WHITE PAPER Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Deploying fiber to MDUs, such as apartment complexes, condominiums, townhouses, and other multi-family locations, represents a lucrative market for broadband service providers. At the same time, these applications present unique challenges in both greenfield and overbuild scenarios. This paper addresses the key elements of MDU construction practices, including the physical plant from backbone to premise and the architectural decisions required for a successful MDU application. It will also cover additional network considerations for equipment and connectivity techniques. MDU connection strategies for fiber-to-the-premise (FTTP) deployments will differ from site to site and the type of structure will often dictate the strategies for fiber cabling and connections within the structure. In every case, there are key building blocks that include indoor and outdoor fiber distribution hubs (FDHs), fiber distribution terminals (FDTs), riser cables, drop cables, raceway systems, and wall plates. MDU applications typically require additional drop cables, raceways, and outlets for completing the interconnection and extending fiber into every living unit. Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Page 3 The MDU architecture Every MDU is served by at least one telecommunications room (TR). Ideally, there is one TR per floor that is recognized as the connection point between the backbone cabling connection to the central office (CO) or head-end and the horizontal pathways and cabling to the living units or office spaces (see Figure 1). The “backbone” cable of an MDU architecture refers to the fiber-optic riser cable in multi-floor buildings, but generally refers to the pathway between entrance facilities, equipment rooms, floor-serving terminals, TRs, common equipment rooms, or common telecommunications rooms. TRs will typically house the entrance facilities and the main cross-connect, horizontal cross-connect (floor distributor), and intermediate cross- connect (building distributor). Vertically-aligned TRs with connecting sleeves or slots are the most common types of backbone pathways. They offer better flexibility by providing accessibility to the backbone cable sheath on each floor and enable circuits to be distributed as needed. It should be noted that proper fire-stopping techniques should be maintained at all times. With TRs aligned in a vertical pathway, a means for cable pulling should be provided in line with the sleeves or slots at the uppermost room of each vertical stack, such as a steel anchor pulling iron or an eye-bolt embedded in the concrete. Where pulling irons are not available, the building steel may act as a sufficient pulling mechanism location. A goal should be to position cable sleeves or slots adjacent to a wall that can support backbone cabling. However, sleeves or slots cannot obstruct wall terminating space by placement above or below the wall space intended for termination fields. Modifications or changes to any MDU structure must be approved by a structural engineer. Further, all sleeves and slots must conform to all national and local building and fire codes. The “backbone” or riser cable in a vertical riser shaft may be extremely heavy (high strand count) optical fiber cable. There are several considerations for deciding the best method of installation. The preferred practice is to place the fiber-optic riser cable into a vertical pathway from the top down. There may also be tensile strength considerations in the cable’s manufacturing specifications. The cable can be placed vertically in an open riser shaft; through cores, sleeves, or slots; or within a large conduit. The cable installer should determine the size and type of reel for loading the cable, particularly in a high-rise MDU situation where the cable must be spooled to each floor’s TR with enough slack for splicing to a terminal. Cable lengths must be verified for end-to-end distance – do not rely on the manufacturer’s cable-run label. The riser cable should be secured to a back board support by at least three cable clamps at the top and a single clamp at the bottom. Slack storage is accomplished by single clamps above and below each storage spool, with the spool secured to the back board. Plywood back boards should be at least ¾” and painted with fire-retardant paint. Nth Floor 1st Floor 2nd Floor 3rd Floor 4th Floor 5th Floor 6th Floor 7th Floor 1 - 78 mm (3-in) Trade Size Conduit between TRs minimum Telecommunications Room (TR) 103 mm (4-in) Trade Size Conduits 103 mm (4-in) Trade Size Sleeves 103 mm (4-in) Trade Size Conduits Main Terminal/Equipment Room Entrance Room/Facilities 103 mm (4-in) Trade Size Conduits 103 mm (4-in) Trade Size Conduits TR 103 mm (4-in) Trade Size Sleeves Figure 1. Telecommunications Room Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Page 4 FTTP network architectures for MDU applications consist of four basic building types – high-rise (100 or more living units on 10 or more floors) , medium rise (less than 100 living units on multiple floors), low rise or garden style (single living units on each floor), and horizontals (each unit resembling a single family unit). Each building type presents its own set of unique challenges for the network installer (see Figure 2). High-rise and medium rise MDUs The most difficult MDU applications are typically in existing high-rise and medium-rise structures, since the plan must adapt itself to each building’s unique architectural design. Therefore, there is never a right or wrong way to install the network – the installer must adapt to the building’s layout and design. Although the considerations are basically the same for any high-rise, the techniques and strategies will be different, particularly in existing structures. Typically, a feeder cable is routed from the serving FTTP equipment to the structure and connected to an indoor FDH located in the basement or other usable ground-level location. The placement of these cables must be well thought out. For instance, care must be taken not to place cabling or electronics within the elevator shafts. Keep in mind, however, that the location for the FDH must be secure from intruders and protected from the elements. The optical splitting function and connection of the network within the building is performed in the FDH. For most MDUs, a centralized splitter configuration works best. However, circumstances could also dictate using either a distributed splitter configuration or a combination of both types. Riser cables are distributed to the various floors through established pathways. Because the floor-to-floor access and entrance to the living units may be limited, new conduits may be required. Metal tracking systems may also be used within an existing system. If allowable, using an existing cable TV infrastructure may be a