18 August 1998
(3) Routers connect network segments (or different networks using identical protocols) of
different media types. Routers are the basis for large internetworks made up of smaller networks each
with its own logical identity. Routers direct packets between networks using the most efficient route
based on packet type, destination and available network resources.
a. Fiber optics uses the wideband properties of light traveling through transparent fibers. Fiber
optics is a reliable communications media best suited for point-to-point high speed data transmission.
magnetic radiation emission; hence, fiber optics can be used in secure areas.
b. Fiber optic cable consists of small fiber cores encased in a thin, light-reflective plastic or glass
jacket referred to as the cladding. The cladding is enclosed by a thicker plastic or teflon jacket. A light
source at one end of the cable introduces coded light pulses into the fiber. The light source may be a
laser diode or a light-emitting diode (LED). The light pulses are transmitted through the fiber to a photo
diode at the other end, which receives the light pulses and converts them to electrical signals. Fiber
optic cables (but not fiber optic equipment) can be installed in explosive and flammable environments.
Fiber optic cables can tolerate severe weather conditions and can be immersed in many fluids with
appropriate jackets. The bandwidth of this media is virtually unlimited, and extremely high data
transmission rates can be obtained. The signal attenuation of high quality fiber optic cable is very low.
The type of fiber optic cable typically used for UMCS data transmission is multimode fiber with 62.5 -
micron fiber diameter. When the data transmission system interfaces with existing government furnished
networks, however, the designer will evaluate the specific fiber required for interface or extension.
c. The use of fiber optics in a data transmission system requires that equipment be provided to
encode, decode and regenerate digital data into the fiber optic media. Typical fiber optic equipment
includes the following.
(1) Fiber optic modems allow full duplex, asynchronous, point-to-point communications. Fiber
optic transmitter and receiver modules which convert electrical digital signals into optical signals are an
integral part of fiber optic modems.
(2) Fiber optic repeaters extend the range of the fiber optic data transmission. A repeater is a
signal regenerator used at specified distances to restore signals to their proper level and quality.
Repeaters can be simplex (containing one transmitter and one receiver module) or duplex (containing two
transmitters and two receiver modules). Repeaters are required for distances between data transmission
equipment of 1 to 2 miles.
(3) Fiber optic transceivers convert signals between fiber optics and other UMCS
communication media. One type of fiber optic transceiver converts an ethernet 10 Base-T (wireline)
signal to a 10 Base FL (fiber optic) signal.
(4) Fiber optic drop/repeaters combine the features of fiber optic repeaters with fiber optic LAN
transceivers in a multidrop bus topology.
(5) Fiber optic active star units (or fiber optic switched hubs) extend a fiber optic bus topology
into a multi-segment star topology.
d. The use of fiber optics equipment and connectors will introduce optical signal losses/gains that
must be accounted for during the design. Optical flux budget/gain will be calculated during UMCS data
transmission system design.