Information Technology Reference
In-Depth Information
AB/BA Fiber Polarity Orientation
Fiber-optic cabling standards, including 568SC and FDDI standards, specify a dual
fiber connector that helps maintain polarity. The TIA/EIA-568-C method uses a
polarized AB/BA orientation of the dual connector to incorporate polarity into the
fiber connector. The method proposes to make the user connections foolproof, so
that a user never has to worry about polarity. If the fiber cables are properly
installed, the proper polarities at the user connections are assured. Unfortunately,
that places all of the burden of maintaining proper polarity on the installer.
The polarity with the SC connection 3 is achieved by using a nonsymmetrical
dual-connector body and labeling each position either A or B, as shown in Fig. 7.14.
The SC connector fiber termination was discussed in Chapter 6. The fibers of a given
cable are not literally called “transmit” or “receive,” but are numbered consecutively,
paired, and alternately placed into either the A or B position at each cable end in such
a way that the transmit connector on the equipment at one end is connected to the
receive connector on the equipment at the other end. This is a variation of the old
metallic cable proposal that would have made all equipment interfaces the same and
all cables crossed over (transmit and receive reversed end-to-end). It is perhaps ironic
that the metallic version was abandoned, only to be resurrected in fiber.
If you are accustomed to placing wire in connectors according to pin numbers
and color codes, the fiber-optic polarity method at first may seem confusing. Don't
Plane (frontal) view
BA
AB
Horizontally mounted
B
A
A
B
Vertically mounted
FIGURE 7.14
The polarity with the SC connection is achieved by using a nonsymmetrical dual connector
body and labeling each position either A or B. The two orientations are called AB and BA,
reading either left to right or down.
3 TIA-568-C still uses the SC connector for illustration purposes, although the SFF connector may be
used.
 
Search WWH ::




Custom Search