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.