Home-based batteries or network-powering are the most viable back-up methods for primary-line cable voice services, but as VoIP enters the fold, some operators may take a third option–nothing at all.

To stun or perhaps dethrone a champion, a challenger has to be at least as good or better than the titleholder.

In the world of telephony, that means cable operators must attack with a primary-line service that's competitive or better than the incumbent local exchange carrier's offering. That also means operators must provide the necessary backup power, and crank up service availability to the lofty five-nines (99.999 percent) benchmark. Several MSOs, including AT&T Broadband, Cox Communications and Insight Communications, are doing that today via traditional constant bit rate-based services.

"The going-in assumption for constant bit rate was to compete with primary-line service," says Stan Brovant, Arris' vice president of marketing, broadband. "Dealing with backup power was a presumed must-do."

That's typically done today through two primary methods: use of a locally placed battery for backup or by sending power down the coax cable. Each has its own set of advantages and disadvantages–and both work well.

Brovant estimates that about 33 percent of the installed base of Arris' U.S. customers use a local power supply device. While the majority of Arris' cable telephony customers are employing network power, others, including AT&T Broadband, are using a mixture of the two (70 percent network, 30 percent battery).

When carrier-class voice-over-IP services start to emerge further down the road, operators that offer traditional CBR might have to re-think their backup powering strategies. Others might choose to forgo backup power altogether.

Batteries go local

Although local source batteries are sometimes touted as having a 10-year life span in a climate-controlled laboratory setting, that length of time is curtailed significantly when the rigors of the real world are factored in. Even with proper maintenance, a battery will only last in the neighborhood of two to five years.

A battery's most dangerous enemy is heat, which can halve its life span, says Allen Birne, senior applications engineer for American Power Conversion Corp., a supplier of home-based batteries and network-powering systems.

Batteries are also more difficult for an operator to maintain than their network powered cousins. "Instead of having several dozen power nodes on the outside plant providing network power, you can have several hundreds or thousands of [local battery] installations that require maintenance," adds Eric Wentz, vice president of marketing at Alpha Technologies, a designer and manufacturer of backup powering systems.

Although employing local-source batteries can create logistical nightmares and revenue-sapping truck rolls for cable operators, techniques are in place or being discussed today to relieve some of those headaches. For one, telemetry-based monitoring can anticipate when a battery is running low or notify the operator if it has failed.

In the case of APC's PowerShield product, each unit can deliver four types of signals: "on-battery" (an indication that the network interface unit is sucking power from the battery), "replace battery," "battery missing," and "low battery."

A low battery signal will alert the operator that the NIU has been drawing significant energy from the battery and will indicate how much juice remains. A replace battery signal gives the operator between 30 and 40 days to make the change before it's completely dead, says John Precopio, senior product manager for APC's broadband division.

Another idea under discussion directly involves the cable customer. For example, APC is proposing a battery recycling program under which the operator would ship replacement batteries to customers, who, in turn, would switch out the bad one and send it back via pre-paid mail. For their trouble, an operator could offer a discount, under the assumption such a program would reduce truck rolls.

Although MSOs haven't taken APC up on that offer yet, Birne says such a program could head off potential recycling legislation for smaller lead-acid batteries.

Flipping on network power

While batteries are still used to back up cable telephony customers, and might make more short-term financial sense, network-based powering is generally seen as a more cost-effective option over the long haul. And some say it's technologically more sound, too. "From a technical standpoint, the consensus is that [network powering] is the preferred method of deploying the system," says Wentz.

Though battery life spans can average up to six years, extensive heat can cut that figure in half.
At the same time, the historical rub against network powering is the capital expense requirement. While local batteries represent a direct match of capital and service deployment, network power installations are over-engineered in a sense, because they are engineered to serve homes that may or may not buy phone service from the cable operator.

"The cost of doing the network upgrade is very dependent on what you think your penetration rates are going to be," Arris' Brovant says.

In addition to capital, the network power alternative also requires a much more comprehensive installation program than the local power source option. Building a power node requires the proper right-of-way and some extra elbow grease before it's capable of serving a 300- to 500-home service area. Those costs also extend into hardware, installation and maintenance.

The hardware is typically comprised of a weather-resistant outside plant enclosure, the internal power electronics, batteries and, in some cases, an integrated generator system, Wentz explains, adding that the installation portion usually runs roughly 10 percent to 25 percent of the hardware costs.

The preventive maintenance piece of the network power pie, he adds, "is the most overlooked component of cost of ownership."

While AT&T Broadband has deployed a mix of local batteries and network powering, Cox Communications, which has signed up more than 500,000 residential phone subscribers so far, has taken the network powering approach in all of its circuit-switched telephony systems.

Although the economics of network powering has come under criticism by MSOs such as Time Warner Cable, Cox has kept those costs in line by installing backup systems in concert with bandwidth upgrades.

Albert Young
"If you're in the middle of an can put in the power-passing tap housings as you go," says Cox Vice President of Telephony Technology Albert Young. "You're touching them anyway, so the cost of the housings isn't such a big deal. It's the labor that's the big deal."

Young acknowledges, however, that cable operators with upgraded plant will face an uphill financial battle if they decide later to install network powering for carrier-class telephony services.

