Information Technology Reference
In-Depth Information
between the various connectors. The TIA-568-C standard contains suggestions for
migrating to the new connector systems. The reason the standard has chosen to
allow the SFF connectors is to encourage innovation and allow quick
connection/disconnection and easily combined polarized pairs.
To convert between fiber connector types, you need to use a hybrid adapter or
a conversion cable. A hybrid adapter is a passive coupler that joins two different
connector types, while a conversion cable simply has one connector type on one end
and the other type on the opposite end.
For example, to convert an ST equipment interface to SC, you need a fiber
cable with one of the connectors on each end. The duplex (two-fiber) cord described
later is convenient to use, because you will need two fibers for each link connection.
Some of the other types of fiber connectors usually have no built-in polarization, so
you will have to pay attention to which connector goes to transmit and which to
receive. The standard, at present, gives no guidance as to which A or B position of
each orientation (AB or BA) should contain the transmit signal and which the
receive. The designation of one fiber as transmit and one as receive is a little diffi-
cult anyway, because the transmit from the one end of a cable is the receive from the
other. You will have to create your own standard practices for which connector
position at the patch panel is transmit or receive.
Fiber-optic patch cords are usually made from flexible duplex fiber cables,
often referred to as “zip cords” because of their resemblance to the household elec-
trical cords by the same name. Fiber zip cords differ in that the conductors are
replaced by fibers, insulation does not have to meet any electrical specifications, and
color is usually bright. Because the fibers are always patched in pairs, the dual-fiber
construction is handy in that it easily splits out for two individual connectors.
Most SFF connectors are duplex by nature, and A/B orientation is part of the
design. A duplex clip can be used to attach the two SC connectors together. Fiber
connector pairs that are thus clipped together have an orientation just as the
adapters do. This is so that the A and B connections will be placed into the proper
position in the mating adapter. There are two orientations for the connectors of a
fiber patch cord, the AB and BA orientation, which were described in Chapter 7. It
does not really matter which orientation you use for each end of the patch cord, as
long as the two ends of the cord have opposite orientations, and the fiber polarity
is flipped between the two ends.
Adapters and connectors may be marked with a distinctive color, such as red
or white, to assist in the installation and later connection of mating plugs. The
TIA standard does not specify or define these “shadings” at the present time, but
you can use them in your facility to help differentiate the A and B positions of the
mating connections. Remember that neither the A nor B designation specifies the
