Information Technology Reference
In-Depth Information
From the connectors to the very fiber itself, every feature of a fiber link must be
appropriate for the application and for the equipment with which it will be used.
For this reason, we will spend some time describing the two types of fiber-optic
cabling standards that are currently in use. These standards are the structured
cabling system and centralized cabling.
Structured Fiber Cabling—TIA Standards
The tried-and-true method of fiber connection is the structured cabling system con-
ceptualized in TIA-568-C. As you recall, this standard allows for both single-mode
and multimode fiber, although the earlier -A version really encouraged the use of
multimode in the horizontal structure and single-mode in the backbone. Multimode
fiber and the lower-speed LED optics have traditionally been less expensive than sin-
gle-mode fiber and laser optics. As a result, much of the fiber that has been installed
in conformance with the structured wiring pattern is multimode fiber.
Multimode fiber in the structured environment works equally well for Ethernet,
Fast Ethernet, and Gigabit Ethernet. This is quite an accomplishment, when you
think about it. Part of the reason for this high-speed capability is the 90-m horizon-
tal runs of structured cabling. This short distance limit is really dictated by the atten-
uation and crosstalk parameters of twisted-pair cable, when tested to 100 MHz. It is
no small irony that fiber advocates can thank the use of Category 5e copper cable for
this relatively short run, and the consequent longevity of multimode fiber. The game
now is to standardize multimode for 55 and 100 m runs for 10 Gigabit Ethernet.
As you can see from Fig. 11.7, backbone cabling runs are made from a central
distribution point, such as the main cross-connect (MC) shown, to the telecommu-
nications rooms (TRs) throughout the building. At each TR, a fiber hub or switch
distributes the network signal to individual horizontal fiber runs, one per worksta-
tion to be served. An optional multiuser telecommunications outlet adapter
(MUTOA) may be placed in the horizontal run, between the TR and the work area
outlet/connector (WOA). As explained in Chapter 10, open-office wiring practices
allow the use of the fiber-optic MUTOA.
In the strict sense, the run from the MUTOA to the workstation is supposed to
be a user cord that plugs directly into the workstation. However, the designer may
wish to use a fixed WOA to protect the longer fiber run back to the MUTOA. This
is not permitted for copper cables, primarily because each termination and intercon-
nection adds significantly to the crosstalk problem. With good fiber terminations,
only a few tenths of a decibel of additional link loss are added, and the additional
interconnection at the WOA is generally insignificant. In addition, the potential for
damage to the duplex-fiber user cord is greater than with the more robust copper
