Managing Information Technology

66 Part I • Information Technology

commonplace. When a digital service such as DSL is used
on the telephone network, a speed of 256,000 bps is
common, with outbound DSL speeds ranging up to 896
kbps and inbound DSL speeds up to 12 million bps
(12 mbps). Much higher speeds can be obtained when
twisted pairs are used in LANs. Multiple twisted pairs in a
single cable—such as Category 5e cabling—can support
speeds up to 100 mbps when used in a Fast Ethernet LAN,
or even up to 10 billion bps (10 gbps) with Gigabit
Ethernet (more on these LAN types later). The speeds of
twisted pair and other media are summarized in Table 3.2.

COAXIAL CABLE Coaxial cable (coax)is another common
transmission medium. A coaxial cable consists of a heavy
copper wire at the center, surrounded by insulating material.
Around the insulating material is a cylindrical conductor,
which is often a woven braided mesh. Then the cylindrical
conductor is covered by an outer protective plastic covering.
Figure 3.2 illustrates the construction of a coaxial cable.

Because of its construction, coaxial cable provides a

good combination of relatively high transmission speeds

and low noise or interference. Two kinds of coaxial cable

are in widespread use—baseband coax, which is used for

digital transmission, and broadband coax, which was

originally used for analog transmission but which is now

used for digital transmission as well.

Baseband coax is simple to use and inexpensive to

install, and the required interfaces to microcomputers or

other devices are relatively inexpensive. Baseband offers a

single digital transmission channel with data transmission

rates ranging from 10 million bits per second (10 mbps) up

to perhaps 150 mbps, depending primarily on the

distances involved (longer cables mean lower data rates).

Baseband coax was widely used for LANs and for long-

distance transmission within the telephone network,

although much of this coax has now been replaced by

fiber-optic cabling.

Broadband coax, which uses standard cable

television cabling, was originally installed for analog

transmission of television signals, but it increasingly

employs digital transmission. A single broadband coax can

be divided into multiple channels, so that a single cable can

support simultaneous transmission of data, voice, and

television. Broadband data transmission rates are similar to

those for baseband coax, and high transmission speeds are

possible over much longer distances than are feasible for

baseband coax. Because of its multiple channels and addi-

tional capacity, broadband coax has been more enduring

than baseband. Broadband coax is still widely used for

cable television and LANs that span a significant area,

often called metropolitan area networks.

WIRELESS Strictly speaking, wireless is not a transmis-

sion medium. Wirelessis broadcast technology in which

radio signals are sent out into the air. Wireless communi-

cation is used in a variety of circumstances, including

TABLE 3.2 Telecommunications Transmission Speeds

Transmission Medium Typical Speeds

Twisted pair—voice telephone 14.4 kbps–56 kbps

Twisted pair—digital telephone 128 kbps–24 mbps

Twisted pair—LAN 10 mbps–100 gbps

Coaxial cable 10 mbps–150 mbps

Wireless LAN 6 mbps–600 mbps

Microwave 256 kbps–1 gbps

Satellite 256 kbps–1 gbps

Fiber-optic cable 100 mbps–3,200 gbps

KEY: bps = bits per second
kbps = thousand bits per second, or kilo bps
mbps = million bits per second, or mega bps
gbps = billion bits per second, or giga bps

Copper

Core

Insulating

Material

Braided

Outer

Conductor

Protective

Plastic

Covering

FIGURE 3.2 Construction of a Coaxial Cable