Quantcast Backbone Design

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MIL-HDBK-1012/3
meter in accordance with Method B of EIA/TIA 526 14, Optical
Power Loss Measurements of Installed Multimode Fiber Cable Plant.
In accordance with EIA/TIA 568 a maximum loss of 2.0 dB is
allowed for the fiber link which is defined as 90 m (295 ft.) of
fiber and two connectors.  Test results exceeding 2 dB shall be
further tested using an optical time domain reflectometer (OTDR)
to isolate the problem and correct the discrepancy.
1.8
Backbone Design.  The most common function of a
telecommunications backbone is to distribute voice/dial tone from
a common switch to remote users and to connect data and video
hubs to the network, via a bulk media path.  Backbone design is
applicable whenever or wherever multiple termination points
require connectivity to a single location via an intermediate
cross connect point.  Backbone cabling is used to provide
connectivity between buildings and floors, or, if a floor is of
sufficient size, between multiple telecommunications closets on
the same floor.  Backbone connectivity is germane to both voice
and data applications.  NFPA 70, Articles 700 and 800 delineate
requirements associated with the selection and installation of
vertical backbone cabling.  These articles address considerations
such as cable housing and sheath print requirements, and
miscellaneous support facilities.  A primary function of these
articles is to establish baseline requirements to prevent the
spread of flame and smoke from floor to floor.  A copper cable
identified as a communications riser (CMR) in accordance with
NFPA 70, Article 770, or a fiber optic cable with an optical
fiber conductive (strength member) riser (OFCR) or optical fiber
non-conductive (strength member) riser (OFNR) designation is
suitable for use as a building vertical backbone cable.  In
addition to the determination of cabling schemes, the RCDD must
also determine the physical support structure appropriate for
implementing the backbone system.
1.8.1
Voice Backbone Cable Requirements.  Utilization of a
backbone system design will vary according to the type of
signalling to be carried by the backbone.  Because of the
principal use of copper cable in voice applications, without
multiplexing or other electronic interface, it is relatively easy
to compute the size requirements for a backbone cable.  Total the
copper pair counts to each of the workstations to be serviced by
the cable, increase the quantity by a factor of 50 percent,
unless otherwise specified by the major claimant , and select the
multipair cable which most closely meets or exceeds the pair
count requirement.  The standard multipair copper cable sizes
available within the commercial industry are (pairs):  6, 12, 18,
25, 50, 75, 100, 150, 200, 300, 400, 600, 900, 1200, 1500, 1800,
2100, and 2400.  Distribution of backbone cabling in large
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