Multi-dwelling units (MDUs) rank very high on the list of targeted market segments for service providers that are deploying fiber-to-the-premises (FTTP) networks. It’s easy to understand why, for research shows that up to one-third of U.S. residents, half of European residents, and more than three-quarters of Latin American and Asian residents live in MDUs. Those figures add up to a worldwide total of 670 million living units.

Yet designing and installing fiber networks within MDUs demand that service providers tackle several, often conflicting, challenges:

• First, building owners and tenants understandably don’t want their lives disrupted, so technicians must get into the building, install the fiber network and get out as quickly as possible.
• However, the enormous diversity of MDU building types and architectural layouts often makes it difficult for technicians to get access to certain areas of a building.
• Thirdly, while trying to get where they need to go and do their work quickly, technicians nevertheless must complete every step of the installation correctly, thereby ensuring network reliability and quality.
• Finally, as if all that were not enough, service providers are under competitive pressures to keep their installation costs to a minimum.

To tackle these diverse challenges and capture a share of the MDU market segment, service providers need FTTP installation and service turn-up solutions that are designed to save time and money, and ensure long-term network reliability.

Vendors have responded with advanced connectorization technologies, equipment designed specifically for MDUs and reduced bend radius fibers, which together significantly reduce installation time and costs.
 
Multi-Fiber Push-On… What?
Many service providers already have discovered that using connectors, rather than splicing techniques, in MDU fiber deployments speeds up network construction, which in turn reduces installation costs and minimizes disruption to building owners and tenants.

The cornerstone of a connectorized plug-and-play strategy is the multi-fiber push-on (MPO) connector. Typically, an MPO connector has 12 fibers, so a technician can use it to mate several fibers and terminations together with a snap -- and thereby eliminate the time and cost involved with splicing 12 discrete fibers. In addition, technicians can save even more time and money because they do not have to test any MPO connectors for reliability during the installation process; each MPO connector has already been tested in the factory.

Contrast the fast and easy MPO connector technique with a splicing approach. First, a splicing technician usually takes about an hour to splice 12 fibers. Then, installers have to test each splice between the fiber distribution terminal (FDT) and the fiber distribution hub (FDH) for reliability. Add up the labor costs of specialized splicing technicians, the capital equipment costs of splicing machines, and the installation time required, and it’s obvious that connectorization is a far more cost-effective approach and faster approach.

Splice In This MDU Fiber Network?
An FTTP deployment in a high-rise building with 23 floors and 15 units per floor illustrates the advantages of using connectors instead of splicing. On the lower level, installers using the splicing approach deploy a 432-fiber indoor FDH in a stub-pull configuration with three 144-fiber stubs. They then deploy on each of the above 22 floors a FDT, which routes 12 or 24 fibers down to the indoor FDH; there, a technician splices in each one -- a total of 432 fibers between the FDH and the FDTs.

The next phase of the installation centers on the FDT on each floor, from which technicians route an individual fiber drop to an optical network terminal (ONT) at each residential unit. That means that 345 individual drop cables (22 floors x 15 living units per floor) run from the FDTs to the ONTs. Because installers cannot predict the exact length of each drop, this scenario creates another series of potential splice points.

It’s easy to understand why, for research shows that up to one-third of U.S. residents, half of European residents, and more than three-quarters of Latin American and Asian residents live in MDUs.

Finally, installers use a loop-through configuration to pull several 72-fiber (or larger) distribution cables between the 432-fiber FDH on the lower level and all the FDTs on higher floors. An installer on each floor then:

1. routes one of the distribution cables through the FDT,
2. opens it,
3. opens 2 of the 12-fiber ribbons, and
4. routes 15 individual fibers (one for each living unit on the floor) to the splice tray in the FDT.

Basically, this means that installers have to splice 345 fibers between the FDH and the FDTs. Plus, with 345 individual drop cables running from the FDTs to the ONTs, installers face another series of potential splice points. Keep in mind that per-splice costs are even higher in this scenario because the technicians must spend even more time routing distribution cables through the FDT and opening them.

