Tài liệu It''''s Happening in the Hub pdf

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It's Happening in the Hub
It’s Happening in the Hub
Fiber Distribution Hubs (FDH) continue to play a vital role in supporting rapid
deployment and connection in FTTP networks. Innovation in FDH design occurs
at a rapid rate and next generation features appear in newer FDH enclosures.
Key innovations include:
• Miniaturized splitter modules with plug-in installation that allow easy
additions and upgrades
• High-density termination fields with connectorized harnesses allowing
modular growth and flexible rearrangement
• A wide range of sizes and mounting configurations that retain craft-friendly
fiber management and maintenance features
• Highest performance optical connectors and splitters available; all the
optical components and enclosures have completed a rigorous regiment
of independent testing far beyond any test program seen in the industry
to date.
As a result, FDH products have been widely accepted in FTTP networks. FTTP
is now seeing large-scale deployment and FTTP deployment is definitely still
happening at the hub.
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After years of research and experimentation with
access networks, many network providers have settled
on Passive Optical Network (PON) architectures as
the direction for future subscriber access. The PON
architecture has been adopted as a standard in ITU-
T G.983.x that defines the protocols, data rates and
operating wavelengths necessary to support network
services. At the same time, the standards have
established power budgets and parameters for the fiber
optic plant to ensure reliable transport all the way to the

home. The technology of high-speed PON equipment,
combined with broadband fiber offers the potential for
connecting high bandwidth services directly to the home.
The standards ensure interoperability of equipment
and therefore have driven down the cost of deploying
all optical networks. When adding in the cost savings
associated with operating an all-passive optical plant,
PON networks are attractive for overbuild as well as new
network construction.
The initiative to build PON networks is often referred to
as Fiber-To-The-Premises (FTTP), to emphasize the vision
of connecting fiber from the central office/headend
(CO/HE) all the way to the premises. A typical FTTP PON
distribution network is depicted below. PON architecture
includes Optical Line Terminal (OLT) equipment at
the CO/HE that bundles voice and data services. OLT
equipment utilizes wavelength division multiplexing
(WDM) technology to provide bidirectional voice and
data services (1310nm/1490nm) over a single fiber.

Additional WDM components at the CO/HE allow
integration of video services onto the same fiber at the
1550nm wavelength.
OLT equipment ports are connected through optical
splitters, thus allowing a single port to serve multiple
subscribers. The split ratio in PON networks can vary, but
typically networks are planned with 32- or 16-way splits.
The architecture may be configured by concatenating
the splitters at a single point. Most networks are planned
with 1x32 splitters centrally located for easy access for

additions, service and maintenance.
PON architecture includes Optical Network Terminal (ONT)
equipment at the premises for resolution of voice, data
and video services. Standardization of ONT equipment
allows the same equipment to provide services for Fiber-
To-The-Home (FTTH), Fiber-To-The-Business (FTTB) and
Fiber-to-Multiple-Dwelling Units (MDU) applications.
Combining these applications into the FTTP network
architecture provides economies of scale for construction
and service deployment.
The Optical Distribution Network provides physical
connection between the CO/HE and the premises and
includes various cabling segments including feeder,
distribution and drop. These various segments are
typically joined together by connectors and splices. The
Fiber Distribution Hub (FDH) is one of the key elements
located between the feeder and distribution segments
and contains optical connectors and splitters to provide
easy access and flexibility. The advantage of configuring
the network with connectors is to allow flexibility for
service provisioning and for network testing.
It's Happening in the Hub
Fiber-to-the-Business
ONT
FDH
CO/HE
OLT
Optical Distribution Network
Fiber-to-the-Home
Fiber-to-the