viable solution. In any case, proper bend radius must be maintained throughout the placement of the riser cabling. Each FDT is connected to the riser cabling – using connectorized interfaces is recommended for enabling easy technician access to each living unit for turning up services, maintenance, and troubleshooting. Drop cables are installed into each living unit and routed to that floor’s FDT. Final interconnections can then be made as each subscriber requests services. Again, it’s important to ensure proper bend radius when routing cables to and within each living unit. In a typical greenfield application, the common equipment room would be located in the basement, with a common telecom room for every three floors. Using a centralized architecture, 1x32 splitters are located at the indoor FDH with a high-count fiber riser cable extending through the building. The riser cable would be intercepted with 12-fiber and 24-fiber cables to each indoor FDT on each floor. Additional drop cables, raceways and outlets complete the interconnection to the living units on each floor. Horizontal MDU Central Office Headend Residential Businesses Indoor Fiber Distribution Terminal (iFDT) Indoor Fiber Distribution Hubs (iFDH) High-Rise MDU Medium-Rise MDU Low-Rise/Garden Style MDU Drop Cable Fiber Distribution Hub (FDH) Indoor/Outdoor Drop Cables Outdoor Fiber Distribution Terminal (oFDT) Feeder Distribution Drop Figure 2. Network Architecture with MDUs Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Page 5 Garden-style and horizontal MDUs The garden-style and horizontal MDU configurations are typically less complicated, since these structures are usually just two or three stories with walk-up access. But because most have not been designed with future- proofing in mind for adding new cabling networks, they will usually offer significant challenges to installing an FTTP architecture, particularly in existing structures. Depending on the number of living units involved, the FDH is placed at a strategic location. A feeder cable from the street “right-of-way” and a distribution cable feed the complex. Once an order for service turn-up is generated, the installer runs a fiber-optic jumper from the feeder cable to a distribution cable assigned to the specific living unit. Distribution cables can be terminated in pull boxes throughout the property, replacing above-ground pedestals to maintain aesthetics. Larger capacity cables are spliced into smaller cables that feed directly into specific buildings. Network interfaces between the outside plant and drop cables tend to be either on the exterior surface or closeted just inside the building entrance, often co-located with other utilities. In new construction, drop cables can easily be routed through the framing structure in conduits or directly into the walls before they are sealed. A new build also presents the option of installing micro-ducts during construction for blowing fiber into living units once services are requested. An outside FDT can be mounted on the side of the building and grounded. Fiber drop cables from each living unit can then be spliced into the FDT. Outside FDTs provide splicing and conectorization within the same units and should be NEMA 4 rated to protect against the elements and sprinkler systems. If fiber drops are routed through exterior molding, color matching is also important. Since the construction is new, additional micro-ducts and composite cables can be placed at various locations within the MDU structure to ensure future-proofing. The entire infrastructure should always be planned in a manner that will ease the installation of the FTTP network. For example, the optical network units (ONTs), along with media facility boxes, can easily be placed into each living space. The facility box can hold the micro-duct from the central telecom room and the ONT, as well as a router for data distribution, a battery back-up, and the power supply. There should be a conduit to the media distribution box where all the home cabling is terminated, as well as the AC powering. Both the ONT and the media facility boxes can be flush mounted within each living unit’s utility closet. In order to provide multiple services, each wall outlet should have, at a minimum, two category 5e cabling connections – one for voice and one for data – as well as a single RG-6 coaxial cable connection for video. A wall outlet should reside within each room for every living unit. In all MDU designs, the drop cable installation will be the most time consuming process. Careful planning is required when existing spaces require retrofitting. Time and cost can quickly be added to the process as drop cables are routed through attics, basements, or around the exterior of a structure. New MDU molding raceway systems are making it easier for technicians to install drop cables inside the structure. There are many possible options for placing the riser cable, depending on the characteristics of the structure. One alternative is to use factory pre-connectorized cables and a connectorized FDT, enabling an easy plug-and-play solution. However, although this is simpler in concept, it also requires very careful planning. There are really only a few options for placing the ONT – using a recessed cabinet style facility box or simply surface mounting. An ONT may be placed in each unit or, to save costs, several living units can be serviced by a single ONT. Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Page 6 Careful consideration To summarize, there are truly no “one size fits all” solutions for building FTTP networks for MDU applications. The architectural and topological choices must be considered carefully, but are always driven by the type of MDU structure, the design of the common equipment room/common telecom room, and logical placement of the active electronics. The overall efficiency of these networks is determined by proper riser cable placement and determining whether to use a centralized splitter architecture, a distributed splitter architecture, or some combination of both. While MDUs offer very lucrative opportunities for service providers, increased competition is demanding that they “get it right the first time.” Understanding and effectively deploying the correct available solution for the job at hand is critical. Once the plan is carefully laid out, system connectivity can be developed and optimized for any structure – securing future services for the MDU occupants and healthy returns on investment for service providers. 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WHITE PAPER Multi-dwelling unit (MDU) Applications for greenfield and overbuild scenarios Multi-dwelling unit (MDU) Applications for greenfield. ONT may be placed in each unit or, to save costs, several living units can be serviced by a single ONT. Multi-dwelling unit (MDU) Applications for greenfield