Speeding up fiber deployment to MDUs

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By Tom Leblanc


Plug-and-play fiber products are enabling “fast in, fast out” fiber installation in MDUs—and making these structures a prime target for network installers

The significant advantage to a plug-and-play optical network system is the increased speed of installation. This advantage is amplified when it comes to bringing fiber into new multiple-dwelling unit (MDU) structures. Allowing fiber network installers to get in and out of the building quickly creates a huge incentive for the building owner to decide in favor of a fiber-to-the-premises (FTTP) architecture.

The various types of buildings pose some very unique challenges when deploying fiber into MDUs (see Fig. 1). Each requires fiber to be routed differently on multiple floors, between townhouses, down multifamily hallways, and every other situation imaginable. But with all the shapes and sizes, building owners want their networks installed quickly to get the maximum possible return on their investment. Plug-and-play architectures do just that.

Benefits of plug-and-play

Installing fiber into MDU environments has never been an easy process. But over the years, installers have learned valuable lessons and realized several benefits, particularly in connectivity. Using connectors in place of traditional splicing at logical points of the network saves both time and money. To appreciate the benefits of plug-and-play systems, one only has to look at a typical fiber installation in a mid-rise or high-rise MDU structure.

In this scenario, an indoor fiber distribution hub (FDH) is located on the lower level with several 144-fiber stubs. On each subsequent floor or level, a fiber distribution terminal (FDT) routes 12 or 24 fibers down to the FDH, where each is spliced in (see Fig. 2). In a large building, 288 fibers might be spliced between the FDH and all the FDTs. Fiber drop cables are then routed from each FDT to the optical network terminals (ONTs) at each living unit. Since the distances traveled are not predictable, each drop cable would be cut and spliced on at least one end.

Although estimates vary, it typically takes an hour to splice 12 individual fibers, with labor costs running as high as $100 per hour. Add to that the cost of the splicing equipment required—splice machines, cleaving machines, and stripping equipment, for example—and the total costs for this method increase significantly.

The same fiber installation using a plug-and-play architecture offers tremendous advantages. In this case, an FDT still resides on each building floor or level, but a multifiber push-on (MPO) connector is mounted on the stub of each. Fiber is routed from the 12-fiber MPO connector on each FDT to another 12-fiber MPO connector on the indoor FDH. The fibers are simply plugged into the FDH from each floor. The entire MDU installation can be completed by mounting the enclosures and making easy plug-and-play connections with the fiber cables.

In the end, fiber installers are not only in and out of the building more quickly but multiple splices are eliminated and replaced by snap connectors. Since a major headache associated with FTTP networks involves the amount of time and money consumed by splicing operations, which is multiplied in MDU applications, plug-and-play represents a tremendous advantage.

Challenges meet innovation

The entire premise for the development of plug-and-play architectures for MDUs is to meet the unique challenges these applications pose—timeliness, aesthetics, cost, and ease of installation. Yet the same best practices for fiber management followed in other applications must be adhered to while routing through tighter spaces and sharper corners.

Space inside most MDUs is a challenge faced by installers who must find areas to locate FDHs that protect equipment while allowing easy access for technicians. Limited space availability in MDU closets, basements, and telecom rooms has demanded new, low-profile FDH technology. These indoor FDH products are shaped to fit on walls with minimal depth protrusion to allow more options to the installer while adding plug-and-play features for additional cost savings.

Aesthetics must always be considered in structures containing multiple living units. Nobody wants to see cables and ducts running through hallways and rooms or equipment in plain view of occupants. Although most enclosures are mounted inside closets, the fiber cables require routing throughout all areas of the building. Molding systems are used to cover these cables while blending into the decor.

However, traditional molding systems presented challenges. They only came in rigid precut lengths, required several components to create joints, and were slow and cumbersome to install. This has led to the development of flexible, spooled molding designs that improve the speed of drop cable installation. Desired lengths are cut from spools and easily installed; they attractively hide fiber drops with seamless routing.