Multi-Dwelling Unit
Network Architectures
It's Happening in the Hub
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The Fiber Distribution Hub is a key interface between
feeder cables extending from the central office to
distribution fibers routed to subscribers. The FDH
serves an analogous function to serving area cabinets
(SAC) used in copper-based networks to interconnect
the feeder and distribution segments of the network.
The hub becomes a primary point of flexibility in the
network to connect subscriber circuits. As service is
required, technicians access the FDH enclosure to route
connections to complete subscriber circuits. The FDH also
serves as a central location for fiber optic splitters. This
is where the PON network differs significantly from a
copper network.
The optical splitters allow the PON OLT port to be
shared among multiple subscribers via the 1xn split, thus
defraying the cost of the OLT. By locating the splitters in
the outside plant close to the serving area, the cost of
feeder fiber is also significantly reduced. For instance,
when a 1x32 splitter is placed in the FDH, one feeder
fiber may be routed into a neighborhood and provide
service connection to 32 subscribers. Another reason to
locate splitters in the FDH is that splitters can be deferred
until they are needed to satisfy service requirements. The
FDH can be accessed to add splitters as service demands
grow. Newer hub designs accept modular splitters
that quickly plug into the FDH to allow capacity to be

expanded within a few minutes.
Typically, the FDH is equipped with one stub cable that
is spliced into a feeder cable and another stub cable
that is spliced to a distribution cable. Construction is
usually completed using standard splicing techniques
(usually mass splicing) with splices stored in standard
splice closures.
Key FDH Capabilities –
and Innovations
The FDH enclosure provides a crucial craft interface in
the outside plant environment. Therefore each major
function of the hub supports easy craft access for service
and maintenance.
FDH Pad and Pole
Central Office/Headend
Underground Distribution
Aerial Distribution
Fiber Management Parking Adapter
Termination Splice Shelf and Trays
Splitter Shelf
and Modules
FDH Network Function
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Termination Field
The termination field provides a location for terminating
fiber distribution cable on optical connectors and
adapters. The termination field is sized to support the
number of subscribers located in the distribution serving
area downstream from the FDH. FDH enclosures support
a range of termination field sizes (144-, 216-, 432-, 576-,

816- or 1152-terminations).
The termination field provides easy access to both sides
of the adapter to facilitate cleaning and maintenance.
ADC FDH enclosures feature a unique swing frame
design, a hinged chassis containing all the key optical
components including splitters, connectors and splices.
The design allows easy access to optical components
from the front and rear for cleaning and troubleshooting
and is especially valuable in installations where access is
limited to the front of the cabinet only, for example in
pole mounted applications. Large cabinets deployed in
ground mount applications feature doors on the front
and rear to allow full access to connectors and splitters
from the front and back.
Terminations in the field are clearly marked to provide
accurate identification of each subscriber termination.
The termination field provides organization and
protection for fiber jumper connections as they transition
into the fiber management section of the enclosure.
Recent FDH innovations include high-density
component packaging resulting in significant reduction
of enclosure sizes. High-density termination fields with
connectorized harnesses allow modular growth and
flexible arrangements.
High-Density Termination
Early FDH termination requirements were often matched
exactly to the requirements for subtending living units
in the immediate fiber serving area. For instance, a 216
fiber hub was specified to support a fiber serving area
of approximately 200 subscribers, providing a small

(approximately five to ten percent) portion of spare
fibers routed into the serving neighborhoods. With more
experience, planners realized that additional fiber capacity
downstream could be required for unforeseen changes
in the network or in services supplied. However, while
specifying increased numbers of spare fibers, resulting
in increased fiber termination requirements, users were
reluctant to increase the overall size of the enclosures.
Therefore, fiber termination fields had to handle the
increased capacity within already defined enclosure
sizes. This involved increasing termination density and
also increasing the fiber handling capacity for a particular
enclosure. For example, enclosures previously handling 216
fibers were upgraded to terminate 288 fibers. This increase
in density provides the desired fiber counts along with the
spare growth capacity required for typical fiber serving
areas, while maintaining the overall size of the enclosure.
Modular, Scalable Distribution
In overbuild scenarios, the termination field on the
distribution side is fully populated with connectors at
the initial installation and the enclosure is provided with
fully-terminated stub cables sized for the enclosure’s
direct termination needs. Network planners, however,
considering newer greenfield developments, look for
ways to defer cost and match the FTTP build to the
pace of the development’s build. A new development,
constructed in phases over a period of years, may
not initially require an FDH with a fully-populated
termination field. This situation may be better served
by gradually deploying terminations as needed. To