Or Just Connect It Out of the Box?
Now contrast that approach with one in which installers use MPO connectors between the indoor FDH and the FDTs to deploy a fiber network in the same building. In this scenario, the indoor FDH features a 12-fiber MPO connector mounted on each FDT stub, while each FDT deployed on each floor of the building also has built-in, 12-fiber MPO connectors.

Installers only have to plug each connection from every floor into the FDH. That means that deploying an FTTP network in this MDU requires them only to mount the enclosures and make plug-and-play connections with the cables. They do not have to set up, strip and clean fibers, align a splice, fuse the fibers or apply a splice protector or sleeve; they only have to clean and plug in the connectors.

A connectorized plug-and-play system, if it includes a built-in fiber spool on the FDT, simplifies and speeds up the installation process even more. Because the distance varies between each floor's FDT to the indoor FDH on the lower level, this type of system enablers installers to pull fiber from the built-in spool on each FDT and route it to the FDH. There, they only have to snap together MPO connectors to make 12 simultaneous fiber connections. In other words, installers can "fiber up" the entire MDU by mounting the FDTs on each floor and making easy plug-and-play connections to the FDH.

With the spool holding up to 500 feet of fiber cable, installers simply spool out the length of cable needed to reach the FDH and then plug it in. They don't have to cut cables to length or deal with slack and/or cable storage; the spool pays out precisely the length of cable required, and stores up to 200 feet of cable slack. To cover and protect the excess fiber, installers can use a shroud and lock down the box containing the spool. The connectorized approach requires only one splice: to connect the feeder cable to the FDH.

However, the advantages of connectorized plug-and-play techniques do not stop at the FDT. Installers can wrap 15 individual drop fibers -- one for each living unit -- into a single bundle with 15 SC/APC connectors at one end, plug the connectorized end into the FDT and run the drop-cable bundle down a hallway or other common area, passing all 15 living units and dropping a single fiber from the bundle at each unit.

At each living unit, installers deploy a wall plate equipped with a very small spool which contains a single fiber. When residents of a given living unit request service, a technician spools off that single fiber over the appropriate distance and field splices it to a fiber dropped from the bundle. This completes the end-to-end service connection and enables a rapid service turn-up.

Knocking Down Barriers to MDU Market Entry
Augmenting the advantages of connectorized installations in the MDU market is the emergence of a fiber flexible enough to accommodate the toughest building twists and turns. Typical MDU installations require technicians to route the fiber along walls and around 90-degree corners, as well as through walls and floors. Traditional fiber products, which require ample slack-storage space and very careful fiber management, are not well-suited to MDU installations. Recognizing the problems, vendors have significantly improved reduced bend radius fiber (RBRF) to the point that it is service providers' fiber-of-choice for today's MDU installations. In fact, because these improved RBRF products bend more tightly than previous versions, with no discernable increase in attenuation, they are helping to accelerate even more FTTP deployments in the MDU arena.

Capturing a share of the potentially very lucrative MDU market is an essential element of service providers' strategies to deliver fiber-based bandwidth, strengthen their ability to compete and, in the process, improve their profitability.

Until recently, the MDU market segment, with its architectural diversity and inherent pressures to reduce installation time and costs, has been a tough nut for service providers to crack. Now, though, by adopting a connectorization strategy in their MDU network buildouts and using advanced RBRF products, they can:

• Reduce network planning time
• Minimize the number of required splices and associated costs of splice equipment and highly-skilled splice technicians
• Simplify and speed up installation time
• Achieve a higher, and faster, return on capital investment
• Accelerate delivery of revenue-generating services.

 About the Author
Tom Huegerich, a 25-year veteran of the fiber industry, is Vice President of Global Fiber Engineering for ADC's Global Connectivity Solutions Business Unit. Huegerich joined ADC in May 2004 with its acquisition of The KRONE Group. Since then he has had overall profit responsibility for ADC's fiber connectivity product lines, and served as a Director of Product Management and as General Manager of ADC's optical cable business. Prior to ADC KRONE, Huegerich held a number of management positions with Corning Cable Systems during his 16-year tenure there. For more information, visit www.adc.com.

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