ONT powering options abound

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Unlike traditional telephony service, which is powered from the network itself, fiber-to-the-home (FTTH)-based voice, video, and data services must be powered from the home. A separate power supply unit is used to power the optical network terminal or unit (ONT or ONU) that resides at the subscriber’s premises. Typically mounted within the subscriber’s residence, the power supply unit also features a battery backup unit (BBU), sometimes called a battery backup power supply (BBPS), which is responsible for supporting voice service for a given duration in the event of power outage. While home-based powering seems to be the norm, the industry has not yet determined its method for battery replacement.

The FTTH industry is not the first to wrestle with the issue of home-based powering versus network powering. “There was a huge controversy in the cable industry starting in the mid-1990s about whether you should power the [cable] box on the side of the home with battery backup power from inside the home or whether you should power it from the network,” recalls Jim Farmer, chief technology officer at Wave7 Optics (Alpharetta, GA). “About twice a year, the pendulum swung from one extreme to another because, in fact, there were problems with both.”

Under a network-powered scenario, the cable company would be obligated to pay for power. While each box consumed a small amount of power, there were a lot of boxes in the network, and the cable companies were not happy about this additional expense.

But the proponents of home-powered equipment faced an even bigger hurdle: safety. “If I’m passing a good bit of power down a drop, guess what? Drops sometimes get disconnected. Drops sometimes break,” says Farmer, who adds that the cable industry’s biggest fear was a curious child who might mistake the severed drop for a piece of licorice. Eventually, the UL published power protection requirements, but by then “the industry was swinging the other way, saying battery backup in the home was probably good enough,” says Farmer.

Fast-forward a decade, and this is the same conclusion reached by the FTTH industry. “Most people have accepted powering from the home at this point,” says Farmer. “Even the big telcos seem to have accepted this now, which, in the past, they never would have done.”

Powering and providing battery backup within the subscriber’s premises is the norm with the FTTH community today, concurs Joe Martin, director of product management at Wave7 Optics, though the ONT can be network-powered as well, he adds. In such configurations, the fiber-optic cable running to the subscriber’s home also would contain a copper pair, which would draw power from the network to the ONT. But this method is both expensive and problematic, says Martin, who notes the difficulty of carrying power over such long reaches.

In the typical FTTH installation, the power supply is mounted in the subscriber’s basement or, in milder climates, in the garage. Power then is provided by the closest available utility outlet. An indoor installation with BBU typically costs less than $50 on average, reports John Hewitt, vice president of sales at Alpha Technologies (Bellingham, WA), provider of BBUs for FTTH installations.

At an additional expense, the power supply and BBU also can be installed on the outside of the subscriber’s home and powered via an AC outlet on the home’s exterior. For this type of installation with battery backup, the service provider is looking at a price tag of just under $125, says Hewitt. The outdoor configuration is more expensive because it requires environmental hardening and supplemental heating to provide extended runtime in adverse weather conditions.

The ONT also can be powered from the existing utility meter on the side of the house, using a meter collar that attaches to the meter head and taps off power for the ONT. Municipal and utility broadband providers, in particular, favor this method because many already have close ties with-or are part of-the electric utility company. “If you’re already providing power, what better way than to use the meter ring and apply it to the power meter that you already own on the side of the subscriber’s home?” muses Martin.

In addition to its main power source from the home, the ONT also must have backup power in the event of an outage. According to Hewitt, there are no standards or regulations in place for the backup power. “There has always been this infamous eight hours of backup that has come out of the RBOC world,” he says. In general, most batteries provide eight hours of standby and two to four hours of talk time.

Carriers like BellSouth, which has adopted a fiber-to-the-curb (FTTC) architecture, do not have to worry about battery backup. The FTTC network is line-powered from the central office (CO); there is no need for battery backup at the customer premise. Unlike the ONT, which services a single-family home, the curbside distribution cabinet supports an average of 12 homes. Optical fiber extends only so far as the cabinet, which is typically about 500 ft from the customer premise. Twisted-pair copper cables run from the cabinet to the subscriber’s premise, including a spare copper line that brings power from the CO to the cabinet. “In that type of deployment scenario, as long as the central office is powered, the [cabinet] will be powered,” notes Tom Doiron, product marketing manager at Tellabs (Naperville, IL).

The average lifecycle of the BBU is between three and five years, which raises an obvious question: Is it incumbent upon the service provider to replace the battery, or should that responsibility fall to the homeowner?

According to Alpha Technologies’ Hewitt, service providers sometimes opt to assume this responsibility, though it is more burdensome with indoor installations. “What do you do when the power supply is in the house, in the person’s basement, and it’s three years old?” he muses. “If they are not looking at the alarms, or if you have an alarm that is telling you there’s a bad battery, it’s already hard enough to schedule appointments to do installations at people’s houses,” he says. Assuming there isn’t a fence around the house or a particularly menacing dog in the backyard, outdoor installations afford service providers the luxury of replacing the BBU when it is most convenient for them.

Some service providers establish battery replacement programs, whereby they mail subscribers a replacement battery, thus shifting the burden of replacement on the subscriber. But this, too, is problematic. What becomes of the used battery? Does the service provider provide an additional mailer for its return? Under this option, the service provider would then be responsible for recycling or disposing of the battery in accordance with Environmental Protection Agency (EPA) regulations.

Moreover, what if the customer doesn’t replace the battery in a timely fashion? “You can mail a battery to your subscriber and have him do it, but what if the subscriber doesn’t do it, there’s a power outage, Grandma has a heart attack, and they can’t call 911?” muses Farmer.

To date, not many of the FTTH installations have outlived the lifecycle of the BBUs, and service providers are in a wait-and-see holding pattern. “It’s a cost versus reliability of getting the replacement done right versus the image you’re presenting to the homeowner,” notes Farmer. “But a lot of times it comes down to a cost issue.”

FTTH leader Verizon (New York City) has decided to make its subscribers responsible for the BBU. The carrier provides a 12-V sealed lead-acid battery free of charge at installation, and that battery will last from one to four years, depending on environmental conditions. After that, the customer must replace the battery, which is a standard unit that can be purchased at any retail outlet, including Radio Shack, Home Depot, and Lowe’s. 0603lw1 17 23

Meghan Fuller is the senior news editor at Lightwave.

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