The cost connected to network powering is rather tricky and difficult to grasp, because it largely depends on service penetration levels. Using a 20 percent penetration per 1,000-home node model, Young says network powering can cost about $125 per customer. That total is part of the incremental capital Cox spends ($600 to $700 per phone customer) when other elements such as the switch, access platform, and customer premise equipment are factored in.

Certain Arris Touchstone telephony modems offer an internal battery backup system.
Early on, Cox analyzed both powering options, and determined that the cost of network power installations would be palatable enough if they were done in conjunction with the upgrades. Plus, the use of home-based batteries would require expensive truck rolls, and telemetry monitoring tools weren't available at the time the decision was made, Young notes.

Still, Cox has used local source power back-ups on rare occasions, if only for a short period of time. During the winter season in some areas, for example, an operator can't bury a drop because the ground is frozen solid, and a powered drop can't be installed above ground. In those cases, Young says, Cox used local power supplies, but later installed the proper drops.

As for obstacles, Young said Cox discovered early on that trying to install natural gas generators at every power supply proved difficult. Instead, Cox employs battery backup at the network power supplies, analyzes outage patterns in each service area, and installs gas generators only when it's justified. Populating the majority of the network with battery backups instead of gas generators also provides the foundation for an easier case when plans are presented to local franchise authorities, Young says.

Typically, Cox installs an average of 2.5 power supply sites for every 1,000-home node. Young says that figure fluctuates, depending on how densely the area is populated and how much plant is being covered.

Though local source batteries can last five to six years on the high end, batteries employed for network powering systems have much longer lifespans, says Tucker Mixon, director of marketing at DayStarter North America.

Depending on the sophistication of the charging system, DayStarter's batteries for network powering systems can last up to 15 years, Mixon claims. Although that figure is based on controlled simulations, DayStarter's patented "MX" grid design and advanced alloys are designed to eliminate failures brought on by corrosion.

A bit of both?

Network powering systems have
gained traction with operators that offer
carrier-class telephony services.
Instead of an either/or decision, telephony power backup could be implemented via a combination of batteries and generators, notes Robert Strachan, strategic account manager at Generac Power Systems Inc., which manufactures powering systems for cable headends, network operations centers and outside plant applications.

In that scenario, Strachan suggests a duo consisting of a smaller, more compact battery bank capable of providing about two hours of back-up power plus a reciprocating engine generator.

That combination would create an uninterruptible power supply. If a city's utility power were to go out, for instance, the battery could run interference until the generator kicked in. In turn, the generator would start recharging the battery and take over the entire site load. The battery could then back-up the generator, which would have to eventually be shut down for maintenance during a prolonged utility power outage.

Challenges ahead for VoIP

By leveraging telemetry technology, local source batteries can alert a cable operator when they’re running low on power.
For VoIP, Arris' Brovant outlines three classes of strategies operators are considering for backup power: network power, local power and none at all.

The network power option closely mirrors the most widely used option for carrier-class CBR. Instead of an NIU, a multimedia terminal adapter (MTA) would be fixed to the side of a home and pull power from the network in the event of a commercial outage.

"That's the smallest segment of the market at this time," Brovant says.

The more popular VoIP option involves indoor units with stand-alone local power supplies, Brovant says. Arris, for example, offers integrated MTAs with a battery backup, including models designed for DOCSIS and EuroDOCSIS networks.

"I think [the backup battery option] comes out the best on the business case when you compare the incremental cost of doing the network powering option," Brovant says.

The third option pertains to operators that don't provide backup power. Time Warner Cable, for example, takes that tack in its VoIP trials with Road Runner customers in Portland, Maine; Rochester, N.Y. and Tampa, Fla., forgoing the added expense in the process.

APC’s TSP product line provides modular backup power over
cable networks.
However, Arris maintains that offering carrier-class voice service over IP or traditional CBR is the only way cable operators can hit the telcos where it hurts. "For not much more capital investment, you end up with a service that's equal or superior to the ILEC," Brovant says. "If you replace the ILEC's service, you've deprived them of their primary revenue."

While that has worked well with CBR, VoIP has a few kinks to work out when it comes to backup powering. Though Arris tries to keep the average power consumption levels of its CBR-based NIUs below two watts (including ringing current and talk/idle time), maintaining that level could prove difficult in an IP environment.

"VoIP is going to present a challenge for all of us," Brovant says. "It adds functionality to the box, and they're running at a higher modulation level, and that consumes more power."

He adds that Arris is on track by the end of this year to mirror power consumption levels among its home-based CBR and VoIP equipment. "It's going to be really hard. But that's the goal," Brovant says.

Consumption issues aside, Young adds that Cox will likely revisit the powering discussion when IP telephony services come into the fold. That's because potential differences may loom in how backup power is supplied to customer premise devices. While traditional cable-based constant bit rate phone service powers an outdoor NIU, VoIP services could be linked to indoor multimedia terminal adapters that customers can buy on their own. Cox and other MSOs will have to decide how that equipment will be serviced, and how or if backup power will be provided.

"We have a whole list of questions we have to ask and develop a strategy for, so we'll rethink power at that point," Young says.