Cabletron Systems 100BASE-FX, Cabling Manual

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FDDI Media
11-10 Cabling Types
Multimode
Multimode fiber optic cabling is designed and formulated to allow the
propagation of many different wavelengths, or modes, of light. Multimode fiber
optics are the most commonly encountered fiber type in FDDI installations, due to
their lower cost compared to other fiber types.
The FDDI MMF-PMD specification specifies the Media Interface Connector, or
MIC, as the standard connector for MMF-PMD networks. The LCF-PMD
specification recommends the use of the SC-Type connector for all station
connections. Other connector types are nonstandard and their use may result in
poor network performance. The MIC and SC connectors are described in greater
detail in the Connector Types section of this chapter.
Single Mode
Single mode fiber optics are designed specifically to allow the transmission of a
very narrow range of wavelengths within the core of the fiber. As the precise
wavelength control required to accomplish this is performed using lasers, which
direct a single, narrow ray of light, the transmissive core of single mode fiber
optics is typically very small (8 to 10
µ
m). Single mode fiber is more expensive to
produce than multimode fiber, and is typically used in long-haul applications.
The FDDI networking technology allows for the creation of single mode fiber
optic cabling runs of up to 58 km.
Due to the very demanding tolerances involved in connecting two transmissive
media with diameters approximately one-quarter as thick as a sheet of paper,
single mode fiber optics require very precise connectors that will not move or
shift over time. For this reason, single mode fiber optics should only be
terminated with locking, preferably keyed, connectors. The FDDI Single Mode
Fiber Physical Medium Dependent (SMF-PMD) specification requires that all
fiber optic cabling used in the FDDI network, regardless of type, should be
connected only with MIC connectors, which are discussed in detail later in this
chapter. Some FDDI devices for single mode fiber optics use the SC connector
used by the LCF-PMD specification.
Low-Cost
In response to the expensive media and bulky connectors of the MMF-PMD and
SMF-PMD standards, the Low Cost Fiber - Physical Medium Dependent, or
LCF-PMD has been proposed. The LCF-PMD specification uses multimode fiber
optics, and is terminated with smaller, less expensive connectors.The LCF-PMD
specification allows for connections that are not longer than 500 m (1,640 ft).
LCF-PMD links are designed for connections between concentrators and end
stations.
The LCF-PMD specification uses the SC Connector, a modular, keyed connector
designed much like the FDDI MIC connector (discussed in the Connector Types
section of this document).