Information Technology Reference
In-Depth Information
Figure 6.2
Types of Guided Transmission
Media
Twisted-pair wire (left), coaxial
cable (middle), fiber-optic cable
(right)
(Source: © Greg Pease/Getty
Images.)
high-speed links that connect groups of computers or to move data stored in large databases
on large computers to stand-alone storage devices.
The Niagara Falls Bridge Commission (NFBC) is a joint United States and Canadian
agency that monitors three border crossings spanning the Niagara River between western
New York State and southern Ontario. NFBC also operates a fourth site that processes more
than seven million border crossings per year. The NFBC relies on a 10 Gigabit Ethernet
network to carry video and other data from border locations to its operations center in
Lewiston, New York. Video data from 170 cameras is used to support monitoring for unusual
or suspicious activity along the border as well as to manage the flow of traffic.
5
Coaxial Cable
Figure 6.2 (middle) also shows a typical coaxial cable, similar to that used in cable television
installations. When used for data transmission, coaxial cable falls in the middle of the guided
transmission media in terms of cost and performance. The cable itself is more expensive than
twisted-pair wire but less than fiber-optic cable (discussed next). However, the cost of in-
stallation and other necessary communications equipment makes it difficult to compare the
total costs of each medium. Coaxial cable offers cleaner and crisper data transmission (less
noise) than twisted-pair wire. It also offers a higher data transmission rate.
Cable companies are aggressively courting customers for telephone service, enticing them
away from the phone companies by bundling Internet and phone services along with TV.
For example, Comcast provides new movies on demand the same day as the DVD release to
its more than 24 million subscribers through its Project Infinity.
6
Fiber-Optic Cable
Fiber-optic cable, consisting of many extremely thin strands of glass or plastic bound together
in a sheathing (also known as a jacket), transmits signals with light beams (see Figure 6.2,
right). These high-intensity light beams are generated by lasers and are conducted along the
transparent fibers. These fibers have a thin coating, called
cladding
, which effectively works
like a mirror, preventing the light from leaking out of the fiber. The much smaller diameter
of fiber-optic cable makes it ideal when there is no room for bulky copper wires—for example,
in crowded conduits, which can be pipes or spaces carrying both electrical and communica-
tions wires. Fiber-optic cable and associated telecommunications devices are more expensive
to purchase and install than their twisted-pair wire counterparts, although the cost is
decreasing.
Verizon has been building a fiber-optic network since 2004 at a budgeted cost of $18
billion. This has required Verizon crews to remove traditional twisted-pair wires used to carry