Another challenge in MDUs is the ability to efficiently install individual drop cables through walls and down hallways while protecting the fibers. One solution is to bundle 12 drop cables together while allowing easy access to each cable. Bundling the drop cables together strengthens the overall cable to enable the use of smaller fibers—as small as 1.6 mm. Each cable is numbered for easy identification. These fiber drop bundles can be routed down long hallways, dropping one fiber at each living unit.

Still, there is the challenge of not knowing the length for each final drop cable into every living unit. This would typically require field splices to connect or terminate each drop cable. Fortunately, spooled wall plates are now available that incorporate a built-in spool that allows any length of drop (up to 300 ft) to be used while storing excess fiber on the spool. Both ends are connectorized for easy plug-and-play deployment of the final drop cable to each living unit.

The great enabler

There is one innovation that is the “great enabler” and most responsible for the growth of the MDU market for fiber-optic deployments. Without the continual improvements in reduced bend-radius fiber, MDUs would be a much tougher environment for fiber installers. The ability of these fibers to endure tighter bends without significant bandwidth performance or attenuation effects makes them ideal for MDU deployments.

Although several bend-resistant designs—such as “holey fiber”—were offered years ago, the penalties associated with their use remained significant. Many still showed greater insertion loss with tighter bends or were incompatible for splicing to standard fibers. Expense was an additional deterrent, since manufacturing costs were greater for these specialty fibers.

However, the improved performance of the current generation of reduced bend-radius fibers makes them the only option for MDU deployments, and a definite option to consider in other FTTP deployments. Plug-and-play for the MDU is virtually made possible due to the vast improvements in reduced bend-radius fibers.

And the world is catching on

Plug-and-play fiber architectures are an attractive option in the United States because of the time and money saved. However, recent indications show that connectorization is becoming more attractive on a global level. For example, China represents a significant FTTP market; a population of more than 1.3 billion people represents enormous potential for fiber deployments. In fact, China ranks 16th among the 20 world economies with the highest market penetrations of fiber to the home (FTTH). About 214 million Chinese citizens access the network via broadband connectivity, and the ever-increasing demand for more bandwidth make this a prime market for fiber.

The connectivity choice in China, as in all areas of the world, is between splicing and plug-and-play connectorization. Even though splicing is much more labor intensive than using connectors, extremely low labor rates in China and other countries have made it easier to make a case for splicing. The issue of minimizing loss budgets by splicing inputs to the splitters furthered the cause for splicing. But splicing fiber to splitters creates other challenges, such as the amount of time required for installing each splitter. Technicians also must have the required skill sets, and more time is consumed whenever a qualified splice technician is unavailable. Testing for initial turn-up also adds time because technicians must splice pigtails to connect each input to the test equipment.

In essence, even though money is always a major concern for service providers anywhere in the world, time-to-market is another viable concern. When customers are pushing for more bandwidth now, good business sense dictates that capacity be delivered with as little delay as possible. With that in mind, Chinese service providers and vendors formed various forums to determine the appropriate connection strategy—splicing or plug-and-play connectorization. In early 2008, China’s Minister of Information Industry (MII) released the China FTTH National Standard advocating a connectorized approach throughout the network, including feeder cables.

More and more service providers in other nations are also opting for connectorization. As connectors improve in quality and performance, loss attributed to connectors has declined to about one-tenth of a decibel. Plug-and-play architectures deliver the lowest cost of network ownership, decreasing both capital and operational expenses. This approach adds flexibility, decreases deployment time, and contributes to a reliable FTTP network.

Tom LeBlanc is an FTTX market manager for the Global Connectivity Solutions Group at ADC (www.adc.com), headquartered in Eden Prairie, MN.

Links to more information

Lightwave Webcast: Speeding Deployments to MDUs with Plug and Play Architectures
Lightwave: Choices Determine Expansion of FTTP to Multiple-Dwelling Units
Lightwave: Comparing Bend-Insensitive Singlemode Fibers

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