Hybrid PON solution on the horizon?

Oct. 1, 2001


Alloptic Inc. (Livermore, CA) has achieved what it claims is a milestone in Ethernet passive-optical- networking (EPON) technology: a successful field trial implementing the company's GigaForce product line over a reach of 69 km, a distance the company says was previously unattainable with traditional ATM-based PONs (APONs). While the trial should increase the credibility of EPONs in the near term, APONs are not likely to disappear. The future could yield a hybrid solution, capturing the best of both technologies. A crop of new standards bodies seems to indicate a growing cooperation between the camps.

PONs are generally targeted at the last-mile bottleneck between the service provider's central office or headend and its business and residential customers. Knology Inc. (West Point, GA), a provider of bundled communications services in the southeastern United States, conducted the EPON trial to find a solution able to bridge the 69 km between its central office and a remote office on its private network.

Knology, which signed a nondisclosure agreement with Alloptic for the duration of the trial, isn't talking, but Burnie Atterbury, senior director of product marketing at Alloptic, contends the carrier was also looking for a solution that would deliver greater bandwidth capacity than the dial-up modem technology it was using.

"They wanted to emulate what could be a regular business setting," says Atterbury. "It's not just doing one T1, but a 100-Mbit Ethernet connection. We are able to scale that up to a gigabit depending on what the customer's requirements are."

While Atterbury wouldn't name names, he did admit that "it felt wonderful to go in there and see a big competitor's box on the side that they were getting ready to ship back because it just didn't work."

He cites ATM's inherent limitations in terms of distance and bandwidth capacity as one reason why his competitor's box wasn't up to the challenge. "Some might tout that they can do DWDM overlays to approach our bandwidth, but the kind of failing logic with that is that if you do that type of thing, you start disintegrating some of the value of PON," says Atterbury.

APONs, on the other hand, have the advantage of guaranteed quality of service, claims Bart Alvarez, director of marketing and business development at Paceon Corp. (Duluth, GA), whose ATM-based solution is known as a Broadband Passive Optical Network or BPON. "We have embedded checks and balances to make sure that the packet gets to the other side with 100% integrity," he explains, though he does admit that Alloptic's GigaPON solution has its merits.

"It's very fast and can quickly ask for a retransmission if there's a problem," he says. "However, it can't really give you any guarantees, and we like the idea of being able to have some guarantees."

From Alvarez's perspective, the technologies are not mutually exclusive. ATM is a deployment-ready solution, whereas he views Ethernet as the next step in the evolution of PON technology.

According to Maria Zeppetella, vice president of Probe Research Inc. (Cedar Knolls, NJ), "ATMs are already standardized and are presumably pretty far ahead of the game, while Ethernet is viewed as being further behind. It is not standards-based yet, but there is a lot of development going on."

Organized by British Telecom with the help of several large international carriers, the Full Service Access Network (FSAN) Coalition was established in the Spring of 1995 to develop a common system based on the ATM protocol. A modified version of the FSAN standard was adopted by the International Tele communications Union (ITU-T Rec. G.983) in 1999.

In November 2000, the EPON community established its own study group, dubbed Ethernet in the First Mile (EFM), within the IEEE to standardize the Ethernet protocol for use in the access space. Membership is not limited to EPON vendors, however. "We have certainly participated in the IEEE study group," claims Paceon's Alvarez, "and we've been watching what the EPON vendor community has been talking about, as we think it's fascinating."

EPON and APON vendors have also come together under the auspices of the Fiber-to-the-Home (FTTH) Council, formed in July of this year by Corning Inc. (Corning, NY), Alcatel (Paris), and Optical Solutions Inc. (Minneapolis, MN). Dedicated to education, promotion, and the acceleration of the deployment of FTTH broadband access in North America, the group comprises representatives from 46 companies, including equipment manufacturers, integrators, and service providers.

The council met for the first time in Rochester, NY, in August to elect a board of directors and explore FTTH issues and opportunities.

A similar group is also getting together under the FSAN umbrella, says Alvarez. Though initially developed for ATM-based architectures, the FSAN standard is broad in scope and does not preclude non-ATM protocols. According to the folks at Alloptic, much of the G.983 specification could be incorporated into an EPON standard.

Whether the standards groups decide upon straight EPONs or ATM-encapsulated EPONs, trials like Alloptic's will continue to prove the technology's viability in the near term. Zeppetella, for one, is optimistic.

"According to most PON vendors I've talked to, there are very big RFPs [re quests for proposals] and RFIs [requests for information] out there from all the major ILECs [incumbent local-ex change carriers] and many international players as well," she says.

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