Navigating the Transition to a Fiber-Fueled Future

The topologies make up an alphabet soup of acronyms, but there’s one issue no one is talking about … and it’s spelled P-O-W-E-R

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The topologies make up an alphabet soup of acronyms, but there’s one issue no one is talking about … and it’s spelled P-O-W-E-R

The future of voice, data and video transmission is fiber. Current projections suggest 70 percent of U.S. homes will have broadband Internet access by 2012—that means 36 million new broadband subscriptions in the next four years.

But the transition to fiber isn’t without its own issues and challenges. Electronics still will be required to translate sounds and images into pulses of light for transmission and back again to electronics for hearing and viewing. And electronics require sources of DC power.

One of the dominant questions facing telcos today is: “Who will provide this power, and where will it be located?”

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Traditionally, the telco has maintained an active copper network, providing 48V DC power with battery backup to energize copper transmission lines in the Central Office (CO) and at other points along the network to overcome resistance in the copper. Pulses of light carried by fiber optic cables do not require power to overcome resistance. Ultimately, fiber will reach all the way from the CO to the home or premise in passive networks, with no power needed between the optical switch in the CO and the Optical Network Terminal (ONT) installed at each subscriber’s location. This transition has just begun and could take decades to complete.

In the meantime, as this migration from copper to fiber has progressed, a variety of sometimes-confusing acronyms has arisen: FITL (Fiber In The Loop), FTTN (Fiber To The Node), FTTC (Fiber To The Curb), FTTP (Fiber To The Premise), or FTTH (Fiber To The Home). While nearly every telco has utilized one or more of these topologies in portions of its network, the bulk of the network remains copper, and traditional DC power solutions will continue to be required for years to come.

These power solutions may change shapes, they may change voltages, and they may change sizes. They may be located in cabinets on pads, on poles, on rooftops, in basements or on your inside garage wall, but they will still be there.

As we make this transition to a fiber-fueled future, it is important to understand what is driving the transition to fiber, the differences between the various FTT(x) topologies, how the fiber network is being powered today and how it will be powered in the future.

Triple-Play Players

Telcos traditionally have been strong in voice communication, improving in data, but weak in video. Cable companies, on the other hand, have been strong in video, fairly strong in data and weak in voice. Both are now competing to improve all their offerings and capture new customers. In this race for subscribers, both telcos and cable companies are offering bundled “triple play” services, where, for a flat rate, they will offer all three services at a significant savings compared to a separate phone line, an internet connection and cable or dish video service.

To compensate for the decrease in land lines and to stave off the cable companies, telcos are extending fiber deeper into their networks, replacing portions of their traditional “Home Run” CO-based copper architectures so that they can offer these “triple play” services requiring high bandwidth (voice, data, high-definition video).

The cable network, on the other hand, was built with large sections of fiber, with the final segments to the subscriber carried on coaxial cable. At present, the cable companies are committed to maintaining their network as it stands and are looking for new technologies (like Voice Over Internet Protocol [VOIP]) that will allow them to improve their offering of triple play services.

The telcos may contend VOIP is not dependable, but the proliferation of cell phones has accustomed a large part of the market to an occasional dropped call, and the convenience of bundling has considerable appeal. So at the end of the day, it becomes a pricing issue.

Breaking the Loop

FITL —Fiber In The Loop —was one of the earliest fiber topologies and has been used for years. It deployed fiber by building a 5- to 10-mile fiber ring around a service area, with cabinets at various junction points. From these points, the network branched out to serve subscribers with other fiber topologies such as Fiber To The Curb. Power solutions to convert optical signals to electronic were installed at various points throughout the network.

The advantage of FITL is that, if the fiber loop is broken at one place, service still can be delivered from the other direction. Fiber loops still are used for concentrations of commercial subscribers. However, to satisfy today’s greater bandwidth demands, no more than 1,000 feet of copper can be used in the network, and the newer FTT(x) topologies get fiber much, much closer to the premise.

Copper Under Glass

Fiber To The Node—FTTN—topology is implemented by overlaying the portion of the traditional Home Run copper network closest to the central office with fiber. The initial strategy was to extend fiber to a “node” close enough (1,000 to 3,000 ft.) to concentrations of customers to be able to deliver the desired massive amounts of bandwidth over existing copper, without the cost of extending the fiber all the way to the premise. At the node, which includes a dedicated power solution, the optical signals are converted to electrical signals and transmitted the rest of the way to subscribers over the existing copper network.

However, there are limitations to FTTN, depending on the actual distance from the node to the subscriber. Broadcasting capability for high definition signals over copper pairs is challenged constantly. How many high-definition signals can be transmitted over one copper pair, and are they true high-definition 1080 interlaced signals, or will they be 720 signals?

At first, nodes were being located an average of 2,800 to 3,000 feet from the premise. Now, telcos are bringing that number down closer to 1,500 feet because they realize they can’t get as many high definition signals as needed to subscribers. Providers have learned that once a subscriber gets used to a high-definition signal, the subscriber normally wants high-definition service for all the sets in the home. Three or four high-definition signals, along with the other triple-play services, are difficult to deliver over more than 1,500 feet of copper.

