Passive Optical Networking Comes of Age

Posted 04/01/2001

Passive Optical Networking Comes of Age
By Paula Bernier

"The first early adopters will probably be the cable guys because it looks a lot like cable infrastructure. It's a shared media, multidrop implementation."--Deb Mielke, principal, Treillage Network Strategies Inc.

New demand for bandwidth and advances in electro- optics have turned passive optical networking (PON) into an attractive option to bring fiber to the customer. Vendors now say PON, which eliminates active elements on the loop, offers cost savings up to ten times that of SONET, and is reaching cost parity with DSL and hybrid fiber coax (HFC). And the combination of PON and WDM increases bandwidth availability and cost advantages even further.

"You'll see some pretty heavy deployments [of PON] in the first half of 2001. ILECs and PTTs are going into trials now and expect deployments by the end 2001," says Jeff Gwynne, co-founder and senior vice president of marketing for Quantum Bridge Communications Inc. (www.quantumbridge.com). The vendor recently won PON contracts with Comcast Corp. (www.comcast.com) for an undisclosed amount, and Advanced TelCom Group Inc. (www.callatg.com) for $50 million.

"What's neat about PON is the first early adopters will probably be the cable guys because it looks a lot like cable infrastructure. It's a shared media, multidrop implementation. The first guys that got it are guys like Comcast," says Deb Mielke, principal at consulting firm Treillage Network Strategies Inc. (www.treillagenet.com).

It costs approximately $1,500 per subscriber in capital costs to get to a subscriber with DSL or HFC, according to Mark Klimek, director of marketing and business development for Alcatel's (www.alcatel.com) access division. The cost of PON is somewhat higher than that, somewhere in the $2,000+ range, he says. But volume orders and manufacturing process improvements driven by carrier interest in PON will enable this technology to reach cost parity with DSL and HFC, he says.

"There are RFPs [requests for proposal] being generated and trials being planned, and all that will help us get there," Klimek says, noting several announcements of PON trials are expected this year. For its part, Alcatel is not currently marketing any PON products, but expects to announce its PON product plan by this month.

How It Works

A PON system typically consists of an optical terminal at the customer site that terminates the optical signal and delivers voice and data; an optical switch or other device that sits at the headend or CO to send the PON protocol to the terminal at the customer premises; and the passive couplers and splitters that actually sit on the fiber loop.

The PON equipment in the loop is placed at a fiber junction to act as a T-connector would on a garden hose, splitting two fibers into eight fibers, for example, to enable multiple customers to share fibers, Gwynne explains. "There is a lot of fiber in the ground, but not enough pairs to go to all businesses," he says.

Those PON devices on the loop, which can be as small as a pen, typically cost only a couple hundred dollars vs. the hundreds of thousand dollars it would cost to install a SONET add/drop multiplexer (ADM) and the environmentally-controlled housing and power to go along with it, Gwynne says. And because PON couplers and splitters are passive--meaning they don't require power--the carrier doesn't have as much ongoing maintenance of the equipment because there's no need for backup power or batteries in the outside plant, Klimek adds.

Using this totally passive technology allows very long reaches between the CO and the customer premises, adds Bart Alvarez, director of business development and marketing at Paceon Corp. (www.paceon.com), a Mitsubishi Electric Co. company. As of late January, the company hadn't named any PON customers, but was finishing field tests with what it expected to be its first customer. He says spans can go up to 12.4 miles in some cases.

Passive Optical Networking

The Full Service Access Network (FSAN, www.fsanet.net), an industry group, has defined PON to support 150mbps of capacity, but is working on a 622mbps standard.

Quantum Bridge and Terawave Communications (www.terawave.com) have both already announced 600mbps+ PON systems.

"Say you have 10 endpoints sharing 150mbps, which is the common way. Each endpoint can only get 15mbps," says Gwynne. "Once you run out of bandwidth, you have to bring out another PON. If you have 600mbps and 10 endpoints, each [user] can have 60mbps." Gwynne adds that the company's dynamic wavelength slicing feature also allows users to slice and share bandwidth as desired. "If you try to use WDM in the access network, you have a cost disadvantage because if you want to serve 30 businesses, 30 wavelengths is too expensive. This lets you share 500mbps."

The FSAN standard says 32 end users can share that capacity, but FSAN is now defining a spec for which 64 users could share a single PON connection.

NTT Communications Corp. (www.ntt.com), which has widely deployed PON in Japan, pioneered the technologies that FSAN eventually adopted. In the United States, BellSouth Corp. (www.bellsouth.com) and SBC Communications Inc. (www.sbc.com) provided most of the content for FSAN, according to Alvarez. Verizon Communications Inc. (www.verizon.com) has also expressed interest in PON, he says.

PON uses dual wavelengths, one downstream and one upstream, as specified by the original 983.1 FSAN standard. But a newer standard called FSAN 983.WDM provides a wavelength overlay to PON, resulting in an additional 2.5gbps of capacity for each additional wavelength, says Dilip Modi, Terawave's senior product marketing manager.

Gwynne told xchange in January that his company had plans to announce a beta test in the next couple of months of a WDM product with PON capabilities.

PON Applications

According to Alvarez, the key reason to deploy PON is to decrease the spectral interference created by copper-fed applications like asymmetric DSL (ADSL) and DS-1, which clash if put in the same cable bundles, and instead roll the DS-1 onto a passive fiber.

That results in a service that is less expensive to maintain because there are no active loop devices and because fiber is less expensive to maintain in the long run than copper, says Alvarez. Another benefit is that PON lets carriers go into new markets and share fibers among residential and small business customers like gas stations, strip malls and smaller establishments with automatic teller machines fed by 56kbps lines.

"Our carrier customer will take a PON circuit and allocate 50 percent of the actual throughput at first, so they can have 'provision ready' circuits ready for their customers when needed," he says. "No field personnel then need be sent out, and flow-through provisioning means instant delivery of the service."

Other key applications for PON include buildings that are just out of reach of fiber in a metropolitan network, or even in-building networks that want to bring fiber to additional floors. And once PON is deployed, it offers flexible bandwidth, which is important since business tenants commonly move within or out of buildings.

PON can also be used to backhaul traffic from remote DSLAMs to CO-based DSLAMs, or for wireless backhaul between base station controllers and mobile switching centers, says Sam Trotter, director of marketing at vendor Terawave.

"In the past, when people wanted to do backhaul they had to have dedicated fiber," says Modi. "PON does point to multipoint. We have a 20-kilometer radius in our PON product based on the FSAN standard. In that 20 kilometers, you have a good quantity of devices to aggregate" traffic from and backhaul that traffic.

Optical Solutions Inc. (www.opticalsolutions.com) has a slightly different perspective on PON. Unlike many other vendors in this space that are targeting business applications (at least initially), Optical Solutions to date has been heavily focused on the residential opportunity.

"We started with rural applications because low density applications were the first place where fiber proved in economically because it's expensive to deliver voice, video and data over long reaches of metallic because you need to regenerate the signal," says Bob Lund, Optical Solutions' CTO.

About half of Optical Solutions' business comes from rural applications. The company is also working with companies like Futureway Communications Inc. (www.futureway.com), a Canadian CLEC, on new residential builds.

Optical Solutions' system is not FSAN-compliant, but like FSAN systems is ATM-based and delivers 250mbps per PON connection. The company, which has been shipping PON product for four years, has already delivered 8,000 subscriber units to 19 carrier customers across North America.

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