satisfy this requirement, the FDH enclosure includes
modular blocks that allow terminations to be added as
required. Termination blocks can easily be spliced into
the enclosure or the enclosure can be connectorized with
multifiber connectors (MFC) to provide quick connection
to termination blocks as they are installed. The modular
termination block allows upgrades to the FDH to match
the requirements of the FTTP network deployment, thus
deferring hardware costs.
Improved Overall Performance
Advances in planar splitter technology have dramatically
decreased the amount of signal loss when a single fiber
is split into several outputs. Innovation in component
performance has resulted in lower loss connections, in
both the termination fields and the splitters. Improved
connector performance for both the widely used SC,
as well as MFC connectors proposed for modular
components, allows connectorization to replace
splicing on both feeder and distribution fibers while still
meeting the overall loss limits within the FDH. Using
connectorization for input fibers and distribution panels
greatly reduces the amount of time required to install and
upgrade an FDH.
It's Happening in the Hub
It's Happening in the Hub
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Splitter Field
Splitter modules are designed to snap-in to the splitter
field and can be added as required by service demands.
The splitter field protects, organizes and routes both

the input and output fibers. The optical splitter modules
provide up to 32 connectorized pigtail outputs and one
pigtail input.
Early generations of FDH were deployed fully loaded with
splitter modules that featured storage ports, sometimes
referred to as parking lots, located on the front of the
module to stage splitter output pigtails temporarily until
they were connected into service. The splitter module
assembly included modular “parking adapters,” each
holding 16 or 32 connectors. As a splitter module was
installed, the fibers were fed into the fiber management
trough and the parking adapters were snapped into place
in the parking area. Individual connectors were then
easily separated from the parking adapter and routed to
the termination field during service turn-up.
Recently, the parking lots have been relocated to a spot
in the FDH away from the splitter modules. The parking
adapters are removed from the splitter module, allowing
the splitter module to be reduced in size. One design
includes hinged parking that allows 50 percent reduction
in splitter module size, and hence FDH enclosures that
are 50 percent smaller.
Today, most carriers take an incremental approach to
adding splitter modules – deploying FDH enclosures
initially with just the splitter modules required to begin
service connections. This reduces the number of parking
lots required for pigtail outputs. In essence, splitter
outputs “time share” parking lots; as the outputs of the
initial splitter modules are placed into service, the parking
lots associated with those outputs become available for

parking subsequent splitter module outputs This allows
a significant reduction in the size of the parking lot, and
consequently, a reduction in the size of the FDH.
“Blind-Mate” Connections
New miniaturized splitter modules feature planar optical
splitters and are 75 percent smaller, another contributing
factor in the reduction of the FDH’s size. Additionally,
innovation has improved the way splitter modules are
installed into the enclosure. First generation modules
were designed with the splitter module input extended
as a pigtail, which was spliced to feeder fibers. As
each subsequent splitter was installed, it was spliced to
feeder fibers staged in splice trays. Splicing consumes
valuable time, and adds costs to service turn-up. Earlier
improvements included connectors on the feeder fibers
that allow quick connection during splitter module
installation; a connector on the pigtailed input and a
connector on the feeder fibers mated at a connector
panel in the enclosure. This approach provides a simple,
much improved method for quickly installing splitters.
Connectorization of the feeder fibers at the FDH also
allows testing on the feeder from the FDH if required.
However, connectorization of the feeder fiber also
raised a safety concern regarding high power when
analog video is transmitted over the path. To address
this concern, connectors can be angled or adapters
with shutters provided to prevent a technician from
accidentally looking into the high-powered termination.
Further innovations have resulted in a backplane
connector system for installing splitter modules. In

