Serving Up Ethernet

Ethernet has long been the foundation of the LAN. Gigabit Ethernet made quite a splash with its extreme speeds, and has since formed the backbone of many enterprise networks. But the Ethernet gods weren't satisfied with that, and made it even faster, releasing 10-Gigabit Ethernet, a telecommunications technology that provides an extremely efficient and comparatively inexpensive solution to moving data over backbone connections. Running over optical fiber, 10-Gigabit Ethernet, also known as Carrier Ethernet, can become an effective replacement, or complement to, ATM or SONET technology.

As a WAN/MAN technology, Carrier Ethernet can support up to 300 meters on multimode fiber, or 40 kilometers on single-mode fiber. Its development is overseen by the Metro Ethernet Forum (MEF), and it is rapidly gaining carriers' attention as a way of delivering new, high-bandwidth services to both business and residential customers. An increasing number of carriers have already started phasing out Sonet/SDH in favor of Carrier Ethernet.

Carrier Ethernet is now rapidly moving into the space that was previously the exclusive domain of SONET technology, including high bandwidth, Quality of Service, and self-restoration. There are five defining factors that bring Carrier Ethernet into the realm of telco providers: Scalability, protection, hard QoS, TDM support and services management. The protection attribute makes Carrier Ethernet competitive with SONET's self-healing functionality; Carrier Ethernet offers an end-to-end restoration capability in the event of failure.

The 802.3ah, Ethernet in the First-Mile (EFM) standard, has gone a long way in pushing Ethernet into carrier networks. The release of the EFM standard was the final link in the chain necessary to bring Ethernet up to the next level. This standard creates several new Ethernet physical layers for multimegabit transmission over P2P fiber, PONs, and copper pairs, while also adding the carrier-class attributes mentioned above.

ATM, when it was first released, brought many advantages to the telco world in terms of QoS and intelligent switching; Carrier Ethernet evens out the playing floor for service providers rolling out network infrastructures. Is there any reason to still use ATM? It's expensive and unwieldy, it's complicated, and there are far too many acronyms involved. For a brand new WAN/MAN rollout, 10Gig-E is a no-brainer, but there are a number of situations where retaining the old ATM network may be advantageous, particularly in the event of a migration. Gradual migrations are often the best as opposed to an all-out cut-and-switch, and in that case, running the ATM network alongside Carrier Ethernet would be essential. Although early on, carriers were a bit hesitant to embrace Ethernet as a carrier technology, its predominance in the enterprise market has made it a winner in the carrier realm as well.

The two alternatives for serving up Ethernet services are Ethernet over IP/MPLS, or Ethernet over SONET. RBOCs and other providers who met the demand for providing Ethernet services by adding Ethernet interfaces to existing SONET networks did so to take advantage of the QoS and resiliency offered by SONET, but there are limitations to this approach. SONET does work spectacularly for voice and private-line TDM traffic, but is not nearly as cost-effective in delivering Ethernet services.

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