Ethernet in the First Mile: broadband access, finally?

Telecommunications Americas, Nov, 2004 by Bridget Mintz Testa

Stories abound of Japanese teenagers playing videogames over 100 Mbps connections while many American businesses struggle along with 1.544 Mbps T1 lines. It's enough to make you want to grasp at any broadband access solution, no matter how wacky. Fortunately, the IEEE 802.3ah Ethernet in the First Mile (EFM) Task Force came up with a far-from-wacky solution when it finalized the EFM standard back in June.

Basically, 802.3ah specifies three transmission methods:

* Ethernet over a point-to-multipoint passive optical network (EFMP or EPON), with a data rate of 1 Gbps over a distance of up to 20 km;

* Ethernet over dual or single single-mode fiber (EFMF) at 100 Mbps or 1 Gbps over distances of at least 10 km;

* Ethernet over copper (EFMC), covering copper wiring categories 1 through 5. EFMC offers a data rate of 10 Mbps over a standard twisted pair for at least 750 m, or 2 Mbps up to 2700 m.

Having a new first-mile broadband standard is only the start. The rest of the story is about implementation, which may not be easy. Both EPON and EFMF require optical fiber. For greenfield or replacement scenarios, fiber is a reasonable choice, but right now, according to research firm Vertical Systems, only 10.2 percent of buildings with more than 20 employees in the United States have fiber access. If you don't have fiber access, and you don't use dial-up or cable modem, chances are you have DSL. "The United States spent lots of money in the 1990s to build out an optical infrastructure for SONET, ATM, and DSL-over-copper as access," says Craig Easley, president of the EFMA. Carriers are comfortable with this infrastructure. "They're in year three of a 99-year payout," Easley says.

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What could discomfit carriers? "The competitive landscape has changed with the influx of VoIP via cable," says Matt Davis, director of broadband access technologies at The Yankee Group. Cable's poaching of voice is forcing a new look at telecom subscriber services. "For the first time," Davis says, "RBOC engineering departments are really trying to figure out how to deliver video."

EFMF or EPON could easily handle video--even HDTV. EFMC, at 10 Mbps, could handle NTSC (ordinary broadcast video) or the very lowest grade of HDTV, which is really just digitized NTSC. But 2 Mbps EFMC can't handle any form of HDTV. It can't handle NTSC, either, which requires a minimum data rate of around 3.5 Mbps.

However, the EFMC physical layer can increase data rates and distances through DSL modulation techniques and by "bonding" multiple copper pairs into one channel. A single pair with DSL modulation could provide 100 Mbps out to 100 m; eight bonded pairs could provide 100 Mbps out to 750 m or even 20 Mbps out to 2700 m. It's possible to transmit one decent HDTV signal at 12-15 Mbps. If this perhaps sounds less than promising for carrier competition with cable, we should note that the specified 802.3ah data rates are minimums. According to the EFMA, most EFMC systems currently available support much higher rates. So EFMC does offer the potential of carrier competition with cable operators.

Video may be a driver for the implementation of EFM, but it's not the primary reason for the new standard. "The significance [of EFM] is as a standard to deliver Ethernet services into a large variety of access network topologies, whether existing or greenfield," says Easley. "It makes infinitely more sense to carry Ethernet natively from the desktop to the core across the access network."

How long until EFM starts? It depends on whom you ask. Michael Howard, principal analyst and co-founder of Infonetics Research, says, "If we're talking about a large-scale roll-out, I think that could happen in Q2 or Q3 2005." Easley thinks telecom carriers will require two to five years. Whenever it happens, EFM's simplicity and its promise of higher bandwidth in the access loop will make it very welcome.

The new EFM standard specifies 23 new port types.

Read all about them at www.ieee802.org/3/efm/index.html or at the EFMA home page www.efmalliance.org