Information Technology Reference
In-Depth Information
worry; the confusion will probably not go away, it will just become more tolera-
ble. Figure 7.15 shows the interconnection of two duplex cables at an adapter
interface. The term
adapter
is defined as a fiber-optic coupling between two fiber
connectors of the same type, that is, two SC connectors, in this case. (The term
hybrid adapter
is used to describe a coupling designed to mate two unlike-like fiber
connectors, e.g., an ST and an SC.) Because of the narrow fiber spacing, SFF con-
nections require an adapter cable instead of a hybrid adapter. Note that the adapter
actually does a polarity reversal by having opposite orientations between its two
sides. The A connector position is always placed into the A adapter position, but
that passes through to a B connector position, through the panel to the opposite
side of the adapter.
The end-to-end connections of all fiber cables are also reversed. This includes
the horizontal and backbone fiber cables as well as all patch cords and user equip-
ment cords. The pattern of reversals should be standardized in an installation, but
it is up to the installer to maintain this discipline.
One way to accomplish this is to designate a correspondence between the fiber
buffer color and a fiber number. Then terminate all odd numbered fibers as A fibers
and even numbered fibers as B fibers in the TR. Do the opposite at the station out-
let. For example, in a two-fiber cable, you could designate fiber 1 as an A connec-
tion in the TR and as a B connection at the outlet. (Of course, the adapters at each
end reverse the A and B, but that takes care of itself.) Be very consistent in your fiber
polarity designations at every fiber termination.
Simplex
connectors
Cabling
side
A
B
B
Duplex
connector
Or
A
B
A
Patch
panel
Legend:
User
side
= Position “A”
= Position “B”
Note: Shading for
clarification only
FIGURE 7.15
The interconnection of two duplex cables at an “adapter” interface.