Almost There

Fiber To The Curb —FTTC —is similar to FTTN, except instead of dropping fiber from the CO into a node a few thousand feet from the subscriber, the fiber is brought to a High Density Terminal (HDT) located at what is referred to as the “curb,” typically near an existing copper cross connect, 500 feet away from an office, building or home. The HDT includes equipment to translate optical signals to electronics and a dedicated power solution that carries electronic signals to the subscriber.

That last 500 feet can be covered with copper pairs, or, where bandwidth demands are great or the existing copper is too corroded, with fiber directly to the premise. Essentially, it is a hybrid architecture that blends together FTTN with Fiber To The Premise —FTTP.

FTTC gets deployed where you have a mix of business and residential subscribers (particularly Multiple Dwelling Units [MDUs]) within the same service area, as well as in “greenfield” areas. Many businesses and MDUs are going to have bandwidth needs much higher than a single-family residence, so the telco can take dedicated fiber from the HDT located on the street corner, straight to the larger businesses and MDUs, and twisted pairs to the smaller businesses and private residences.

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When the fiber goes all the way to the premise, the optical-to-electrical translation occurs at an Optical Network Unit (ONU) serving single subscribers or an Optical Network Terminal (ONT) serving multiple subscribers. When the telco is responsible for powering the ONU or ONT, “SPAN” power is often used to bridge the power gap between the dedicated power solution in the HDT and the optical network translator at the subscriber’s premise.

With SPAN power, you utilize existing twisted pairs to carry the required electrical energy. It is necessary to raise the voltage of the power from the normal 48V up to 190V to overcome resistance in the copper pair. This is the big difference between FTTN and FTTC. The FTTN node does not output anything higher than about 48V. The HDT will output 48 or 190V power or optical signals to serve the differing needs of the service area. HDT power consumption is about twice the rate of the FTTN node cabinet. HDT boxes are significantly bigger than FTTN nodes. The size reflects the amount of electronics and power conversion equipment inside.

Home Run Fiber

Just as copper once provided an electrical path all the way from the CO to the subscriber, FTTP/H —Fiber To The Premise/Home —will provide a totally optical path, particularly in “greenfield” and “brownfield” areas where there is no existing copper network to “save.”

An FTTP network should be much easier to maintain, without a large number of cabinets, electronics, and batteries to service. There will be far fewer problems with lightning strikes, floods and storms because most of the deployment is aerial, optics don’t draw electricity, they’re not grounded, and glass doesn’t attract lightning. Also, FTTP is a passive optical network. Once the light signal leaves the CO on an optical cable, it passes through a series of optical cross connects and splitters, but there is no power conversion or amplification until it gets to the end user.

While this topology eliminates the need for conventional OSP power solutions, transmission needs at the CO will remain, and a lot of new power gear is being deployed in COs as they migrate from legacy equipment to new power technology. Also, the optical signal still must be converted back to electronics at the subscriber, requiring a DC power source.

Several companies are making optical translation equipment (ONUs, ONTs) containing power conversion cards and DC-powered electronics that normally will operate on 110V utility power provided by the subscriber. Since the fiber will carry lifeline (911) services, the “lighting” of the fiber at the CO will be protected by battery backup. However, to utilize these lifelines during utility power outages, the ONUs and ONTs also must incorporate 48V or 12V battery backup.

Great Debate

This has resulted in a great debate yet to be resolved. Who is responsible for battery backup? Some telcos have promised to keep the optical fiber lit at the CO and claim that is where their accountability ends. They maintain this is no different than a homeowner providing battery backup for a security system.

Other telcos have agreed to share responsibility for the battery by adding alarm features to the ONU or ONT that will send signals back to the subscriber over the optics saying that the battery is dead and should be replaced. The terminal also may include warning lights alerting the subscriber to a dead battery. If the ONU/T is mounted on the outside of the premise giving the telco 24/7 access, the telco can assume responsibility. If it is mounted inside the subscriber’s garage, for example, it will be up to the homeowner to provide an AC outlet and maintain the battery.

During utility power outages, the system may cut off your video to reduce the power draw, allowing the battery to support voice and data service for longer periods. A small 12V battery, the type most likely to be used in an ONT, will keep the electronics powered up for 6-12 hours during a power outage, depending on what services shut off. It may be possible to run up to four hours with everything on and 24 hours with just voice. The actual times depend on the battery condition, the ambient temperature, etc.

Muddy MDU Picture

Getting fiber optics all the way to tenants in Multiple Dwelling Units is not nearly as neat and clean as delivering it to single dwelling units. While getting the optical signal to the subscriber isn’t much different than running twisted copper pairs, it’s converting the signal back into electronics that is the challenge.

There may be a powered main community Fiber Distribution Hub (FDH) somewhere in the building that converts the optical signal to electronics. The telco may decide to locate it in the basement and bring coax or Cat. 5 cable up through conduits to the individual subscribers. Or they may bring the optics up from the basement and then have individual conversion boxes (ONTs) inside each apartment or attached to the side of each condo. Deployment will be extremely variable, depending on the physical structure and number of units.

