Ethernet wide-area network (WAN) access has become the connection service of choice for businesses. Why? Ethernet's history inside local-area networks (LANs), as well as its economics, speed, and ability to converge applications over a single network, single it out as the best connection method.

Nevertheless, Ethernet WAN access could stumble if it fails to exceed the capabilities of existing technologies or fails to put buyers in charge of the pace and method of deployment.

For example, examine the history of VCRs and DVD players. The adage, "out with the old, in with the new" does not apply. Industry estimates that there are almost 100 million VCRs still in use, even as DVD players and TiVo threaten VCR obsolescence. Newer, better technologies rarely find overnight acceptance. Older, familiar, functioning technologies tend to live longer than expected.

Thus, broad marketplace penetration for Ethernet access services requires accommodation of existing technologies.

Ethernet over Anything

Many enterprises understand the benefits of Ethernet access for WANs, yet they remain well-served by investments in heterogeneous infrastructure and services with proven reliability, quality, and flexibility. It is the service provider's task to leverage existing network resources while opening a path to high-quality, lower-cost Ethernet services. Doing so keeps the enterprise in charge of the evolution of services and avoids forklift replacement decisions for both enterprises and service providers.

A typical regional or national service provider has a wide range of infrastructure in place, including a synchronous optical network (SONET), copper, direct fiber or wavelength, and Internet protocol/multiprotocol label switching (IP/MPLS). In short, service providers are challenged to offer "Ethernet over anything" to maximize their market reach. They must also guarantee consistent Ethernet service availability, quality, and management over disparate access and metro networks.

The Bar Is High

Enterprises may give up some "nice to haves" to take advantage of new services, but regardless of savings, they will not sacrifice: 1) the ability of all office locations to communicate seamlessly and 2) the guaranteed quality of service (QoS) they enjoy from existing asynchronous transfer mode (ATM), frame-relay, and time division multiplexing (TDM) infrastructure.

Despite its high costs, many enterprises and service providers have employed ATM due to three highly valued virtues: 1) it carries any type of data, voice, or video media; 2) it delivers end-to-end, circuit-like connections for each data transmission; and 3) it guarantees delivery of mission-critical applications with highly specific quality metrics on a per-session level. ATM also can run over copper as well as fiber, making it the underlying transport and QoS mechanism for both high-end enterprise and residential digital subscriber line (DSL) services.

These same virtues mark the bar for Ethernet WAN service. Ethernet already matches ATM's ability to converge media. With help from the now mature traffic-engineering technology known as MPLS, Ethernet also can deliver end-to-end connections not previously possible in "connectionless" IP or Ethernet environments.

Multiservice edge router technologies now enable service providers to overcome Ethernet's former flexibility, QoS, manageability, and ubiquity challenges by offering Ethernet services that do the following:

• Protect existing services and revenues by providing interworking between new Ethernet and IP services and disparate existing transport media
• Match existing service quality, reliability, and security with assured Ethernet QoS across those access protocols
• Travel over copper as well as fiber connections

"Over Anything" Interworking

Enterprises with mixed protocol access need to have all offices communicate seamlessly with one another. Since few enterprises will agree to replace all of their frame-relay, TDM, or ATM access services overnight, Ethernet service providers must offer both pure Ethernet WAN access and services over existing access protocols with communication between the protocols-a technology known as service interworking.

Multiservice edge routers enable this service interworking by incorporating access-side interfaces to existing protocols. Furthermore, multiservice interworking eliminates multiple overlay backbone networks, collapsing multiple network elements into a single edge router that aggregates all traffic onto one MPLS backbone.

By solving multiprotocol access interworking, the multiservice edge router offers the best of both worlds: Layer 2 switching and QoS capabilities with the flexibility and intelligence of Layer 3 routing. This combination makes Ethernet WAN services more secure, reliable, and flexible for the enterprise.

Deterministic QoS

To match or exceed existing quality and reliability, Ethernet access service must support any-to-any connectivity and deterministic QoS. ATM technology set the bar for service guarantees with its per-session QoS mechanisms by addressing bandwidth reservations and guaranteeing delivery of each session with regard to latency, jitter, and availability.

Premium enterprise customers are accustomed to choosing various ATM QoS tiers according to the applications they support, including the following:

• Constant bit rate (CBR) for high-end applications such as real-time video
• Variable bit rate (VBR) for bursty but critical applications such as financial transactions, voice, or videoconferencing
• Available bit rate (ABR) for bursty but less critical applications
• Unspecified bit rate (UBR) for applications such as file transfers that can tolerate delays

These deterministic QoS mechanisms are analogous to passengers on a commuter train. They guarantee that each passenger will arrive whole (without jitter or missing packets) and at the specific time promised. This result is far more deterministic than typical router guarantees, which employ only IP/Ethernet class of service (CoS) mechanisms, such as IP precedence or DiffServ packet tagging. In essence, CoS mechanisms do no more than assure that one train car will arrive sooner than another, whether late or on time.

Ask any business to choose between guaranteed on-time, quality arrival and priority position on a potentially "late train." Most will choose the route that offers the equivalent of CBR, VBR, ABR, and UBR guaranteed service levels on a per-application, per-session basis.

The service provider also gains a distinct advantage from multiservice edge architecture. By passing all traffic through the same edge device, the provider gains a position in the network that unifies visibility and controls to manage all Ethernet services, regardless of how they enter the router.

Service Ubiquity

At the physical access network layer, optical connections remain the exception to the rule in enterprise access. Millions of commercial locations are served by 1.5-Megabit T1 connections dominated by frame relay or integrated frame relay and TDM traffic. The majority of those locales will not have access to fiber any time soon.

The Ethernet access trend cannot afford to overlook this largely copper-connected market segment (approximately 80% of businesses) if it is to have widespread impact. Fiber-only Ethernet service proposals simply will not suffice.

Multiservice access equipment that offers interfaces to both copper and optical access media enhances customer options. Such equipment empowers larger enterprises to migrate one copper-connected branch office at a time while offering smaller customers a full range of access choices.

The success of Ethernet WAN services lies at the service provider edge, which must offer more than super high-capacity Ethernet access. The Ethernet-in-every-access-line dream, like the DVD player in-every-living-room dream, will become reality only to the degree that its purveyors place the customer in charge of embracing the best of both the new and the old.

About the Author

Michael O'Malley is a marketing manager in Tellabs' Global Portfolio Marketing group. In this role, he is responsible for application marketing, business-case development, and product and market segmentation across the entire Tellabs product portfolio. Previously, O'Malley held a variety of positions in marketing, product management, and product planning across Tellabs data, access, and transport products. Prior to his current position, O'Malley held domestic and international marketing positions across Tellabs' IP/MPLS, VoIP, SONET, DWDM, digital cross-connect, and cable telephony products. O'Malley has more than 12 years of telecommunications industry experience and holds a master of business administration degree, a master's degree in electrical engineering, and a bachelor's degree in electrical engineering from the University of Illinois.

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