Cabletron Systems 100BASE-FX, Cabling Manual

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Cabling Types 9-9
Token Ring Media
In much the same way that UTP cabling is available in two-, four-, 25-, and 50-pair
cables, strands of fiber optic cabling are often bound together with other strands
into multiple strand cables. These multiple strand cables are available with
anywhere from two to 24 or more strands of fiber optics, all gathered together into
one protective jacket.
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 network installations,
due to their lower cost compared to other fiber types.
Token Ring fiber optic devices that meet the IEEE 802.5j specification are
terminated with ST connectors. Older network installations may utilize the IBM
biconic connector or the Sub-Miniature Assembly (SMA) connector.
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 12
µ
m). Single mode fiber is more expensive to
produce than multimode fiber, and is typically used in long-haul applications.
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. Token Ring fiber optic
installations must use the ST connector to be compliant with the IEEE 802.5j
specification.
TIP
Cabletron Systems recommends that customers planning to
install fiber optic cabling not install any facility fiber optics
(non-jumper cabling) containing fewer than six strands of
usable optical fiber. The minimum number of strands needed to
make an end-to-end fiber optic link between two network
devices is two. In the event that a strand within the cable is
damaged during installation or additional fiber pairs become
desired along the cable path, the availability of extra strands of
optical fiber will reduce the likelihood that a new cable must be
pulled. The existing, unused pairs of optical fiber can be
terminated and used immediately.