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If you have 500 residences in a building, and you are going to put the electronics in the basement, you won’t just need a 300W power supply; you will need a small DC plant in the building that the telco will have to maintain in the bas ement. This means the telco will need to have rights and access to the basement, 24/7. There are all kinds of tenant rights and ownership rights involved.

Some buildings have basements, some don’t; some have closets, some don’t. It might be necessary to put an FDH on the roof and drop Cat. 5 or coax down somewhere. How do you bring this fiber technology to New York City, for example? Getting the fiber to the individual apartments and having each dwelling unit provide a power supply with battery backup would be the obvious solution, but some buildings don’t allow you to have batteries in the building because of fire codes.

With service providers, subscribers, building owners, landlords, local governing bodies, trades and other factions all involved, there is no clear picture of MDU deployment.

Where to Put the Power

As we have seen, telco distribution network power needs range from power everywhere (Home Run CO based copper) to power almost nowhere (FTTP/H). While the power picture is changing, a large number of power opportunities and issues remain, particularly because AT&T is advocating and deploying FTTN with the same enthusiasm as Verizon is pushing FTTP/H.

Traditional DSL Deployment

In the traditional Digital Subscriber Line deployment, the Digital Subscriber Line Asynchronous Multiplexer (DSLAM) is deployed in close proximity to an existing copper cross connect in the Digital Service Area (DSA) and fiber is run from the CO to the DSLAM. To power the translation electronics in the DSLAM and carry the electronic signals over twisted pairs to nearby subscribers, a power pedestal is installed and connected to local AC power. In addition to the translation electronics, the DSLAM houses battery backup. Copper cable connects the DSLAM to the cross connect.

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While relatively simple, this deployment usually requires additional space, may involve Right-Of-Way (ROW) negotiations, may be subjected to height limitations and can be considered a source of visual and noise pollution, particularly in residential neighborhoods.

FTTN/C Power Deployment

Fiber To The Node and Fiber To The Curb deployments are similar to DSL deployments, which is why a lot of people are comfortable with them. There may already be a DSL cabinet on a pad and, to upgrade the network, they may only have to put another cabinet (Node or High Density Terminal) alongside it. If the neighborhood is used to looking at one cabinet, what’s one more?

If there are several cross connects in a highly populated area, the telco may deploy one large power node with battery backup and trunk the power to each of the cross connects, onto which they have hung mini DSLAMs (conversion electronics). The fiber in the ground goes directly to each cross connect/mini DSLAM. This architecture is not getting used extensively, except in highly populated areas. While the mini DSLAM eliminates the need for an additional pad, ROW issues may arise over the “air rights” to the space occupied by the overhanging mini DSLAM.

FTTP/H Power Deployment: Single Residences

When fiber is trenched in, it will come into a service entrance and have an ONU (with an integrated power solution and battery backup). The subscriber will be responsible for powering the ONU and maintaining a battery capable of 4-16 hour backup. Where fiber is transmitted overhead, optical nodes will be hung onto wire and serve multiple homes (6-10), as long as the nodes are close to the residence (500 feet or less). The telco will be responsible for providing the power in this situation, along with 8-40 hour battery backup.

FTTP/H Power Deployment: Multiple Dwelling Units

As previously discussed, powering FTTP/H in MDUs will entail multiple options, depending on local laws, owner preferences, physical structure limitations and other factors. With 30-40 million MDUs in the U.S. alone, any number of powering schemes and arrangements will be tried and developed by the time fiber reaches all the MDU subscribers who want or need it.

Keeping Ahead of the Curve

A lot of attention has been paid to fiber topologies because of media coverage and the major players associated with the various configurations, but the power issues remain off the mainstream radar. But the realities are inevitable.

Providers may initially decide to cut off their fiber feed somewhere short of the subscriber’s premise as a stop-gap measure to keep subscribers from defecting to cable companies and to utilize existing copper where possible. However, many suspect these topologies (FTTN, FTTC) will be abandoned in 5-10 years and telcos will be forced to install fiber cross connects and fiber splitters to finally bring fiber within 500 feet or less of every subscriber’s ONU or ONT.

The demand for high-definition TV may well be what signals the end for FTTN and FTTC. Once a subscriber gets one high-definition signal, it likely will be just a matter of time before the subscriber wants high-definition for each of the 4-6 TVs on the premise. This, in combination with data and voice, will be more than the limitations of copper will allow.

Cable companies already run fiber deep into their networks and say that coax can handle the broadband demand now. But by 2015, the demand may well exceed the capacity of the coax portions of their networks and the cable companies will be forced to run fiber all the way as well, further blurring the distinction between the phone company and the cable company.

The need for power in each FTT(x) scenario is clear. It’s just a question of which one will win out, and how to stay ahead of the power curve. As we look at the different architectures, DC system requirements (and backup power systems) to power the electronics are a constant—even if the shapes and sizes may change.

About the Author: David Michlovic is product manager, Small DC Power Systems, Emerson Network Power’s DC Power business.

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