Tài liệu Above vs. Below Ground Drop Splicing pdf

Considerations for Drop Cable Connections in the FTTX NetworkAs fiber-to-the-x FTTX architectures gain momentum as a means for delivering high-speed broadband services to homes and small

Above vs Below Ground

Drop Splicing

Considerations for Drop Cable Connections in the FTTX Network

As fiber-to-the-x (FTTX) architectures gain momentum as a means for delivering high-speed broadband services to homes and small businesses, many questions have surfaced regarding the best way to connect the large number of drop cables feeding into the network Drop cables typically connect each optical network terminal (ONT) at the subscriber premise to a fiber access terminal where they are then connected to a main fiber distribution cable

The fiber plant will likely be built in one of two categories: above ground (aerial)

or below ground (buried) With an aerial plant, the service terminal is typically mounted on a stand or pole In a buried plant, the drop cable will be buried below the frost line This paper will discuss the methods of service terminal access from a buried plant and the key considerations for selecting the method that best suits the service provider’s requirements

To provide more detail regarding splicing or using connectors at the fiber access terminal, ADC has published a previous paper that discussed the pros and cons for both (see Splicing vs Connectorization in FTTP Networks released 9/21/04)

In this paper, ADC points out that a connector pair is a better choice at any location where technicians will need to go on a regular basis to test, turn-up, and reconfigure services At these locations, a connector interface will provide both significant operational cost and time savings advantages over fusion splices The fiber access terminal is one such location Therefore, connectorization is the most economical option

Hand Hole vs Pedestal Access

The two common methods for creating access points at the drop cable and distribution cable junctures are hand holes and pedestals

A hand hole is, quite simply, a hole in the ground that the technician can open

to access the network Hand holes are placed at any location that would require access for maintenance, connecting additional drop cables, or troubleshooting Use of an above-ground pedestal provides easier access for the technician With the pedestal, the distribution cable and drop cables are underground Both are brought up through the bottom of the pedestal and connections are made

Above vs Below Ground

Drop Splicing

inside the unit The obvious advantage being that it is

easier to enter a terminal than to work through a hand

hole

Another consideration for using pedestals centers around

cost From a construction standpoint, it is typically less

expensive to install a pedestal than to place a hand hole

Placing a hand hole requires a very large digging

operation, whereas a pedestal only requires a very small

hole for mounting, thereby lowering construction costs

significantly

The other benefits of a pedestal include better test access

for troubleshooting or working on a connection in the

future Of course, there are some possible disadvantages

to using pedestals Untrained technicians can also gain

access, as can any curious person who may want to

break in or vandalize the pedestal and equipment

Pedestals are also out in open areas where vehicles could

collide with them More importantly, some

neighborhoods may frown on having a pedestal every

two to four houses for aesthetic reasons

Environmental Issues

In cases where pedestals may not be aesthetically

appealing or there is concern about possible damage

from vehicles or vandals, it may make better sense to

deploy terminals below the ground Putting them below

the ground requires a hand hole Inside the hand-hole,

another splice closure provides environmental protection

This splice closure connects the drop cables within the

hand hole and, therefore, must be substantially more

robust in design as compared to the above-ground

pedestal

Placing it below the ground line presents more

opportunity for a flooded environment, so it must be

able to withstand submersion under fairly significant

water, as well as the possibility of freezing and thawing

in northern climates There are very good splice closures

available in today’s market that will hold up very well

under these environmental conditions

It’s also worth noting that hand holes used in harsh

winter environments are subject to being iced over or

frozen shut The technician may spend considerable time

and effort just finding a way to chip or melt the ice away

to gain access Once open, there may still be

considerable ice and slush to clear away before being

able to work, making maintenance particularly difficult

during the winter months

Effects of Temperature

A final consideration is the affects of temperature on

connectors used in either a pedestal or hand hole

environment An earlier ADC white paper discusses these

effects in detail on outside plant (OSP) cable assemblies

(see Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP released 1/26/05) Basically, components used to construct OSP cable assemblies are typically made of plastic and, therefore, tend to shrink in cold temperatures

Exposing cable and cable assemblies to low temperatures

is typically the most common cause of signal transmission problems and failures in OSP architectures Insertion loss failures, for example, are a direct result of cable and cable assembly component shrinkage due to low temperatures If this shrinkage isn’t addressed in some way during the manufacturing process and deployment plans, the optical fibers and components could eventually fail

As temperatures decrease to -40 degrees, the effect on the cable assembly becomes significant as it begins to shrink The optical fiber in the cable, however, remains at its original length This can cause the optical fiber to bunch up inside the temporarily shortened assembly, causing microbends and high insertion loss at 1550 nm The hand hole access method provides some protection against cold temperature, since everything is below ground and a cover acts as an insulator for the cable, drops, and interfaces In a pedestal environment, however, temperature changes will be much more apparent The temperatures inside the pedestal will likely

be as cold as outside temperatures in the winter, and probably warmer than outside temperatures in the summer since the enclosure itself heats up if exposed to direct sunlight

It is important for network architects to consider the temperature challenges at each network location and the possible affects on drop cable connections Whether above or below the ground, the drop cable connection points must be protected against potentially harmful environmental characteristics

ADC provides access equipment and connectorization components that meet or exceed specifications for dealing with every environmental situation Their long history of listening and responding to customers’

network requirements enables ADC to provide the right solutions to solve the most critical networking issues

ADC Telecommunications, Inc., P.O Box 1101, Minneapolis, Minnesota USA 55440-1101 Specifications published here are current as of the date of publication of this document Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice At any time, you may verify product specifications by contacting our headquarters office in Minneapolis ADC Telecommunications, Inc views its patent portfolio as an important corporate asset and vigorously enforces its patents Products or features contained herein may be covered by one or more U.S or foreign patents An Equal Opportunity Employer

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