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Engineering & Design: Going the extra mile

As a new IEEE initiative - Ethernet in the First Mile (EFM) - works its way through committee toward ratification as a standard, optical Ethernet is gaining credibility as the technology of choice to ...


August 1, 2003  


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As a new IEEE initiative – Ethernet in the First Mile (EFM) – works its way through committee toward ratification as a standard, optical Ethernet is gaining credibility as the technology of choice to bridge the gap between local and wide-area networks.

Metropolitan networks come in all shapes and sizes and transfer data using a variety of different transports and protocols over a variety of physical connections. But they all need operations, administration and maintenance support features to ensure the maintainability and uptime required to support broadband access services.

So, for service providers of all descriptions who are on the line to provide the metro access services that power today’s cost-conscious businesses, that means being able to achieve end-to-end simplification of the deployment and ongoing maintenance of the equipment.

Nowhere is this more critical than in the all-important “first” mile between the customer and the public network, where the need for cost-effective, high-bandwidth, easy-to-provision solutions would seem to make high-speed Ethernet the obvious choice.

What is it?

The “first mile” is known by many names: First mile, last mile, local loop, metro access and subscriber access network. Whatever name it’s called, it is the critical link between the business or residential end user and the public network. Today, most users (or subscribers) connect to the network with DSL, ISDN, cable TV, T1/E1 or T3/E3 lines, using SONET/SDH, Frame Relay and ATM.

Current first-mile solutions have significant shortcomings from the customer’s perspective, ranging from performance bottlenecks, fixed bandwidth increments, limited scalability, lack of flexibility and provisioning complexity to quality of service issues and a high cost structure.

Ethernet resolves “the mismatch between current solutions and customer needs. Subscribers have networks capable of supporting tens of megabits of bandwidth, and the metro core supports gigabits of bandwidth.

So why isn’t Ethernet more widely deployed as a first-mile solution? With its origins as a LAN technology, where “best effort” delivery and 99.96 per cent uptime were acceptable, Ethernet was never considered to be a candidate for achieving “carrier-class” status.

Nor have the largest network providers been willing to forego all the sophisticated management and troubleshooting tools to which they’ve become accustomed in SONET-based networks.

The large carriers have been skeptical of Ethernet, continuing to view it as a LAN technology that lacks carrier-class operations, administration and maintenance capabilities which they require to be able to provide the same high-quality support end to end across the entire network.

The longest mile

From a business perspective, carriers and subscribers both stand to gain from the deployment of Ethernet in the first mile (EFM). Users will get better, more cost-effective service with greater bandwidth, while network operators and carriers will gain new sources of revenue, lower their costs, increase margins and will be able to streamline their provisioning process, using less expensive, less complex technology and shortening deployment cycles.

From a technology point of view, EFM offers increased bandwidth, incremental scaling, simpler provisioning, seamless LAN/WAN data transfers (end-to-end Ethernet over IP) without protocol conversion and a single, unified standard for copper and fiber topologies.

While it was once called the “last mile,” the IEEE is now calling it the first mile in acknowledgement of the importance of looking at it from the customer rather than the vendor perspective. For service providers and their customers, it often seems the longest mile.

Why? Because it’s the most important distance in terms of its greater impact on operating expenses and capital expenditures than all other network miles combined – and yet there have, until recently, been no real initiatives to standardize OAM (operations, administration and maintenance) support required for Ethernet broadband access in this most-critical MAN mile.

OAM features are critical to accelerating the adoption of Ethernet as the first-mile technology of choice, because without carrier-class operations, administration and maintenance support, it will be difficult to convince large carriers of the viability of Ethernet as a first-mile technology.

In the beginning…

The EFM initiative began in November 2000 when the IEEE formed an Ethernet in the First Mile Study Group. In the third quarter of 2001, the IEEE 802.3 Ethernet Working Group created the 802.3ah EFM Task Force to begin work on a standard describing support for subscriber access topologies, provide physical layer specifications for both fiber and copper connectivity and define operations, administration and maintenance support features.

The EFM standard will define subscriber access topologies, physical layer specifications for both fiber and copper connectivity and common EFM OAM (operations, administration and maintenance) support.

Physical layer specifications (PHYs) for both copper and fiber are part of the proposed EFM standard: 1000 BASE-X PHY over single-mode fiber, the EoVDSL PHY for single-pair copper, and the EPON PHY for optical fiber with 16:1 split ratio. Three access topologies are also being defined as part of the 802.3ah draft standard:

Point to point copper over existing Cat3 copper at speeds of 10 Mbps and distances up to a 750-meter minimum (also referred to as Ethernet over VDSL or EFMC);

Point-to-multipoint optical fiber over optical fiber at 1Gbps for up to 20-km distances is also known as P2MP Fiber, EFMP or EPON, Ethernet Passive Optical Network;

Point to point fiber (also called P2P Fiber or EFMF) over single-mode fiber at speeds of 100 Mbps and 1000 Mbps over a distance of at least 10 kilometers.

Each of these topologies has certain advantages and disadvantages. Copper is ubiquitous, making point-to-point copper is the least costly and complex technology to implement today, and it can coexist with current solutions, but lacks the capacity of fiber to scale in terms of both capacity and distance. It works well for both MTUs and MDUs (multi-tenant and multi-dwelling units).

Point-to-multipoint fiber (more commonly referred to as EPON or P2MP) offers connections that are both higher speed than copper and less expensive than P2P fiber in the near term, because the amount of fiber required is minimized.

But over the lifetime of the infrastructure, the higher cost of maintenance and troubleshooting associated with P2MP may offset its short-term cost advantage.

Point-to-point fiber (P2P Fiber) topology supports both higher speeds and greater distances than copper by using single-mode optical fiber.

For greenfield and overbuild applications and new office buildings with fiber inside and out, it may well be the best fiber choice.

Products that support a direct P2P connection between the customer premises and the CO or POP offer a viable alternative to existing T1/T3 lines, which are both expensive and bandwidth constrained. The bandwidth demands of high-intensity commercial applications may also require the scalability of P2P, which will tend to have a longer lifecycle over which it can satisfy those demand. P2P fiber may also offer better “future-proofing” than other EFM topologies.

The IEEE802.3ah proposed standard provides for certain operations, administration and maintenance standards for Ethernet Last Mile solutions.

Among these are Receive Failure Indication (RFI) that includes notification of receive path failure at both ends for P2P topologies and at the head end only for P2MP topologies, Dying Gasp (power supply failure), and remote loopback capability. Line quality monitoring will need to support CMIP (Common Management Information Protocol) or its equivalent as well as errored symbol period, errored frame seconds and errored frame period.

The promise of OAM support for the First Mile may well do more than anything else in the proposed standard to accelerate the adoption of Ethernet as the met
ro access option of choice since it addresses the costly operating expenses that a carrier needs to reduce.

The challenges and requirements of OAM are to reduce the overall cost of ownership (both capex and opex), accelerate time-to-revenue and increase customer satisfaction in order to encourage network providers to adopt and deploy EFM.

Optical Ethernet is finally coming into its own as a solution that even a carrier can learn to love. It enables customers and service providers alike to enjoy the best of both worlds – carrier-class services and troubleshooting capabilities at the lower cost, easier deployment and data-optimized transport of an Ethernet infrastructure.

Paul Amsden is the Director of Product Architecture and Planning at Metrobility Optical Systems, Inc. in Merrimack, N.H.