MIL-HDBK-2051(SH)
5.3.1.2.2 Quantity of allocated and not used fibers (trunk) . The number of allocated trunk spares should be determined from the system specification
or system drawings. Redundant trunk fibers should not be provided for normal and alternate channel trunk fibers unless required by the system. In those cases where redundant local fibers are required by a system, redundant trunk fibers should also be provided to connect between the redundant local fibers. Redundant trunk fibers may be provided for NRC trunk fibers if this redundancy is judged to be beneficial by the system designer and the FOCT designer.
5.3.1.2.3 Quantity of unallocated fibers (trunk) . Growth fibers should be provided in the trunks for future users that have not as yet been identified.
The quantity of growth fibers provided in a trunk should not be less than 20 percent of the total number of allocated fibers in that trunk. Spare trunk fibers should also be provided (the percentage of fibers required to be designated as spare should be found in the ship specification). Generally, the number of spare fibers required is calculated as a percentage of the number of allocated fibers. A minimum of 5 percent of the allocated and used fibers within a cable should be provided as spares.
5.3.1.3 Local fiber quantity allocation . The number and type of local fibers required for each end user equipment is determined by reviewing the system drawings. The nearest interconnection box that those fibers should be routed to is determined by reviewing the FOCT configuration drawing.
5.3.1.3.1 Quantity of allocated and used fibers (local) . The number of allocated and used local fibers is determined from the system drawings and the ship configuration drawing. Fibers for systems planned but not installed
prior to ship delivery should not be included in the allocated and used local cable or fiber determination.
5.3.1.3.2 Quantity of allocated and not used fibers (local) . The number of system allocated spare fibers in local cables should be determined from the system drawings or specification. Redundant or growth local fibers or cables should not be provided unless required by the system.
5.3.1.3.3 Quantity of unallocated fibers (local) . For local cables which penetrate decks or bulkheads the number of spare fibers should be as specified
in the ship specification. In this case, a minimum of 5 percent of the allocated and used fibers within a cable should be provided as spares. For all other local cables, spare fibers are generally not required.
5.3.1.4 Trunk cables . The number of trunk cables required between inter- connection boxes depends on the number of trunk fibers required. There are
four standard fiber counts for Navy fiber optic cable, 4, 8, 24 and 36 fibers; any of these cable sizes may be used. The following design principles should be observed when developing the trunk cable information:
a. The number of allocated and used fibers in a trunk cable should not be greater than 75 percent of the total number of fibers in the cable.
b. Multimode and single mode fiber should be put in separate cables
(standard Navy cables do not mix the fiber types).
c. Redundant fibers should be put in separate cables from their
respective NRC fibers.
d. Redundant cables should be routed as described in 5.3.1.6 and
5.4.1.1.
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