Information Technology Reference
In-Depth Information
but be assured that if the cable is run alongside metallic cables, as is frequently the
case in aerial runs (between telephone poles), a direct lightning strike will blow a hole
in this type of cable just the same. An interesting technique wraps a steel wire around
the length of the nonmetallic cable to add strength to the cable runs between poles.
Outside plant cable may also be duplexed with a steel cable (called a
messen-
ger cable
) for aerial installations. For direct burial applications, a metal-armored
cable is used. The armor is often a wound layer of copper, steel, or lead (Pb) tape
that is placed between two outer jacket layers.
Fiber-Optic Connectors
Fiber-optic technology is notable for its use of an incredible number of incompatible
connectors. In defense of the fiber industry, traditional fiber-optic applications have
been more esoteric than copper applications,
4
and the interactions of the fiber, the con-
nectors, and the transceivers have been far more complex and subtle. This has resulted
in a parade of improved connection technology that has attempted to address a pro-
gression of assembly, usage, and alignment issues that have arisen over the years. Fiber
connectors have tended to be redesigned to meet performance and convenience objec-
tives, rather than the radical technology changes of copper networking.
Table 11.2 lists some of the more popular fiber-optic connectors, listed in
approximate order of their introduction (except for the SFF connectors, which have
all been introduced at about the same time). A surprising number of the legacy con-
nectors are still in use.
The latest issues that have demanded further modifications of connector stan-
dards are pluggability and duplexing. Prior to the -A revision of EIA/TIA-568, the
SMA and ST connector types were in common use.
The SMA is a threaded single-fiber connector, whereas the ST is a bayonet
(push and turn to lock) single-fiber connector. Both are rather like miniature, opti-
cal versions of the type N and BNC connectors (respectively) that we are familiar
with from the early days of Ethernet.
Unfortunately, the SMA and ST connectors had to be mated to corresponding
chassis or patch connectors individually. Even if the connectors were somehow marked
4
Ethernet cabling has encompassed three incompatible connector types: Type N, BNC, and 8P8C
modular (RJ type) for the medium-dependent interface. A fourth type that is semi-compatible with the
8P8C is under consideration for Cat 6 and Cat 7 applications, and a noncompatible Cat 7 variation
has also been chosen. Token-Ring has used three: data connector, 9-pin D-shell, and 8P8C modular.
Some readers may be familiar only with the newer 8P8C modular connectors used with
10/100BaseTX. Copper applications have rapidly obsolesced the older connector types as the technol-
ogy has progressed.
