Managing Information Technology

72 Part I • Information Technology

goes out, there are alternative routes to almost every node
or device on the network. We will take a closer look at an
extremely high-speed national research network named
Internet2 later in this chapter.

Types of Networks

Thus far we have considered two key elements of
telecommunications networks: the transmission media
used to send the communications and the arrangement or
topology of the networks. Now we turn to the categoriza-
tion of networks into basic types, including computer
telecommunications networks, LANs, backbone networks,
WANs, the Internet, and Internet2.

COMPUTER TELECOMMUNICATIONS NETWORKS It is
almost easier to describe this initial type of network by
what it is not. It is not a LAN, a backbone network, a
WAN, or the Internet. What we are calling a computer
telecommunications networkis the network emanating
from a single medium, large, or very large computer or a
group of closely linked computers. This type of network
usually is arranged as a tree (see Figure 3.4) with coaxial
cable and twisted pair as the media. Until the early 1980s,
this was usually the only type of network (except for the
telephone network) operated by an organization that did
business in one building or a group of adjacent buildings

(a campus). In many organizations even today, the predom-

inant communication with the central computer is through

the computer telecommunications network. This type of

network is controlled by the central computer, with all

other devices (e.g., terminals, microcomputers, and printers)

operating as subordinates or “slaves” on the network.

IBM’s mainframe architecture was originally based on this

type of network, although LANs and other network types

may now be linked to a mainframe or large computer.

This is not a bad arrangement, but it puts a tremendous

communications control burden on the central computer. For

this reason, it is quite common to add a front-end processor

or communications controller to the network—between the

central computer and the rest of the network—to offload

the communications work from the central computer (see

Figure 3.5). A front-end processor or communications

controller is another computer with specially designed

hardware and software to handle all aspects of telecommuni-

cations, including error control, editing, controlling, routing,

and speed and signal conversion.

LOCAL AREA NETWORKS Alocal area network(LAN)

is first and foremost a localnetwork—it is completely

owned by a single organization and generally operates

within an area no more than 2 or 3 miles in diameter.

LANs are data networks that generally have a high data

rate of several million bps or more.

Mainframe

Computer

Front-end

Processor

Controller Controller Controller

Terminal Printer Fax Terminal Micro Terminal Printer Micro Micro Terminal

FIGURE 3.5 Computer Telecommunications Network