this configuration, feeder fibers are terminated with a
standard connector pre-positioned on the backplane to
receive a plug-in splitter module with a mating connector.
The backplane connector is shuttered for safety so that
a technician cannot accidentally look into an unmated
splitter module. As a splitter module is inserted into
the backplane receptacle, the module presses open
the shutter to allow the splitter module connector to
mate with the backplane connector. This “blind-mate”
approach using a common backplane technology
improves efficiency in future expansion activities.
It's Happening in the Hub
Page 7
Splice Area
The FDH features a splice area to connect feeder fibers
or other cables routed into the enclosure. One use for
this area is the splicing of additional splitter modules
to feeder fibers as the modules are added to the FDH
enclosure. An alternative to splicing the input is to
include a connector at this location.
Factory Pretermination
FDH enclosures typically include two preterminated stub
cables. One stub cable is pre-connected to the optical
splitter module input so that it can be field-spliced to the
feeder cable. The other stub cable is pre-connected to
the termination field, so that it can be field-spliced to the
distribution cable. These cables attach to the enclosure
using standard grip clamps and liquid-tight compression
fittings seal the cables at the enclosure entrance.
Orientation of the enclosure stub cables varies, depending

on the FDH’s mounting method.
Craft-Friendly Fiber Management
The FDH provides total fiber management using a
unique front facing cross-connect design. The front fiber
management allows splitter module outputs to be routed
and staged within the enclosure for efficient connection
into service at a later date.
Vertical channels using storage loops manage excess fiber
slack. The entire cabinet can be interconnected without
congestion. Connectorized pigtail ends are stored on
bulkhead adapters on the front of the module so that
connector ends can be identified quickly and connected
into service. Fiber strain relief and radius control is
provided through the enclosure.
Indoor Configurations
As FTTH moves into densely populated areas, the use
of indoor fiber distribution hubs becomes popular due
to the number of units within a particular building, as
well as space restrictions outside the buildings. Indoor
FDHs provide all the same features as an outdoor FDH,
but are typically smaller and lighter. They do not need
to meet the same harsh environmental requirements as
the outdoor FDHs. Fiber count capacity ranges from 72
fibers to 432 fibers, accommodating small to large

high-density buildings.
Below-Grade Configurations
Another option for high-density areas, as well as areas
that do not allow above ground enclosures for zoning
reasons, are below-grade Fiber Distribution Hubs. These

compact enclosures are stored in below-grade vaults
when not being accessed for service configurations.
Qualification
A complete FDH qualification program draws from a
wide array of existing standardized tests with existing
procedures. In some cases, new test procedures have
been developed and refined to support the new
configurations and new technologies. The overall
program is composed primarily of testing regiments
drawn from Telcordia Generic Requirements. First and
foremost, the qualification program involves testing
optical connectors to GR-326-CORE, Issue 3. All
connectors utilized in the FDH enclosure are subject to
the complete outdoor service life requirements and to the
full spectrum of long-term reliability tests. In addition to
testing at 1310nm and 1550nm as required in GR-326,
the test programs included additional test wavelengths of
1490nm and 1625nm to assure users that all operating
wavelengths and all potential maintenance channels
would function under the harshest conditions.
Optical splitters are fully tested to ensure trouble free
performance over the life of the network. The splitters
use planar technology and follow a qualification program
aligned with service life testing in GR-1209-CORE and
long-term reliability testing in GR-1221-CORE. Because
of the nature of testing very large devices (1x32 ports),
special sampling techniques were developed for optical
measurement characteristics such as directivity. Splitter
qualification is conducted at the full operation spectrum
of four wavelengths including 1310, 1490, 1550 and

1625nm. All testing is done in the format of the optical
module that plugs into the FDH enclosure, representing
the exact configuration deployed in the field. Tests for the
new enclosures include a full range of environmental and
mechanical tests. Optical characterization is conducted
at the same four wavelengths as the connectors and
splitters. Additionally, several of the tests such as thermal
cycling and seismic qualification are optically monitored
during the test at 1625nm, which represents the worst-
case scenario from a fiber integrity perspective.
Independent testing of the qualification program
demonstrated the FDH’s reliability, assuring a performance
level and longevity expected in an FTTP network.
Successful testing of all aspects of the enclosures,
including performance of optical connectors and splitters,
have given users the evidence and confidence to support
wide scale deployment of FDH enclosures in the access
portion of FTTP networks.
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Specifications published here are current as of the date of publication of this document. Because we are continuously
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