient and deterministic manner over standardizedequipment platforms. These services underpin the multitude of customer applicationsthat are emerging across voice, data, and video. Specific components that define thisattribute comprehensively are defined next.Standardized Services Ubiquity Carrier Ethernet enables ubiquitous Ethernet services provided viastandardized equipment, independent of the underlying media and transport infrastructure. This is a critical prerequisite to extending Ethernet’s appeal globally(similar to LAN Ethernet).Ethernet Services Carrier Ethernet supports two types of services: Point-toPoint (also referred to as Ethernet Line or E-LINE) and multipoint-to-multipointEthernet LAN (referred to as E-LAN) Ethernet services. These services are discussed in greater detail later in the chapter and are expected to provide the basisfor all Ethernet services.Circuit Emulation Services (CES) Carrier Ethernet supports not onlyEthernet-based services delivered across different transport technologies but alsoother (TDM) services transported over Carrier Ethernet itself. As noted previously, TDM services still remain an overwhelming contributor to Service Providerrevenues and realistically need to be supported (and delivered over a convergedEthernet-based infrastructure). TDM-based voice applications especially need tobe accommodated and characteristics of such applications such as synchronizationand signaling need to be emulated.Granularity and Quality of Services (QoS) The services supported by CarrierEthernet provide a wide choice and granularity of bandwidth and quality of serviceoptions. This flexibility is vital in Service Provider networks with its multitudeof end users, each with slightly different application requirements and, typically,operating equipment from multiple vendors. QoS capability is crucial to enforcingthe deterministic behavior of Carrier Ethernet.